ANN ARBOR---For decades astronomers have known that Jupiter, like Earth, has auroras at its poles. Now, thanks to new instruments on the Hubble Space Telescope and a specially designed filter, University of Michigan astrophysicist John Clarke has produced the best images yet of this planetary phenomenon---pictures which should give researchers a much better understanding of Jupiter and its moons.
Taking advantage of Hubble's Imaging Spectrograph (STIS) and Wide Field Planetary Camera 2 (WFPC2), Clarke, a research scientist in the U-M Department of Atmospheric, Oceanic and Space Sciences, was able to make images of the auroras 10 times more sensitive, and with higher angular resolution, than previously possible.
When the space telescope took snapshots of the giant planet in 1994, researchers got their first good look at the curtains of electromagnetic activity that make its atmosphere glow. At that time, Clarke and others were able to capture the effect of Jupiter's moon Io on the planet's atmosphere in blurry but visible detail. The "Io footprint," a bright belt starting on the far left side of the planet and moving rightward, is believed to be the result of the collision of material dragged from the moon's atmosphere into Jupiter's hot soup of Hydrogen ions. Magnetic field lines are the conduit for the million-amp current---sufficient to power 1.2 million 100W light bulbs.
This enormous current produces bright but localized auroras where it enters Jupiter's atmosphere in both the northern and southern polar regions. These comet-shaped swaths of light are distinct from the polar auroras, and their rightward-trailing "tails" represent the most sensitive detection of ultraviolet emissions from Jupiter to date.
Jupiter has many other moons, and one of the most significant discoveries of the new views is that the small moon Ganymede also appears to leave a slight but detectable electromagnetic footprint on Jupiter's atmosphere.
The work was funded by NASA and the Space Telescope Science Institute. Images are available for viewing at: http://oposite.stsci.edu/pubinfo/pr/98/04.html