Scientist Involved in Extended Missions to Comets, New Mission to Moon (12/24/2007)

A scientist with The University of Arizona Lunar and Planetary Laboratory will discover more about comets and Earth's moon, thanks to spacecraft on extended and new NASA missions.

Regents' Professor H. Jay Melosh, a scientist who helped plan and analyze the comet-slamming Deep Impact mission to comet Tempel 1 in July 2005, will get another look at the same comet with cameras aboard the Stardust spacecraft in February 2011. Melosh is on the science team for Stardust-New Exploration of Tempel mission, or Stardust NExT mission. Stardust is the spacecraft that returned a capsule with a coma sample from comet Wild 2 to Earth in January 2006.

NASA has sent Deep Impact, sans its copper projectile that was fired into comet Tempel, on its own extended mission. The Deep Impact spacecraft will swing by Earth on New Year's Eve, using our planet's gravitational pull to redirect its course toward comet Hartley 2 for an encounter in October 2010. Deep Impact's imaging cameras will take pictures of the surface of comet Hartley 2 as part of its extended mission, called EPOXI. The spacecraft will need three trips around the sun before the encounter.

En route to the comet Hartley, scientists will use the larger of Deep Impact's two telescopes to do transit searches for small planets around five stars known to be orbited by large planets. Transit searches detect planets when they cross the faces of their stars.

The goal of the comet missions is to get more images of comet surfaces, Melosh said. So far, no two appear to be alike.

"Basically, Deep Impact gave us a very different view of what comets are made of," he said.

"Scientists have got a good look at the nuclei of comets Wild 2, Tempel 1 and Boethin, which was imaged by Deep Space 1, and they're all different. Deep Impact showed us that Tempel is basically powder, a low-density powder puff mixture of silicate dust and very cold ice dust. We want to get as close to Hartley 2 as we possibly can for a good look at it," Melosh said.

Melosh is one of six scientists on the new, Massachusetts Institute of Technology-led NASA mission named Gravity Recovery and Interior Laboratory, or GRAIL, to be launched to the moon in 2011. It will put two separate satellites into polar orbit around the moon to precisely map variations in the moon's gravitational pull.

Other spacecraft have taken, are taking and will take gravity measurements of the moon that are vital to lunar navigation and future exploration. But the moon's gravity field on its far side is still Luna pessime cognita, that is, only crude moon gravity maps exist, Melosh said.

GRAIL will fly two satellites about 100 kilometers apart between 30 kilometers and 50 kilometers above the surface of the moon. Each satellite will carry a transponder for signaling its relative position to the other. Even when flying on the moon's far side, out of the line of sight with Earth, the twin satellites will be able to measure gravity anomalies with extreme precision, down to millimeter deviations in their orbits.

A third of the yearlong moon mapping mission is to get engineering data for navigation. The rest is for science. Melosh said the science team is mainly interested in the distribution of mass near the surface of the moon because "Gravity gives us a lot of hints about what's going on geologically." GRAIL data will help them interpret such features as lava flows, mounds, faults, and impact craters, especially on the moon's far side.

Note: This story has been adapted from a news release issued by the University of Arizona

Post Comments: