April 12, 2007
Through a Telescope Darkly
Fourteen thousand feet above the vast fetch of the Pacific Ocean, Diana Blaney announces, "Guide Dog is ready. Big Dog is ready."
"Roger," says telescope operator Paul Sears. "Guide Dog is on. Big Dog is on."So begins a night of Mars-watching at NASA's Infrared Telescope Facility atop Hawaii's dormant Mauna Kea volcano. Here, astronomers work by night to discover things that can't be seen by day. Big Dog is the software that controls the spectrometer that measures wavelengths of light. Guide Dog takes pictures that document where the telescope is pointed.
The All-Nighters of Science
On this night, cloud cover makes Mars-watching especially challenging. Blaney, a member of the Mars Exploration Rover science team at NASA's Jet Propulsion Laboratory, and Sears, a year-round employee of the University of Hawaii, will spend it trying to measure about 1,000 different wavelengths of infrared light.
"All molecules vibrate," says Blaney. "You can kind of think of atoms as a bunch of masses on springs. When sunlight hits them, they start vibrating at a given frequency. What we're doing is measuring that frequency."
From a distance, the IRTF resembles a cookie tin topped by a shiny, metallic dome. Heavy metal doors protect the telescope against fluctuations of light or temperature, the sworn enemies of astronomers. Anyone who has gazed into the night sky knows how hard it is to see anything with artificial light or desert thermals invading the field of view.
Making the Invisible Visible
Blaney and Sears will spend the night in a cavernous room, seated in office chairs, fiddling with control panels and computers, waiting for a break in the clouds. Blaney has waited months for one night of viewing. Even a little bit of data is better than none. She is on a mission to find minerals that tell the story of water on the Red Planet.
In particular, Blaney is searching for minerals widely found in nature in which atoms of sulfur are bound with atoms of oxygen. Sulfur is the stuff that makes matchsticks burn. Oxygen is what humans breathe. Mars has been described as a sulfate planet. On Earth, sulfur is found in deserts, left behind when water evaporates.
If humans could see the part of the electromagnetic spectrum known as infrared light, we could look at a mineral like gypsum and see that it contains water molecules. In this way, we could tell a story of environmental change.
Like a rainbow that separates visible light into discrete bands of color, the telescope separates infrared light into individual components. "That's how we do most of the remote sensing of Mars," says Blaney, "for mapping everything from water vapor in the atmosphere to clays on the surface."
Spacecraft measuring infrared light at Mars have found minerals with water and sulfur at the poles and in Valles Marineris, the solar system's largest canyon.
Stream channels and rock layers bear evidence of liquid water in the past. Scientists have lots of different ideas about how it got there. Perhaps it was transported by volcanic gases, acid rain, flowing streams, glaciers, lakes, mud flows, or even oceans.
Ideal Spot for Mars-Watching
Blaney has been observing Mars at the IRTF since 1986. Besides being a great place to view Mars, the summit of Mauna Kea looks a lot like Mars. The volcano's shape, the colors of the rocks, the absence of vegetation are reminiscent of Mars.
"We're above most of the weather in Hawaii," says Blaney. "It's colder. It's drier. You don't get as much rain. You don't have plants, which influence how things weather."
Measured from the ocean floor, Mauna Kea is the tallest mountain on Earth, rising 10,203 meters (33,476 feet). The volcano's summit punches into the lower reaches of the stratosphere. There's not much oxygen, and when the sun sets, the temperature drops to about 35 degrees F. (2 degrees C). Given a choice between a down jacket and a heater, an astronomer will choose the down jacket. Heat causes distortions, like mirages on a desert highway.
Martian Soils and Weathering
Mauna Kea is a shield volcano. Its gently rising flanks and central peak resemble the exterior face of a warrior's shield. Like Hawaiian volcanoes, Martian volcanoes are made of a lava rock known as basalt, rich in the elements iron and magnesium and poor in silica, the most common constituent of sand.
"One of the things we're trying to do," says Blaney, "is figure out how rocks made of black lava turn into the richly colored, weathered materials we see on Mars today. You can kind of compare the process of weathering on Mars to rusting a nail. That rusty material is the iron oxide that makes the surface red."
Role of Water
Blaney gestures toward mounds of reddish rocks. "Those are cinder cones. They're created when a little bit of water from rain or groundwater gets into the lava and reacts explosively."
Given the presence of water in the past, scientists wonder if Mars could have supported life. They also wonder if Mars has enough water ice to sustain human exploration.
"There have been times up there on Mauna Kea," says Blaney, "when the sky has been so dark, I could see Halley's Comet with my own eyes or see the Milky Way in great detail. The stars up there are just different. It's like being in a different world."
For additional information about Mars, visit: http://mars.jpl.nasa.gov/index.html.