Pluto
Since its closest approach to Pluto in July, New Horizons has taken most of the headlines when it comes to solar system exploration; and does so with good reason. It has improved our understanding of Pluto literally millions of times over. Alan Stern, the mission's Principal Investigator, told an All Space Considered audience earlier in the year that our previous best images of Pluto couldn't resolve a continent and New Horizons would be able to resolve features just 10s of meters across. For various engineering reasons, the images of highest resolution are just arriving now. Here's one of the many stunners.
Since All Space Considered happened, a color version of the above photo (taken from this press release) has been released. This really illustrates the contrast in geography on Pluto. To this non-expert, it seems pretty clear the surface is undergoing major changes on a pretty regular basis. Apparently, to many trained experts, some of the pictures seemed to indicate icy volcanoes on Pluto. Some features resembling shield volcanoes on Earth were seen in some of the images. In the words of Oliver White, a researcher at NASA's Ames Research Center, "Whatever they are, they're definitely weird. Volcanoes is the least weird hypothesis at the moment." For more details, see this article at space.com.
Titan (Saturn's largest moon)
This moon of Saturn has become a favorite of mine. Between its size (10th biggest object in the entire solar system), thick atmosphere, rocky terrain, standing lakes of methane and salty subsurface water oceans, it has a level of complexity and strangeness I personally find matched only by Earth. Some new images of Titan came back from Cassini and, as usual, we saw something we didn't expect. Here it is.
Titan seems to have a belly button. That belly button is actually a cloud formed during the transition of Titan's south pole from fall to winter. We're watching seasons change ON ANOTHER FRICKING PLANET! There's a full(er) explanation of the whole phenomenon in NASA's press release. My favorite tidbit is that the clouds form by subsidence (new vocab word for me). For reasons beyond my understanding, warm gases sink in Titan's atmosphere. As the warm gases from the northern hemisphere circulates to the colder, southern hemisphere, the sinking takes them through progressively colder surrounding temperatures. Different gases will condense out at different altitudes, forming clouds along the way.
Phobos (Mars's largest moon, for now)
Mars's largest moon, Phobos, has some funny geological features. In the picture below, they can be see as striations emanating from the large crater in the lower right. After lots of analysis, it's been discovered that Mars is pulling Phobos apart. Tidal forces from Mars's gravity is causing Phobos to stretch enough to cause the fracturing and cracking that is seen here. This is a bit of a happy accident, as Phobos is surprisingly light. Its density is only about 1/3 that of Earth or about 60% that of the moon. This means it's easier for tidal forces to act on it, especially at the fairly close distance Phobos is to Mars.
Based on all this data, it appears that Phobos will be ripped apart in 20 to 40 million years. On human scales, that's a pretty long time, but on astronomical scales, that's pretty soon. Also, in the intervening time, we can keep looking at Phobos. What's really cool about this is that when Phobos breaks apart, it may form a ring around Mars. It's suspected some of the inner planets may have had rings in the past, when the structures and material in the solar system were much more dynamic. It would be cool if one of the inner planets could join the gas giants in having a ring.
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