DPS 34th Meeting, October 2002
Session 8. Inner Planets
Oral, Chair(s): T. Widemann and R.M. Nelson, Monday, October 7, 2002, 4:00-5:00pm, Room M

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[8.01] The Sodium Tail of Mercury

A.E. Potter (National Solar Observatory), R.M. Killen (Univ. of Maryland, College Park), T.H. Morgan (NASA HQ)

Mercury is difficult to observe because it is so close to the Sun. However, when the angle of the ecliptic is near maximum in the Northern Hemisphere, and Mercury is near its greatest eastern elongation, it can be seen against the western sky for about a half hour after sunset. During these times, we were able to map sodium D2 emission streaming from the planet, forming a long comet-like tail. We mapped the tail when sky conditions were favorable during 2000, 2001 and 2002. On May 26, 2001, we mapped the tail downstream to a distance of about 40,000 km, and on May 02 and 04, 2002 we could follow the tail downstream to a distance of about 80,000 km. On June 05, 2000 and April 25, 2002 we mapped the cross-sectional extent of the tail at a distance of about 17,500 km downstream. At this distance, the half-power full-width of the emission was about 20,000 km. We estimated the transverse velocity of sodium in the tail to range from 2 to 4 km/sec. The velocities we observed imply source velocities from the planet surface of the order of 5 km/sec, or 4 eV. Particle sputtering is a likely candidate for production of sodium atoms at these velocities. The total flux of sodium in the tail was approximately 1 to 10 % of the estimated total production rate of sodium on the planet.

This work was supported by the NASA Planetary Astronomy Program.

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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.