NASA's freeze frames Camera: The agency enlists two Beltsville scientists to create and photograph simulations of Martian snow.

November 19, 1998|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

Using a camera designed to photograph microscopic bugs and worms, William Wergin and Eric Erbe have snapped shots being critiqued by NASA of a substance alien to planet Earth: Martian snow.

Wergin, a cell specialist, and Erbe, a botanist, began using earthly matter to simulate and photograph crystals like those that cover the Martian icecaps about a year ago at the request of NASA scientists.

Working at the Agricultural Research Service's Nematology Lab

in Beltsville, they shot their one-of-a-kind pictures using the same microscope they used in 1994 to create three-dimensional photos of earthbound snow crystals.

NASA scientists say the black-and-white stills will help them chart the thickness of the red planet's icecaps, track its atmospheric conditions, predict climatic changes and come to a greater understanding of how the planet functions. And if humans ever land there, they'll know better what to expect.

"It'll help in measuring the planet's snowpack, and if you can measure the snowpack and see variations from year to year, you'd be able to start looking into why there are these variations and how they affect the atmosphere," said James Foster, a climatologist at NASA's Goddard Space Flight Center in Greenbelt.

Scientists at the National Aeronautics and Space Administration came to the Beltsville researchers last year looking for help designing sensors for satellites that would measure the depths of Mars' icecaps.

Microwaves emitted by Mars change during the seasons depending on the snowpacks, so the planet's snowpacks and icecaps can be measured with microwave signals.

But to design effective sensors, NASA had to know something about the size and shape of the snow crystals that covered Mars' polar ice caps, Foster said.

He said numerous aerial photographs have been taken of Mars' icecaps, but that none show the shape or the size of the snow that forms them.

"We know that it's white, it's nearly as bright as the snow on Earth, and the feeling is that it's very weak and brittle," Foster said. "But we were not sure what size or shape the [snow] crystals would be."

Now they are.

Up close, the Martian snow looks nothing like its earthly counterpart.

It is more brittle and falls in eight-sided crystals that are much smaller and not quite as bright as earthbound flakes.

Scientists say that most of the differences between the two types of snow can be traced to Mars' chillier climate.

For one thing, Martian snow is not made from water but from carbon dioxide -- a compound that exists as a gas in Earth's atmosphere.

On Mars, which is considerably farther from the sun than Earth is, winters are much longer and get so bitterly cold -- more than 200 degrees below zero -- that carbon dioxide commonly freezes into solid crystals.

"Nobody had ever visualized CO2 [carbon dioxide] crystals before," Wergin said, adding that he was intrigued by NASA's request last year but knew there was no way to bring snow back from Mars.

So Wergin and Erbe took commercial dry ice -- frozen carbon dioxide used to chill everything from medical supplies to meats -- and raised the temperature of the dry ice so it would "sublime," or convert into a gas.

They then chilled the gas to the temperatures of the Martian winter: -240 degrees Fahrenheit.

At that temperature, the carbon dioxide gas turned into Mars' brittle, white snow and Wergin and Erbe photographed it, just as they had done four years ago with earthly snow.

In 1994, they published articles in several scientific journals reporting that they had created three-dimensional, microscopic photographs of snow.

The photographs helped climatologists determine the amount of water in Rocky Mountain snowpacks, a key for predicting the amount of spring runoff available to irrigate farmlands in Western states, Wergin said.

Wergin and Erbe give much of the credit to their camera, which was retooled about five years ago with the addition of a "cold platform," which lets them snap shots of frozen tissue samples of nematodes, bacteria and fungi that infect everything from crop soils to tree leaves.

"Couldn't have done much without it," Erbe said, patting the lens affectionately.

Whether it's the camera or the photographers, NASA scientists say the photos will help them understand Mars.

"We know that there is weather up there on Mars, and it does vary," Foster said. "The more you know about the overall conditions, the more you can tell about those variations and what causes them."

Pub Date: 11/19/98

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