Messenger this week completed is first perihelion passage from orbit, its first superior solar conjunction from orbit and its first orbit-correction maneuver -- all milestones, NASA officials said Thursday in a release.
"Those milestones provide important context to the continuing feast of new observations that Messenger has been sending home on nearly a daily basis," said the craft's principal investigator, Sean Solomon of the Carnegie Institution of Washington.
Tens of thousands of images of major features on the planet are available in sharp focus to provide details about Mercury's surface, scientists said.
Landforms -- patchy deposits revealed to be clusters of rimless, irregular pits -- are unlike anything investigators have seen on Mercury or the moon, said Brett Denevi, a staff scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., and a member of the Messenger imaging team. "We are still debating their origin, but they appear to have a relatively young age and may suggest a more abundant than expected volatile component in Mercury's crust."
Observations also revealed substantial amounts of sulfur at Mercury's surface, suggesting Mercury's original building blocks may have been less oxidized than those that formed the other terrestrial planets, NASA said. The result also hints that sulfur-containing gases may have contributed to past explosive volcanic activity on Mercury.
"We are assembling a global overview of the nature and workings of Mercury for the first time," Solomon said. "Many of our earlier ideas are being cast aside as new observations lead to new insights ... and we can expect more surprises as our solar system's innermost planet reveals its long-held secrets."