Messages from Mercury

After its first Mercury solar day (176 Earth days) in orbit, MESSENGER has nearly completed two of its main global imaging campaigns: a monochrome map at 250 m/pixel and an eight-color, 1-km/pixel color map.

Apart from small gaps, which will be filled in during the next solar day, these global maps now provide uniform lighting conditions ideal for assessing the form of Mercury's surface features as well as the color and compositional variations across the planet.

The orthographic views seen here, centered at 75 degrees E longitude, are each mosaics of thousands of individual images. 

At right, images taken through the wide-angle camera filters at 1000, 750, and 430 nm wavelength are displayed in red, green, and blue, respectively. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

MESSENGER scientists will highlight the latest results on Mercury from MESSENGER observations obtained during the first six months (the first Mercury solar day) in orbit.

These findings were presented in 30 papers and posters as part of a special session of the joint meeting of the European Planetary Science Congress and the Division for Planetary Sciences of the American Astronomical Society in Nantes, France.

Scientists will also look ahead to MESSENGER observations still to come and to the dual-spacecraft BepiColombo mission of the European Space Agency and the Japan Aerospace Exploration Agency later this decade.

"This is the first major scientific meeting at which MESSENGER orbital observations are being presented to the scientific community," says MESSENGER Principal Investigator Sean Solomon of the Carnegie Institution of Washington.

"As the first spacecraft to orbit our solar system's innermost planet, MESSENGER continues to reveal new surprises every week. It is timely to sum up what we've learned so far and to seek feedback from our international colleagues across planetary science on our interpretations to date."

After three successful flybys of Mercury, the MESSENGER spacecraft entered orbit about the innermost planet on March 18, 2011. The orbital phase of the mission is enabling the first global perspective on the planet's geology, surface composition, topography, gravity and magnetic fields, exosphere, magnetosphere, and solar-wind interaction.

Studying Mercury can help astrobiologists understand the diversity of rocky bodies that potentially exist in the Universe. This information is important in determining where best to hunt for habitable worlds around distant stars. Mercury can also provide clues about how our own planet, Earth, formed and evovled into the habitbable world we know today.

Mercury's Global Magnetic Field
The magnetic and gravity fields of Mercury are the primary clues scientists have on the structure deep in the interior of the planet, which in turns helps develop general theories for how planets form and evolve. Orbital data reveal that Mercury's magnetic field is offset far to the north of the planet's center, by nearly 20% of Mercury's radius.

Relative to the planet's size, this offset is much more than in any other planet, and accounting for it will pose a challenge to theoretical explanations of the field.

"Although we don't know how to explain that yet - it is no doubt an important clue to the workings of Mercury's dynamo," says Brian Anderson, MESSENGER Deputy Project Scientist and a space physicist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.

This finding has several implications for other aspects of Mercury, says Anderson, who co-authored several of the presentations in the MESSENGER session. "This means that the magnetic field in the southern hemisphere should be a lot weaker than it is in the north. At the north geographic pole, the magnetic field should be about 3.5 times stronger than it is at the south geographic pole.

"The big difference in northern and southern surface field strengths means that energetic particles, solar wind, and high-energy electrons will preferentially impact the surface in the south, and this situation should lead to asymmetries both in sources of atoms, ions, and molecules for Mercury's exosphere and in the discoloration of the surface by charged particle bombardment," he continues. "Both should occur more strongly in the south."