Mission Status Report #41 Star Date: February 2, 2001
FUSE on the "Move"
Caption: (Left) Artist's concept of the Cassini spacecraft approaching Jupiter. (Photo courtesy NASA/JPL). (Right) Hubble Space Telescope STIS/UV image of Saturn showing the polar aurorae. (Photo: NASA/STScI). FUSE has made observations of both of these planets during the last month.
All continues to go extremely well on the FUSE project, with the satellite hardware behaving nominally, and ground operations at JHU going smoothly.
The last month has seen a number of significant observations by the FUSE telescope, perhaps none more captivating than several observations of the solar system targets Jupiter and Saturn.
Observations of solar system objects are especially difficult because these targets "move" with respect to the background stars, especially when viewed from earth orbit. Hence, instead of just grabbing and holding a set of fixed guide stars, FUSE must grab the guide stars and move them as a function of time to keep the spectrograph pointing at the moving target position. The fact that we have successfuly performed these technically difficult observations is another sign that FUSE mission operations have matured to a significant level.
The Jupiter observations had an added element of interest since they were made in support of the closest approach of the Cassini satellite to Jupiter as it passed by on its way to Saturn (picture at upper left). Hence, while Cassini was making measurements of Jupiter and its environs in situ, FUSE was obtaining a global perspective from its position in earth orbit. By comparing the data sets obtained in these different ways, scientists obtain a different kind of information than from either set of observations alone. FUSE observed Jupiter's aurorae and the plasma torus (a "donut" of hot gas encircling the planet) during the Cassini encounter period.
A few days later, FUSE was trained on the planet Saturn, obtaining spectra of its lovely south aurorae, seen in the Hubble picture at upper right. These aurorae are formed when high energy particles from the solar wind get caught in the planet's magnetic fields and are funneled down onto the upper atmosphere. The emission that is excited to glow arises primarily from the molecular form of hydrogen. By studying FUSE spectra, scientists can better understand how the energy gets deposited in the atmosphere and study the otherwise invisible magnetospheres of these giant outer planets.
You can, of course, see both of these planets very well right now, in the constellation Taurus, just to the northwest of Orion. While most of the objects the FUSE satellite observes are much too faint to be see without a telescope, these two planets are some of the brightest objects in the nightime sky!
Reported by: Bill Blair, Chief of Observatory Operations
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