Tag Archives: Sputnik Planum

Pluto’s Broken Heart

Scientists studying the data from New Horizons have had an absolute wonderland to play in, but one of the most compelling features right from the start was definitely Pluto’s “heart” — a vast white plain called Sputnik Planum that covers a huge portion of the surface.  It’s completely unlike the rest of Pluto’s visible surface, is clearly very young, geologically speaking, and has a curious geometrical coincidence: it’s directly in line with the the Pluto-Charon barycenter.  Pluto and Charon are mutually synchronous — that is, due to tidal interactions between the two bodies, they have settled into an arrangement where one rotation of Pluto is the same as one rotation of Charon and also one revolution of Charon.  Our own Moon rotates synchronously — it is tidally locked to the Earth, which is why we only ever see one side of it.  But the Pluto-Charon system has evolved further: not only is Charon locked to Pluto, but Pluto is locked to Charon.  If you stood on Sputnik Planum, you would see Charon fixed immobile in the sky above you, going through its phases as you experience day and night, the stars and Sun and planets wheeling through the sky behind it.  It would be a very strange sight to us.

It’s also very suggestive of a positive mass anomaly (a region which is much denser).  Charon is quite large relative to Pluto, and orbits fairly close; this means that tidal interactions will inevitably drive the system towards a condition where the densest part of Pluto points towards Charon, and that is exactly what appears to have happened.  Planetary scientists believe that Sputnik Planum was created when a very massive asteroid impacted Pluto – not big enough to produce Charon or anything like that, but big enough to liquify a lot of the planet, leaving a huge scar similar to the massive impact basins on the lunar nearside that we call the maria.  If there is still an enormous liquid water reservoir below Sputnik Planum, it would explain a lot of the surface features as well as the positive mass anomaly that is believed to exist in that location, because as anybody drinking a glass of ice water can easily see, liquid water is considerably denser than solid water.  This weird feature of water could entirely explain Sputnik Planum and its location on Pluto.  Doing the math, researchers estimate the ocean below Sputnik Planum could be 100 km deep, and about 30% salinity (comparable to the Dead Sea on Earth, and so not beyond the limits of what we know life can handle).

It also means that Pluto doesn’t just have a heart — Pluto has a broken heart.  But out of that broken heart comes beauty that no one had ever dreamed of:

Along the margin of Sputnik Planum, huge red mountains rise and craters reappear. Sputnik Planum itself is characterized by strange rounded areas that are likely convection cells, new material gradually rising up through the icy surface. Pluto contains a great deal of water ice, but is cold enough that the snow on its surface is nitrogen.

 

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New Horizons’ best Pluto imagery yet!

New Horizons is still transmitting data from the Pluto encounter (and will be doing so for many more months).  NASA has just released an image strip that is the most detailed yet.  This snippet shows the highest resolution portion of the strip, showing the weird bumpy texture, almost like a mogul field, of the cellular nitrogen ice plains in Sputnik Planum:

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Here’s a video (with no audio) panning down the entire strip, with annotation:

You can download the full strip at maximum resolution here, at the Planetary Photojournal.

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Getting to the Heart of Pluto: Solving the Mystery of Sputnik Planum

Pluto’s vast, smooth yet oddly textured heart-shaped terrain called Sputnik Planum was a glorious surprise to the New Horizons team, because nobody had ever seen anything like it before.  It pointed to a geologically active body, rather than the ancient dead lump everyone was expecting, and the mountains adjacent to it looked straight out of the Rockies, except blockier and less organized, complete with what look like glacial flows.

New Horizons still has the majority of its data queued up for transmission, but already they have enough data to start understanding why this terrain looks the way it does: Sputnik Planum is a gigantic impact basin.  Sometime in the geologically recent past, something vast smacked into Pluto, carving out this area and liquifying it and causing nitrogen to spurt out from under the dark substrate that forms the bulk of Pluto and flood the plain.  It has yet to fully resolidify, and so the material is more like a nitrogen slush.  Nitrogen freezes at the temperatures found on Pluto, but frozen nitrogen is a very weak, smooshy material.  Any heat at all could easily produce the bubbly surface in it.  Meanwhile, the chaotic mountains around Sputnik Planum were a surprise as well, because nitrogen ice should not be able to support itself to those heights.  So it turns out the mountains are water ice, and water ice is less dense than nitrogen ice.  The mountains are basically gigantic icebergs floating on top of the nitrogen, shattered and kicked up by the impact that formed Sputnik Planum and huddled around its margins.

There are more mysteries, and far more data still to come; Christmas has come for the New Horizons team, and will keep on coming for a long while yet!

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Space Probe Catchup: Hayabusa 2, Curiosity, New Horizons, and Dawn – Occator Crater revealed!

I’ve been busy lately, so I have not had much time to write, so here’s the latest on three different deep space probes!

First off, Hayabusa 2 made a successful flyby of the Earth on December 3, flying about 3,090 km above Hawaii at closest approach.  The spacecraft was performing a gravity assist maneuver, and controllers now report the maneuver was performed flawlessly: Hayabusa 2 is right on target to encounter asteroid 162173 Ryugu in 2018.  Hayabusa 2 is a follow-on to the original Hayabusa mission, which encountered serious difficulties but still managed to return samples from asteroid 25143 Itokawa.  Hayabusa 2 builds on the lessons learned from that mission and should be able to return much larger samples, scheduled for 2018.  It will also deploy a set of landers, both Japanese and European.

Earth from Hayabusa 2, just after the gravity assist.  Summer has reached the South Pole.

Earth from Hayabusa 2, just after the gravity assist. Summer has reached the South Pole.

Here’s a fantastic animation showing its flight:

Next, Curiosity!

The Mars Science Lander “Curiosity” is now well into its mission exploring Mount Sharp in the center of Gale Crater.  Its latest object of interest is a field of sand dunes.  The going will be difficult, and the team will be very cautious, since it was sand dunes that irretrievably mired MER-A “Spirit”.  This is the rippled surface of “High Dune”, within a dune field named Bagnold Dunes.

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The texture and particles are very intriguing, and Curiosity may learn a lot when it samples them.  They’ve already used the wheels to help get a peek below the surface:

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And still New Horizons returns data!

The probe is continuing its long, slow plod through the enormous data set that it collected at Pluto.  Color data is now available for those high resolution images taken at closest approach, and it only looks wilder:

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Click for the larger image.  It’s really quite weird looking.  The geology must involve some processes that simply don’t happen on Earth, although some of it looks distinctly familiar to our eyes.

Last but not least, Dawn!

Dawn has continued studying 1 Ceres, the closest of the dwarf planets, and there is new information on the mysterious lights in Occator Crater!   Occator Crater has by far the brightest spots on Ceres, but the small world is sprinkled with bright spots.  New spectrographic analysis is consistent with all of those spots being a salt called hexahydrite, which is a type of magnesium sulfate.  Furthermore, all of the spots are associated with impact craters.  This allows them to rule out ice volcanism.  They  believe the spots are salt left behind after water sublimated away following impacts which exposed a briny water layer just below Ceres’ crust.  They aren’t yet suggesting that layer to be liquid, by the way.  It could well be ice, which would rapidly boil away in the sunlight this close to the Sun.  (Ceres is near the limit of our Sun’s golidlocks zone.)  Occator Crater they think is brightest because of relative youth, and possibly also a more energetic impact digging deeper into this layer.  It appears that the water may not have finished sublimating away from Occator Crater, as there is evidence of water vapor accumulating in the crater from both Dawn and also the Herschel Space Observatory.

Another team was analyzing for evidence of ammonia compounds on Ceres, and came up with a lot of evidence, locked up in clays.  This is particularly interesting because surface ammonia is even more volatile than water; that Ceres has some suggests it formed further away from the Sun than its present position.  Perhaps interactions with the giant planets pushed it in.  Ceres is also unusually rich in water ice for a main belt asteroid, which would tend to suggest the same thing.

Here is a color-enhanced image of Ceres rotating.  The enhanced colors help to pick out subtle differences but should not be interpreted as what the human eye would see.

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