Mercury: A Hot Little Planet

"This Just in: Mercury More Exciting Than Mars"
Wired Science (April 30, 2009)

"Mercury was once seen as a cold, dead little world, spinning around the sun unchanged for the past 4 billion years.

"No longer: Observations from the Messenger spacecraft say it’s anything but.

"NASA's orbiter is sending back evidence of massive volcanism, strange impact craters and magnetic tornadoes that funnel plasma directly from the sun to the planet’s surface.

" 'It's definitely not this picture of an ancient world where everything that happened to it happened billions of years ago and nothing happened since then,' said Tom Watters of the Smithsonian Institution in Washington, DC. 'We’re seeing a very dynamic planet that has a lot going on today.'..."

Space.com ran an article on the same subject:

"Huge Impact Crater Discovered on Planet Mercury"
Space.com (April 30, 2009)

"New observations from NASA's MESSENGER spacecraft reveal about 30 percent of the planet Mercury that has never been seen up close before. A giant crater and evidence of ancient volcanoes are among the findings.

"The photos show a giant impact crater that spans a length equivalent to the distance between Washington, D.C., and Boston.

"MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft) made its second close-approach flyby of Mercury in October 2008, after being launched in 2004. The spacecraft is the first to visit the diminutive planet since the Mariner 10 spacecraft's sojourn in the 1970s.

"Until recently, scientists say the closest planet to the sun remained the least understood of the four terrestrial planets – Mercury, Venus, Earth and Mars. For a long time it was thought to be very similar to Earth's moon in composition, since both worlds have a similar gray, pockmarked appearance...."

What it boils down to is that there's much more going on in Mercury than we thought: something's generating a magnetic field, there's evidence of (geologically) recent vulcanism - and there's a crater with odd radial wrinkles.

As so often happens, the more we know - the more we know that we don't know.

Other posts, about "Mars, Mostly."