—by Brian Anderson

Just as invention is often born of necessity, the 3-D Tour of the Solar System sprang from the seed of one man's frustration with a specific scientific problem.

"I wanted to know how deep the craters were on the icy satellites," said Paul Schenk, the senior author of the CD-ROM recently released by the Lunar and Planetary Institute. "The methods that were available were kind of primitive, and I thought it would be a real big help if we had stereo images so I could measure the features directly."

Soon afterward, Schenk came across some stereo images of Uranus' satellite Miranda and realized a valuable scientific resource may have remained untapped.

"I began to investigate whether there were any unused stereo images in the Voyager dataset," Schenk said. "I found out that most of the outer planets had stereo coverage, which surprised me. Once I had that, it was natural to extend it to the rest of the solar system."

After discovering a wealth of viable stereo images, Schenk and co-authors David Gwynn and James Tutor began the arduous process of sifting through the datasets of various missions to select representative images of the nine planets, their satellites, and the asteroid belt. Most of the stereo pairs, save for some dedicated stereo images taken on Apollo and Magellan missions, had to be constructed using existing orbital photographs.

"I think this has been the first chance anybody has had to explore these images," Schenk said. "A few people had looked at a few examples, such as Miranda, but I think a lot of people just assumed there was no useful stereo coverage."

Over a period of about a year, Schenk and his coworkers processed, cleaned up, and reprojected the selected original images to create optimum stereo pairs. ("Your mind would just explode if you saw the originals," Schenk explained.) In addition, for many of the images, the scientists compiled data sheets of relevant factors such as spacecraft altitude, image width, and stereo baseline.

"We were all surprised by the amount of work that was involved," Schenk said.

From left to right, James Tutor, David Gwynn, and Paul Schenk.

Paul Schenk observes as participants at the 28th Lunar and Planetary Science Conference explore the Solar System in 3-D.

The resulting product, the first collection of true stereo images from the solar system, contains more than 150 images. The images are viewed using red-green 3-D glasses (included with the CD) and highlight important geological features such as impact craters, volcanos, and faults, in keeping with Schenk's original focus.

"It gives you a very different perspective on what other planets look like. One can actually sense how rugged the mountains are and how deep the craters are," Schenk said. "We tried to put in several examples of all the prominent features on planets. It's a useful way of illustrating specific geological features and the deposits and structures that are associated with them."

Some of the stereo pairs reveal dramatic geological features not visible in standard photographic images. Many of the volcanos on the outer satellites turned out to be flatter than expected, for example, and images of Ra Patera on Io revealed a connection between a lava flow and a high plateau east of the volcano.

"This wasn't detected at all with the standard images," Schenk said.

Although 3-D vision in one sense emulates the depth perception of human eyesight, the stereo images on the 3-D Tour are exaggerated to show vertical relief and geological detail. Whereas human eyes are separated by only a few inches, Schenk tried to select images that were spaced apart at distances equal to or greater than the altitude at which they were taken. Essentially, these images give a Paul Schenk observes as participants at the 28th Lunar and Planetary Science Conference explore the solar system in 3-D. "giant's eye" view of terrain, revealing features in striking stereo detail that would not be apparent in normal orbital views.

"If you were in orbit, you wouldn't be able to tell anything about these features," Schenk said.

Schenk, who earned a Ph.D. in planetary sciences in 1988 and joined LPI's scientific staff in 1991, notes that geologists have long relied on stereo images for gauging distances on Earth and that NASA continues to use the technology for navigational purposes in rover operations such as Pathfinder. He believes stereo imaging will play an increasingly important role in studying the icy satellites and Mars, and he hopes to focus his own research in that direction.

"I plan to use the stereo images to actually map the topography of the icy satellites, which hasn't been done, focusing on Io and Ganymede. Those are the first on the list, then Mars. Some of this has been done on Mars, but it hasn't been done everywhere."

In addition to pursuing his own research interests in the coming years, Schenk will oversee the production of future editions of the 3-D CD-ROM, including an interactive multimedia version for younger audiences that is already in the works.

"I definitely have plans to do more such products and to make them bigger and better," Schenk said.

The 3-D Tour of the Solar System can be sampled on the LPI Web site.

(Mr. Anderson is a member of the Publications and Program Services Department staff at the LPI.)