New close-up images and data provided by NASA's MESSENGER -- MErcury Surface, Space ENvironment, GEochemistry and Ranging -- spacecraft have revealed an unforeseen class of landforms on the planet closest to the sun.

The high-resolution images have revealed the first close-up views of Mercury's hollows, the first direct measurements of the chemical composition of the planet's surface and the first global inventory of plasma ions within its space environment. The analysis of the new data has also shown that flood volcanism has been extensive on the planet, a NASA report said.

We have viewed the polar regions clearly for the first time, we have built up global coverage with our images and other data sets, we are mapping the elemental composition of Mercury's surface, we are conducting a continuous inventory of the planet's neutral and ionized exosphere, and we are sorting out the geometry of Mercury's magnetic field and magnetosphere, said MESSENGERs' principal investigator, Sean Solomon of the Carnegie Institution of Washington.

New data has also revealed that the north polar region of Mercury is surrounded by a huge expanse of smooth volcanic plains, which covers more than 6 percent of the planet's total surface area.

The results were published Friday in a set of seven papers in a special edition of Science magazine. According to James Head of Brown University, who was the lead author for one of the Science reports, an analysis of the volcanic deposits on the planet shows that the lavas are as thick as two kilometers in places.

If you imagine standing at the base of the Washington Monument, the top layer of the lava would be something like 12 Washington Monuments above you, Head said.

Scientists have also found vents, 25 kilometers in length, which appear to be the source of some of the huge volumes of hot lava that have rushed out over the surface of Mercury. These volumes of lava have created valleys and teardrop-shaped ridges in the terrain.

Earlier images of Mercury's surface, collected by the Mariner 10 and Messenger flybys, showed very bright blue-colored floors and central mountain peaks of some impact craters. But because higher-resolution images were lacking, these bright crater deposits remained unexplored.

The new closeup images of these craters, provided by Messenger's orbital mission, have revealed that bright areas are composed of small, shallow, irregularly shaped depressions that are often found in clusters. In order to distinguish these features from other types of pits seen on Mercury, scientists have used the term hollows, said David Blewett, a staff scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., and lead author of one of the Science reports, said.

Analysis of the images and estimates of the rate at which the hollows may be growing led to the conclusion that they could be actively forming today, Blewett said.

MESSENGER's Gamma-Ray Spectrometer (GRS) measured Mercury's surface and revealed a great quantity of the radioactive element potassium. Together with MESSENGER's X-Ray Spectrometer (XRS), it also showed that Mercury's average surface composition is different from those of the moon and other planets.

Scientists believe that Mercury has many more surprises in store for us as the MESSENGER mission progresses.

These revelations emphasize that Mercury is a fascinating world that is unmatched in the solar system, Blewett said.

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