Unusual Velocity Structures of Neutral Sodium Near Io's Wake

Details Unusual Velocity Structures of Neutral Sodium Near Io's Wake Unusual Velocity Structures of Neutral Sodium Near Io's Wake

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.5909s&link_type=abstract

American Astronomical Society, DPS meeting #40, #59.09; Bulletin of the American Astronomical Society, Vol. 40, p.507

Astronomy and Astrophysics

Astronomy

Scientific paper

New high-resolution spectra of Io sodium have identified an unexpected velocity structure near Io's wake and Jupiter-facing hemisphere. We used the 3.6-m Telescopio Nazionale Galileo in the Canary Islands with its SARG echelle spectrograph at a resolving power R=115,000. The observations targeted Io as it neared eclipse behind Jupiter. The slit was oriented parallel to the jovian equator, enabling spectra ahead of of Io and behind it along the orbit. The region ahead of Io along the orbit is also the downstream wake region in a magnetospheric sense; the Galileo spacecraft showed this to be a region of cold, dense, stagnated plasma. Our spectra of this region in the hour before eclipse show three distinct spectral features. The first two are well known: the slow sodium "banana cloud" and fast sodium ejected in the anti-Jupiter direction and hence highly red-shifted. The unexpected third feature is clearly blue-shifted, indicating an ejection from Io towards Jupiter, either from Io's trailing or inner hemisphere. At present there are no known ejection mechanisms that satisfy the observed properties. We will present preliminary analysis of the spatial and velocity distributions of this feature, along with a discussion of plausible source mechanisms.
This work has been supported by NSF's Planetary Astronomy Program, INAF/TNG, and the Dipartimento di Astronomia, Università di Padova.

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