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He 584 Å airglow emission from Venus: Mariner 10 observations
Author(s) -
Kumar Shailendra,
Broadfoot A. Lyle
Publication year - 1975
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl002i008p00357
Subject(s) - venus , airglow , atmosphere of venus , exosphere , physics , helium , altitude (triangle) , atmosphere (unit) , ionosphere , atmospheric sciences , solar wind , planet , mixing ratio , astronomy , astrobiology , ion , plasma , atomic physics , meteorology , geometry , mathematics , quantum mechanics
Observations were made across the bright limb of Venus by the ultraviolet spectrometer on Mariner 10 as the spacecraft flew by this planet on February 5, 1974. The altitude variation of the brightness of 584 Å emission is interpreted with respect to the helium distribution in the atmosphere. Resonance scattering of solar radiation is considered as the source of this emission. The comparison of model calculations with the data shows that the observed altitude profile is consistent with a He density of 2 ± 1 × 10 6 cm −3 at 145 km altitude (mixing ratio 1.0 ± .5 × 10 −5 ) and with an exospheric temperature of 375 ± 105K. If the major loss of helium is by solar wind scavenging only, the present helium content on Venus can be maintained by an outgassing rate of about 2 × 10 5 cm −2 sec −1 from the planet crust. By using these neutral helium measurements we find that the He + ion density in the outer ionosphere (Z > 250 km) would be ∼200 cm −3 .