UA-Led Team's Mission Concept Selected for Further Study in Mars Scout Program

Lori Stiles
June 14, 2001

A University of Arizona scientist's proposed Mars Atmospheric Constellation Observatory (MACO) is among 10 mission concepts selected for further study under the "Mars Scout" mission program, NASA has announced.

"The idea is to put four small satellites in orbit around Mars to send and receive microwave signals between each other as they slip behind the edge, or limb, of the Red Planet, " said Robert Kursinski, associate professor of atmospheric sciences and principal investigator for the proposed MACO mission.

Meteorologists have used microwave signals in taking "active limb soundings" of Earth to get weather and climate data of very high accuracy and vertical resolution anywhere on the planet. Kursinski and his team propose to adapt and extend the technique for a dedicated mission at Mars.

"We are trying to understand how other climate systems work. Mars is interesting because it presently doesn't have water like Earth has. It has some water, but dust plays many of the roles that water plays in our atmosphere. And Mars' atmosphere is in vapor-pressure equilibrium. Also, the distance to the sun varies far more over a year than Earth, and the tilt of its spin axis has also varied much more in the past. The similarities and the differences between Mars and Earth are really quite amazing.

"The whole history of Mars' water is fascinating, and we'll shed some light on what happened. To some degree all of this will help us better understand how to prepare for the human exploration of Mars."

Microwaves will be slowed and bent by refraction as they pass downward through varyingly dense layers of the martian atmosphere. Scientists will measure the angles of refraction to derive very accurate vertical profiles of air temperature, air pressure and pressure gradients that drive Mars' winds and dust storms. Mission scientists also will measure dust with an infrared sensor and derive measurements of atmospheric water from the microwave signals.

"We also will be looking with particular interest at the ratio of deuterium to water vapor in the atmosphere," Kursinksi said. Deuterium, also called heavy hydrogen, is an isotope of hydrogen whose atoms have twice the mass of ordinary hydrogen. The ratio of deuterium to water in Mars' atmosphere is higher than in Earth's atmosphere. "That indicates that Mars has lost a lot of its atmosphere to space," Kursinski said.

The ratio also might be used to detect regions where water vapor may be leaking from the ground because a lower ratio would indicate subsurface water, he added.

"We're really going to try to nail the hydrologic cycle of Mars to characterize the water in the atmosphere and variations in the deuterium-to-water ratio as well by region, season and diurnal cycle so we can see the sources, sinks and fluxes of water in the atmosphere of the present planet. We need to understand what processes are going on in the present atmosphere to understand what has happened in the past.

"We also want to study the carbon dioxide cycle and the details of carbon dioxide exchange between the surface and atmosphere," Kursinski said. "The surface pressure of Mars changes by 30 percent over the year as the polar cap grows and shrinks. We will be able to measure that change in surface pressure accurately."

Further, scientists would use the hefty volume of MACO data to both test and refine global atmospheric circulation models of Mars. Scientists have had limited data for testing models. More fully tested models "are sure to present some striking and insightful contrasts to global atmospheric circulation on Earth," Kursinksi said.

MACO will return much higher resolution data that will other planned Mars missions, Kursinski noted. "MACO's claim to fame is its very high vertical resolution, at the 80 meter to 400 meter level, versus other planned missions which are at the 5 kilometer level. Our observatory will give one to two orders of magnitude higher resolution, and one to two orders of magnitude greater accuracy as well."

One side benefit to MACO is that, if selected, it will provide a relay network that other missions can use for communications to Mars' surface, Kursinksi noted.

Kursinski, who earned his doctoral degree in planetary science from the California Institute of Technology, was with the Jet Propulsion Laboratory in Pasadena, Calif., before he joined the UA last August. His research focuses on using remote sensing techniques to understand climate dynamics.

Co-investigators on the MACO team include scientists from the Jet Propulsion Laboratory, Caltech, Ames Research Center, Stanford, Wisconsin, Harvard, Goddard Space Flight Center, and researchers from France and the United Kingdom.

NASA has awarded Kursinski's team and 9 other science teams up to $150,000 each to further develop Mars Scout mission concepts during the next six months. The ten winners were selected on the basis of overall scientific merit and potential for implementation under a total mission cost cap of $300 million. The proposed missions will compete for a possible launch in 2007.


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