Cornell's -- and Bill Nye's -- Mars sundial gets its day in the sun

By David Brand

Two views of the MarsDial taken on Mars by Spirit's panoramic camera. Scientists use the sundial to adjust the rovers' panoramic cameras, while students participating in NASA's Red Rover Goes to Mars program will monitor the dial to track time on Mars. Students worldwide will also have the opportunity to build their own Earth sundial and compare it to that on Mars. The left image was captured near martian noon when the Sun was very high in the sky. The right image was acquired later in the afternoon when the Sun was lower in sky, casting longer shadows. The colored blocks in the corners of the sundial are used to fine-tune the panoramic camera's sense of color. Shadows cast on the sundial help scientists adjust the brightness of images. NASA/JPL/Cornell University

At a press briefing at the Jet Propulsion Laboratory, which is managing the twin-rover Mars mission for NASA, Cornell astronomer Jim Bell, who is leading the panoramic camera (or Pancam) team, described the tiny sundial -- a small aluminum square with an upright post in its center -- as a "photographer's color chart." It is an "important part of Pancam and critical in getting the colors right," he said.

Bell, along with television personality and Cornell visiting professor Bill Nye, was instrumental in developing the sundial.

The rover lander is continuing to present problems in the retraction of deflated airbags, used in the bouncedown landing Jan. 3. On Jan. 7, mission engineers unsuccessfully tried to pull in an airbag section under the lander's left petal. Today they will try again to haul in the tendons attached to the bag. At the news briefing, mission manager Matt Wallace said it's possible that retracting tendons, which stretch from the actuators to various airbag points, have snapped. In that case, he said, it will not be possible to remove the deflated bag from the forward lander deck.

The forward deck -- the planned exit route for the rover -- is 40 centimeters (about 16 inches) above the ground, and the unretracted airbag is 65 to 70 centimeters (26 to 28 inches) above that. "I think we could egress over that, skirting inside the [airbag's] two bubbles, and the airbag height is not so great as to interfere with the solar panels. But we are unlikely to go that route if the airbag is not withdrawn," Wallace said. Added Bell, "Which way we go off the lander is not a critical issue."

A partially inflated airbag, seen at right, may interfere with a forward rolloff of the rover. NASA/JPL/Cornell University

Another problem -- with the lollipop-shaped, high-gain antenna, which provides a direct-to-Earth communications link -- appears to have been solved. It had not been used for data transmission since Jan. 4, when a spike occurred in the amount of electricity drawn by one of its motors, possibly caused by debris. However, the antenna was used for two transmissions Jan. 7 (along with transmissions through the rover's UHF antenna using satellite relay links).

The rover sundial design team included Nye, a 1977 Cornell engineering graduate; Steven Squyres, Cornell professor of astronomy and principal investigator for the rover science program; Bell, who is a Cornell associate professor of astronomy; Woodruff "Woody" Sullivan, sundial enthusiast and professor of astronomy at the University of Washington; Cornell alumnus Tyler Nordgren, an artist and astronomer at the University of Redlands in California; Jon Lomberg, an artist and creative consultant to the Mauna Kea Center for Astronomy Education, University of Hawaii at Hilo; and Louis Friedman, executive director of the Planetary Society.

Unlike ordinary sundials, the Mars sundial has no hour marks -- the rover will be changing position frequently, rendering permanent hour lines meaningless. Instead, Cornell researchers on the rover science team have added hour marks electronically onto Pancam photos of the sundial. The Web site sundial page at http://athena.cornell.edu/kids/sundial.html will be updated every couple of days with new photos of the sundial, and one full day of the mission will be devoted to sundial observation. There also will be a sundial on the rover Opportunity, scheduled to land on Mars Jan. 25.

The Cornell-developed software that made the overlay of the hour marks possible was described at today's press briefing by Courtney Dressing, 15, one of 16 students from 12 countries chosen by the Planetary Society to work with the mission.

Pancam scientists are using the colored blocks in the corners of the sundial to calibrate the color in images of the landscape so that Mars can be seen in its true colors, described by Bell as "brownish, reddish ochre." And pictures of the shadows that are cast by a sundial's center post -- in sundial terminology, the gnomon -- allow scientists to properly adjust the brightness of each Pancam image.

The grayscale calibration rings surrounding the gnomon represent the orbits of Mars and Earth, with two dots representing the planets. The sundial is inscribed with the words "Two Worlds, One Sun" and bears the name "Mars" in 17 languages.

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