Press Release

U.S.-built instrument to fly aboard ESA Mars Express

By SpaceRef Editor
June 2, 2003
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The Mars Express spacecraft, set to launch
today from Kazakhstan, carries one of the most advanced electron
spectrometers ever built as a component of the Analyzer of Space Plasma and
Energetic Atoms (ASPERA) instrument flying aboard the craft. Built by
Southwest Research Institute (SwRI), the electron spectrometer, along with
ion composition and energetic neutral atom imaging components, will help
characterize Mars’ immediate space environment and study its interaction
with the neutral gases of the martian upper atmosphere.

Understanding these interactions enables planetary scientists to
characterize the present state of the martian atmosphere and to reconstruct
its history and evolution over the past 3.5 billion years.

“The fact that Earth can maintain life is a unique condition in the solar
system,” says Dr. David A. Winningham, ASPERA co-investigator and an
Institute scientist in the SwRI Space Science and Engineering Division.
“Mars Express could tell researchers what variables are needed to first
create, then preserve over geological time, oceans and atmospheres.”

NASA provided funding to SwRI to build the electron spectrometer, which will
measure electron fluxes in the energy range of a few to 20,000 electron
volts, for the European Space Agency mission. The Swedish Institute of Space
Physics in Kiruna, Sweden, leads the development of ASPERA in collaboration
with researchers from Finland, Italy, England, Germany, and France.

A strong planetary magnetic field helps maintain the atmosphere on Earth by
shielding it from the solar wind — the hypersonic stream of charged
particles that flows out from the sun. Without this magnetic shield, ionized
gases in the Earth’s upper atmosphere would be swept away, leading to a
significant loss of atmospheric material over geologic time. Mars has no
intrinsic magnetic field, or at best only a very weak one, leaving its
atmosphere unprotected from erosion by the solar wind.

ASPERA will acquire data on the charged particles that impinge on the
martian atmosphere and on the atmospheric material that is lost as a result
of interactions with the solar wind. Recent theoretical calculations suggest
that the oxygen lost by these and other processes over the last several
billion years is equivalent to the amount of oxygen in a global layer of
water about 50 meters deep. The ASPERA measurements could help determine
whether liquid water, the primary requirement for life as we understand it,
was ever present on Mars in significant amounts.

The spacecraft, and the ASPERA instrument in particular, will collaborate
with the Japanese spacecraft Nozomi, which is also set to investigate the
martian ionosphere and atmospheric loss. Measurements taken during Nozomi’s
equatorial orbit will complement those of Mars Express’ polar orbit.

For more information about the ASPERA instrument and Mars Express, visit and

SpaceRef staff editor.