MESSENGER sheds new light on Mercury

Physics Today: Data from NASA’s MESSENGER spacecraft have led to a number of new findings regarding Mercury, including possible water ice, unusual tectonic forces, and a massive core. Paul Rincon reports for the BBC that at the 43rd Lunar and Planetary Science Conference this week, Nancy Chabot of the Johns Hopkins University and colleagues presented evidence of possible water ice. They based their findings on topographical data near the planet’s poles showing shadowed craters that strongly reflect radar—a characteristic of ice. Also this week, Amina Khan of the Los Angeles Times reports on two papers that were published in Science. In one study , MIT’s Maria Zuber and colleagues looked at the topography of Mercury’s northern hemisphere and found it to be unusually flat compared with that of the Moon or Mars. They also found that the 1500-kilometer-wide Caloris impact basin is lopsided, perhaps as the result of tectonic forces. In the other study , MIT’s David Smith and coworkers used tiny shifts in the spacecraft’s orbit to measure Mercury’s gravitational field, from which they deduced the planet’s density and composition. They discovered that the planet’s core is more massive than previously thought and that there must be a solid layer of iron sulfide between Mercury’s liquid outer core and its thin mantle. The new information expands humans’ understanding of terrestrial planets. According to Zuber, knowing how different from Earth a rocky planet can look on the inside “takes off the blinders” when analyzing potentially habitable planets beyond the solar system.