Image: Mercury's Debussy crater, imaged during Flyby 2. JHU/APL.

Analysis of data from MESSENGER’s third and final Mercury flyby last September has revealed evidence of younger volcanism than previously recognized, new information about magnetic substorms, and the first observations of emission from an ionized species in Mercury’s very thin exosphere. The results are reported in three papers in this week’s Science Express.

During the first two flybys of Mercury, MESSENGER captured images that confirmed pervasive volcanism in the planet’s early history. The spacecraft’s third flyby revealed the recently named Rachmaninoff basin, a 290-km-diameter peak-ring impact basin, among the youngest yet seen on Mercury. The sparsely cratered Rachmaninoff plains postdate the formation of the basin and apparently developed from material that once flowed across the surface. The team has interpreted the plains to be the youngest volcanic deposits yet found on Mercury. An irregular depression surrounded by a diffuse halo of bright material northeast of the basin points to a volcanic vent larger than any previously identified on Mercury. These observations suggest that volcanism on the planet spanned much longer into solar system history than previously thought. To read more, see the full MESSENGER and CIW press releases.