Pluto: Why So Smooth?

Fantastic news, Science Fans! It took it's sweet time (about 4.5 hours at the speed of light) but we finally got the first data from the New Horizons spacecraft. And even better than that: there is already a genuine mystery to puzzle out. So far we have two great pictures and some data on methane density.

The first picture, below, is of Pluto itself; it is a close up of the now famous 'heart' region. For scale, some of these peaks are about 11,000 feet high, which is comparable with mountains here on earth. What is interesting is that there are hardly any craters at all in this picture. It's very unlikely that this is because Pluto hasn't been hit by any meteors so we have to conclude that it means this surface is a very new one, and when we say very new here we mean about 100 million years old. Therefore, in the recent geological past, a process must have occurred to create this new surface. Generally this could be achieved by the planet being geologically active, like the earth is, with earthquakes and volcanoes and such churning up the place and destroying any evidence of crater impacts; or, a very large mass nearby can literally cause tides in the rock that cause them to grind and move and create heat again destroying any impact craters that might be around. The problem is that Pluto is both too small and cold to be geologically active and there is nothing large enough nearby to create tidal forces. We have a mystery.

The next picture, below, is of Pluto's largest moon, Charon, and here we see the same puzzling phenomenon. It's surprisingly smooth, there aren't all that many obvious craters; conjure (or Google) an image of our pock marked moon for comparison and the lack of craters will be much more obvious. The same argument applies here as to Pluto and we simply don't yet have an explanation. I guess it's not completely impossible that just by chance the two bodies have avoided impacts for several billions of years, but given that we know the Kuiper belt, of which Pluto is a part, is chock full of rocks and potential meteors this really does seem extremely unlikely. Do not, however, be disheartened. If there's one thing that scientists like it's a mystery. If you ask a question and the answer doesn't throw up at least a dozen new questions then you're doing it wrong.

These images are just the first tranche of what will ultimately be a deluge of data, frustratingly most of that is still on the New Horizon's craft and it will take weeks or even months for it all to be beamed back home. These initial images will have to keep us busy for a little while but one thing is for certain; we have lots of new and exciting discoveries to make about our former planetary cousin.