Craft to let UH sky-gazer espy Mercury

Scientists hope to solve some puzzles about the planet Mercury when the spacecraft Messenger approaches it today on the first visit in nearly 35 years, says a University of Hawaii planetary researcher.

"It's tough to see the picture you're making if you have only half the pieces," said Jeffrey Gillis-Davis, a member of the Messenger science team.

Only about 45 percent of one side of the planet was mapped on the first visit by the Mariner 10 spacecraft in 1974-75, he said. "We will quickly add another one-third or so of the pieces, and we will start to get a global view of what Mercury looks like."

When scientists first saw the far side of Earth's moon in 1967, Gillis-Davis said, "It looked totally different than the near side of the moon. This really dropped scientists' jaws at the time that the two hemispheres were so different. We don't think Mercury will be quite that extreme, but we really don't know."

Gillis-Davis received a $580,000, six-year grant from the National Aeronautics and Space Administration last September as a Messenger participating scientist. The team will monitor the spacecraft's arrival at Mercury from mission control at the Johns Hopkins University Applied Physics Laboratory in Maryland.

It is the first of three flybys of Mercury scheduled before the spacecraft is slowed to go into orbit around the planet in 2011.

Mercury is the smallest and densest of the terrestrial planets, which include Venus, Earth and Mars, and the most mysterious because little is known about it.

"Understanding this 'end member' among the terrestrial planets is crucial to developing a better understanding of how the planets in our solar system formed and evolved," NASA says.

It is difficult to send a spacecraft to Mercury because it is so close to the sun, Gillis-Davis said. However, improved technology over the past three decades now makes it possible, he said.

The Messenger has a special sun shade to protect it from "getting cooked," he said.

Peter Mouginis-Mark, Hawaii Institute of Geophysics and Planetology interim director, said Mercury "has some fascinating similarities and differences with our own moon. It lacks an atmosphere. It's got lots of craters and maybe old volcanoes and, because it's so close to the sun, has higher gravity than our moon does."

He said Gillis-Davis' studies of Mercury and comparisons with the moon will increase understanding of geological processes as more missions are planned to the moon.

Gillis-Davis said he has studied the moon for about 15 years through geology and remote sensing and that he will do similar research with the Mercury data.

He is specifically interested in an area impacted by craters known as the Inter-Crater Plains and flat terrain called Smooth Plains.

The science team is studying the origin of the plains areas to determine if they were created by volcanism or an impact of ejected material from another body, he said.

"The importance is to understand the thermal history of Mercury," Gillis-Davis said. "Did it have volcanism on it?"