MENLO PARK, Calif., Jan. 22 -- SRI International has reported the first observation of visible light emitted by oxygen atoms in the night-side airglow (nightglow) of Venus. According to a report in the journal Science, this provides new insight into the atmosphere of Venus and the composition and chemical interactions taking place in the absence of sunlight.
The W. M. Keck telescope and the associated HIRES spectrometer on Mauna Kea in Hawaii were used by SRI researchers in the Molecular Physics Laboratory to obtain unprecedented detail of the terrestrial nightglow. These results prompted 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 Russian Venera 9/10 orbiters performed the only other measurement in 1975, with a spectral resolution 100 times inferior to that of Keck-HIRES, the report said.
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.
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.