Ingersoll, Andrew P. and Vasavada, Ashwin R. and Little, Blane and Anger, Clifford D. and Bolton, Scott J. and Alexander, Claudia and Klaasen, Kenneth P. and Tobiska, W. Kent (1998) Imaging Jupiter’s Aurora at Visible Wavelengths. Icarus, 135 (1). pp. 251-264. ISSN 0019-1035. http://resolver.caltech.edu/CaltechAUTHORS:20121212-113709740
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On November 9, 1996 and again on April 2, 1997, the Galileo spacecraft's Solid State Imaging (SSI) camera targeted the northern auroral region of Jupiter. These observations represent (i) the first spatially resolved images of the jovian auroral oval either at visible wavelengths or on the nightside of the planet, (ii) the first image at visible wavelengths of an auroral footprint of the Io Flux Tube (IFT), (iii) the first unambiguous detection at visible wavelengths of auroral emission on the jovian limb, and (iv) the first images of the aurora with spatial resolution below 100 km per pixel (46 and 35 km, respectively). Relative to many prior expectations, the visible aurora is (i) lower in altitude, (ii) associated with magnetic field lines that cross the equator closer to the planet, and (iii) more variable in time and space. The 1996 images used a clear (broadband) filter, while the 1997 images used both the clear filter and five narrower filters over wavelengths ranging from violet to 968 nm. The filtered images imply that the visible auroral emission contains atomic hydrogen lines, although there is also a continuum component. We were able to position the aurora in three-dimensional space and found the limb emission to be ∼240 km above the surface of a standard (P≈ 1 bar) reference ellipsoid. Our most accurate analysis of the equatormost part of the oval placed it at 54.5° planetocentric latitude and 168° west longitude. Combined with the latest magnetic field models, our results imply that the particles that cause the aurora originate in Jupiter's equatorial plane ∼13 R_J from the center of the planet. The oval was brighter and wider in the 1996 images than in the 1997 images. The broadband radiance of a typical place on the oval as seen directly overhead varied from ∼80 kR in 1997 to ∼300 kR in 1996. Our estimates of the full width of the oval varied from under 500 km to over 8000 km, partly depending on the signal-to-noise ratio of the image. The radiated power per unit length along the oval ranged from ∼60 to ∼700 W/m, with the associated radiated power from the entire oval varying from ∼109 to ∼9 × 10^(10) W. Appreciable auroral emission also occurred both north and south of the main oval. One image contains the northern footprint of the IFT, which appears as a central ellipse with a tail of emission that lies downstream with respect to the plasma flow past Io. The central ellipse is ∼1200 km downstream by ∼500 km cross stream. The IFT is comparable in brightness to the nearby auroral oval (∼250 kR) and has a total radiated power of ∼3 × 10^8 W.
|Additional Information:||© 1998 by Academic Press. Received September 26, 1997; revised April 8, 1998. For various invaluable contributions we thank Herb Breneman, Amy Culver, Eric De Jong, Ann Harch, Todd Jones, Jim Kaufman, Kari McGee, Helen Mortensen, David Senske, Jan Yoshimizu and other members of the Galileo Project, as well as John Clarke, Jack Connerney, Krishan Khurana, and Joerg Warnecke. This work was supported by Galileo Project funds, NASA, and the NSERC of Canada (B.L.).|
|Subject Keywords:||Aurorae; Jupiter, atmosphere, general; atmothespheres, structure, Jupiter; ionospheres, Jupiter; magnetospheres, Io.|
|Official Citation:||Andrew P. Ingersoll, Ashwin R. Vasavada, Blane Little, Clifford D. Anger, Scott J. Bolton, Claudia Alexander, Kenneth P. Klaasen, W.Kent Tobiska, Galileo SSI Team, Imaging Jupiter's Aurora at Visible Wavelengths, Icarus, Volume 135, Issue 1, September 1998, Pages 251-264, ISSN 0019-1035, 10.1006/icar.1998.5971. (http://www.sciencedirect.com/science/article/pii/S0019103598959711)|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||12 Dec 2012 21:09|
|Last Modified:||12 Dec 2012 21:09|
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