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Investigating the Moon's Atmosphere

WASHINGTON, D.C. -- An intensive effort is underway to determine the
composition of the Moon's tenuous atmosphere. Although conventional 
wisdom says the Moon is devoid of atmosphere, and in layman's terms this
may be close enough to the truth, the space just above the lunar surface is
not a total vacuum. The Apollo program identified helium and argon atoms 
there, and Earth-based observations added sodium and potassium ions to 
the list in 1988.

Extensive searches for additional atmospheric components have been 
made from the lunar surface, from orbital spacecraft, and from Earth, but 
only about 10 percent of the density of the lunar atmosphere can be 
attributed to the four directly observed elements. Scientists believe that the 
Moon's regolith, or surface layer, is a significant source of the atmospheric
sodium. They are therefore seeking to learn which other atoms the regolith
may release and whether they form part of the Moon's atmosphere.

Geophysical Research Letters, a publication of the American 
Geophysical Union, is publishing new findings on the composition of the 
lunar atmosphere by a group of scientists headed by Drs. Urs A. Mall and 
Erhard Kirsch of the Max Planck Institute for Aeronomy in 
Katlenburg-Lindau, Germany.

Titled "Direct Observation of Lunar Pick-up Ions near the Moon," the GRL
paper describes observations of the lunar atmosphere by the Suprathermal
Ion Spectrometer (STICS) instrument aboard the WIND spacecraft. STICS 
has identified ions of several elements, including oxygen, silicon, and
aluminum, but only in small amounts. The quality and quantity of STICS
measurements will increase considerably in November 1998, when WIND 
will spend an extended period of time near the Moon.

In addition to the Max Planck Institute, researchers on this study are 
based at the Institute for Geophysics and Meteorology of the University 
of Cologne, Germany; the Institute for Physical Science and Technology 
of the University of Maryland, College Park; and the Institute for the Study
of Earth, Oceans, and Space of the University of New Hampshire, Durham.