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troutman · 06-16-2011, 03:32 PM

Early MESSENGER science results: Mercury is its own planet, not Moon or Earth
http://www.planetary.org/blog/article/00003067/

There was a press briefing today giving some early science results from MESSENGER and it was surprisingly meaty. I'm going to focus on just one set of the results that they presented. As usual with MESSENGER, the most exciting stuff is not from the "pretty pictures," although there were some of those, which you can see at the page full of visuals for the press briefing. What's most exciting out of Mercury is what we're learning from the other, relatively arcane instruments on MESSENGER. Whenever you send a spacecraft to orbit a planet for the first time, you're going to wreck a lot of people's neat theories, and this mission is no exception.

What's being plotted here is the ratio of the abundance of magnesium to the abundance of silicon on the horizontal axis, and the ratio of abundance of aluminum to the abundance of silicon on the vertical axis. Earth's mantle has a high magnesium-to-silicon ratio, representing its bulk composition. The Moon has a very high abundance of aluminum, a result of its history of having a global magma ocean in which aluminum-rich feldspar crystals floated to the top. Earth's basalts (black lava rock that covers most of the planet's ocean floors) formed from partial melting of mantle rocks, a process in which they get more aluminum- and less magnesium-rich. But Mercury's composition doesn't match the compositions of either lunar or Earth rocks, indicating that its geologic history is unique.

06-16-2011, 03:32 PM	#968
troutman Unfrozen Caveman Lawyer Join Date: Oct 2002 Location: Crowsnest Pass Exp:	Early MESSENGER science results: Mercury is its own planet, not Moon or Earth http://www.planetary.org/blog/article/00003067/ There was a press briefing today giving some early science results from MESSENGER and it was surprisingly meaty. I'm going to focus on just one set of the results that they presented. As usual with MESSENGER, the most exciting stuff is not from the "pretty pictures," although there were some of those, which you can see at the page full of visuals for the press briefing. What's most exciting out of Mercury is what we're learning from the other, relatively arcane instruments on MESSENGER. Whenever you send a spacecraft to orbit a planet for the first time, you're going to wreck a lot of people's neat theories, and this mission is no exception. What's being plotted here is the ratio of the abundance of magnesium to the abundance of silicon on the horizontal axis, and the ratio of abundance of aluminum to the abundance of silicon on the vertical axis. Earth's mantle has a high magnesium-to-silicon ratio, representing its bulk composition. The Moon has a very high abundance of aluminum, a result of its history of having a global magma ocean in which aluminum-rich feldspar crystals floated to the top. Earth's basalts (black lava rock that covers most of the planet's ocean floors) formed from partial melting of mantle rocks, a process in which they get more aluminum- and less magnesium-rich. But Mercury's composition doesn't match the compositions of either lunar or Earth rocks, indicating that its geologic history is unique.