Plasmas fill our solar system and the universe. These ionized gases generate and interact with magnetic and electric fields that are found in most astrophysical settings. Powered ultimately by thermonuclear processes in stars, the plasmas exhibit bulk motion, localized and sometimes explosive heating, and the acceleration of particles such as cosmic rays which have energies up to 10^20 eV. These cosmic rays contain signatures of the birth of stars, while the outwardly expanding solar atmosphere - the solar "wind" - reveals the make-up of solar material. Observing the properties of space plasmas and energetic particles provides a rich source of information about the physical processes which energize the material, and the conditions at the sites where this energization takes place. The Space Physics Group specializes in measurements of the characteristics of space plasmas, and of suprathermal and energetic ions from a variety of solar, planetary, and interplanetary environments.

The plasma and energetic particle observations carried out by the Space Physics Group require novel instrumentation carried on Earth-orbiting satellites and deep-space probes. Instruments are designed and constructed on campus by the group's technical staff, with participation by graduate as well as undergraduate students. The basic instrumentation technique is time-of-flight mass spectrometry, customized for rugged, lightweight systems as required by space missions. The group actively collaborates with other research teams in the United States and Europe.

Experiments built by the group are currently operating on many spacecraft, including the Voyager deep-space probes, the Ulysses probe to the solar poles, and the Cassini probe to Saturn.

Currently operating near-Earth missions include the Interplanetary Monitoring Platform (IMP), Geotail, the Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX), WIND, the Solar and Heliospheric Observatory (SOHO), the Advanced Composition Explorer (ACE), the Imager for Magnetopause to Aurora Global Exploration (IMAGE), and the 2-spacecraft Solar-Terrestrial Relations Observatory (STEREO) mission.

The work for which the group is internationally recognized includes studies of the composition and ionization states of the solar wind, solar energetic particles, and interstellar neutral atoms which have been "picked up" in the solar wind. This work, carried on at Maryland since the late 1960s, has given key insights into solar energetic particle acceleration and conditions in the solar atmosphere. Other work has provided fundamental information about the energization of particles by traveling interplanetary shocks, and such diverse topics as the origin of oxygen and sulfur ions in Jupiter's magnetosphere from the volcanoes on the moon Io, and the composition and energy content of the Earth's radiation belts.