Disk-resolved Millimeter Observations Of Io's SO2 Atmosphere

Details Disk-resolved Millimeter Observations Of Io's SO2 Atmosphere Disk-resolved Millimeter Observations Of Io's SO2 Atmosphere

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.6401m&link_type=abstract

American Astronomical Society, DPS meeting #38, #64.01; Bulletin of the American Astronomical Society, Vol. 38, p.612

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We present spectral maps of Io's SO2 atmosphere obtained with the Plateau de Bure Interferometer (PdBI) in winter 2005, on the leading and trailing hemispheres of Io.
The PdBI was in its extended configuration, providing a 0.5x1.5 arcsec synthetized beam at 1.3 mm, and allowing to resolve Io in its longitudinal direction.
Continuum analysis in the UV plane indicates a mean continuum brightness temperature of 100K, rather constant
with longitude and local time, suggesting sub-surface sounding.
The SO2 216.643 GHz line was detected on both hemispheres, with disk-integrated line contrasts of 55 and 25 K.
On the leading side, the data indicate a 400 m.s-1 limb to limb spectral
shift difference. On both sides, the SO2 emission is spatially narrower than the continuum emission, indicating a localized atmosphere. Moreover, the emission appears to be displaced with respect to continuum emission, to the East on the leading side, to the North on the trailing side.
We tried to model the observations by assuming emission from an hydrostatic atmosphere in LTE conditions,
using SO2 distributions determined from HST UV disk-resolved data (Feaga, 2005) and IR disk-integrated observations (Spencer et al, 2005).
The line contrasts imply atmospheric temperatures around 150-200 K. On the leading side, the line shifts and widths (about 700 m.s-1) can be reproduced by a zonal superrotation with 300m.s-1 speed. However, the modelled SO2 line emission map appears spatially broader than the observed
emission. On the trailing side, the Northern displacement cannot be reproduced by the assumed SO2 distributions.
We are currently testing the volcanic plume models of Zhang et al. (2003) by implementing a radiative transfer model including local variations of number density, temperature, and velocity. The ultimate goal is to distiguish between
SO2 sublimation and volcanic outgassing as the dominant source for Io's SO2 atmosphere.

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