NASA spacecraft MESSENGER's final flyby of the planet Mercury before entering its orbit in 2011 had a disappointing glitch but was “;mostly successful,”; says a University of Hawaii planetary researcher.

Jeffrey Gillis-Davis, a researcher on the MESSENGER science team, said the flyby produced “;a great image of a new pit crater we hadn't seen before. It's nice to see the number of these features increasing and distribution around the globe of Mercury increasing. ... It's some global geologic phenomena.”;

The new pit crater is much longer than many of those observed before “;and may shed some clues into not only its formation but the formation of other pit craters on Mercury,”; he said.

The flyby produced about 600 images, about half of what scientists had anticipated to fill out the picture provided by the first two flybys in January and October last year.

A signal loss just before the closest approach—about 142 miles above the planet's surface—caused the spacecraft to go into a safe mode and shut down its instruments, Gillis-Davis said.

That happened as the spacecraft was going into Mercury's night side Sept. 29 and the solar-generating power switched to battery power, he said.

But it's “;just a little hiccup,”; with no irreversible damage to the spacecraft or instruments, he said.

Data up to that point had been saved and downloaded, Gillis-Davis said.

But MESSENGER has imaged about 95 percent of the terrain. “;Once we get into orbit we'll be able to finish off the remaining 5 percent,”; Gillis-Davis said.

Mercury is the smallest and densest of the terrestrial planets and closest to the sun. It wasn't well known because of the difficulty of sending a spacecraft there until technology advanced.

The spacecraft's name MESSENGER is an acronym for “;Mercury Surface, Space Environment, Geochemistry and Ranging.”;

Sean Solomon, principal investigator at the Carnegie Institution in Washington, said in a NASA news release: “;As enticing as these flybys have been for discovering some of Mercury's secrets, they are the hors d'oeuvres to the mission's main course-observing Mercury from orbit for an entire year.”;

The flyby succeeded in slowing the spacecraft so it can be captured by Mercury's gravity in March 2011, Gillis-Davis said. “;That sets up nicely our time to go into orbit around Mercury.”;