The landing site for Curiosity, the next Mars rover, has been narrowed down to two choices. Curiosity will either explore Eberswalde crater, an ancient river delta, or Gale crater, the home of a three-mile high mountain. 

Like the faces of veterans comparing war wounds, the surface of our moon is scarred by a lifetime of damage—impact craters pockmarked with even more craters, sprayed ejecta, discolored regions laid down by volcanic flows. Studying these characteristics can reveal much about the processes that formed them, say Caltech graduate student Meg Rosenburg and her advisor Oded Aharonson, who have created the first comprehensive sets of maps revealing the roughness of the moon's surface.

Earlier this month, Eris—the distant world first discovered by Caltech's Mike Brown and colleagues back in 2005, paving the way for the eventual demotion of Pluto from planet to dwarf planet—passed fortuitously in front of a faint star in the constellation Cetus. That passage, or occultation, allowed the first direct measurement of Eris's size.

Hundreds of extrasolar planets have been found, most solitary worlds orbiting their parent star in seeming isolation. Further observation has revealed that planets come in bunches. Most systems contain planets orbiting too far from one another to feel each other's gravity. In a handful of cases, planets have been found near enough to one another to interact gravitationally. Now, however, Caltech's John A. Johnson and his colleagues have found two systems with pairs of gas giant planets locked in an intimate orbital embrace.