I'm always a bit disappointed with myself when I find out that there's been a space mission that I didn't know about. But I was really annoyed with myself for not keeping up with MESSENGER (a slightly tenuous acronym standing for MErcury Surface, Space ENvironment, GEochemistry, and Ranging), because its findings have been really quite impressive and surprising.
So, before discussing one of the more recent findings, reported in a paper published this week, lets get acquainted with MESSENGER, who has been slaving away in a rather inhospitable corner of the solar system for over 3 months now. Of the rocky planets, Mercury is the one that we know least about, and because it is the smallest, the densest, the one with the oldest surface, has the largest daily variations in surface temperature, it can constrain our models of planet formation significantly, and this is why MESSENGER is going there.
Ralph McNutt put the findings very succinctly, stating "Mercury ain't the Moon". Quite. In fact, Mercury is very much unlike any other planet in the solar system.
There are six key questions about Mercury that MESSENGER is hoping to shed light on. These are, with links to more info...
2. What is the geologic history of Mercury?
3. What is the nature of Mercury's magnetic field?
Before MESSENGER, we only had about 45% of the surface mapped. MESSENGER has produced some very pretty pictures of the surface,
This is the crater Degas. Impact melt coats the floor, and as the melt cooled and shrank, it formed the cracks observed across the crater.
Mercury has a fairly strong dipolar geomagnetic field. Surprising isn't it, considering that Venus, Mars, and the Moon don't? This magnetic field seems to be dynamic, just like the Earth's, and seems to be generated by fluid motions in the outer core, just like the Earth's.
Interestingly, though, the magnetic field is a bit lop sided; the field lines are much more open in the south, meaning that the surface south region is a bit more vulnerable to solar wind.
This gives us a couple of predictions, which hopefully MESSENGER will be able to confirm. The south region is predicted to have suffered greater space weathering because of this increased flux. Moreover, because this process is responsible for Mercury's feeble atmosphere, there is thought to be a greater atmospheric pressure at the south.
