DPS Pasadena Meeting 2000, 23-27 October 2000
Session 23. Moon and Mercury
Oral, Chairs: B. Hawke, M. Grande, Tuesday, 2000/10/24, 2:20-3:30pm, Little Theater (C107)

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[23.07] Space Weather at Mercury

R.M. Killen (SwRI), A.E. Potter (NSO)

We observed Mercury's sodium atmosphere during the week of November 13 - 20, 1997, with the stellar spectrograph at the McMath-Pierce solar telescope on Kitt Peak, Arizona. During this week the total sodium content of the atmosphere increased by a factor of three. Although the solar EUV flux observed by the SEM instrument onboard SOHO showed that the EUV flux at Mercury increased by about 20 alpha flux increased by 5 dynamic pressure as inferred by heliospheric tomography increased by a factor of about 20. We have modeled the atmospheric sources, including meteoritic vaporization, photon-stimulated desorption and ion sputtering. We conclude that the increase in exospheric density was primarily due to ion-sputtering. A best fit to the data gives a 15 dependence on solar wind momentum, indicating that a small portion of the surface is affected. Our model implies that impact vaporization supplies about 10 content. There may be a dual role of solar EUV radiation and solar wind charged particles in mobilizing the sodium atoms.

This work was partially supported by the NASA Planetary Astronomy and Planetary Atmospheres Program.

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