Venus E.U.V. measurements of helium at 58.4 NM from Venera 11 and Venera 12 and implications for the outgassing history

Details Venus E.U.V. measurements of helium at 58.4 NM from Venera 11 and Venera 12 and implications for the outgassing history Venus E.U.V. measurements of helium at 58.4 NM from Venera 11 and Venera 12 and implications for the outgassing history

Jul 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986p%26ss...34..585c&link_type=abstract

Planetary and Space Science (ISSN 0032-0633), vol. 34, July 1986, p. 585-602.

Astronomy and Astrophysics

Astronomy

3

Astronomical Spectroscopy, Helium Ions, Outgassing, Spaceborne Astronomy, Ultraviolet Spectra, Venus Atmosphere, Emission Spectra, Extreme Ultraviolet Radiation, Planetary Evolution, Radiative Transfer, Venera 11 Satellite, Venera 12 Satellite

Scientific paper

The He I 58.4 nm resonance emission from the dayside upper atmosphere of Venus was recorded by two extreme ultraviolet (EUV) spectrophotometers flown near Venus on Venera 11 and Venera 12 in December 1978. Scans across the illuminated disc are compared with models for which the radiative transfer equation in a spherically symmetric atmosphere is solved. The optical thickness of helium above the CO2 absorption level (approximately equal to 140 km) is determined to be tau = 3.5 + or - 1.5, independently of any calibration factor. This corresponds to a number density at 150 km of 2.2 + or - 1 x 10 to the 6th atom./cu cm compatible with original PV ONMS (Orbital Neutral Mass Spectrometer of Pioneer Venus) and Mariner 10 EUV measurements, but a factor of 2 below the Bus Neutral Mass Spectrometer Measurements. There are also indications that the density increases at high latitudes above 60 deg, which might be related to the complex thermal structure (cold polar collar) observed around 70 deg of latitude and approximately equal to 70 km of altitude. The escape rate from the top of the atmosphere is then estimated approximately equal to 500,000 sq cm/s, and implications for the outgassing history of Venus are briefly discussed.

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