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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.

9 thoughts on “Will the Real Earthlike Planets Please Stand Up?

  1. For me they are many other worlds like earth
    And for me the human being never has to go there
    He’s too cruel don’t respect nature and life
    And too they are many civilisations outter space
    They know about the human being
    That planet is a hell
    The NASA know a lot about space civilisations and artefacts
    Me i already disgusted by the human being

  2. And then there’s the issue of “time” when we’re interested in the possibility of life existing on an “appropriate” Earth-like world. Life may be possible but never got a start. Or, it may have begun and been terminally wiped out by “nature” or themselves. Part of the variables in your dad’s famous equation.

  3. Let us try and put as much effort as they are about whats out there than trying to solve the real problems here on earth

    1. Scientific value is not a linear process. There are microscopes that are helping women avoid cancer that were built to help the Hubble space telescope peer into space. The study of light and magnetism was not done with the purpose of resonance scanning in a doctors office. The benefits of a specific scientific understanding to the human condition in most cases is unknowable. Scientific understanding of the processes in our world and the universe is a noble endeavor by its own right. The scientific pursuit has proven its value time and time again. By the very contributions of what scientific investigations have given us even when the science was done only for the purpose of knowledge is so enormous it has earned the right to be supported in its investigations of all phenomenon no matter how irrelevant it may seem to the casual observer

      . It is very possible a child will enter science because they are excited by the discovery of these new worlds. What new technology in medical, energy, or other field will be transformed because that one child was drawn to science by the fascination of the discoveries of these planets.

      Its also fair to say that it is scientist who are working on trying to solve man kinds greatest challenges on earth. The answers to our issues in many ways are already clear. The problem isn’t the science. It is the political and social will to make the necessary changes to live in more harmony with our natural environment. Having a system that shares more of the fruits of the earth with all instead of being hoarded by the powerful and wealthy few. Working to reduce the burden on resources by slowing down the population increase on the planet. Much of which is happening in the poorest regions on the planet.

      Science and scientist can only show us what the reality of the world is. If we ignore or deny what they tell us, that is on all of us. It can not be blamed upon the scientist or science for delving into some science you find less valuable. As science by its very necessity must be the investigation and discovery of all the mysteries of our reality if it is to be truly and fully robust.

  4. As an 8,000 year old civilization in a 13.7 billion year old observable universe, we’re lucky to have lived at the same time as David Bowie, let alone an entire alien civilization.

  5. I’m going to make some wild estimates which I hope will make a point.
    a. What % of the galaxy [any galaxy?] contains stars with planets containing possible carbon-hydrogen-oxygen-nitrogen based life? Estimate: 25%. Central galaxy planets may be in hyperenergetic environments [high energy X-Rays, gamma rays etc.] making a successful combination of organochemicals impossible.
    b. % of stars with orbiting planets: 50%
    c. % of planets with temperatures, masses, atmospheres, liquid water, light and heavy metals, etc. that MIGHT produce initial life: Highly optimistic assumption: 0.1%.
    d. initial molecular “life’ organized into first “cell”: Who knows, but lets give it 10%.
    e. The chance that the initial cell ‘evolves’ to the [more-or-less] bacterial equivalents: 10%.
    f. The chance that ‘prokaryotes’ evolve to produce eukaryotic cells: 10%
    g. The chance that unicellular eukaryotes evolve to simple multicellular organisms: 10%
    h. The chance that simple multicellular organisms evolve into complex organisms: 10%
    i. The chance that complex organisms evolve into human-level intelligence: 1.0%
    j. The chance that the human species overlap with the above intelligent life temporally: We don’t know how long the human species will last but let’s assume that we are now at the mid point and that the human species goes extinct in another 200,000 years, for a total species time of 400,000 years which is roughly is about 0.005% the time the Earth is estimated to be able to support complex life. Let’s make similar temporal assumptions about intelligent life on another world which means that the chance of our living at the same time as intelligent life on another world is about 0.000025%, all things being equal. But all things aren’t equal. Intelligent life probably takes a long time to evolve, just like on Earth, so we can ‘improve’ our number to 0.0001%.

    So let’s add ’em up: The galaxy contains 100,000,000,000 stars of which 75% are excluded, leaving us with 25,000,000,000 stars. Half of these stars have planets: 12,500,000,000 stars. How many of these planets might conceivably produce the most primitive life? 12,500,000. How many of these planets might develop ‘bacteria’? 125,000. The first eukaryotes? 12,500. The first complex life: 1,250. The number of planets on which human-level intelligent life might develop: 12.5.

    So, using my very, very rough calculations 12-13 worlds in the Milky Way Galaxy might develop intelligent life. But the chance that such intelligent life my overlap with us temporally, is about 0.0012%, so that the odds are very much against our bumping into one of these aliens….but….the Universe contains 100,000,000,000 galaxies [give or take a few tens of billions] so, using my estimates, there should be about 100,000,000 worlds out there harboring intelligent life during the time of man on Earth.

    But: This intelligent life won’t be related to us. We are more closely related to the radish in our garden than we could possibly be to life–intelligent or not–on another world. After all, we share a genetic lineage with the radish.

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