Venus Thermosphere: In situ Composition Measurements, the Temperature Profile, and the Homopause Altitude

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Science  23 Feb 1979:
Vol. 203, Issue 4382, pp. 768-770
DOI: 10.1126/science.203.4382.768


The neutral mass spectrometer on board the Pioneer Venus multiprobe bus measured composition and structral parameters of the dayside Venus upper atmosphere on 9 December 1978. Carbon dioxide and helium number densities were 6 x 106 and 5 x 106 per cubic centimeter, respectively, at an altitude of 150 kilometers. The mixing ratios of both argon-36 and argon-40 were approximately 80 parts per million at an altitude of 135 kilometers. The exospheric temperature from 160 to 170 kilometers was 285 ± 10 K. The helium homopause was found at an altitude of about 137 kilometers.