New pictures of never-before-seen parts of Mercury taken by NASA’s Messenger spacecraft are revealing surprises about the solar system’s innermost planet.

Usually the deepest craters are the biggest, but on Mercury there are two craters right next to each other that are about the same size even though one is four times deeper than the other. What’s going on?



The shallow crater basin, which is about the size of the greater Washington, D.C. and Baltimore metropolitan area, has been filled in with a massive amount of lava, according to Maria Zuber of MIT, one of the leaders of the Messenger mission. The 3,600 cubic miles of lava would be enough to cover the cities in a 1.5-miles thick layer.

The lava comes from volcanoes that were first discovered on Messenger’s first flyby of the planet in January.

"The surprise is that it appears to be more volcanic than the moon," Zuber said at a press conference. "Very few people would have thought that before the first Messenger flyby."

The latest images were taken during Messenger’s second flyby of Mercury on Oct. 6. Combining the images with Zuber’s altimetry data gave the features depth and yielded a wealth of new information about the planet. The spacecraft will make one more flyby in the future and eventually settle into orbit around the planet in 2011. But scientists are already poring over the data they’ve collected.

"I am just absolutely thrilled with the result," Zuber told Wired.com,

"for somebody who does tectonic and volcanic modeling, I am in my element."

Our first glimpses of Mercury came from three flybys by Mariner 10 in the 1970s that captured 45 percent of the surface of the planet. Messenger’s first flyby took the first-ever pictures of Mercury’s western hemisphere, adding an additional 21 percent to the viewed surface. After the second flyby on Oct. 6, 90 percent of the planet has been imaged at 1 km (3,280 feet) resolution. Once in orbit, Messenger will boost the resolution to 850 feet.





The double image at the top of the post shows Mercury’s true colors on the left, and an exaggerated false-color image on the right taken using 11 different color filters. The video was made the same way. Bringing out the color this way can help geologists make guesses about the age and composition of the terrain.

Younger, rougher ground, such as the ejecta from a meteorite impact, shows up yellow. Over time, smaller impacts and the solar wind will wear it down and turn it more red. Orange areas are likely from volcanic eruptions, and the blue areas are still somewhat of a mystery. Once in orbit, Messenger will pass over the surface more slowly and gather detailed data that will help scientists understand the mineral composition of the different areas.

More ‘Hidden’ Territory on Mercury Revealed [NASA]

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Images and video: NASA