A Blog by

Uncertain Future for Earth’s Biggest Telescope

The Arecibo Observatory, easily recognizable from feature films and a symbol of the search for extraterrestrial life, may not be around for much longer. A harsh funding climate is forcing the National Science Foundation to make some hard decisions about which facilities to keep around. (NSF/Wikimedia)

(Hear Nadia Drake interviewed live about the Arecibo telescope on Science Friday from Public Radio International, on Friday June 10 at 2 p.m. EST/11 a.m. PST.)

Tucked into a sinkhole in the Puerto Rican jungle, the world’s largest single-dish radio telescope scans the skies for signs of distant galaxies, elusive gravitational waves, and the murmurs of extraterrestrial civilizations nearly 24 hours a day. For more than a half-century, whether those waves traveled to Earth from the far reaches of our universe or much closer to home, the Arecibo Observatory has been there to catch them.

But the enormous telescope, with a dish that stretches 1,000 feet across, may not be around for much longer.

On May 23, the National Science Foundation, which funds the majority of Arecibo’s annual $12 million budget, published a notice of intent to prepare an environmental impact statement related to the observatory’s future.

That might sound innocuous – after all, isn’t it a good idea to study the context in which our science facilities exist? Yet it’s anything but benign. Putting that environmental assessment together is a crucial step NSF needs to take if it plans to yank funding from the observatory and effectively shut it down.

“It appears that NSF is following the formal process established, in part, by the National Environmental Policy Act of 1969, for decommissioning of a federal facility,” says Robert Kerr, former director of the observatory. “The good folks at Arecibo are scared to death.”

The decision to close Arecibo hasn’t been made yet, but the move follows an ominous drumbeat of similar announcements and reports that have accumulated over several years, most urging NSF to send its resources elsewhere. Now, options for Arecibo’s future range from continuing current operations to dismantling the telescope and returning the site to its natural state. It’s a decision NSF hopes to make — with input from the public — by the end of 2017, says Jim Ulvestad, director of NSF’s Division of Astronomical Sciences.

Above the 1000-foot dish, a 900-ton platform is suspended from three tall towers. The platform's height varies by about a foot as temperatures rise and fall. (Nadia Drake)
Above the 1000-foot dish, a 900-ton platform is suspended from three tall towers. (Nadia Drake)

The most extreme option, which could include explosively demolishing the giant dish, might affect such things as ground water, air quality, and ecosystems – thus the importance of studying the environmental impact of potential futures, especially ones that involve shutting the telescope’s eyes.

“On a practical level, the telescope would in time — perhaps a short time, given the tropical site — become very unsafe,” says Cornell University’s Don Campbell, a former observatory director. “Short of permanently guarding it, deconstruction would be necessary.”

Not surprisingly, this notice of intent is causing significant concern among astronomers and the local community. Arecibo is the most sensitive radio telescope in the world; and despite its age, it’s still involved in world-class science, like the search for gravitational waves. Importantly, it also helps boost a sagging local economy, and has inspired many Puerto Ricans to pursue science and think about the mysteries of the universe.

“Puerto Rico feels a sense of ownership and pride for the observatory,” says Emmanuel Donate, an astronomy graduate student at the University of Georgia who started a petition to keep the observatory funded. “I consider using it, especially in person as I’ve been doing the last couple weeks, one of the highlights of my life and a tremendous personal honor.”

A Tropical Icon

Construction at Arecibo began in 1960, when – among other things – the U.S. government wanted to find out if Soviet ICBMs could be detected using charged particles in their atmospheric wakes. The telescope didn’t work well at first, but after a few upgrades it was the most sensitive cosmic radio wave detector in the world. That’s not it’s only trick, though: In addition to collecting photons from space, Arecibo is also capable of sending radio waves into the cosmos, a talent scientists use to scrutinize potentially catastrophic asteroids on Earth-crossing orbits.

The Arecibo Observatory, as seen on Google Earth.
The Arecibo Observatory, as seen on Google Earth.

In the intervening decades, Arecibo has been involved in loads of top-notch science, including work that was awarded a Nobel Prize. But it’s also become a recognizable symbol of humanity’s quest to understand our place in the cosmos (my dad, a former observatory director, used Arecibo to send Earth’s first intentional postcard to the stars in 1974), and is a semi-frequent character in popular films and TV series, including The X-Files, Contact, and GoldenEye.

To say the telescope is iconic is not an overstatement.

 Stormclouds on the Horizon

But a frustratingly flatlined budget is forcing the National Science Foundation to ration its resources. To do that, NSF relies on a somewhat contorted process of soliciting input from external reviews and panels, federal advisory boards, and the National Research Council’s decadal surveys, which prioritize science goals for the coming decade.

“NSF, like most federal science agencies, has much more worthy science proposed to it than it is able to fund,” Ulvestad says. “Within the constraints of its resources, NSF responds as well as possible to those community and governmental science priorities and recommendations.”

The most recent decadal survey, published in 2010, prioritized science requiring new facilities instead of experiments that could be conducted at places like Arecibo. That survey, in combination with the dismal funding situation, is what’s causing NSF to look for facilities to dump.

Arecibo's dish is suspended above the floor of the natural depression it sits in. Beneath it, fields of shade-tolerant plants grow. (Nadia Drake)
Arecibo’s dish is suspended above the floor of the natural depression it sits in. Beneath it, plants grow like crazy. (Nadia Drake)

Despite its iconic status, Arecibo is an easy target – newer, shinier telescopes are coming online, and it’s got a relatively small number of users compared to optical telescopes across the United States, many of which are individually less expensive to run.

Over the past decade, multiple panels have called for severe reductions in funding for the observatory, starting with a 2006 NSF review that recommended finding alternative sources of cash for Arecibo. “The [senior review] recommends closure after 2011 if the necessary support is not forthcoming,” the report says. “This raises the important question of the cost of decommissioning the telescope, which could be prohibitively large.”

That review was followed by a 2012 assessment of the facilities funded by NSF’s astronomical sciences division. While somewhat less gloomy – the committee recommended keeping the observatory in NSF’s portfolio – the 2012 panel suggested revisiting Arecibo’s funding status later in the decade, “in light of the science opportunities and budget forecasts at that time.”

NSF followed that review with a 2013 letter saying it would begin studying the costs and impact of decommissioning the giant telescope – a matter that would be complicated by the telescope’s history and location in a region of high biodiversity, “thus these reviews should be started as soon as practicable.”

The cloudy outlook intensified this year, when NSF’s Astronomy and Astrophysics Advisory Committee urged the agency to proceed with divestment “as fast as is practical.” That was quickly followed by another NSF review that advised a 75% reduction in funding from the agency’s Atmospheric and Geospace Sciences division (AGS), slashing contributions to atmospheric research from $4.1 million to $1.1 million.

And now, the sky is looking dark indeed.

“The timing of the federal register announcement in juxtaposition with the AGS review is being received by most as the final death sentence for Arecibo,” Kerr says.

Ulvestad says that before any such decision is reached, communities that rely on the observatory will have an opportunity to share their concerns. On June 7, the first of these meetings will take place in Puerto Rico, and a public comment period is open until June 23. After the results of the draft environmental impact statement are released, a 45-day public comment period will follow.

And then? Either the storm will hit or it won’t.

“To be fair to the NSF, AST and AGS are reacting to a very difficult budget situation — no significant increase in several years and none forecast,” Campbell says.

Scanning the Cosmos

Looking down at the dish from above. (Nadia Drake)
Looking down at the dish from above. (Nadia Drake)

Now, Arecibo’s projects include detecting mysterious bursts of radio waves coming from far, far away, testing cosmological models by studying small galaxies in the local universe, and studying those potentially planet-killing asteroids – as well as the moons of distant planets.

“There is much concern, not just in the small bodies community, but in the planetary science community as a whole regarding the future of Arecibo,” says Nancy Chabot of the Johns Hopkins University Applied Physics Laboratory. Chabot chairs NASA’s Small Bodies Assessment Group, which published a report earlier this year urging NASA to continue supporting the observatory, in the name of preserving “the nation’s science and security interests.”

Among astronomers, perceptions are that NSF’s move to decommission Arecibo has been gaining momentum as challenges from new facilities arise. One potential thorn in Arecibo’s side is ALMA, the ultrasensitive array of radio telescopes recently completed in the Chilean Atacama. Some scientists speculate that with continued resources devoted to ALMA, NSF could be looking to share the relative wealth and spend its money on something other than radio. And that might make sense, especially given that China is nearly done constructing a single-dish radio telescope that will be larger than Arecibo. Called the Five-hundred-meter Aperture Spherical Telescope, the behemoth could possibly open its eyes this fall, though real science observations won’t begin right away.

Despite its size, FAST won’t necessarily be more sensitive than Arecibo, and it won’t have a built-in radar, which can be used to give the most accurate orbital information for asteroids which might impact the Earth.

Cornell University’s Jim Cordes points out that newer facilities don’t necessarily have to replace older, high-quality telescopes, especially when those older facilities still provide unique capabilities. They can be complementary, he says, pointing out that scores of similar optical telescopes exist in tandem, such as the two nearly identical Keck telescopes at the summit of Hawaii’s Mauna Kea. “It’s sort of like there’s a disconnect in the way people think about radio telescopes and optical telescopes,” Cordes says.

More importantly, Cordes notes, some experiments actually require multiple extremely sensitive telescopes. One of these, called NANOGrav, uses Arecibo and a telescope at the National Radio Astronomy Observatory in Green Bank, West Virginia to search for gravitational waves. The project does this by observing pulsars, spinning stellar corpses that act as astronomical clocks. As these dense, dead stars rotate, they emit beams of radio waves that can be detected from Earth; gravitational waves, similar to those detected earlier this year by the LIGO collaboration, sweep through and disrupt the signals coming from those spinning clocks in observable ways…as long as a sharp set of eyes is paying attention.

“NANOGrav’s goal is to open a gravitational wave window that parallels what LIGO did so spectacularly,” Cordes says, noting that the two experiments look for waves produced by wildly different cosmic collisions. “The NANOGrav band is as different from the LIGO band as radio waves in the FM band are different from the X-rays used by your dentist. A full understanding of the universe requires instruments that sample all frequencies.”

Losing Arecibo would mean losing the ability to precisely monitor half of NANOGrav’s roughly 50 pulsars. “This will push back detection by a few years, at a time when we are almost there,” says NANOGrav chair Xavier Siemens, of the University of Wisconsin-Milwaukee.

A scientist who shall remain anonymous once described empirically testing whether a motorcycle could be ridden up the catwalk to the telescope's platform. The answer is yes, which will not come as a surprise to James Bond. (Nadia Drake)
A scientist who shall remain anonymous once described empirically testing whether a motorcycle could be ridden up the catwalk to the telescope’s platform. The answer is yes, which will not come as a surprise to James Bond [note: this is the roof on the catwalk]. (Nadia Drake)
A National Inspiration?

It seems clear that Arecibo won’t go down without a fight, but it’s not exactly clear what form that fight will take. Interestingly, former observatory director Robert Kerr threw one punch by beginning the process for listing Arecibo as a national historic site.

“It was entirely my intention that the National Historic Registry be an impediment to site closure,” he says, adding that “others assisting with that application may have had other motivations, such as enhanced tourist appeal.”

And NASA, which funds the planetary radar experiments at Arecibo, also may have something to say about NSF shutting down the facility. It’s also possible that another institution, or someone with enough spare cash might decide to step in.

“I hope that they do find another institution to contribute to the costs but it will depend on the conditions,” Campbell says. “The alternative is grim for science, for Puerto Rico and, especially given Puerto Rico’s current situation, for the Observatory’s local staff. The staff are an incredible hard working and supportive group.”

Indeed, generations of Puerto Ricans have visited the observatory, in addition to those who have worked, studied, and lived there.

“I grew up in the city of Arecibo, I grew up knowing that in the mountains south of the city great science was being done,” says Pablo Llerandi-Román, a geologist at the University of Puerto Rico, Rio Piedras. For Llerandi, science became more than just a subject in school when he visited the observatory as a student and talked with the researchers on site. “If Arecibo shuts down,” he says, “A major aspect of my arecibeño and Puerto Rican scientist pride would be lost.”

Carlos Estevez Galarza, a student at the University of Puerto Rico, says he hopes Puerto Ricans will one day be as celebrated for their commitment to science as they are for their passions for arts and sports – and he thinks the observatory plays an important role in that.

“The Arecibo Observatory and its staff were the only ones who believed in me, when no one did,” Galarza says. He worked as a student research assistant at the observatory, studying Mars, and has since presented his work at international conferences and submitted his first paper to a science journal.

“The most important thing about my experience at the Arecibo Observatory is that I found my purpose,” he continues. “There are many talented Puerto Rican students who deserve the chance that I had.”

One of those students is still in high school. Now 16, Wilbert Andres Ruperto Hernandez wanted to be an astronaut as a kid – and he wanted to get some hands-on experience in science and engineering. So he enrolled in the Arecibo Observatory Space Academy, which offers high school students the opportunity to design experiments, then collect and analyze data. Now, Hernandez says, he wants to study mechanical engineering or space sciences in college, and has discovered a yearning to understand how the universe works – something that emerged while working with and talking to scientists at the observatory.

“The fact that we have yet to discover and learn more about ourselves, where we live in and all the things that surround us, motivates me the most to investigate and study these fields,” he says. “Being part of Arecibo Observatory and AOSA has been the greatest experience in my life.”

Around sunset, Arecibo comes to life with the stubborn songs of coqui frogs. (Nadia Drake)
Around sunset, Arecibo comes to life with the stubborn songs of coqui frogs. (Nadia Drake)
A Blog by

Help Map the First Human Outpost on Mars

Mt. Sharp on Mars
Someday astronauts might navigate the Martian landscape (here, the Curiosity rover’s view of Mt. Sharp).

With the tantalizing possibility of a manned mission to Mars in the offing, NASA’s most recent call for astronaut hopefuls resulted in a record 18,300 applications. But if you missed the deadline (or have an aversion to spending seven to nine months in a cramped spacecraft with three other people), there’s another way to get involved: Make a map for astronauts to use on Mars.

Sure, NASA has plenty of scientists hard at work mapping the geology of potential Martian landing sites. But designing maps to help humans navigate, study, and survive in an alien landscape will require an entirely different set of skills—the kinds of skills that cartographers, graphic artists, and people who love maps might have.

So, the International Cartographic Association is holding a competition to come up with the best map design for astronauts who would spend about a year on the surface of Mars as part of a mission proposed for the 2030s.

One of the most interesting parts of this challenge is to design a map that will probably be displayed with technology that has yet to be invented. “The field maps will most likely be digital dynamic maps, shown on display, VR glasses, projected onto the helmet or made visible by a yet-to-discover technology,” according to the contest instructions.

“This project is on the boundary between scifi, game design, graphic arts and science, like cartography is,” NASA planetary scientist Henrik Hargitai told me in an email. Hargitai is also the chair of the ICA’s Commission on Planetary Cartography, which sounds awesome.

One of 47 possible exploration zones on Mars that could be visited by humans.
One of 47 possible exploration zones on Mars that could be visited by humans.
H. Hargitai/NASA/ARC

Competitors can use free mapping software with high-resolution surface images and information about geology and resources on Mars. They will choose one of 47 possible 200-kilometer-wide (about 125 miles) exploration zones—like the one to the left—and map everything that would be important to the astronauts, also known in NASA jargon as “proximal humans.” 

This includes things they need to live, like a habitat, power plant, and greenhouse; the places where they will conduct their research, such as geological outcrops and other spots that scientists have deemed worthy of inspection; areas that have resources they will need to survive, including water, loose rocks and dirt for building roads, and metals like iron and aluminum that could be mined; and landmarks for navigation.

Clearly this task will require some mapmaking skills. But more importantly, it’s going to take a lot of creativity to imagine what it would be like to live and work on the surface of another world. If you think you’re ready to do your part, here are a few ideas to help you put yourself in those astronauts’ Mars boots.

First, check out Curiosity’s view of the Red Planet. This rover has been cruising around Mars for almost four years, doing some of the kinds of things humans would also do out there—like drilling into rocks—and documenting it all with thousands of photographs, like as the one below. And the humans on Mars will also have some rovers with them, which makes Curiosity’s perspective even more relevant.

How Curiosity rover sees Mars.
How Curiosity rover sees Mars.

Next, you can study the experiences of the Apollo astronauts who walked on the moon. For example, this description from astronaut David Scott from the documentary “In the Shadow of the Moon” is revealing: “One of the problems on the moon is that there’s nothing of familiar size—no trees, houses, roads—so it’s very difficult to tell a large rock at a great distance from a smaller boulder nearby.”

After that, take a look in at NASA’s animated conception of a Mars exploration zone (which doesn’t look all that different from the outpost depicted in “The Martian”) in the video below.

And finally, consider immersing yourself in the stories of some of the great science fiction authors that take you to Mars and other planets, both real and imaginary. After all, some of these writers have a knack for actually predicting real future technology.

Hargitai says there’s a good chance that concepts and design elements from the contest submissions will be incorporated into the final product that lands in the hands (and helmets) of astronauts heading to Mars. For example, they need well-designed symbols for things like the deep space habitat that will be the astronauts’ living quarters. “We do hope that our awardees’ map designs will have an echo in the final products made some 20 years from now,” he says. And the maps can be tested much sooner on Earth in simulated Martian environments such as the Mars Desert Research Station in Utah.

In addition to the chance to be involved in planning the first human mission to another planet, the contest offers prizes for the winners of three categories: middle and high school students, college students and young professionals aged 18-35, and “citizen scientists” of all ages. And, the winner’s maps will be sent to the scientists in charge of the exploration zone they mapped.

The ICA is currently in the process of making the competition an official collaboration with NASA through a NASA Space Act agreement. Hargitai hopes the project will follow in the crowdsourced footsteps of previous successful NASA citizen scientist projects like crater counting and Martian spider identification.

“The goal partly is to encourage young professionals and students, to inspire them, to work on science projects that may have a real impact,” Hargitai says. “They will be the future planetary scientists and astronauts.”

—Betsy Mason

A Blog by

Will the Real Earthlike Planets Please Stand Up?

Three Earth-size planets orbit a small dim star. Are they Earth-like? It's not clear yet. (ESO/M. Kornmesser)
Three Earth-size planets orbit a small, dim star. Are they Earthlike? It’s not clear yet. (ESO/M. Kornmesser)

Earlier this week, a string of somewhat breathless news stories reported that three Earthlike exoplanets could be the most likely hosts for life outside the solar system. But that’s not exactly true. There’s a lot we don’t know about these newly revealed planets, and a vast ocean of data that needs gathering before an Earth-size world can make the leap to truly Earthlike. Already, a new study has suggested that two of these planets could be desiccated, parched, and decidedly un-Earthy.

Yet even if the trio aren’t as Earthlike as advertised, they’re still interesting and notable—even without trumped up reports of habitability.

“All of the stuff about habitability, surface environments, etc., is merely idle speculation and conjecture,” says Greg Laughlin of the University of California, Santa Cruz. “Even with our own solar system, there’s been zero success in predicting what surface environments for a large moon or planet look like until the body is viewed up close.”

The journey from Earth-size to Earthlike depends on which definition is at the destination. How much of an Earth twin does a planet need to be to fit the description? Does a similar size and temperature qualify? Or does it also need to orbit a star like the sun and have an Earthlike composition, atmosphere, and ability to host life?

My guess is, that definition varies depending on who’s using it, and it’s worth clarifying what it means each time.

Right now, most of those latter characteristics are complete unknowns in the system. At this point, all scientists know for sure are the sizes, orbits, and potential temperatures of the two innermost planets, which are so close to the star they keep the same face pointed inward all the time. The team knows the third planet’s size, but its orbital period is mostly a mystery. And they know the planets are basking in infrared light, which is what most of the TRAPPIST-1 star’s light is—which is very different from the sun.

But while studies of other exoplanets suggest it’s likely the planets are a mixture of ice and rock, it’s not clear at all what they’re actually made of, whether they have atmospheres that affect surface temperatures (and if so, how), and if liquid water could pool on their surfaces, at least in narrow temperate bands bordering the regions of perpetual day and night.

And what about the worlds’ ability to support life—either as we know it or in a form that has evolved to thrive on infrared photons? That’s a completely different set of questions, and one that isn’t even close to being answered.

Still, “it looks like the middle planet, with the 2.42-day orbital period, could potentially be quite Earthlike in its properties,” Laughlin notes. “I don’t know of any other exoplanet that is potentially as Earthlike.”

How is Laughlin defining “Earthlike” here?

“I mean a planet that is close to Earth’s radius and which receives a similar energy flux from its parent body. I definitely don’t mean oceans, plate tectonics, dolphins, stock markets …,” he says. “As the authors argue, however, it’s likely that the planet is spin-synchronized so that it presents one hemisphere to the star, which is very different from Earth.”

OK, so the planet is definitely not Earth’s twin, but it’s not exactly unrelated, either.

Regardless, the worlds are still noteworthy, and for a slew of reasons. They live around a tiny and cold star known as an ultracool dwarf; until now, scientists weren’t sure these stars, which comprise 15 percent of the stars nearest the sun, could host relatively large worlds. And it turns out that answer is yes, which means—to put it simply—more planets! Second, at roughly 40 light-years away, the system is so nearby that closely scrutinizing the planets is not only possible, but it’s possible now. Those observations will be even easier because the star is so dim, meaning that disentangling which information is coming from the planets and which is coming from the starlight is much simpler. And lastly (for now), studying the system will help scientists learn more about how planets evolve around stars very different than our own—which is the subject of the follow-up paper taking a look at water loss on worlds around ultracool dwarfs.

In short, it’s worth remembering that responsibly covering science means being faithful to the discoveries and the data—shortcomings, vagaries, and all. Sure, it’s fun to speculate about what we might eventually learn, but it’s not worth overstating findings and misleading readers for the sake of clicks. The beauty of science is in its complexity, in its messiness, in its rigorous examination of the unknown, in amassing enough data to reasonably interpret—and then using that as a foundation to start the whole process over again, with a different set of questions.

Three Earth-size alien worlds circling a nearby stellar underdog? That’s fantastic.

A Blog by

Scientists Discover a Dark Moon in the Distant Solar System

Makemake and its dark little moon, known for now as MK2, are shown in this illustration. (NASA/ESA/Alex Parker)
Makemake and its newly discovered moon, known for now as MK2, are shown in this illustration. (NASA/ESA/Alex Parker)

Dwarf planet Makemake, which orbits the sun once every 310 Earth-years, has a dark little moon. Just 100 miles across, the moon evaded detection for more than a decade, hiding in the glare of its parent planet.

But it couldn’t escape the stare of the sharpest eye in the sky forever: When scientists aimed the Hubble Space Telescope at Makemake for more than two hours in April 2015, they discovered a faint point of light moving through the sky along with the icy world.

Until now, Makemake was the only officially recognized distant dwarf planet without a moon, a dubious distinction that has now been lost.

Is That … a Moon?

At first, Alex Parker wasn’t sure he’d spotted a new moon in the Hubble observations.

“I was sure someone had seen it already,” says Parker, of the Southwest Research Institute. So, he approached collaborator Marc Buie and asked, “Has anyone seen the moon in the Makemake data?”

Buie’s reply — “There’s a moon in the Makemake data?”— convinced Parker he was onto something.

“It was at that point that everything got exciting and kicked into high gear,” says Parker, who along with Buie reported the discovery of the moon, known as MK2 for now (or S/2015 (136472) 1, more officially) on Tuesday.

Hubble image of Makemake and its moon. (NASA/ESA/Alex Parker)
Hubble image of Makemake and its moon. (NASA/ESA/Alex Parker)

By carefully studying the orbit of MK2, scientists will not only be able to determine how the moon formed—whether Makemake’s gravity snatched it or it grew out of a collision—but also learn more about Makemake itself. Specifically, the moon’s orbit will reveal the mass of the small, icy world. From there, they’ll be able to calculate Makemake’s density and determine what it is likely made of, and compare it to other far-flung icy worlds such as Pluto, Eris, and egg-shaped Haumea.

“The wide range of densities of the dwarf planets is one of the most interesting mysteries out there. But we still have so few objects that each one adds a critical part of the story,” says Caltech’s Mike Brown, who, with his colleagues, discovered Makemake in 2005. “I’m accepting bets currently.”

Makemake’s Dark Mystery

Makemake is a strange world. Shaped like a flattened sphere about 870 miles across, it lives in the Kuiper Belt—the icy debris ring beyond the orbit of Neptune—and is reddish in color. Like some other Kuiper Belt objects, Makemake spins very quickly, pirouetting every 7.7 hours. Its slightly oval orbit takes it much farther from the sun than Pluto, which treks around the sun in a comparatively snappy 248 years.

Finding MK2 in orbit around Makemake could solve one of the abiding mysteries about the icy dwarf planet, Parker said.

When scientists first observed the whirling Makemake, they noted that it was continually bright, meaning that its surface is probably uniformly covered in bright, reflective ices. But heat signatures from the faraway planet were slightly varied, suggesting that at least one warm, dark patch might be present on Makemake’s surface. Years of observations failed to reconcile the two data sets, as a dark patch never showed up in observations.

“Well, imagine that the dark material isn’t on Makemake’s surface … it’s in orbit!” Parker said. “If the moon is very dark, it accounts for most previous thermal measurements!”

Indeed, MK2 is much darker than Makemake itself, which is about 1,300 times brighter than its companion.

What else is hiding in our solar system, waiting to be discovered?

A Blog by

Scientists May Have Spotted Buried Lava Tubes on the Moon

This dark splotch could be a portal to a buried lava tube on the moon. (NASA/GSFC/Arizona State University)
This dark splotch could be a portal to a buried lava tube on the moon. (NASA/GSFC/Arizona State University)

THE WOODLANDS, Texas—A system of buried, empty lava tubes hides beneath the moon’s surface, remnants of a bygone age when the volcanically active moon launched fountains of fire into space.

At least, that’s what scientists think.

For years, teams have hunted for these elusive sublunar tunnels, which can be large and sturdy enough to house entire cities. In fact, lunar lava tubes could be ideal locations to establish a moon base, as their thick roofs would shield humans from harmful radiation and small meteorite impacts. But until now, the strongest observational hints of the tubes’ existence came from a smattering of detectable surface features, including skylights and rilles, channel-like depressions thought to form when tubes collapse.

This week, scientists announced that the signatures of at least ten buried lava tubes could be written into a map of the moon’s gravitational field.

It’s “the strongest evidence yet that shows signals consistent with that of buried, empty lava tubes on the moon,” said Purdue University’s Rohan Sood, who presented the observations at the Lunar and Planetary Science Conference.

Sood and his colleagues began their search for lava tubes in the Marius Hills region, where scientists suspect that a skylight has opened into one of the buried tunnels. That portal, discovered by Japan’s moon-orbiting Kaguya spacecraft and reported in 2009, is approximately 65 meters wide and 80 meters deep. It also sits by two rilles boringly known as A and B. In other words, there are multiple lines of evidence suggesting that lava once oozed and flowed beneath the Marius Hills.

“We see a skylight that is along this rille, but we don’t know if that is an access point into a lava tube or not,” Sood says. “Can we pick that up using gravity data?”

Images of the Marius Hills pit as observed under different solar illumination conditions by the SELENE/Kaguya Terrain Camera and Multiband Imager [JAXA/SELENE].
Images of the Marius Hills pit as observed under different solar illumination conditions by the SELENE/Kaguya Terrain Camera and Multiband Imager (JAXA/SELENE).
The short answer is yes, most likely.

Sood and his colleagues searched for the Marius Hills tube using data from NASA’s twin GRAIL spacecraft, which flew in tandem above the moon’s surface as they measured and mapped its gravitational field (in 2012, the spacecraft were purposely crashed into a site now named after astronaut Sally Ride). The moon’s gravitational field is affected by masses below the surface, as is Earth’s. Put simply, large chunks of mass will produce an increase in gravity, Sood says, but “if you fly over a lava tube, there’s going to be a dip in gravity.”

The team spotted a gravitational signature that could be a lava tube near the skylight, and then wondered if it would be possible to detect similar signatures in areas with no obvious rilles or skylights. Turns out, the GRAIL data contain at least ten telltale anomalies resembling lava tubes, slithering and twisting beneath the moon’s surface. They’re all located on the moon’s near side, near the dark stains left by ancient volcanic seas, and some of the candidate tubes are more than 100 kilometers long and several kilometers wide—large enough to swallow a small city.

Of course, it’s not certain that the tubes are actually there. The GRAIL data provide the strongest evidence for their presence, but definitive proof would require a moon-orbiting spacecraft that uses ground-penetrating radar to peer beneath the moon’s surface. Sood and his colleagues have proposed just such a space robot, called LAROSS.

“The proposed radar will not only help confirm our findings but will also give us an opportunity to find smaller lava tubes, ones that were beyond the resolution of GRAIL gravity data,” Sood says.

Maybe someday, after looking for lava in all the right places, space-faring humans will not only solve the mysteries of Earth’s closest celestial companion but use it as a giant shield against the dangers of space.

Full citation: Detection of buried empty lunar lava tubes using GRAIL gravity data. R. Sood, L. Chappaz, H. J. Melosh, K. C. Howell, and C. Milbury. LPSC abstract here.

A Blog by

Ceres, the Dwarf Planet Formerly Known as an Ocean World

Occator crater, home of the bright spots on Ceres, has a mound in its middle. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI/LPI)
Occator crater, home of the bright spots on Ceres, has a mound in its middle that is covered in salt. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI/LPI)

Update, June 29, 2016: The composition of Ceres’ bright spots is no longer a mystery: Wednesday in Nature, scientists revealed those enigmatic splotches are rich in sodium carbonate, a salt that is tightly linked to watery conditions on Earth. In fact, there’s so much of the stuff in Ceres’ Occator crater that the pit holds the record for the largest such deposit in the solar system aside from Earth.

Just how those salts ended up on Ceres’ surface is still a mystery, though. Instead of containing large amounts of ice, as some scientists had expected, Ceres’ interior is considerably drier than suspected, reports a second study published Wednesday in Nature Geoscience. That makes it hard to explain how the dwarf planet’s surface ended up covered in formerly dissolved salts. Now, researchers are trying to sort out how Ceres made those salts and moved liquid brines to the surface; they suspect impacts may be to blame for simultaneously melting buried ice and excavating the planet’s salty sea, leaving bits of it to shimmer in the sunlight.


Today, Ceres is a salt-covered dwarf planet whose main claim to fame is that it’s the largest body in the main asteroid belt. But back when it was younger and hotter, scientists have found, Ceres was an ocean world—much like the watery moons of Jupiter and Saturn. 

“Ceres appears to have been one of these in the past,” Carol Raymond, deputy principal investigator for NASA’s Dawn mission, said Tuesday at the Lunar and Planetary Science Conference. The Dawn mission put a spacecraft in orbit around the tiny planet in March 2015. “What we’re looking at now, we believe, is the remnants of a frozen ocean.”

Scientists hoped that when Dawn arrived at Ceres, it would help solve the mysteries of this strange little world. But instead, Ceres is throwing puzzle after puzzle at the team and proving to be a much tougher space-nut to crack than anticipated.

Among Ceres’ enigmas are those perplexing bright spots, which scientists first thought could be extremely reflective water ice. But closer inspection reveals the spots are likely to be salts – perhaps leftover from a briny, frozen ocean that’s exposed when impacts gouge craters into Ceres’ crust. “We’re interrogating the chemistry, essentially, of that ocean-rock interface,” Raymond said.

Occator Crater, home of the bright spots. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI)
Occator Crater. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI)

The brightest and best-known spots are in Occator crater, a 92-kilometer-wide hole in the ground that is roughly 80 million years old. Occator is covered in vaguely blue, young terrain at its bottom, and shaded somewhat reddish and older around its edges. But it’s the formation on the crater’s floor that has most intrigued scientists: There, among the brightest of the bright spots, is a pit. And rising out of that pit is a fractured, reddish dome.

It’s possible that when Occator formed, the impact not only excavated the crater but heated a portion of the subsurface material enough for ice and other volatiles to waft into space, said Tim Bowling of the University of Chicago. “If you remove all the ice from a region, then you’re able to form a pit,” he said, during a presentation at the meeting. And when that happened, the materials left in the resulting hollow should be the reflective salts.

But how about that dome? Stay tuned. “I just found out yesterday there’s a mound inside the pit,” Bowling said.

It’s no secret that craters are sprinkled across Ceres’ surface. Take a spin around the dwarf planet and multiple pockmarks will fill each frame. But what’s noticeably absent are extremely large craters, the ones more than several hundred kilometers across. These, based on the collisional history of the solar system, should also be carved into Ceres – and yet, they’re missing.

“We must think that those craters formed, and then they got erased,” said Simone Marchi of the Southwest Research Institute. “The question is, How can you erase all those large craters?”

Ahuna Mons is a young, perplexing mountain on Ceres. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI)
Ahuna Mons is a young, perplexing mountain on Ceres. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI)

And then there’s that mountain, a pyramidal oddity called Ahuna Mons. About 5 kilometers tall with steep, bluish slopes, Ahuna Mons looks as though it has been thrust straight out of Ceres. “The mountain is really coming out from the subsurface and taking the surface features, which are a little bit older, up the mountain,” said Ralf Jaumann of the German Aerospace Center. It’s not the only mountain on Ceres, he said, but the others are older and less developed.

Those are just a few of the Cererean enigmas scientists are trying to solve. It’s also possible the world is still alive and venting water vapor into space, that icy volcanism is continually resurfacing parts of it, and that Ceres may not have been born in the asteroid belt – but is instead a wanderer from much farther out in the solar system.

As Dawn continues to spiral around the world, these and other questions may be answered. And then again, they may not. If nothing else, space can be incredibly good at keeping its secrets close.

A Blog by

Need to Punch Some Holes In Mars Rocks? Practice Here.

When NASA launches its next Mars rover in 2020, the robot will search for signs of ancient life on the red planet -- and stash rock samples for a future rover to retrieve. (NASA/JPL-Caltech)
When NASA launches its next Mars rover in 2020, the robot will search for signs of ancient life on the red planet — and stash rock samples for a future rover to retrieve. (NASA/JPL-Caltech)

Not all rocks are created equal. It’s a mundane but inescapable fact that turns out to be particularly problematic if you’re designing a drill for a robot that will be poking holes in Mars.

But who really worries about such things? A team at NASA’s Jet Propulsion Laboratory, where the newest Mars rover is being readied for a 2020 launch to the red planet.

That’s who.

When it’s millions of miles away from Earth, the new rover will not only need to search for signs of ancient life, it will need to be prepared for all the alien rocks it meets. Especially because, unlike its cousin Curiosity, this next-gen robot won’t just be drilling holes in those rocks: It will also be collecting rock cores and stashing them in various spots on the planet’s surface. If all goes well, the rock samples will be picked up and returned to Earth by a future rover, kind of like an interplanetary golden retriever. It’s a complicated strategy that forms the next step in NASA’s long-term plan to explore our small reddish neighbor, a plan that could eventually add human footprints to the rover tracks already pressed into the dusty, formerly wet Martian surface.

But first things first. The Mars 2020 rover needs to be able to drill, extract, store, and deposit all those cores.

“We don’t quite know what we’ll encounter when we get to Mars,” says JPL’s Matt Robinson, deputy product delivery manager for the rover’s sampling and caching subsystem. “We need to have a range of rocks we’re going to test.”

Guinea rocks are piled high along the walls of the rock room. (NDrake)
Guinea rocks are piled high along the walls of the rock room. (NDrake)

Robinson and I are standing in a cavernous lab on the JPL campus, in a place appropriately called the Rock Room. Somewhat ominously, there’s a sign on the door warning against the dangers of inhaling pure nitrogen gas. “Two breaths of 100% nitrogen can cause immediate unconsciousness with no warning,” it says in all-caps, which seems a bit out of place, considering that Mars wears a thin, gassy veneer of carbon dioxide. But no matter.

As its name suggests, the rock room is filled with baskets and baskets of rocks, mostly collected from sites in southern California. There are hard rocks and soft rocks and in-between rocks, and they’re all the geological equivalent of guinea pigs for the drill prototypes Robinson and his colleagues are developing. Like these rocks, some of the Martian targets will be hard and less likely to yield to the machinations of a nosy robot, while others will easily crumble under pressure. As evidence of the team’s ongoing experiments, there are piles of rocks bearing numerous cylindrical gouges.

“It’s somewhat of a design-by-test,” Robinson says. “You do the mechanical design, you build a prototype, then you come into the test bed and you test it.”

Opposite the rock piles are illuminated racks of clear plastic tubes, each holding a 4-inch-long cylindrical rock core. These dozens of tubes are the handiwork of the 2020 drill prototypes, and are almost exactly the type of thing the rover will be stashing on the Martian surface. The various cores are different colors and consistencies, and there’s more material in some tubes than others.

Drill prototypes have collected dozens of cores from test rocks. (NDrake)
Drill prototypes have collected dozens of cores from test rocks. (NDrake)

It occurs to me that it would be bad for the rover to accidentally cache an empty tube for future retrieval.

“Will the tubes on the rover be clear? Could you see into them?” I ask.

“It’s going to be a metal tube so you can’t really see into it, but there’s a camera that will look in and see how much sample there is,” Robinson assures me. He pauses, thinking. “But it would be nice to – like in Star Trek IV — have transparent aluminum…that would be really cool.”

Whales on Mars would also be nice.

Alien humpbacks aside, the plan right now is for the 2020 rover to retrieve as many as 42 rock cores and distribute them in strategic sites that are still TBD. That way, a future rover will only need to visit several locations to retrieve the cached samples instead of inefficiently retracing 2020’s path.

“This is our ambient robotic coring station,” Robinson continues, showing me one of the three drill prototypes the team is currently working with. As imagined, the 2020 drill would have a variety of bits available for tackling rocky obstacles; when the rover encounters an enticing rock, all it needs to do is shove its arm into a tool carousel and select the bit that’s best for the task. When it’s done with one tool, the rover can easily swap it out for another.

Right now, the retinue of options being tested includes a brush that will help smooth rock surfaces pre-drilling, as well as a dozen different bit prototypes. The team is also experimenting with stabilizing legs so the rover can achieve maximum rock-punch, as well as having the rover collect loose material from the surface, called regolith.

“The great thing about this test bed is it’s got a drill press that’s easy to set up and operate,” Robinson says, before the clamor of an ongoing test drowns out the rest of his sentence.

Test rocks await their fate on a platform that can be transformed into a Mars-like environment. (NDrake)
Test rocks await their fate on a platform that can be transformed into a Mars-like environment. (NDrake)

We move into the space where the third prototype lives, and it looks like I’ve stepped into a concert hall. On a small stage, the proto-arm is surrounded by multiple rocks, each with multiple lights and cameras aimed at it. The stage, it turns out, is hydraulic powered – and when the team wants to test the drill under Mars-like conditions, the whole platform can be launched upward until it docks with a pressure chamber hovering overhead.

“We actually raise it up and there are clamps up there which it clamps onto,” Robinson says. “You can pump down to Martian pressure and Martian temperature.”

On Mars, the surface pressure is about 60 0.6 percent that of Earth’s, and temperatures range from a wintry day in Ithaca, NY to somewhere you absolutely wouldn’t want to be. Robinson says the team runs roughly half its tests in the Mars-chamber, under the watchful eye of all those cameras.

But there are more differences between Mars and Earth than simply temperature and pressure.

“Does the different Martian gravity have any effect on the drill?” I ask.

“Gravity actually does affect the robotic arm quite a bit,” Robinson says. He explains that the team has to factor in weaker Martian gravity when teaching the rover where to retrieve bits and stash tubes. “If you were to go to those same joint angles on Mars, it would not work,” he says. “So we have to compensate for that in software. On the flipside, we’re now more capable because we carry less weight. So it’s both tricky and it’s good.”

All of this means that when NASA’s next rover arrives on Mars, expect the red planet to be poked, prodded, zapped and drilled into with all the precision that a wheeled, nuclear-powered robotic surgeon can offer – courtesy of these piles of geologic guinea pigs collected from spots on Earth.

In other words, as Albert Markovski astutely notes in the movie I Heart Huckabees: “You rock, rock.”

A Blog by

How Can We Find Planet Nine? (And Other Burning Questions)

How much do we really know about this faraway world? (Caltech)
How much do we really know about this faraway world? (Caltech)

A large, undiscovered planet lurking on the fringe of the solar system is a compelling idea—and it’s nothing new. It’s been proposed many times. And those predictions have always been wrong.

So what about this latest prediction, the one that might actually be right?

(In case you missed it, a new study from Caltech suggests there might be a large world way out there—a planet whose gravitational hand is sculpting the orbits of distant, icy worlds and forcing them to take weird paths around the sun.)

How can we figure out if the planet is actually there? And will it even be bright enough to see? Here are some answers to these and other pressing questions.

Are we sure it’s there?

No. The evidence is tantalizing, but it’s circumstantial. UCSC astronomer Greg Laughlin gives the planet a 68.3 percent chance of actually existing (“That’s odds-on, but it’s not huge odds-on. It’s also not a coin flip.”) Konstantin Batygin, who’s half of the Caltech team, says he’d put the planet’s chances at 83 percent (“I made that up right now…I’m just being a little bit more realistic than Greg.”)

Others aren’t quite so sure. “I’m very skeptical of this turning up because I’ve seen so many predictions like this—and so far they’ve never turned out,” says Alan Stern, principal investigator of the New Horizons mission that sent a spacecraft zooming by Pluto this summer. “But I’m sure that they ultimately will. I have no doubt that there are lots of planets out there.”

And then there’s Alessandro Morbidelli, of France’s Côte d’Azur Observatory, who told The New York Times he’d bet $10,000 the planet is real.

Want to weigh in? You can log your predictions here.

How do we know it would meet all the criteria to be a planet?

If you mean the criteria defined by the International Astronomical Union in 2006, then we need to know whether the potential planet orbits the sun, is round, and has enough gravitational heft to dominate its orbit.

This planet would obviously orbit the sun, and something with 10 Earth masses is more than massive enough to be round. Regarding the last point—the clearing of small bodies and other junk from its orbit—“Planet Nine is forcing any objects that cross its orbit to push into these misaligned positions. It fits that concept perfectly,” Caltech’s Mike Brown, the other half of the Caltech team, said to the Washington Post.

What would this planet be like?

Cold, for sure. At its closest, the planet is still 200 times farther from the sun than Earth is, and at its most distant is a whopping 600 to 1,200 times farther away than Earth.

At somewhere around 10 Earth-masses, the frigid world will be more like a gassy, mini-Neptune than a rocky planet. This inference is based on information from exoplanets, which tend to show up most frequently in this mass range. So far, though, this type of extremely common planet has been notably absent from the solar system.

Could it have moons?

Possibly. “It would be very interesting to know if it has satellites,” Laughlin says. If those moons are big enough to see, then we could determine the mass of the planet and get a better idea of what it’s made of.

What should we call this planet?

For now, whatever you want, really (but not Nibiru. This is not Nibiru). The world hasn’t been detected yet, and if it ever is, naming the thing will be a formal and lengthy process. The Caltech team is calling it Planet Nine, which is a pointed reference to the controversial reclassification and removal of Pluto from the planetary lineup in 2006, a decision was motivated in part by the work of Mike Brown, who could now be on the ironic cusp of resurrecting a ninth planet.

But…this could also be Planet Ten, based on how you define planet (hi, Pluto!). Or Planet Fourteen (hello, Ceres, Haumea, Makemake, and Eris). Or Planet One Hundred and Something (hey, every round thing). “Apparently, Caltech can’t count,” Stern says.

How could scientists find it?

“Go to a big telescope with a wide field of view, and look at as much sky as possible,” says the Gemini Observatory’s Chad Trujillo, who has spotted a number of very distant solar system objects. “Take three images of the sky, with maybe 1.5-2 hours between each image, and look for things that move. Things that move fast are asteroids and are nearby, and things that are slower are farther out.”

In short, to find Planet Nine, scientists will need to channel Clyde Tombaugh, who spotted Pluto in 1930 after staring at photos of distant starfields and looking for a shifting speck of light.

Yet Planet Nine, if it’s there, will be a bit harder to find than Pluto. It will be dimmer and farther away, and scientists estimate that it takes between 10,000 and 20,000 years to orbit the sun once—so it will move very slowly across the sky.

We don’t know where the planet is in its orbit, but chances are it’s not nearby (because of the way orbits work, this planet spends a lot of time hanging out very far away). Plus, the patch of sky its orbital path covers is huge and crosses the plane of the Milky Way twice. Pulling a planetary needle from a cosmic haystack is difficult under the best of circumstances, but pulling that needle out from a star-studded galactic streamer is even harder.

But it’s not impossible. Scientists could manage to catch a glimpse of something on the fringe using several telescopes on Earth, Trujillo says. He and others say the Subaru telescope on Mauna Kea, as well as a smaller telescope in Chile are capable of finding something that faint and far away. If teams do see something moving, they’ll try to get at least three observations of the object so they can plot a preliminary distance and brightness. And then, over many months of observations, they’ll work to pin down the exact orbit. Brown and Batygin are already looking; Trujillo may start searching next month. “We’re racing, but it’s a friendly race,” he says. “We don’t try to trip each other or anything.”

Wait…how bright is it? 

The real answer is no one knows for sure. A planet’s brightness depends on its size, distance, and composition—and we don’t really know any of those things right now. But there are ways to estimate how bright the world could be, which is something astronomers refer to as magnitude. Because astronomers sometimes like to do things backwards, the magnitude scale is a bit counterintuitive: Objects with higher magnitudes are actually dimmer. For example, Pluto is currently around magnitude 14. The sun? That’s –26.74. If you’re in a big city, you probably can’t see anything dimmer than magnitude 3, maybe 4 at best.

Batygin and Brown have calculated that when it is closest to the sun, this planet is around 18th magnitude, which is bright enough to be picked up with high-end backyard telescopes. That’s why it’s unlikely to be close to the sun now—we would have already seen it.

At its farthest, the planet would be around 24th magnitude, or about 10,000 times dimmer than Pluto. That’s not too dim for a telescope to see, but it doesn’t make spotting the planet easy. Remember, this faint speck of light is going to be moving very slowly through a dense field of stars.

How did they do that brightness calculation, given we don’t know how big it is, where it is, or what it’s made of?

Batygin and Brown assumed the planet is between two and four times larger than Earth (more on that in a minute) and has a Neptune-like reflectivity, which is a property that matters when you’re thinking about how much light bounces off an object. Reflectivity is known as albedo, and is reported on a scale from 0 (very dark) to 1 (very bright).

The reason for the Neptune-like assumption is that, at roughly 10 Earth-masses, this planet is likely more of a gas-shrouded mini-Neptune than something with a hard, rocky surface. Not surprisingly, different atmospheres have different reflectivities (and what if it’s covered in bright white clouds?), so there is some uncertainty in this portion of the calculation.

But the biggest uncertainty in the brightness calculation (aside from distance) comes from the planet’s size, which could be between two and four times bigger than Earth, and the area of a reflecting surface scales as the square of the radius. “The size uncertainty of a factor of 2 leads to an area uncertainty of a factor of 4,” says Andy Rivkin of The Johns Hopkins University Applied Physics Lab. “That corresponds to 1.5 magnitudes all by itself.”

Overall, that kind of uncertainty isn’t terrible, and most estimates of this planet’s brightness at its farthest point tend to hover between 23rd and 25th magnitude. “I would say that at a given distance there’s probably 1-2 magnitudes of uncertainty in the prediction,” says Laughlin, who independently reached a conclusion very similar to Batygin’s and Brown’s, assuming a world that is ¾ the size of Neptune and has the same albedo.

Could we use a similar technique to find planets around other stars?

Yes, if we could make such detailed observations of small bodies around other stars (which we can’t). The question would then become, is it easier or harder to prove the existence of an exoplanet based on how it perturbs exo-smallthings?

Laughlin argues that it would be easier. Discoveries in the solar system, he says, are held to a higher standard of proof than discoveries around other stars. “If there was some mechanism for returning very accurate observations of comet orbits in an exoplanet system, and you saw this amount of evidence, I think it would just be a no-brainer that there’s a 10-Earth-mass planet perturbing that stuff.”

Stern agrees. “I’m trying to think about whether that’s sociological or actually scientific,” he says.

NASA’s Natalie Batalha, a member of the planet-hunting Kepler team, notes that planets around other stars have already been discovered based on how they perturb other objects—notably, other planets. In 2011, scientists described a planet called Kepler 19c. The planet hadn’t been directly detected, but its presence was inferred from the way it jiggled its planetary sibling, called Kepler 19b. As the pair orbits its star, 19c’s gravitational hand pulls on 19b, changing the frequency with which 19b periodically blocks out its star’s light. Scientists can use those slight variations, called transit timing variations, to constrain the orbital period and mass of the invisible, perturbing planet, and the method is thought to be sensitive enough to detect low-mass planets.

It’s not clear whether transit timing variations offer more precise constraints than the whacked-out orbits of icy worlds in the faraway solar system, but it’s certainly interesting to think about.

Is this planet the fifth giant that scientists think Jupiter kicked out way back when?

No. First of all, the idea that our solar system once had a fifth giant planet comes from simulations of our neighborhood’s early days. Plunk a fifth world in the realm of the giants (Jupiter, Saturn, Uranus and Neptune), and you end up with a solar system that looks much more like the one we live in today. If that fifth large sibling was there, it would have been punted into space by that jerk Jupiter’s gravity hundreds of millions of years after being born.

Batygin and Brown think their planet would have been thrown outward within several million years after the sun formed. Back then, our star was still in its native birth cluster and the surrounding stars would have helped keep the flying planet from hurtling forever into space (it’s worth mentioning that some scientists, such as Hal Levison of the Southwest Research Institute, don’t consider this scenario to be incredibly likely).

What’s more, this planet would have been less of a full-fledged giant and more of a planetary core—something like a seed from which a larger planet could have grown, had it been given the chance.

“These two events are both ejections, but they are well separated in epoch,” Batygin says. “The planet that was ejected during the giant instability of the solar system—which, by the way, coincided with the formation of the Kuiper Belt—that planet, if it was there, it was just ejected. It doesn’t get to stick around.”

A Blog by

The Curious Case of the Blood-Stained Moon

Mysterious red streaks are painted on Tethys. (NASA/JPL-Caltech/SSI)
Mysterious red streaks are painted on Tethys. (NASA/JPL-Caltech/SSI)

Curving across the surface of Saturn’s moon Tethys are crimson streaks – and scientists have no idea what the material is or how it got there.

“It’s clearly painted on the surface in some way that we do not as yet understand,” says Paul Schenk of the Lunar and Planetary Institute, who presented the observations Tuesday at the American Geophysical Union’s annual meeting. “We basically have a little mystery.”

At just a bit more than 1,000 kilometers across, Tethys is a medium-sized moon and is made almost entirely of water ice. Aside from the bloody arcs, its surface is pretty normal as far as outer solar system moons go: There are a bunch of craters, including a 450-kilometer-wide behemoth called Odysseus, and a lot of fractures. And then there are the streaks, which are a few kilometers wide and hundreds of kilometers long.

“We have these bloody stains on Tethys,” Schenk says.

Tethys (back) and Enceladus (front) are lined up in front of Cassini's camera. (NASA/JPL-Caltech/SSI)
Tethys (back) and Enceladus (front) are lined up in front of Cassini’s camera. (NASA/JPL-Caltech/SSI)

The red streaks were faintly visible in early images from NASA’s Cassini spacecraft, which swooped into the Saturn system in 2004. But it wasn’t until April that Cassini got a close look at the extraterrestrial artwork. Now, after a close flyby in November, scientists can peer even more closely at the smudges. And what they’re finding doesn’t make a lot of sense.

“You don’t see any trace of scarps or ridges or depressions of any kind,” Schenk says, meaning there are no obvious landforms associated with the smears – or at least nothing that’s big enough to see at Cassini’s current resolution. Some of the nearby craters have odd, dark material inside them, but it’s not clear what that material is, how it got there, or if it’s associated with the streaks at all.

Instead, it appears as though someone simply painted the moon red.

“If you didn’t have the color, you wouldn’t know they were there,” Schenk says.

Perhaps the best clue about where the streaks are coming from can be found by plotting their locations on the moon. When Schenk mapped the lines onto the moon’s surface, he saw a pattern suggesting the moon is being squeezed or deformed by some kind of global stress – such as irregular rotation, a shifting orbit, or the migration of its poles. But simulations of those processes don’t produce landforms that quite line up with where the streaks are.

One thing is clear, though: The streaks are relatively young. Normally, dust from Saturn’s E ring and charged particles from space would erase the smudges. But they’re still there. And, they’re drawn on top of the Odysseus basin, meaning that the crater came first. Scientists aren’t sure precisely how old Odysseus is, but Schenk suggests it couldn’t have been made more than 2 billion years ago.

The enormous Odysseus crater on Tethys is 450 kilometers across and nearly 10 kilometers deep. (NASA/JPL-Caltech/SSI)
The enormous Odysseus crater on Tethys is 450 kilometers across and nearly 10 kilometers deep. (NASA/JPL-Caltech/SSI)

Schenk’s best guess now is that the streaks are associated with fractures that Cassini can’t quite see, and that those fractures are currently forming or have been reactivated recently, exposing material that might not be water ice like the rest of the surface.

As Cassini’s days of exploring the Saturn system wind to a close, scientists are hoping to solve this little mystery – and spy on a host of otherworldly enigmas associated with the giant, ringed planet and its clutch of moons.

A Blog by

Dawn Finds Evidence for Salty Spots, Morning Mist on Ceres

Occator crater on Ceres is home to the dwarf planet's brightest spots, which scientists now think are rich in salts. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
On Ceres, Occator crater is home to the dwarf planet’s brightest spots, which scientists now think are rich in salts. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

The largest world in the asteroid belt is sprinkled with bright, enigmatic spots, could have craters that fill with haze each morning, and may even be a transplant from far, far, away, scientists report today in Nature.

These preliminary conclusions are based on data from NASA’s Dawn spacecraft, which has been orbiting the dwarf planet Ceres since March. Large, round and watery, Ceres isn’t quite like the rest of the space rocks that live between Mars and Jupiter. And the more scientists learn about the place, the stranger it gets.

“Ceres has been a mystery,” says UCLA’s Christopher Russell, principal investigator for the Dawn mission, noting that there are no pieces of Ceres that have fallen to Earth. “We had to go out there and see what it was because we didn’t have the clues.”

Dried Up Salty Spots?

Another view of Occator crater. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
Another view of Occator crater. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

Before Dawn even spiraled into orbit around 950-kilometer-wide Ceres, scientists were transfixed by what appeared to be extremely bright splotches on the world’s surface. For months, the Dawn team guessed the splotches might be made of highly reflective water ice –- and even suggested that one of them could be spitting water into space. Now, as often happens in science, it looks like those early guesses weren’t quite right.

As Dawn neared Ceres, the team realized the spots were dimmer than they’d expected – and not nearly bright enough to be water ice. (In fact, Ceres itself is more or less as reflective as freshly laid asphalt – which is to say, not very bright at all.)

“The next brightest thing is salt,” Russell says, referring to the spots. “There’s a number of different salts that could have been made in the interior by the chemistry that goes on between rocks and water.”

The team doesn’t know precisely what the spots are made of, but scientists suggest they could be reflective, sulfate-containing salts – the kind of stuff that might be left behind as ice tucked into salty crystals warms and turns into water vapor, says Andreas Nathues of the Max Planck Institute for Solar System Research.

“The bright spots are remnants of a water ice sublimation process,” he says.

So far, Dawn has taken its closest look at the cluster of spots in Occator crater, which are the biggest and brightest, and also among the youngest. Mostly found inside craters, more than 130 of the enigmatic splotches sprinkle the world’s surface. Nathues notes that the spots’ occurrence within craters is no accident, and that the team suspects impacts trigger their generation by digging into a buried, frozen layer of water. So it’s likely that while water ice still exists in Occator, it has disappeared from the older spots.

“We think these bright spots have the same origin,” Nathues says. “Most of them are today dehydrated.”

Morning Mist?

Some scientists suggest that when sunlight reaches Ceres' Occator Crater, a kind of thin haze of dust and evaporating water forms there. (Image and caption:
Some scientists suggest that when sunlight reaches Ceres’ Occator Crater, a kind of thin haze of dust and evaporating water forms there. (Image and caption:NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

But there’s more: Observations suggest that each morning, as the sun rises, a morning haze or mist fills two of Ceres’ craters, Occator and Oxo. The haze isn’t very thick and is likely less than a few hundred meters high – and it disappears by dusk, only to reappear the next morning. Nathues suspects the morning mist could be produced as buried water ice is warmed by the rising sun. If it’s there, that hovering water vapor could explain a 2014 observation made by the Herschel space observatory, which showed that Ceres had thin tufts of water vapor surrounding it.

“The longitudinal position at which Herschel found the strongest water vapor absorption line fits with the longitude of Occator,” Nathues says.

But it’s still too soon to say if the haze is really there, says William McKinnon of the Washington University in St. Louis. He’s unconvinced that what appears to be haze isn’t just an artifact of the angle at which Dawn is peering into these craters, and says he’d like to reserve judgment until the spacecraft can take an even closer look at what’s going on.

“It’s not a slam dunk,” McKinnon says. “Dawn is going into its lowest orbit, so presumably will be getting even more and better pictures of this puppy in the coming months.”

An Outer Solar System Origin?

In 2008, McKinnon suggested that Ceres may have been born in the outer solar system – way far out, near where Pluto and countless other icy worlds live. It has much more water than its fellow asteroids, he argued, and early estimates of its density were similar to those of objects in the Kuiper Belt, an icy debris ring beyond the orbit of Neptune.

At a recent conference, scientists shared some observations that might support this idea, and the same observations were published in Nature today: On Ceres’ surface, Dawn spotted what appear to be clays containing ammonia, which isn’t a compound that’s normally found in the warm inner solar system. Here, ammonia-containing ice would just evaporate. That’s why Maria Cristina De Sanctis, an astronomer at Rome’s National Institute of Astrophysics, says she wasn’t expecting to see this particular type of clay, known as ammoniated phyllosilicates.

“So the question boils down to, where does the ammonia come from?” McKinnon asks. “Maybe stuff from the outer solar system got mixed into the asteroid belt and got widely distributed. Or maybe Ceres as a whole got implanted in the asteroid belt.”

This graphic shows two different explanations for how ammonia got to Ceres. In the top panel, it was delivered by materials from the outer solar system. The bottom panel shows Ceres itself being implanted into the main asteroid belt.
This graphic shows two different explanations for how ammonia got to Ceres. In the top panel, it was delivered by materials from the outer solar system. The bottom panel shows Ceres itself being implanted into the main asteroid belt. (L.Giacomini)

The only solid surfaces where significant amounts of ammonia have been found are in the outer solar system: Charon, Pluto’s largest moon; Orcus, another body in the Kuiper Belt; and Miranda, the innermost moon of Uranus.

But both McKinnon and Andy Rivkin, of the Johns Hopkins University Applied Physics Laboratory, note that recent work has uncovered tiny amounts of ammonia in meteorites that have been chipped off of main belt asteroids. “If it turns out to be ammoniated phyllosilicates, which is a decent if not slam dunk bet, that doesn’t mean it has to be an escaped Kuiper Belt Object or necessarily have these outer solar system pebbles,” Rivkin says.

It’s also possible, they both say, that Ceres was once much more active, and that water percolating through its interior may have helped form and push the the ammonia-containing clays to the surface, concentrating whatever small amounts of ammonia were naturally inside Ceres into a region where Dawn could see it.

Determining which of these scenarios actually took place will be complicated, especially from orbit – but as Dawn snuggles in close to Ceres this week, scientists will give it their best shot.

A Blog by

Now Orbiting Cloud-Shrouded Venus, Akatsuki Sends New Images

It’s not every day you hear about a troubled spacecraft making a desperate attempt to cling to a planet — for the second time.

After missing its first chance to orbit Venus, Japan’s Akatsuki spacecraft circled the sun for five long years, waiting for the right time to try again. That moment came on Dec. 7, a half-decade to the day after a broken nozzle sent Akatsuki hurtling toward the sun instead of falling into the gravitational clutches of Earth’s sister planet. But with its large, main engine crippled, the spacecraft needed another way to slip into orbit. That responsibility went to four smaller thrusters that are normally used to adjust where the spacecraft is pointing; for 20 minutes they fired, nudging Akatsuki onto a course for capture as it skimmed the Venusian cloud tops.

(Akihiro Ishita/JAXA)
This image, illustrated before Akatsuki took its second shot at Venus, depicts a scene very much like what happened as it fired its thrusters on Dec. 7. “I was deeply moved to realize it,” says Akatsuki’s project manager Masato Nakamura. (Akihiro Ikeshita/JAXA)

And then the team commanding the spacecraft, at the Japan Aerospace Exploration Agency, waited. Shifts in the radio waves Akatsuki uses to communicate with Earth would indicate whether the spacecraft had changed course. If it hadn’t, there was a small window in which the team could try again, using an alternate set of thrusters. And if that didn’t work? Well, no one wanted to think about that. The third time might be the charm on Earth, but in space, getting even a second chance is exceedingly rare.

An hour later, scientists shared the exciting news: “It is in orbit!!” reported Sanjay Limaye, of the University of Wisconsin-Madison, who was with the team in Sagamihara, Japan. The question was, which orbit? Was it stable? Could the team talk with the spacecraft? Is Akatsuki healthy?

It would take two days of analysis to work out the precise path Akatsuki is taking around the cloud-shrouded world. On Dec. 9, scientists announced that the orbit is a bit more stretched out than anticipated, though it’ll do. Now, Akatsuki takes a little more than 13 days to orbit Venus, swinging from 400 kilometers above the planet’s surface out to 400,000 kilometers away. Over the next four months, engineers will reshape the spacecraft’s path so it will complete one trip around Venus in fewer days — and then in April, the real science observations will begin.

Akatsuki's current path around Venus, and the one it will slip into as science observations begin. (JAXA)
Akatsuki’s current path around Venus, and the one it will slip into for science observations. (JAXA)

For now, the team will be making sure that all the instruments on board the spacecraft are working. After all, Akatsuki was originally designed for a two-year mission in space — an amount of time it has already surpassed while circling the sun. The spacecraft’s extended trip around the solar system brought it closer to the sun than scientists had intended, meaning Akatsuki’s instruments have encountered temperatures a bit warmer than they were designed for.

So far, though, the team says the spacecraft is healthy — and as proof that at least some of the onboard cameras are undamaged by Akatsuki’s sojourn in space, has released three images taken as the spacecraft slipped into orbit (see gallery, above). These are the first closeup images of Venus we’ve seen in a while, and with no new missions to the planet on the schedule, they could be among the first of the last for the foreseeable future.

If all goes well, Akatsuki will hover above the planet for the next two years, peering into the churning, super-rotating atmosphere that whips around Venus faster than the world itself rotates. Once thought to be very much like the Earth, the Venus of today is a hellish wasteland, transformed into a planetary inferno by runaway greenhouse gases. It has the hottest recorded temperature in the solar system (aside from the sun), a young surface that shows signs of recent volcanism, and sulfuric acid clouds that flash with lightning.

But from afar, Venus shines more brightly than just about anything else in the sky. It’s a shimmering, tranquil pinprick of light that has bewitched astronomers, poets and entire cultures for millennia — and now, after a drama of interplanetary proportions, it has a plucky little robot friend once again.

A Blog by

Japanese Spacecraft Gets Rare Second Chance to Visit Venus

After five years orbiting the sun, Akatsuki fired its thrusters and headed for Venus. (Akihiro Ikeshita/JAXA)
After five years orbiting the sun, Akatsuki fired its thrusters and headed for Venus — a second time. (Akihiro Ikeshita/JAXA)

In space exploration, second chances are rare. Yet today, just before 4 p.m. U.S. Pacific time, a Japanese spacecraft called Akatsuki fired its thrusters and attempted to rendezvous with Venus.

An hour later, the team commanding the spacecraft shared some good news.

“It is in orbit!!” reported Sanjay Limaye of the University of Wisconsin-Madison, who is working with the science team in Sagamihara, Japan.

This isn’t the first time Akatsuki has attempted to orbit Earth’s twisted sister – that happened five years ago to the day, in December 2010. Back then, though, something went horribly wrong. Instead of putting on the brakes and pulling into orbit, Akatsuki zoomed past Venus without stopping. Engineers would later determine that a valve in the spacecraft’s propulsion system had cracked, rendering the main engine useless. But the team didn’t give up, and instead decided to let Akatsuki try again…even though it meant waiting half a decade.


Today, Akatsuki relied on a set of smaller thrusters to head toward Venus. Four of those thrusters were programmed to fire for about 20 minutes, gently adjusting the spacecraft’s course so it could be captured by the planet’s gravity. If all went well, the spacecraft’s new orbit around Venus should take it between roughly 5,000 and 300,000 kilometers of the planet’s surface.

“We had a perfect operation!” says project manager Masato Nakamura, of the Japan Aerospace Exploration Agency‘s Institute of Space and Astronautical Science.

That’s not as close to the cloud-shrouded planet as scientists had originally planned, but the team says it should be able to complete its science objectives as long as Akatsuki is healthy. From its perch, the spacecraft will study Venus’s dense, toxic atmosphere, which whips around the planet at speeds exceeding 300 kilometers per hour (faster than Venus rotates.)

“We have to wait another two days to confirm the orbit,” Nakamura says. “I am very optimistic. It is important to believe in success!”

A Blog by

Highest-Res Pluto Images Reveal A Complex, Beautiful World

Two weeks ago, I wrote about how difficult it can be to focus on science when the world is tearing itself apart. As this latest terrible chapter is being written into the already overwhelming history of violence on Earth, I worry I might find myself seeking solace from that post’s optimism more often than I want to.

In it, a friend reminded me that tales of science and adventure can be powerful antidotes to stories of suffering and destruction. Exploring new worlds and uncovering new knowledge? “That’s what we should be doing,” Kareem Shaheen, who covers the Middle East for the Guardian, told me.

And so today, when NASA revealed the newest images of Pluto taken by the New Horizons spacecraft, I switched off everything and dove into the intricate, exotic landscapes of an alien world. These are the highest resolution images of Pluto we might see in our lifetimes — images where features smaller than a football stadium are visible. In them, we see jumbled blocks of ice-mountains that look as though they’re being pushed to the shoreline of a frozen sea that’s bubbling in slow motion. Impacts that excavated chunks of Pluto’s surface reveal curiously colored layers beneath its crust. There are pits and ridges that look as though they’ve been stretched and bent as Pluto’s ices move across its surface, areas where erosion has sculpted some intricate landscapes, and things I’m having a hard time even describing.

There’s no question that exploring this distant, icy world is a story about the human mind and spirit at its best; so give yourself a break and zoom over these Plutoscapes.

A Blog by

Pluto’s Heart Has Been Broken for Billions of Years

Sputnik Planum, the bright icy region that forms the western half of Pluto's heart, sits in an ancient impact basin. (NASA/APL/SwRI)
Sputnik Planum, the bright icy region that forms the western half of Pluto’s heart, sits in an ancient impact basin. (NASA/APL/SwRI)

Billions of years ago, a piece of interplanetary debris smashed into Pluto and left an 825-kilometer-wide crater. But instead of turning into an ugly pockmark, that mighty scar may be responsible for one of Pluto’s most charismatic features: Its icy heart.

New data from NASA’s New Horizons spacecraft, which flew past Pluto in July, are helping scientists better understand the incredibly varied features on the world’s surface, which include smooth icy plains, parallel blades known as “snakeskin terrain,” and potential ice volcanoes.

Recently, observations revealed a circular feature surrounding the western ventricle of the striking, heart-shaped region known as Tombaugh Regio.

“The question is, could this be a relic giant impact basin?” asked Paul Schenk, at the 47th meeting of the American Astronomical Society’s Division for Planetary Sciences. “The key to that question is, is it deep? And the answer is yes.”

The basin is about 4 kilometers deep and stretches roughly one-third of the way across the icy world, said Schenk, of the Lunar and Planetary Science Institute. Finding a similarly sized gouge means going all the way to the other end of the solar system – to Mercury, where the Caloris impact basin stretches roughly one-third of the way across that roasted, dense world. (To put this in Earthly perspective, it would be as if a crater obliterated everything between Mexico and Canada, from California to North Carolina — aka, the majority of the United States.)

On Pluto, the smooth icefield known as Sputnik Planum sits within the basin. It’s a region that — unlike the possibly 4-billion-year old scar — is relatively young, at about 10 million years old. The edges of the basin are steep in the north but degraded in the south, where a large portion of the rim is missing. But the general shape is still obvious.

“It is indeed circular, except for the southern extension,” Schenk said. “The floor is basically flat.”

The smooth, icy plain called Sputnik Planum sits in an old impact basin. (NASA/JHUAPL/SwRI)
The smooth, icy plain called Sputnik Planum sits in an old impact basin. (NASA/JHUAPL/SwRI)

The impact created a depression that may have been perfect for accumulating flowing ices, especially given its location on the side of Pluto that never sees its large moon, Charon, said Douglas Hamilton of the University of Maryland, College Park. Pluto and Charon are locked in a whirling dance in which they keep the same face pointed at one another all the time. So Charon never fills the skies over Sputnik Planum – and none of the meager sunlight it reflects as Charonshine ever warms the cockles of Pluto’s heart.

That geometry helps make the region an efficient cold trap, or an area where ices can congregate. And that does seem to be what’s going on here. Will Grundy, from the Lowell Observatory, reported at the meeting that Sputnik Planum is full of basically every type of ice that has been spotted on Pluto, including carbon monoxide, nitrogen, and methane. The only species that’s conspicuously absent is water ice, which makes up the planet’s soaring mountains.

In fact, Sputnik Planum is more like an ice cap than anything else.

“We see ice caps throughout the solar system — ice caps on Earth, ice caps on Mars,” Hamilton said. “What we have to do is explain why this ice cap is at 30 degrees north on Pluto.”

It will take a bit of work to sort out exactly what happened, but scientists are well on their way to solving the mystery of Pluto’s heart.

A Blog by

Charon: A Dark Moon With a Dark Past

Something is rotten in the state of Charon, Pluto’s giant moon. OK maybe not rotten, exactly, but it’s just not…right.

Before the New Horizons spacecraft took a tour of the Pluto system in July, scientists guessed they might see a few interesting features on Charon — things like craters, and more craters, and maybe some notable landforms because Charon’s water ice surface is sturdy and capable of supporting dramatic landscapes. Several team members even dared to suggest that Charon would be surprisingly interesting — perhaps even more interesting than Pluto.

But overall, guesses seemed to converge on Charon being a dead, cratered husk.

“Craters were the number one thing people said we’d see on Charon,” said Amanda Zangari of the Southwest Research Institute, who conducted a survey of New Horizons team members before the flyby. But, she noted back in June, “I think we’re going to find that Charon is not just a dull, gray featureless thing.”

Turns out, Charon is totally not a dull, gray featureless thing.

It has curiously few craters, especially in its southern hemisphere, and a surface riven with massive canyons (some of which have cool informal names, like “Serenity Chasma”). It even has a mountain in a moat. Charon’s north pole is reddish — the same color red as the band near Pluto’s equator — and there’s a dark blotch on the hemisphere that faces away from Pluto.

In fact, the whole moon is dark, way darker than Pluto. Charon might not look especially shadowy in the image above, but that’s because of how those pixels were processed. If you look at the giant moon in relation to Pluto, its companion in binary planethood, you’ll see just how spooky it is. While Pluto is splattered with bright ices and colorful smears, Charon looms in the background like a scarred, charred world emerging from the darkness.

Paintballed Pluto and dark, charred Charon. Click for full-size image. (NASA/JHUAPL/SwRI)
Paintballed Pluto and dark, fractured Charon shine in this enhanced color composite. Images of both worlds were processed identically, so their colors — and sizes — can be compared. Click for full-size image. (NASA/JHUAPL/SwRI)

To me, it looks like half of Charon’s crust is missing, as if someone started peeling it like an orange and gave up after the southern hemisphere. The remaining northern rind is cratered, stained and old, while the southern pith is younger and smoother. The real story is probably much more interesting (yes, even more interesting than a giant peeling a moon). One early idea explaining the startling differences in terrain between Charon’s hemispheres invokes cryovolcanism, or the eruption of icy, frozen, maybe oozy materials. Icy satellites in the outer solar system appear to be particularly good at generating flavors of frozen “lavas”: Think geysers on Enceladus, plumes on Triton, and (possible) ice volcanoes on Titan.

Once upon a time, as the story might go here, a buried ocean sloshed inside Charon’s icy shell. At some point, as the moon froze, pressure started to build in the liquid water locked inside. As that pressure forced the water upward, it found a weak spot in Charon’s shell — and then all hell broke loose. Like water bursting through a crack in a dam, the ocean spilled onto Charon’s surface, coating part of it in smooth, young plains and erasing all the stuff that was there before. Younger crust, explains The Planetary Society’s Emily Lakdawalla, would be denser and thus sink below the older crust, explaining the elevation differences between Charon’s halves.

See? Icy volcanism at the solar system’s edge is way more interesting than imaginary cosmic giants, and perhaps not that uncommon on larger worlds in the Kuiper Belt.

If that did happen, it’s not the only violent event in Charon’s history. After all, the Pluto system was born from a giant impact — a collision that knocked proto-Charon into proto-Pluto and chucked out all kinds of icy shards that ended up forming the smaller moons. How the system evolved into the spectacularly diverse cast of characters we see today — paintballed Pluto, fractured Charon, super-dark Kerberos, odd-looking Nix, and so on — is still a mystery.

*Thank you to Emily Lakdawalla and Sarah Hörst for helpful discussions.*