The 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. institution.

SwRI engineers will build part of the analyzer of space plasmas and energetic atoms (ASPERA-3) instrument -- one of a suite of instruments aboard Mars Express that will examine the present and past states of the martian atmosphere. Whether water on the planet might have sometime sustained life will also be addressed.

"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."

Magnetic and gravity fields help maintain an atmosphere on Earth. When the solar wind, the supersonic stream of charged particles flowing out from the Sun, interacts with the planet, ion and electron particles become ionized and remain trapped in the magnetic field, enabling Earth to sustain an active, living atmosphere. The Earth's magnetic field acts as an invisible force that reflects away some of the harmful components, such as cosmic rays, brought by the solar wind.

On Mars, interactions with the solar wind also ionize particles, but they fly away because the planet lacks a magnetic field and a strong gravitational field. Over time, the release of particles continuously erodes the martian atmosphere. By examining the ionic composition with the Mars Express instruments, researchers will be able to determine whether particles, especially water particles, continue to fly away.

After combining the data with theory, researchers can estimate the length of time atmospheric changes have been occurring. The spacecraft will also help researchers determine which component, if any, was missing from the martian atmosphere that allowed the planet to eventually become geologically inactive.

The ASPERA-3 instrument will measure the ion and electron particles of the planet's atmosphere. An additional neutral atom imager will return a volumetric image of the martian atmosphere to help characterize its present state -- how particles are flying away in a volumetric sense, for example -- and how the atmosphere has evolved. Data will also help determine if the changes contributed to the dehydration of Mars and the loss of its oceans and atmosphere, says Winningham.

SwRI has provided a family of imaging instruments, with different adaptations for varying conditions, for a number of NASA and ESA missions. The plasma experiment for planetary exploration (PEPE) instrument was launched aboard Deep Space One in October 1998, and the Cassini plasma spectrometer (CAPS) was launched aboard Cassini in October 1997. Similar instruments will also fly aboard the ESA missions Astrid 2 on December 10, MUNIN in late 1999, and Rosetta in 2003.