Interesting recent observations have been made by various space probes. Some that I find interesting from the past few weeks are from Stardust, Opportunity and Spitzer Space Telescope. These are somewhat related in that they deal with impacts and planetary evolution.
Over about the last 70 years we've learned an incredible amount about the formation of planets. There are theories about how the planets condense from the stuff surrounding their mother stars, about how they form, age, and die. Without ways to test the theories or evidence that mechanisms from the theories have actually occurred, the theories aren't much more than words.
Some of the theories include ways that planets become heavily modified during and after formation. For instance, it is thought that Mercury may have had it's crust stripped off of it by a massive collision at some point. If there were evidence that this could have happened, it might help explain what we see today.
Spitzer Space telescope recently captured what looks like evidence of such a collision.
Other theories suggest mechanisms like Comets impacting with planets, bringing down many of the chemicals necessary for life to form. These almost seem far-fetched, there isn't much evidence to support such notions. For one, the chemicals would have to be found to exist in comets. We've managed to bring back some dust, etc, from a comet, but it might be a little far-fetched to expect that we could bring back chemical traces. Or… would it? The aerogel sample trays in a recent experiment were designed to preserve the chemicals in the traces it captured.
Recent findings from the Stardust space craft indicate that indeed, chemicals such as glycine are present in comets.
Opportunity found a great bit of evidence to support the theory that Mars once had a thick atmosphere. A meteorite named Block Island has been found, based on it's size and that it's intact indicates that when it struck Mars, Mars probably had a thick blanket of atmosphere. If we can date the meteorite – when it hit Mars – we will have a "stick in the sand" to help figure out how long ago Mars had atmosphere, and possibly help figure out the mechanisms by which it lost that atmosphere. Evidence to help confirm that Mars once had a thick atmosphere is very important right now as most of our current evidence points towards a past wet and well-atmosphered Mars. It will also give us more evidence to test theories out against – for instance, dating this meteorite will give an "upper bound" to how long Mars has been without atmosphere, which in turn gives us evidence to help evaluate some theories about how Mars has evolved. (The thickness and composition of atmosphere greatly affects how weathering occurs, etc.)
It's exciting to see how more and more evidence is supporting some theories of planetary evolution, including how life may develop. Once these mechanisms become well understood, we may apply the knowledge to our search for distant earth-like planets. Right now – with all those collisions – building planets doesn't seem much different than a blacksmith pounding out iron. It boggles the mind to think how many stars out there may be pounding out and shaping their own "solar systems" in their own planetary forges.
One of my friends likes to challenge me: "so what does this mean for me?" I think on one hand it's a question each person needs to answer for themselves, but in general, understanding more about planetary evolution in general means understanding more about the evolution of the Earth in specific, and the roles we play in influencing that process. We build purely scientific probes, like Gravity Probe B, partly to learn how to build such probes, and to look for scientific evidence. Purely scientific missions lead to the creation of instruments that can tell us what's going on with Earth's environment, like regional problems with water supplies. Even if it doesn't mean anything directly to you today, it may mean a lot to you tomorrow.[all of the devices mentioned above run various versions of VxWorks for Rad6000.]