Messenger reveals secrets of fleet-footed Mercury

Caroline Morley, online picture researcher

(Image: NASA/JHUAPL/CIW-DTM/GSFC/MIT/Brown University. Rendering by James Dickson and Jim Head)

It's scarred and heavily sun-damaged, but then it has sat next to our star for rather a long time.

A year ago the aptly named Messenger probe reached Mercury and began orbiting the tiny, sun-baked planet. Now an analysis of over 100,000 images has given us a better picture of the closest planet to the sun.

Two papers published in Science focus on the northern hemisphere, looking at the topography of Mercury's surface and its internal structure.

Some of the most prominent features are the vast volcanic plains, as seen in this picture, with white indicating high areas and low altitudes shown in purple.

Parts of the floor of the Caloris impact basin, which is 1550 kilometres wide, have now risen above its rim, suggesting that there are high levels of geophysical activity beneath the surface.

The second team was investigating deeper under the surface using data from Messenger's radio tracking to look at Mercury's gravitational field. Their results suggest that the crust is thinnest at the poles and thickest at lower latitudes. The data also suggest that there is a layer of dense material underneath the crust, perhaps made of solid iron or iron sulphide.

At least one mystery about Mercury remains. In the 1990s, Earth-based radar telescopes detected a highly reflective substance at Mercury's poles.

It was suggested that this could be water ice. You read that right: ice, on the planet that orbits closest to the sun.

At the 43rd Lunar and Planetary Science Conference held this week in The Woodlands, Texas, a paper was presented showing that that the reflective substance only occurs in areas of permanent shadow supplied by deep craters. This is consistent with it being water ice, but it would need to be covered with a thin layer of insulation.

Messenger's mission has now been extended - so watch this space.

Source: http://feeds.newscientist.com/c/749/f/10897/s/1db1db22/l/0L0Snewscientist0N0Cblogs0Cshortsharpscience0C20A120C0A30Cmessenger0Ereveals0Esecrets0Eof0Ef0Bhtml0DDCMP0FOTC0Erss0Gnsref0Fonline0Enews/story01.htm

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