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I've heard from a lot of sources that Pluto doesn't seem to have any impact craters, but I see a few things that look like impact craters, highlighted in this picture:

Pluto impact craters

For comparison, here's something I think looks like an impact crater on Pluto next to an impact crater on Mercury:

Pluto Mercury comparison

Are they impact craters on Pluto? If not, what are they? If they are, why are people saying it has no impact craters?

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  • $\begingroup$ "Not any" might mean "much fewer than expected". This is hand waving astronomy, not surgery. And hardly any craters have been found on the close up images. So it seems that Pluto's surface is more about internal processes than impact history. But maybe there are no large impactors out there? $\endgroup$ – LocalFluff Jul 18 '15 at 7:32
  • $\begingroup$ Since there have been no images of Pluto that could have revealed impact craters before New Horizon's pass any statement more than ~a few weeks old would have been pure speculation. From the image you post Pluto clearly does have impact craters. From what I can see in the above photo the surface is covered with circular scars which appear to me to be relaxed impact features. $\endgroup$ – Conrad Turner Jul 18 '15 at 8:42
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It was predicted by some, before the images arrived, that Pluto's craters would be much shallower than perhaps on other rocky objects/satellites. The reason is the icy composition and the relatively low impact velocities in the outer solar system (Bray & Schenk 2015).

There are indeed reported quotes in recent days that there are no impact craters on Pluto (e.g. here or here), based on the highest resolution images.

However, I'm with you - the things you have marked look like very large impact craters, or the remains of them, and so what we are seeing is that there are no small ones.

The gist of what I have heard/read is that this indicates geological activity on Pluto, which is effectively removing the evidence of relatively small impacts and that the surface we see is mostly younger than 100 million years old. Watch this space, a lot of people are just flapping their lips at the moment (including me).

Another possibility - raised by Wayfaring Stranger - could be that the expected number of impacts was (hugely) overestimated. This is discussed by Singer & Stern (2015). There are indeed uncertainties, and it is hoped that cratering on Pluto & Charon would help constrain the number densities and size distribution of small impactors. My impression is that the uncertainties could be at levels of up to factors of 10 - and this seems to be discussed quite carefully in Greenstreet et al. (2015) (behind a paywall, sorry), who also comment in the abstract that surface ages judged from cratering are " entirely dependent on the extrapolation to small sizes [of the impactor distribution]".

Further Edit: LDC3 suggests all the craters could be too small to be seen. The high resolution images that have been released could resolve craters of a diameter of a couple of km or more and cover a few percent of the surface. According to Singer & Stern (2015), the number of craters at this size and above on Pluto they expected in such an area is $\sim 1000$. So I think that either the planet has been resurfaced recently, the craters have been eroded in some other way or their estimates for the number of impacts/size of the impactors is wrong.

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    $\begingroup$ We don't have good data on numerical density and size distribution of trans-neptunian asteroids yet, do we? Paucity of craters may just indicate fewer things to collide with. $\endgroup$ – Wayfaring Stranger Jul 18 '15 at 13:09
  • $\begingroup$ Or maybe Pluto lacks craters because it has cleared its orbit? Maybe thanks to its orbitally resonant giant Neptune neighbor. And thus scoring the third criteria for being a a a..., no I won't write it out loud. You know what it is, Rob, now that you've seen it. ;-) $\endgroup$ – LocalFluff Jul 18 '15 at 13:40
  • $\begingroup$ @WayfaringStranger Absolutely. I have added a citation to work that looks specifically at this issue. I do think that everyone is surprised by the lack of cratering though. $\endgroup$ – Rob Jeffries Jul 18 '15 at 13:44
  • $\begingroup$ I think we all expected something like Mercury or Callisto. $\endgroup$ – Wayfaring Stranger Jul 18 '15 at 14:03
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    $\begingroup$ Rob, what we are seeing is that there are no small ones. I disagree with that; after all, Pluto is 1/3 the size of the moon and the craters (on Pluto) would be about the size of the smallest craters on the moon. $\endgroup$ – LDC3 Jul 18 '15 at 14:23
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Further imagery has confimed billion year old surface with impact craters on one part and younger which is very recent and smooth on another part.

Jeff Moore, of the New Horizons team has said. “We now know Pluto has some surfaces that are a billion years old,”

Edit... new estimate quote from nasa: Based on the lack of impact craters, scientists suspect the surface of Pluto is less than a few hundred million years old, Read more at http://newsdaily.com/2015/07/nasa-spacecraft-shows-pluto-wrapped-in-haze-ice-flows/#ytDT3emJZSKRbL7b.99

He expects that the bulk of the data that he wants to study wont have been beamed back before early 2016. Large scale image:

http://pluto.jhuapl.edu/images/featuredImages/nh-pluto-mountain-range.png boundary of old and new, old dateable by number of craters recent zone similar to a convection surface

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  • $\begingroup$ This answer could really use some support for its claim. Such as the referenced image or the source for the claims of billion year old and relatively young surfaces. $\endgroup$ – Mitch Goshorn Jul 22 '15 at 11:57
  • $\begingroup$ @ufomorace Better (good enough for me to give it +1, anyway), but do you have a link to the article or whatever it was that gave the Moore quote? $\endgroup$ – zibadawa timmy Jul 22 '15 at 17:52
  • $\begingroup$ Hi sorry i thought that the phrase would be in search engines... here: fortune.com/2015/07/15/nasa-pluto-data-earth $\endgroup$ – com.prehensible Jul 23 '15 at 11:18
  • $\begingroup$ Moore is a planetary geologist from Nasa, i don't know if he said that the surface is so old because he measured the craters or because of the black surface, will be cool to have further information. Given the size of pluto and the fact that it is ice, an impact wiht a large asteroid may be enough to shift it's rotation angle and also melt a sea into it, so perhaps the giant new areas and the zones not exposed to sun(lighter ones) are due to impacts rather than heat inside of pluto. Pluto is perhaps similar to Europa which is 20% larger. .18 and .25 earth diameters. $\endgroup$ – com.prehensible Jul 23 '15 at 11:31

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