Observations by MESSENGER’s Magnetometer showed that Mercury’s magnetic field is offset along the planetary spin axis by about 20% of the planet’s radius.
The temperatures range from 50 K (purple) to 550 K (red).
The permanently shadowed craters near Mercury’s north pole have thermal environments that allow water ice to be stable in these craters either at the surface or a few tens of centimeters below the surface.
MESSENGER measurements have revealed that Mercury is surprisingly abundant in volatile elements that evaporate at moderately high temperatures, ruling out many of the models for its formation and early history that had been proposed before the mission.
Because potassium is much more volatile than thorium, the ratio of the abundances of these two elements is a sensitive measure of thermal processes that fractionate elements by volatility.
The third frame shows a longitudinal average of the neutron flux over the polar region obtained by MESSENGER’s Neutron Spectrometer; the decreased neutron flux at higher latitudes is evidence for the presence of hydrogen (as in water ice) in Mercury’s polar region.
For Mercury, as seen in the first graph, this ratio is similar to that for other terrestrial planets at greater distances from the Sun but significantly higher than that for the Moon, which lost potassium during the giant impact that led to its formation.Particularly high potassium concentrations were observed by MESSENGER's Gamma-Ray Spectrometer at high northern latitudes, as illustrated in the abundance map on the left side of the animation.The first frame shows an Earth-based Arecibo radar image in red overlaid on a mosaic of MESSENGER’s Mercury Dual Imaging System images, enabling for the first time the identification of the host craters for all of the radar-bright deposits.The second frame shows the topography of the region as measured by MESSENGER’s Mercury Laser Altimeter (purple: about 5 km below average surface elevation; red: about 5 km above average surface elevation); illumination models derived from the topography show that the radar-bright deposits are located in regions of permanent shadow.
Relatively high abundances of other volatile elements, including sulfur (right side of the animation), sodium, and chlorine, provide further evidence that Mercury is volatile-rich.
The high sulfur contents combined with low amounts of iron on the planet's surface additionally indicate that Mercury formed from materials with less oxygen than those that formed the other terrestrial planets, providing an important constraint on theories for the formation of all of the planets in the inner Solar System.