Image: Martian sunset
A view from the Opportunity rover's panoramic camera shows the sun setting in the Martian west. The sky near the horizon is reddish because the sun's light is being scattered by red dust suspended in the atmosphere.
By Alan Boyle Science editor
updated 2/27/2004 5:59:43 PM ET 2004-02-27T22:59:43

For the first time in almost seven years, scientists watched a blue-and-red sunset from Mars, courtesy of NASA's Opportunity rover. The new view is appealing from an inspirational as well as a scientific point of view, scientists said Thursday.

"You're observing the sun setting on another planet — how often do you get to do that?" Cornell astronomer Jim Bell, team leader for the Mars rovers' panoramic cameras, told journalists at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It's important not to forget that what we're doing does have special inspirational moments like this."

The time-lapse sequence echoed a similar set of observations conducted during the 1997 Mars Pathfinder mission — the last time that a probe successfully landed on the Red Planet. Sunset photos were also taken by the Viking landers back in the 1970s.

Bell said the latest sunset pictures were "inspirational and beautiful, but there's really some good science in there as well." For example, atmospheric scientists analyzed the way the sun was hazed over as it sunk toward the horizon, and concluded that the Martian air held twice as much suspended dust as it did when Pathfinder snapped its pictures, he said.

"Those of you who live in Los Angeles will be very familiar with this effect," Bell joked.

So far, Opportunity and its twin in Gusev Crater on the other side of Mars, the Spirit rover, have returned 9.1 billion bits of data to Earth, including about 11,000 images from 18 cameras, Bell said.

Beginning next week, the rovers will try taking the first-ever pictures of eclipses as seen from another planet's surface, Bell said. Because of the orbital mechanics involving the two moons Phobos and Deimos, Martian eclipses are thousands of times more common than the earthly phenomenon, though not nearly as spectacular.

Bell said the rovers would take more pictures of sunrises and sunsets, and also conduct nighttime astronomical observations to judge how opaque the Martian atmosphere was at night.

Seeking traces of water
Atmospheric science is a sidelight to the rovers' main mission — a study of Martian rocks and soil to determine whether the planet had liquid water long enough in ancient times to support the development of life.

“Water is the elixir of life,” said Ray Arvidson of Washington University at St. Louis, the deputy principal science investigator for the $820 million mission, “and if we come up with the conclusion that water has been involved in the surface or subsurface at some time in the past, then I think the probability that prebiotic systems could have gotten started and life could have gotten started goes way up.”

But he declined to predict whether the mission would reach a conclusion on the liquid-water question. "That story is right around the corner, but we need to finish the work in progress, get all the data analyzed ... and then I think the story will be known," he said.

Rovers to become more robust
The rovers were designed for a primary mission of at least 90 Martian days, or sols, each one nearly 40 minutes longer than an Earth day. Spirit has reached Sol 53, and Opportunity is at Sol 32 — but the mission team says both rovers could keep going for many days longer than the 90-day "warranty period."

Slideshow: Mars at halftime "Both of them, from a spacecraft health point of view, are fantastic," said mission manager Jennifer Trosper. Engineers are planning to upgrade the solar-powered rovers' software so that Opportunity conserves more of its electricity during the night, and so that both of the rovers are more willing to roll over what Trosper called the "more challenging terrain" ahead.

For the first part of the mission, the rovers' hazard avoidance software was set conservatively, but Trosper said Spirit was entering a more rock-strewn area that would call for a bit more robotic courage. The future upgrade would build more "robustness" into the rovers' navigation software, she said.

Over the next day or so, Spirit would analyze a craggy rock nicknamed Humphrey, then continue on its trek toward a crater called Bonneville, less than 330 feet (100 meters) away. "We hope in a few weeks to two weeks to crest the rim of the crater Bonneville and to look in," Arvidson said.

About the same time, Opportunity should be finishing up its work within the 72-foot-wide (22-meter-wide) crater in Meridiani Planum where it landed a month ago. Arvidson said the science teams for Spirit and Opportunity would then "both be at the rims of craters, one thinking about going in and the other thinking about going out onto the plain."

More pictures to marvel at
Opportunity sent back more pictures for scientists to marvel at, including a look at a scattering of rocks, pebbles and soil on a shelf of bedrock called Charlie Flats.

Bell said an enhanced-color view of Charlie Flats, spanning only half the size of a coffee table, showed "more spectral color diversity than we've seen in almost any other data set on Mars." He said one rock in particular could bear the spectral signature of gray hematite, a type of iron mineral that could have been formed by interaction with liquid water.

Image: Martian "macaroni"
NASA  /  JPL / Cornell
The Martian "macaroni" is the feature just left of center in this enlarged section of a microscopic image. Full-size version is available from Jet Propulsion Laboratory at:
There was yet another tiny Martian mystery as well: an apparent curlicue that could be seen in one of the microscopic images made by Opportunity after its rock abrasion tool drilled into the bedrock. The microscopic piece of Martian macaroni was pointed out by a reporter but drew little more than a shrug from the scientists. Arvidson said he had seen the picture, but speculated that the rover rotini may be a trick of the camera. It could also be an artifact created by the rock abrasion tool itself.

NBC News space analyst James Oberg said that the feature was intriguing, but also illustrated how easy it was to read deeper meaning into raw imagery from Mars.

"What it looks like is a small critter that burrowed through these sediments, probably when they were softer, eons ago," he observed via e-mail. "At least, that's what we want it to look like, so we need to resist that interpretation and just look harder."

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Video: Sunset on Mars


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