The University of Chicago Magazine

August 1997

Rock-solid success for U of C Mars device

Economou poses with his
interplanetary invention.

"The basic question we are tryingto answer is, What is Mars made of?" says Thanasis (Tom) Economou,senior scientist in the University's Enrico Fermi Institute.

For that very purpose, Economu--along with Anthony Turkevich,the James Franck distinguished service professor emeritus in chemistry--designedand built the Alpha Proton X-ray Spectrometer (APXS), one of the key scientificinstruments on board the Mars Pathfinder mission that began on July 4.

The APXS is attached to the Pathfinder's rover, Sojourner,which has roamed across the Martian surface guided by scientists and engineerson Earth. With the mobility provided by the rover and vision provided bya panoramic camera, APXS can be deployed to distant rock outcroppings,providing the first-ever chemical analysis of native Martian rock. Althoughthe first results from the APXS were available almost immediately afterlanding, careful analysis should take several months.

Specifically, Economou says, the APXS has been programmedto detect elements like carbon, nitrogen, and oxygen--basic chemical buildingblocks of life. If they're present, he said, the possibility of life increasesdramatically. However, the instrument cannot determine the molecular structureof the rocks it samples, information needed to find out if indeed lifeever existed on Mars. But the readings should provide the first crucialstep in determining what samples should be brought back to Earth for furtherstudy in a sample-return mission planned for 2005, "which is somethingwe also hope to be involved in," says Economou.

"Down the line we want to be able to find out iflife on Mars developed along the same lines as life on Earth, but we won'tbe able to answer that question until we can bring back samples to examinein laboratories here on Earth," he explains. "Before that canhappen, we have to learn as much as we can about Mars and figure out whatkinds of samples we should bring back. Our instrument will help selectthe proper samples for the next mission."

Turkevich and Economou first developed an alpha protonspectrometer for use on the 1967 and 1968 lunar Surveyor missions (SurveyorV, VI, and VII). These instruments, also designed and built by the technicalstaff at the University of Chicago's Laboratory for Astrophysics and SpaceResearch, provided the first complete and accurate chemical analysis ofthe lunar surface. NASA's 1976 twin Viking landers--the last spacecraftsto land on Mars--did not carry the device because they were not mobile.

Mobility is made possible by the Sojourner, a small, six-wheeledrover that is the first movable craft ever sent to explore the surfaceof another planet. Located on the rover's rear end, the APXS is mountedon a sophisticated mechanism that allows the sensor head to be placed againstsoil and rock samples in almost any position. Alpha particles bombard thesample, and the spectrometer detects alpha particles, X-rays, and protonsthat are scattered or generated in the sample.

Barnacle Bill, a very roughly textured rock, and Yogi,a much larger boulder nearby, were the first rocks analyzed by the APXS.The Pathfinder flight team reported receiving an unprecedented 90 megabitsof data on the chemical makeup of Yogi that alone should keep Economouand his colleagues busy for some time.

A piece of the U of C will remain on the red planet: Economou,Turkevich, and College senior Jonathan Barnes, who customized the computercode used to analyze the Mars data, were among the mission scientists whosigned a gold-plated plaque that will be left behind.

U of C scientists have participated in some 35 space missionsincluding lunar landings, planetary orbiters, and extra-solar missions.John Simpson, the Arthur Holly Compton distinguished service professoremeritus--still active in space missions--took part in the first U.S. missionto Mars in 1965.

The Pathfinder rover, far left, scoots as close as possibleto Yogi so that the attached Alpha Proton X-ray Spectrometer, left, caneasily conduct a study of the rock's chemical composition."

--Tim Andrew Obermiller

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