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a citizen’s journal by Thomas Nephew

Maryland’s messenger meets Mercury

Posted by Thomas Nephew on January 16th, 2008

Messenger image of Mercury
Vivaldi Crater, Mercury.
Credit: NASA/Johns Hopkins University
Applied Physics Laboratory/
Carnegie Institution of Washington

The MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) probe is engaged in its first flyby of Mercury, and is sending images back to Earth:

This MESSENGER image was taken from a distance of about 18,000 kilometers (11,000 miles), about 56 minutes before the spacecraft’s closest encounter with Mercury. It shows a region roughly 500 kilometers (300 miles) across, and craters as small as 1 kilometer (0.6 mile) can be seen in this image.

The voyage is itself something of a triumph of celestial navigation: the probe was timed and programmed to fly by Venus twice to slow it sufficiently to enter Mercury’s orbit — with the first visit taking place when Venus was on the opposite side of the sun (October 2006), and with the final approach to Mercury orbit slated for 2011, after two more fly-bys of that planet. A critical course correction — a.k.a. “trajectory course maneuver,” or TCM — took place late last year, monitored by mission controllers in Laurel, Maryland:

Mission controllers at The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, verified the start of the maneuver about 13 minutes after the start of TCM-19 when the first signals indicating spacecraft thruster activity reached NASA’s Deep Space Network tracking station outside Canberra, Australia.

So what can be learned from Mercury? It’s apparently an unusually dense planet — 60% metal core, twice as much as Earth — and may thus provide a new data point for understanding planetary formation generally, including the Earth’s:

Understanding this “end member” among the terrestrial planets is crucial to developing a better understanding of how the planets in our solar system formed and evolved.

 

(Via Chad Orzel’s delicious astronomy and uncertain principles.)

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