Image: Asteroid Eros and shape model
A NASA image of asteroid Eros (left) and Robert Gaskell's shape model of the asteroid (right).
updated 9/2/2008 6:52:34 PM ET 2008-09-02T22:52:34

Galactic hitchhikers visiting our solar system, if they exist, would probably love to get their hands on a new guide that puts GPS to shame.

A planetary scientist has made the most detailed maps of our local planets, moons and asteroids yet by combining hundreds of spacecraft images to chart all the nooks and crannies of numerous surfaces, including the asteroids Phobos, Itokawa and Eros. Upcoming targets for mapping include the planet Mercury and eight of Saturn's moons, such as frozen Enceladus with its icy geysers, as well as Earth's moon.

"I have three computers crunching away right now," said Robert Gaskell, a planetary scientist based in Altadena, Calif., who works at the Planetary Science Institute. "One's working on the moon, one's working on Eros, and another's working on Mercury."

Gaskell uses many images from different angles and illuminations to figure out the slopes and heights of alien terrains, whether a rocky asteroid or icy moon. His method of stereo-photo-clinometry creates square "maplets" on a computer model of the target, and smaller squares get added as the model receives more detailed data.

A major project involves creating highly accurate maps of the entire surface of Mercury — the closest planet to the sun — based on an expected stream of images from NASA's MESSENGER spacecraft. The probe still needs to swoop past Earth and Venus before settling into a Mercury orbit in 2011.

"Doing the larger bodies like the moon and Mercury, you've got to make an awful lot of maplets," Gaskell told He added that Mercury alone would probably involve 500,000 maplets of varying size.

Gaskell has already begun combining images from an initial MESSENGER flyby of Mercury in January with older Mariner 10 images taken in 1973. But the three Mariner 10 flybys produced photos from the same sun angle, which means Gaskell only has two angles to work with at the moment.

"It won't be until we get overlapping data from different sun directions that it will really start making a lot of sense," Gaskell said. "It does give a reasonable solution now, but I don't completely trust it."

Other map work need not wait until MESSENGER settles into its Mercury orbit in 2011. NASA also wants Gaskell to map eight of the moons orbiting Saturn's ringed visage, including Enceladus.

Mission planners may use the maps as navigational tools for the Cassini spacecraft to revisit Enceladus in October, where a fresh flyby may provide additional data on the moon's geysers.

The accurate map modeling could also help scientists study Saturn's moons for signs of frozen tidal stresses that might reflect the satellites' orbital histories, when they gravitationally tugged at one another in more unpredictable ways.

Gaskell's earlier work has already garnered a NASA Exceptional Achievement Medal. The award recognized the maps of the asteroid Itokawa as "the highest resolution description of an asteroid," at resolutions better than 15.75 inches (40 cm).

The scientist's computers continue working around the clock, but thousands of planetary and other bodies still remain in the solar system.

"So far, I've barely scratched the surface, if you'll pardon the expression," Gaskell said

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