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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.

4 thoughts on “Pluto’s Heart Has Been Broken for Billions of Years

  1. A massive impact doesn’t quite explain all of Sputnik Planum’s mysteries. There is the fact that the ices within the basin appear to be boiling, albeit very slowly. The pattern of irregular polygons that covers most of Sputnik Planum matches the morphology of convection cells. The fact that the size of the evaporation pits within individual cells is smallest in the middle and grows towards cell edges confirms that convective circulation is going on. A pit’s size is related to the age of its bit of the surface. The question is where is all the heat to drive the convection coming from if the impact happened billions of years ago?

    In the north of Sputnik Planum the ices appear to be flowing onto the terrain and around obstacles, distorting the shapes of convection cells. But why is it only happening in the north? Meanwhile, great glaciers are carrying ices into Sputnik Planum from the right side of Pluto’s heart, but how did such vast amounts of the ices get onto the right side of the heart in the first place? There is no sign of any kind of weather on Pluto that might dump the massive amounts of snow needed to fill the lakes or feed the glaciers.

    Craters have raised rims. Really big craters, like Caloris on Mercury, are surrounded my multiple rings of mountains. There aren’t any rings around Sputnik Planum. With all the evaporation happening from Sputnik Planum it seems more like a source of Pluto’s atmosphere, rather than a place for it to collect in.

    The story of Sputnik Planum seems to be more complicated than just being the site of a big impact.

  2. This is a great theory for how this region formed, but it is just that – a theory. Not a single word concerning this “giant impact basin” theory has come out of the actual New Horizons team. So please don’t make definitive statements as if this impact basin is an accepted fact.

  3. First of all, we have to think analogically. What does the image of Sputnik Planum looks like from an earthy perspective?
    For me, most of the features seen here are making sense when you try to imagine the effects of something falling down to a liquid (an very deep ocean) deeply frozen in surface,
    The surface (dark and cratered terrain) will be vaporized (sublimed) near the center of the impact, but broken in pieces at the edges of “the hole” (i.e. the Hillary and Norgay Mnts), Some liquid will be ejected out of the flowing ice hole and be splashed upon the surrounding old terranes (the left part of “the heart” for instance), or infilling a few old (and smaller) impact craters,
    The center part of the impact basin will be made of hot liquid with convective cells during a certain time after the impact, at the edge of the still warm “sea”, small “débris banks” will remain a certain time too, bat as we are on a world that is on a very deep cold region of our solar system, everything will soon be deepfrozen, leaving big water ice cubes (icebergs) high as mountains, convection currents instantly-like frozen, and flow figures in bays along the impact basin.
    No need to speak of mysterious nitrogen-ice flowing abilities, no rim for the impact crater, as it has not impacted on rock-hard ice bedrock, but on rock-hard ice flowing over a deep liquid ocean,
    We may even think that these flow patterns on the shores of Sputnik Planum could have been made by the still warm éjectas flowing back to were they came from, as does water from the waves are flowing back to the ocean, but caught by the cold during their move.
    And the tiny (!) dolines-like holes widely spread on the polygonal patterns can be sublimation along ice cracks too small to be resolved for New Horizons instruments.
    Of course this point of view needs to be refined from the future images we will still recieve, but starting to think on a new basis will certainly be worth of it.
    Just a space stone throwed in a frozen ocean planet, The other craters were made by stones too tiny to break the polar ice crust,

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