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PLANETS by Sean Walker
Mercury, Messenger, and Observers
Amateurs and other ground-based observers are also reviewing these new photographs with a sense of vindication. Because Mercury never ventures far from the Sun as seen from Earth, it's the only planet (besides Earth) that can't be imaged by the Hubble Space Telescope. This leaves amateurs and occasionally the rare observation by a professional observatory as the primary source of information about this enigmatic world.
According to Frank J. Melillo, who coordinates the Association of Lunar and Planetary Observers' Mercury section, this is an exciting time to be observing the planet. Modern cameras available to amateurs have revolutionized the quality of observations possible with modest equipment. Seasoned solar-system photographers such as John Boudreau, Ed Lomeli, and the late Erwin Van Der Velden have imaged what have now been confirmed to be crater ejecta rays (see the comparison below) similar to those seen on the Moon.
Although Messenger has revealed more of Mercury's surface, a lot of it has yet to be seen. Also, the spacecraft isn't going to orbit the planet until 2011, so the next two flybys will likewise offer mere glimpses of the surface, while observers can record the planet's appearance during each favorable elongation.
A good comparison might be observing the Moon. Have you ever noticed that crater rays are not visible throughout the entire month? I'd bet 10-to-1 odds that it's similar on Mercury. So even not seeing something is a valuable observation.
The next few years are going to be the most exciting for Mercury observers!
Posted by Sean Walker, January 23, 2008