Real Hitchhiker’s Guide to the Solar System on the Way

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Thinking about trekking across Titan or meandering around Mercury? Along with your backpack and towel, you’ll also want to pack one of Robert Gaskell’s maps. Gaskell, a senior scientist at the Planetary Science Institute, is working on creating real hitchhiking guides to the various bodies in our solar system. He’s been equated to the final frontier what Lewis and Clark were to the American West – the guy producing the most accurate and detailed maps available. And thanks to current space missions sending back loads of data, Gaskell is beginning to work on creating precise maps of Mercury, the asteroid Eros, and eight moons of Saturn including Enceladus. Gaskell has created sophisticated software that combines hundreds of spacecraft images of varying resolution to create the maps. He’s been developing the software for nearly 25 years, and if you want to map a planet, moon, or asteroid, he’s the guy to ask.

Gaskell uses a method called stereo-photo-clinometry, or SPC. Just as stereo-phonic means sound from different directions, stereo-photo means light from different directions, and clinometry means that slopes, or inclines, are being measured. So SPC means finding slopes from the way the surface looks under different illuminations, and once we know the slopes we can find the heights.

Four computers in Gaskell’s office grind out mapping data nearly 24/7. But despite his quarter century of mapping work, Gaskell says he’s just getting started. “There are thousands of objects in the solar system, and so far, I’ve barely scratched the surface, if you’ll pardon the expression,” he said.

Gaskell has won an NASA Exceptional Achievement medal for his detailed maps of the asteroid Itokawa.

His newest project will create highly accurate maps of the entire surface of Mercury based on images sent back by NASA’s MESSENGER spacecraft. MESSENGER flew by Mercury in January and will fly by again in October before going into orbit of Mercury in 2011.

Currently Gaskell is combining images from the January flyby with those taken by Mariner 10, which visited Mercury in 1973, to produce initial maps. But the sun angle for the Mariner 10 photos was the same for three flybys and so far there is only one flyby for MESSENGER.

“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.”

Gaskell’s maps not only give scientists useful information about a body’s surface, they also can be used for navigating spacecraft, calibrating spacecraft instruments, and gaining information about the geology, internal structure and past history of an object.

In addition to Mercury, Gaskell is mapping eight of Saturn’s moons, including Enceladus, a frigid world punctuated by icy geysers. In October, NASA may use those maps as navigational tools to plot – and possibly adjust – the Cassini spacecraft’s trajectory as it flies past Enceladus.

Once Gaskell’s computers produce maps covering an entire body, they yield a very accurate image of the object’s shape. The moons of Saturn, for instance, have changed orbits during their history and gravitationally interact with one another. Once their shape became fixed, it recorded the tidal stresses at the time they froze, which gives scientists a way of determining the orbital history of the system.

For Io, Jupiter’s highly volcanic moon, mapping its shape provides planetary geologists with part of the data they need to determine what processes may be going on inside its fluid core, which is being heavily torqued by the giant planet’s intense gravitational field.

Describing himself as an evangelical stereo-photo-clinometrist, he is sharing his work with others and recruiting more researchers into the long-term effort to map the solar system. Some of those are at the Jet Propulsion Laboratory, The University of Arizona, the Johns Hopkins Applied Physics Laboratory, and USGS.

With so many planets, moons and asteroids to explore and map, “It’s like being in a big candy shop,” Gaskell said.

Source: Planetary Science Institute