Encounter of Ulysses with Comet McNaught

Details Encounter of Ulysses with Comet McNaught Encounter of Ulysses with Comet McNaught

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsh23c..05g&link_type=abstract

American Geophysical Union, Spring Meeting 2007, abstract #SH23C-05

Physics

2152 Pickup Ions, 2199 General Or Miscellaneous

Scientific paper

Comet C/2006 P1 McNaught was the brightest comet observed from Earth in the last 40 years. On February 3, 2007 the comet at a heliocentric distance of ~0.71 AU was nearly radially aligned with the Ulysses spacecraft at a heliocentric distance of ~2.40 AU and at 79 Deg south heliographic latitude. Thus, during a ~4.5-day interval (February 5-9) Ulysses encountered the tail region of this spectacular comet, the region of disturbance in the solar wind produced by the comet being nearly 10 Mkm wide at 2.4 AU. During the encounter the speed of the solar wind dropped from ~750 km/s to a minimum of 360 km/s, the proton density dropped by more than 2 orders of magnitude, and the proton temperature increased from ~1.5x105 to ~4x105 K, while simultaneously very large fluxes of cometary molecular and singly and doubly charged atomic ions were detected. The slowing, depletion and heating of the solar wind proton beam was a result of charge exchange with neutral atoms and molecules in the cometary atmosphere and with the pickup up by the wind of the newly-born cometary ions. Although no shocks were observed during the encounter, the magnetic field strength was slightly enhanced in broad regions at the leading and trailing edges of the tail of the comet and was generally weaker than in the unobstructed solar wind within the heart of the region of interaction. For most of the encounter, the magnetic field direction was nearly radially inward, and thus reversed from its normal outward direction in the southern polar hemisphere at this phase of the present solar cycle. There were, however, shorter periods when the field pointed nearly radially outward, indicating a filamentary structure of the comet tail. One of the intervals of radially outward field coincided with the interval of minimum flow speed and maximum flux of picked up O+ ions.

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