Energetic Hydrogen and Oxygen Atoms Observed on the Nightside of Mars
- 85 Downloads
We present measurements of energetic hydrogen and oxygen atoms (ENAs) on the nightside of Mars detected by the neutral particle detector (NPD) of ASPERA-3 on Mars Express. We focus on the observations for which the field-of-view of NPD was directed at the nightside of Mars or at the region around the limb, thus monitoring the flow of ENAs towards the nightside of the planet. We derive energy spectra and total fluxes, and have compiled maps of hydrogen ENA outflow. The hydrogen ENA intensities reach 105 cm−2 sr−1 s−1, but no oxygen ENA signals above the detection threshold of 104 cm−2 sr−1 s−1 are observed. These intensities are considerably lower than most theoretical predictions. We explain the discrepancy as due to an overestimation of the charge-exchange processes in the models for which too high an exospheric density was assumed. Recent UV limb emission measurements (Galli et al., this issue) point to a hydrogen exobase density of 1010 m−3 and a very hot hydrogen component, whereas the models were based on a hydrogen exobase density of 1012 m−3 and a temperature of 200 K predicted by Krasnopolsky and Gladstone (1996). Finally, we estimate the global atmospheric loss rate of hydrogen and oxygen due to the production of ENAs.
KeywordsMartian atmosphere atmospheric loss energetic neutral atoms
Unable to display preview. Download preview PDF.
- Anderson, D. E., and Hord, C. W.: 1971, JGR 76(28), 6666.Google Scholar
- Barabash, S., etal.: 2004, ASPERA-3: analyser of space plasmas and energetic ions for Mars Express, 121–139, in Mars Express: the scientific payload. ESA SP-1240, ed. by Andrew Wilson, Noordwijk, Netherlands.Google Scholar
- Barabash, S., Fedorov, A., Lundin, R., and Sauvaud, J.-A.: 2006, Science, submitted.Google Scholar
- Brain, D.: 2006, IMF Draping Direction at Mars, http://sprg.ssl.berkeley.edu/brain/rsrch/drapingdirxn-html
- Dubinin, E., Fränz, M., Woch, J., Barabash, S., Lundin, R., and Yamauchi, M.: 2006c, Hydrogen exosphere at Mars, pickup protons and their acceleration at the bow shock, GRL, in press.Google Scholar
- Galli, A., Wurz, P., Lammer, H., Lichtenegger, H. I. M., Lundin, R., Barabash, S., Space Sci. Rev.: this issue, doi: 10.1007/s11214-006-9089-7.Google Scholar
- Lammer, H., Selsis, F., Penz, T., Amerstorfer, U. V., Lichtenegger, H. I. M., Kolb, C., etal.: 2005, in Tokano, T. (ed.), Advances in Astrobiology and Biogeophysics, Springer-Verlag, Berlin, Germany, p. 25.Google Scholar
- Lichtenegger, H. I. M., Lammer, H., Kulikov, Yu. N., Kazeminejad, S., Molina-Cuberos, G. H., Rodrigo, R., et al.: Space Sci. Rev. this issue, doi: 10.1007/s11214-006-9082-1.Google Scholar
- Wurz, P.: 2000, in Scherer, K., etal. (ed.), Detection of Energetic Neutral Particles, in The Outer Heliosphere: Beyond the Planets, Katlenburg-Lindau: Copernicus-Gesellschaft e.V., 251.Google Scholar
- Yamauchi, M., Futaana, Y., Fedorov, A., Dubinin, E., Lundin, R., Sauvaud, J.-A., et al.: Space Sci. Rev. this issue, doi: 10.1007/s11214-006-9090-1.Google Scholar