By Lori Stiles

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.