In this image, Mercury's northern horizon cuts a crisp line against the blackness of space. The surface in the lower right corner of the image is near Mercury's terminator, the line between the light dayside and dark night side of the planet. Looking toward the horizon, smooth plains extend for large distances, similar to volcanic plains seen nearby during MESSENGER's second flyby of Mercury.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
This story was updated at 10:45 a.m. EDT.
A NASA spacecraft that completed its third and final flyby of the planet Mercury yesterday, snapping new pictures of the innermost planet, had a small data hiccup that has delayed release of the images, mission engineers said today.
The MESSENGER probe skimmed just 142 miles (228 km) above Mercury at its closest approach as it whipped around the planet during the flyby, the last of three designed to guide the spacecraft into orbit around the planet in 2011.
The spacecraft did snap several new images of the rocky planet on the inbound leg of its close approach.
"We do have some new science from the flyby," said MESSENGER project scientist Ralph McNutt of Johns Hopkins University Applied Physics Laboratory.
MESSENGER also took snapshots during its close approach, but "we had a little bit of a hiccup in the data" that has delayed the release of those images, said Eric Finnegan, systems engineer for the mission at Johns Hopkins APL. "It's coming," he added.
The anomaly appears to have happened right around the spacecraft's close approach, so there may not be images from the outbound leg of the journey, McNutt said.
"We missed a little icing on the cake," McNutt told SPACE.com.
Despite the hiccup, the spacecraft is in good health, Finnegan told SPACE.com.
"What is important is that the spacecraft and the instruments are healthy," McNutt said.
The team is sifting through all the data and new images to see just how much they got before the glitch, McNutt added.
"We're all working through this," he said.
MESSENGER made its closest approach to Mercury at about 5:55 p.m. EDT (2155 GMT) when it sped by at about 12,000 mph (19,312 kph). The probe then flew behind Mercury, passing out of communications with Earth for about an hour before restoring contact.
Mercury's gravity was expected to slow MESSENGER by about 6,000 mph (9,656 kph) during the flyby and place it on track to enter orbit in March 2011.
The $446 million spacecraft flew by Mercury twice in 2008 to map the planet in unprecedented detail while using the rocky world's gravitational pull to refine its flight path through space.
The spacecraft is the first probe to visit Mercury since NASA's Mariner 10 mission in the mid-1970s.
When MESSENGER arrives in its final orbit around Mercury, it will begin a long-awaited observation phase that will complete its new maps of the planet. NASA launched MESSENGER - short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging - in 2004. The probe swung past Earth once and Venus twice before beginning its three Mercury flybys.
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