CRISM Joins Mars’ Water Detectives
|Artist’s concept of the Mars Reconnaissance Orbiter at the red planet. Credit: NASA|
With the August 12th launch of NASA’s Mars Reconnaissance Orbiter spacecraft from Cape Canaveral Air Force Station, Fla., the Compact Reconnaissance Imaging Spectrometer for Mars, or CRISM, joins the set of high-tech detectives seeking traces of water on the red planet.
Built by the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., CRISM is the first visible-infrared spectrometer to fly on a NASA Mars mission. Its primary job: look for the residue of minerals that form in the presence of water, the "fingerprints" left by evaporated hot springs, thermal vents, lakes or ponds on Mars when water could have existed on the surface.
With unprecedented clarity, CRISM will map areas on the martian surface down to house-sized scales, as small as 60 feet (about 18 meters) across, when the spacecraft is in its average orbit altitude of about 190 miles (more than 300 kilometers).
"CRISM plays a very important role in Mars exploration," says APL’s Dr. Scott Murchie, the instrument’s principal investigator. "Our data will identify sites most likely to have contained water, and which would make the best potential landing sites for future missions seeking fossils or even traces of life on Mars."
Though certain landforms provide evidence that water may once have flowed on Mars, Murchie says scientists have little evidence of sites containing mineral deposits created by long-term interaction between water and rock. The NASA Rover Opportunity found evidence for liquid water in Meridian Planum, a large plain near Mars’ equator, but that is only one of many hundreds of sites where future spacecraft could land.
|CRISM breaks sunlight reflected off the Martian surface into a spectrum, from which it measures 544 colors. This wide range helps CRISM determine the mineralogy of the surface. For example, this map was made from only three colors (green, red and infrared) in Mars Pathfinder images and shows iron oxide coatings crusted on rocks.
Peering through a telescope with a 4-inch (10-centimeter) aperture, and with a greater capability to map spectral variations than any similar instrument sent to another planet, CRISM will read 544 "colors" in reflected sunlight to detect minerals in the surface. Its highest resolution is about 20 times sharper than any previous look at Mars in infrared wavelengths.
"At infrared wavelengths, rocks that look absolutely the same to human eyes become very different," Murchie says. "CRISM has the capability to take images in which different rocks will ‘light up’ in different colors."
CRISM is mounted on a gimbal, allowing it to follow targets on the surface as the orbiter passes overhead. CRISM will spend the first half of a two-year orbit mission mapping Mars at 650-foot (200-meter) scales, searching for potential study areas. Several thousand promising sites will then be measured in detail at CRISM’s highest spatial and spectral resolution. CRISM will also monitor seasonal variations in dust and ice particles in the atmosphere, supplementing data gathered by the orbiter’s other instruments and providing new clues about the Martian climate.
"CRISM will improve significantly on the mapping technology currently orbiting Mars," says CRISM Project Manager Peter Bedini, of APL. "We’ll not only look for future landing sites, but we’ll be able to provide details on information the Mars Exploration Rovers are gathering now. There is a lot more to learn, and after CRISM and the Mars Reconnaissance Orbiter there will still be more to learn. But with this mission we’re taking a big step in exploring and understanding Mars."
As the Mars Reconnaissance Orbiter cruises to its destination, the CRISM operations team continues to fine-tune the software and systems it will use to command the instrument and receive, read, process, and store a wealth of data from orbit more than 10 terabytes when processed back on Earth, enough to fill more than 15,000 compact discs. The spacecraft is set to reach Mars next March, use aerobraking to circularize its orbit, and settle into its science orbit by November 2006.