Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53b1519m&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P53B-1519
Physics
[2459] Ionosphere / Planetary Ionospheres, [5435] Planetary Sciences: Solid Surface Planets / Ionospheres, [6295] Planetary Sciences: Solar System Objects / Venus, [6297] Planetary Sciences: Solar System Objects / Instruments And Techniques
Scientific paper
Measurements of high energy ions made with the ion mass analyzer (IMA) instrument on the Venus Express spacecraft are being used to constrain rates of solar wind induced atmospheric escape from Venus. This instrument is able to measure ions down to 10eV, the energy at which oxygen ions have the velocity necessary to escape the planet. The measured energy of the particles may be confused by charging of the spacecraft and the velocity of the spacecraft with respect to the ionosphere, though, so it is important to consider these effects when interpreting measurements. In order to disentangle the spacecraft velocity effect, we modeled what the spacecraft would measure if it were encountering ionospheric ions whose intrinsic velocities within the ionosphere are below escape velocity. For the inherent velocity of the ions within the ionosphere, we used output from the Ma MHD model of Venus. Ion velocity vectors were then added to the spacecraft velocity vector along example Venus Express fly-thoughs. To get an idea of what sort of flux might be measured, we used density output from the Ma model. We will present energy-time spectrograms created by our model to the corresponding actual spectrograms measured by the IMA on Venus Express. We found that the spacecraft velocity alone is not usually high enough to create ions with an apparent energy above 10eV, but taking into account that the ions have a velocity within the ionosphere, we can get ions that appear to be above 10eV but that are not actually escaping the planet.
de Pater Imke
Dubinin Edik
Fedorov Arkady
Luhmann Janet G.
Ma Yi
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