The highest resolution image of MU69 taken by New Horizons is now available. Phil Plait explains what it shows and what it can tell us about the population of bodies out there.After the monumentally successful flyby of Pluto in 2015, the New Horizons spacecraft continued on into the outer solar system. After traveling at more than a dozen kilometers per second out an additional billion kilometers or so, it shot past the odd little rocky iceball 2014 MU69 on January 1, 2019, passing it by the razor-thin margin of just 3,500 kilometers … and that was after traveling for over 6.6 billion kilometers from Earth!#Space #Astronomy #Asteroids #NewHorizons #MU69 #UltimaThule #Exploration
New Horizons took a lot of data during this encounter, comparable to what it did at Pluto, and it'll be another year or more before it's all back on Earth. So the New Horizons team did a clever thing: They prioritized what images to send back first. Among the highest priorities was getting the highest-resolution image sent back from the closest encounter as quickly as possible.
And now that image is here.
You might think that being out there, exposed to space out past Neptune for billions of years, MU69 would be covered in craters. For Pluto that's not the case because we think its surface gets repaved, so to speak, from subsurface processes that bubble up liquid from the interior. However, MU69 is far too small for that, and is certainly solid throughout. So a dearth of craters means there must be a dearth of impactors.
Interestingly, some scientists actually predicted this! They used the number of small craters seen on Pluto and its huge moon Charon, together with measurements and estimates of sizes of small objects past Neptune (called trans-Neptunian objects [TNOs], or more specifically in this case the Kuiper Belt), first to try to figure out the size distribution of objects out there capable of hitting MU69, and then to predict the size distribution of craters on MU69. Keep in mind that this was all done before the MU69 encounter!