Abstract
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 âŒ240 km above the surface of a standard (Pâ 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 âŒ13RJfrom 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 âŒ80 kR in 1997 to âŒ300 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 âŒ60 to âŒ700 W/m, with the associated radiated power from the entire oval varying from âŒ109to âŒ9 Ă 1010W. 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 âŒ1200 km downstream by âŒ500 km cross stream. The IFT is comparable in brightness to the nearby auroral oval (âŒ250 kR) and has a total radiated power of âŒ3 Ă 108W.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.