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Headshot of Emily Lakdawalla

Latest New Horizons picture of Charon: oddly familiar

Posted By Emily Lakdawalla

16-07-2015 14:45 CDT

Topics: trans-neptunian objects, New Horizons, pretty pictures, Lunar Reconnaissance Orbiter, Charon, the Moon, dwarf planets beyond Neptune

Today the New Horizons team released one more picture from Tuesday's encounter, one of three high-resolution images from a mosaic that crossed the center of Charon's disk:

New Horizons' first high-resolution view of Charon


New Horizons' first high-resolution view of Charon
This high-resolution image of an area on Pluto's largest moon Charon contains a depression with a peak in the middle, shown here in the upper left corner of the inset. The image shows an area approximately 390 kilometers from top to bottom, including few visible craters. This image is heavily compressed; sharper versions are anticipated when the full-fidelity data from are returned to Earth. The image was taken at 10:30 UTC on July 14, 2015, about 1.5 hours before closest approach to Pluto, from a range of 79,000 kilometers.

The first thing that I notice when I examine this image is compression artifacts: a blocky texture to the otherwise smooth-looking areas. That is a result of the massive amount of compression they had to do to the images in order to squeeze them in to the short downlink time available right after the flyby. The original, high-quality data remains onboard the spacecraft and will be returned eventually, either this fall or sometime next year.

Look past the compression artifacts, and I see four major features in this photo:

The geometry of this image is actually very similar to the geometry of the detail image of Pluto that they released yesterday. It is at the terminator (so the differences in brightness are shape-from-shading, not so much albedo) and it's from a pretty similar distance (77 or 79,000 kilometers), so the scale is the same. But what different landscapes! The mission really did get two completely distinct icy worlds for the price of one with this flyby.

The icy mountains of Pluto


The icy mountains of Pluto

This close-up image of a region near Pluto’s equator reveals a giant surprise: a range of youthful mountains rising as high as 3,500 meters above the surface of the icy body. The mountains likely formed no more than 100 million years ago—mere youngsters relative to the 4.56-billion-year age of the solar system—and may still be in the process of building, says Jeff Moore of New Horizons’ Geology, Geophysics and Imaging Team (GGI). That suggests this region, which covers less than one percent of Pluto’s surface, may still be geologically active today. Moore and his colleagues base the youthful age estimate on the lack of craters in this scene.

The image was taken about 1.5 hours before New Horizons closest approach to Pluto, when the craft was 77,000 kilometers from the surface of the planet. The image easily resolves structures smaller than a mile across.

Anyway, back to interpretation of the Charon image. I honestly don't know what to make of the "mountain in a moat" -- I'm with Jeff Moore, who's quoted in the related image release as saying "This is a feature that has geologists stunned and stumped." So I'm going to ignore that for now and focus on the fissures. I stared at the picture for a long time, trying to decide which icy moon they reminded me of, and I was drawing a blank. I realized I was thinking about the wrong worlds, and Andy Rivkin confirmed it on Twitter: they remind me of rilles in the lunar maria. A helpful Twitter follower suggested Rima Hyginus as a good analog, and it's not bad! Here's a Lunar Reconnaissance Orbiter photo of Rima Hyginus, a set of graben (extensional faults). It could be that we're looking at very similar landscapes: a flood of highly fluid lava solidified and then cooled, and as it cooled it shrank and fractured, forming graben. Except that on the moon, the lava was liquid rock; on Charon, it would have been liquid water.

Comparative planetology is fun! You never know where it is going to take you.

Rima Hyginus from Lunar Reconnaissance Orbiter

NASA / GSFC / ASU / processed by Maurice Collins

Rima Hyginus from Lunar Reconnaissance Orbiter
Rima Hyginus is a linear rille which branches to the northwest and the east of Hyginus crater. Rima Hyginus formed through faulting, and is actually a graben. A graben is a section of the crust that sunk as two parallel faults pulled apart. Collapse craters formed after the graben. Visit the Lunar Reconnaissance Orbiter Camera website for more information.
See other posts from July 2015


Read more blog entries about: trans-neptunian objects, New Horizons, pretty pictures, Lunar Reconnaissance Orbiter, Charon, the Moon, dwarf planets beyond Neptune


Messy: 07/17/2015 08:02 CDT

Here's a thought: How about the lack of craters is proof that Pluto/Charon HAS "cleared the neighborhood"? Thus, it's a real planet after all.....

andyi: 07/17/2015 08:19 CDT

When water freezes it expands, not contracts. That suggests the process is different than the Moon's or that it isn't caused by water.

Michael Paine: 07/17/2015 09:52 CDT

The latest findings from NH add support to my suggestion, in 2000, that Pluto and Charon be regarded as a "binary planet": The barycentre of these 2 objects is above the surface of Pluto so Charon's orbit is not moon-like. This might also be a factor in the perplexing interior heat of Pluto.

aml: 07/18/2015 01:32 CDT

I think you need to be careful about claiming newness of terrain based on lack of craters. Being so far out from the Sun, means it's less likely to get hit. Think of dart board player always aiming for a bullseye: the points that are further away from the bullseye are less likely to get hit, compared to those closer to the bullseye.

aml: 07/18/2015 01:31 CDT

Scap that idea - Pluto is part of the Kuiper Belt!

aml: 07/18/2015 01:39 CDT

What about the idea that the collisions are a lot softer as the momentum is a lot less than those collisions that occur closer to the sun? We see lots of micro craters too. Is the Kuiper Belt providing the gravity source for the geological activity?

Joe: 07/18/2015 01:51 CDT

I think the "mountain in the moat" looks like an object that soft-landed in a high viscosity, high surface tension material like an M&M pushed into a chocolate pretzel treat (mountain=M&M, surface=melted Hershey kiss). But physics make the soft-landing impossible. More likely, the surface crept up on an existing peak.

rickray777: 07/18/2015 03:02 CDT

When we baby-boomers (and before that) came into the world, who would have thought that we'd have actual, detailed close-ups of ALL the classical planets (and their major moons!) within our lifetime? Well, sure we had our planet-hopping space-heroes of the day: Flash Gordon, Buster Keaton, etc. Indeed, when I first began to read about the planets (spring 1971, fourth grade), we were still very much within the Apollo era. We had just sent the first reconnaissance spacecraft to Mars and Venus; but Mariner 10 (to Mercury, ultimately), and even Pioneer 10 (the first spacecraft to cross the asteroid belt, so as to encounter Jupiter) had yet to be launched. Even the King of the Planets, Jupiter, was but a multicolored, banded disk (in even the largest telescopes); the disks of the Galilean satellites were barely discernible. At that time, however, what I really wanted to learn about was Saturn (and its rings!). But in just under 45 years since then: we've now gotten to examine ALL the classical planets, AND their major moons (in at least some detail!). Who would have thought, indeed?

Joe Brooks: 07/18/2015 05:53 CDT

The visual comparison looks spot on to me, with the biggest difference being fewer craters visible in the image of Charon. Good eye, Emily!

sepiae: 07/19/2015 02:52 CDT

Mount Moat is indeed captivating. I'm wrecking my mush about anything comparable. It does look like something one has seen before. Except for the scales. Joe, the 'soft landing' was also the 1st thing that popped into my head, but you're right, the size of it, velocity, anything to do with such an impact, makes it hard to imagine, probably impossible. So it's probably a freak of erosion; it'd be far more unlikely for such freaks not to exist at all. Gosh, that the planet debate is still alive... I wouldn't be any less mesmerized would it be classified as a doughnut system. This will sound cheesy, but is true, I wanted to comment on the previous post and couldn't. I was quite simply speechless. I show this to people around me, and it's, 'yeah, cool. Interesting.' Perhaps it's not coming to everyone immediately. We're looking at this object familiar to us since 1930, much debated and in our 'consciousness, this object and it's entourage, right this moment approx. 31.91865600 au and currently steadily distancing, looking at detailed features and learning. Incomprehensible to me how one couldn't be completely wowed.

sepiae : 07/19/2015 03:06 CDT

The planet-debate remark wasn't aimed at Michael Paine's observation, which I find worth noting, even though I'd stick with dwarf planet, binary or not (and binary does ring right). More interesting I find your suggestion about their dance possibly being a factor for the interior warmth; which also sounds likely to me. andyi, I suggest that your wrong in being right: your physics is correct, ofc, but freezing water would still leave traces like those seen, so the process isn't all that different where it concerns the observable outcome.

Messy: 07/19/2015 07:51 CDT

Ami, as to "neighborhoods and the Kuiper belt.... there have been about 12,850 Near Earth Objects have been discovered. It's estimated that there's at least one megaton explosion per year from a NEO. This is evidence that we haven't exactly "cleared" our own neighborhood and don't precisely qualify as a planet ourselves. With Pluto's thin atmosphere, most objects of that size would have made a crater, and since there there are large swaths of crater-free territory then it stands to reason that there have been very few other objects orbiting way out there in Pluto's "neighborhood" The two KBOs being considered for the next target won't get visited until 2019, which is four years hence and NH had already gotten to Jupiter in less than that amount of time. "neighborhood" has to do with size, and Pluto doesn't seem to actually HAVE one, as the largish rock-free area, a torus surrounding it's orbit, is larger than any of the inner planets.

plaasjaapie: 07/19/2015 03:03 CDT

" It could be that we're looking at very similar landscapes: a flood of highly fluid lava solidified and then cooled, and as it cooled it shrank and fractured, forming graben. Except that on the moon, the lava was liquid rock; on Charon, it would have been liquid water." Won't work. Lava shrinks and cracks, typically, as it cools. Water expands as it turns to ice.

Emily Lakdawalla: 07/20/2015 06:15 CDT

Yes, water expands as it turns from liquid to ice, so as a cryolava flow cooled, it would "inflate" upward in volume. Once it is solid ice, though, like any other solid, it shrinks as it cools further, and would crack, as rock lava does.

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