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SRI International Makes First Observation of Atomic Oxygen
Emission in the Night Airglow of Venus
Science Magazine Details SRI’s Extra-Terrestrial Atmospheric Discoveries in its
January 19, 2001 Issue
MENLO PARK, Calif., (January 18, 2001) – SRI International, a leading research institute based in
Silicon Valley, reported the first observation of visible light emitted by oxygen atoms in
the night-side airglow (“nightglow”) of Venus. Published in the January 19, 2001 issue of the
journal Science, this novel study of a non-Earth atmosphere provides new
insight into the atmosphere of Venus and the composition and chemical interactions
taking place in the absence of sunlight.
Although much is known about the earth's nightglow, in the visible spectral region there
is very limited information concerning Venus or Mars. With the recent discoveries
of planets circling other suns, the time may come when it will be possible to view
the emissions from these planets and compare them to what is known about our own solar system.
Earth-based Look at Venus is a Hundred-fold Improvement Over 1975’s Orbiters
The W. M. Keck telescope and the associated HIRES spectrometer on Mauna Kea, Hawai'i were
used by SRI researchers in the Molecular Physics Laboratory to obtain
unprecedented detail of the terrestrial nightglow. These results prompted Drs.
Tom G. Slanger, David L. Huestis, Philip C. Cosby, and collaborator Thomas A. Bida
(currently at Lowell Observatory) to pursue the investigation of the visible
nightglow on the dark side of Venus. The only previous measurement was done
by the Russian Venera 9/10 orbiters in 1975, with a spectral resolution 100 times
inferior to that of Keck-HIRES.
One of the most prominent features in the terrestrial nightglow is the 5577-angstrom
atomic oxygen green line, first detected by A. J. Angstrom in 1868, then
quantified by Lord Rayleigh in 1930. The Venera probes found this emission to be
absent in the Venus nightglow. The apparent difference between the terrestrial
and Venusian visible nightglows has been attributed to the different atmospheric
compositions: oxygen and nitrogen for the earth, carbon dioxide and nitrogen for Venus.
Initial Discoveries May Inspire Future Extra-Terrestrial Atmospheric Studies
Measurements to record the nightglow of Venus were carried out with the Keck telescope
just before sunrise on November 20, 1999. Analysis of the resultant spectrum at
the position of the oxygen green line showed strong emission from the terrestrial
atmosphere and a comparable signal from Venus, with an intensity some 25 times
greater than the upper limits set by the Venera results.
Further measurements will be needed to determine if the Venus atmosphere really
exhibits such large variations in green line intensity. Until the present result,
the claim could be made that the nightglow green line is only associated with
planets with molecular oxygen in their atmospheres. Now there is evidence that
this is not the case. Therefore the green line is not an effective diagnostic
for atmospheric molecular oxygen, but only indicates the presence of oxygen atoms.
Mars is a potential target for similar observations, which will help to develop a
more coherent picture than presently exists of the nightglows of all three planets.
The research was funded by the Planetary Astronomy section of NASA.
About SRI International
Menlo Park-based SRI International (www.sri.com) is one of the world's foremost independent research and technology development organizations. Founded in 1946 as Stanford Research Institute, SRI has been meeting the strategic needs of global markets for more than 50 years. As part of its strategy to bring its high-value innovations to the marketplace, SRI licenses its technologies, forms strategic partnerships, and creates spin-off companies.
SRI's Molecular Physics Laboratory is known worldwide for its fundamental and applied research in collisional and radiative processes involving ions, atoms, and molecules. The group helps clients resolve key problems in areas ranging from lasers to planetary atmospheres and plasmas.
SRI International is a registered trademark.
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