Complex structure within Saturn’s infrared aurora

Stallard, Tom and Miller, Steve and Lystrup, Makenzie and Achilleos, Nicholas and Bunce, Emma and Arridge, Christopher and Dougherty, Michele and Cowley, Stan and Badman, Sarah V. and Talboys, Dean and Brown, Robert and Baines, Kevin and Buratti, Bonnie and Clark, Roger and Sotin, Christophe and Nicholson, Phil and Drossart, Pierre (2008) Complex structure within Saturn’s infrared aurora. Nature, 456 (7219). pp. 214-217. ISSN 0028-0836

Abstract

The majority of planetary aurorae are produced by electrical currents flowing between the ionosphere and the magnetosphere which accelerate energetic charged particles that hit the upper atmosphere. At Saturn, these processes collisionally excite hydrogen, causing ultraviolet emission, and ionize the hydrogen, leading to H3+ infrared emission. Although the morphology of these aurorae is affected by changes in the solar wind, the source of the currents which produce them is a matter of debate. Recent models predict only weak emission away from the main auroral oval. Here we report images that show emission both poleward and equatorward of the main oval (separated by a region of low emission). The extensive polar emission is highly variable with time, and disappears when the main oval has a spiral morphology; this suggests that although the polar emission may be associated with minor increases in the dynamic pressure from the solar wind, it is not directly linked to strong magnetospheric compressions. This aurora appears to be unique to Saturn and cannot be explained using our current understanding of Saturn's magnetosphere. The equatorward arc of emission exists only on the nightside of the planet, and arises from internal magnetospheric processes that are currently unknown.