Southwest Research Institute (SwRI) News 

ASPERA instrument to study the interaction of the solar wind with Mars' upper atmosphere

SwRI named co-investigator of European Space Agency program

San Antonio -- December 9, 1998 -- NASA has provided $5.3 million to Southwest Research Institute® (SwRI^®) to build one of the components of an instrument that will study the interaction between the solar wind and the upper atmosphere of Mars. The Analyzer of Space Plasmas and Energetic Neutral Atoms (ASPERA) instrument will fly aboard the European Space Agency (ESA) Mars Express spacecraft in June 2003. The Swedish Institute of Space Physics in Kiruna, Sweden, is taking the ESA lead in collaboration with researchers from Finland, Italy, England, Germany, and France. SwRI is a co-investigator and the lead U. S. hardware institution.

SwRI will build the electron spectrometer for the ASPERA instrument package, which also includes an ion composition instrument and an energetic neutral atom (ENA) imager. The ENA instrument will image energetic neutral atoms created by the exchange of charge between energetic ions and Mars’ extended neutral atmosphere. The ENA images and in-situ plasma data provided by the ASPERA investigation will be used to characterize the immediate space environment of Mars and to study its interaction with the neutral gases of the martian upper atmosphere. Understanding this interaction is of central importance to efforts by 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 Winningham, ASPERA-3 co-investigator and an Institute scientist in the SwRI Instrumentation and Space Research Division. “Mars Express could tell researchers what variables are needed to first create, then preserve over geological time, oceans and atmospheres.”

In the case of the Earth, a strong planetary magnetic field helps maintain the atmosphere by shielding it from the solar wind -- the supersonic stream of charged particles that flows from the Sun. Without this magnetic shield, ionized gases in the Earth’s upper atmosphere would become entrained in the solar wind and swept away, leading to a significant loss of atmospheric material over geologic time.

Unlike Earth, Mars has no intrinsic magnetic field -- or at best only a very weak one -- leaving its atmosphere unprotected from erosion by the solar wind. Such erosion results both from the “pick up” of ions from the martian ionosphere by the solar wind’s magnetic field and from the “sputtering” of neutral atmospheric material by some of the heavy “pick-up” ions.

ASPERA will acquire data both on the charged particles that impinge on the martian atmosphere and on the atmospheric material that is lost as a result of ion pick up and sputtering. Recent theoretical calculations suggest that the oxygen lost by these and other processes over the last 3.5 billion years is equivalent to the amount of oxygen in a global layer of water about 50 meters deep. The ASPERA measurements thus bear directly on the important question of whether liquid water -- the primary requirement for life as we understand it -- was ever present on Mars in significant amounts.

SwRI has provided plasma instruments for several NASA and ESA missions. The Cassini Plasma Spectrometer (CAPS) instrument was launched on the Saturn mission in October 1997, and the Plasma Experiment for Planetary Exploration (PEPE) instrument was launched on the Deep Space 1 spacecraft in October 1998. MEDUSA, an SwRI-developed plasma detector, was launched on Astrid 2, a Swedish Earth-orbiting satellite, on December 10; Similiar instruments will be flown on another Swedish spacecraft, MUNIN, in late 1999 and on the ESA comet probe, Rosetta, in 2003. In addition, SwRI is the principal investigator institution for NASA’s IMAGE mission, which will employ the ENA imaging technique to study the structure and dynamics of key plasma regions in the Earth’s inner magnetosphere.

For more information about Mars Express and the ASPERA-3 instrument, visit the NASA web page at quest.arc.nasa.gov/mars/background/express.html.

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