Mercury MESSENGER co-investigator Mark Robinson of Arizona State University reports that new images from the spacecraft's second flyby shows that Mercury's crust is compositionally heterogeneous. He said, "Although definitive compositional interpretations cannot yet be made, the distribution of different components varies both across the surface and with depth - Mercury's crust is more analogous to a marbled cake than a layered cake. Once MESSENGER's suite of science instruments returns a host of data from the orbital phase of the mission, compositions will be determined for the newly discovered color units."
[right, click on image to go to flyover movie. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington]