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NASA
Craters and smooth plains extend for long distances to Mercury's northern horizon. The picture was taken during Messenger's flyby this week.
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updated 9/30/2009 1:15:04 PM ET 2009-09-30T17:15:04

A NASA spacecraft that completed its third and final flyby of the planet Mercury on Tuesday, snapping new pictures of the innermost planet, had a small data hiccup that has delayed release of the best close-ups, mission engineers said Wednesday.

The Messenger probe skimmed just 142 miles (228 kilometers) 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. ET when it sped by at about 12,000 mph (19,312 kilometers per hour). 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 kilometers per hour) during the flyby and place it on track to enter orbit in March 2011.

NASA / JHUAPL / Carnegie
This striking view of Mercury was taken during Messenger's approach to the planet, from a distance of 16,700 miles (26,900 kilometers).

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. Messenger, which was launched in 2004, takes its name from an extended acronym that stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging. The probe swung past Earth once and Venus twice before beginning its three Mercury flybys.

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