Posted on behalf of Ashley Yeager

It’s Messenger to Mercury – take 2.

The spacecraft buzzed past the planet on 6 October for the second of three flybys. Messenger skimmed just 200 kilometres above Mercury’s cratered surface and created the highest-resolution colour images ever obtained of the planet. The new images offer firm evidence that magnesium atoms are floating in the planet’s thin atmosphere and that ancient volcanic processes were important in shaping the its surface.

In 1975 Mariner 10 visited Mercury and produced the first black and white close-up of just less than half of the planet. Messenger, equipped with modern cameras and instruments has now sent back over 1,200 photos that, when compiled, give the first complete view of nearly 95 percent of the planet.

Planetary scientists have analyzed the data and discovered that they now have solid evidence to answer several long-standing scientific questions about what is currently in the planet’s extremely thin atmosphere and about processes that took place on the planet’s surface billions of years ago.

The answers, however, only lead to more questions, mission co-investigator Maria Zuber of MIT said in a press briefing. Questions like how much volcanism was happening 4 billion years ago on Mercury.

These results are the first time magnesium has been identified around Mercury.

Scientists thought the element was in the planet’s soil and detecting it in the exosphere confirms this theory, and also offers insight into the processes that link the planet’s surface to its exosphere. The discovery does not, however, tell scientists what these processes are and what else is in the air and soil, Robinson said.

The spacecraft also caught a glimpse of a thick layer of solidified lava in a crater 100 kilometres across. A hundred kilometres is about the area encompassing the Baltimore-Washington metro area. Fill that area with solidified lava 12 times the height of the Washington monument and that’s the amount of lava in this crater, Zuber said. “That’s an awful lot of lava in one place for such a little planet,” she said. Seeing such thick layers of lava solids “tips the scale” more toward the theory that volcanism, not a crater-ejected dust blanket, gave Mercury many of its smooth surfaces, she added, noting that the observations are limited to only two craters.

Observing more craters and collecting more data on Mercury’s atmospheric and surface composition must wait until at least next September, though, as that’s when Messenger buzzes past the planet on the spacecraft’s third and final flyby.

But, it’s really in 2011, “when we get into orbit, and stay there”, that the team will be able to answer “even more incredible questions” about the solar system’s innermost planet, Robinson added.

Images: colours indicate difference in soil composition, but mineralogy remains unknown, until the team “gets into orbit” / NASA