The Strangest Terrestrial Planet.

The article discusses the U.S. National Aeronautics and Space Administration's (NASA's) MESSENGER mission to the planet Mercury. An overview of two reports within the issue regarding the results of analyses of MESSENGER data by researcher D. E. Smith and colleagues investigating Mercury's moment-of-inertia factor and M. T. Zuber and colleagues investigating the dynamic range of mercurian topography is presented. Also discussed is the internal structure of Mercury, which MESSENGER measurements revealed may contain an anti-crust, and the geological and geophysical effects of the anti-crust.