SCIENCE

Monday, July 9, 2007

Mars Rover at Crater's Edge

The unexpectedly long-lived Mars rover Opportunity was scheduled to make a dramatic and potentially dangerous descent into a crater last weekend, but the worst Martian dust storm in years put the plan on hold. NASA officials said late last week that the winds were calming down and the fine dust was beginning to settle, leaving them optimistic that they might be able to try again to enter Victoria Crater later this week.

NASA announced the imminent descent on June 27, and principal investigator Steven Squyres of Cornell University said the wind and dust began blowing soon after. He said that the dust measurements on both Mars rovers climbed higher than ever recorded and that long-term coverage could damage the rovers' ability to move and operate. Although the dust is more like smoke than a sandstorm, he said, it can rise high into the atmosphere and blot out the sun's rays -- leaving the rovers' solar panels without a power source.

The rover is perched near an outcropping called Duck Bay on the rim of Victoria Crater, which is by far the deepest one that a Mars rover has neared. NASA researchers have been eager for Opportunity to enter the crater since it arrived there last year, but the rover first had to explore along the rim for the best way down. Squyres said the team was especially interested in exposed rock formations down in the crater that may give clues to the planet's history.

The two rovers landed on Mars more than 1,000 days ago and were expected to last only three months. Both, however, defied predictions and remain in operation. Dust storms such as the one that postponed the descent into Victoria Crater have also been partially responsible for the longevity of the rovers, since the high winds have worked to periodically clean the solar panels to a degree unpredicted before the rovers landed.

-- Marc Kaufman

A Rainbow From a Test Tube

Chemists at the University of California at Riverside have found a way to make a test tube of clear water turn into every color of the spectrum.

The trick is achieved by harnessing the capacity of crystals to absorb or reflect specific wavelengths of electromagnetic energy.

A crystal is an orderly packed array of units such as atoms or molecules. The layers of units can split light into different wavelengths and colors, and the overall architecture of the crystal determines which colors are absorbed and which are reflected.

Yadong Yin and his colleagues created a "colloidal crystal," a crystal suspended in another substance, in this case water. Its units were round particles with cores of magnetite, an iron-based compound that can move in response to a magnetic field. Encasing each core was a batterlike coating of polyacrylate plastic.

Polyacrylate has an electrostatic charge. The coating's outer surface was strongly attracted to the water, the inner surface similarly attracted to the magnetite. This combination of forces pulling in different directions made each particle slightly compressible.


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