July 17 - 23, 2000
Galileo - Some Interesting Observations
Did you know that Jupiter, our solar system's gas giant, is almost 143,000 kilometers (89,000 miles) in diameter? That's more than 11 times the Earth's diameter, which also makes Jupiter more than 1300 times larger in volume than Earth. Jupiter also weighs 1.9 x 10^27 kilograms (8.6 x 10^26 pounds), that is 1,900,000,000,000,000,000,000,000,000 kilograms! At that weight, Jupiter contains more than twice as much matter as all of the other planets in our solar system combined!
The Galileo spacecraft is in orbit around Jupiter, playing back science data acquired during flybys of two of Jupiter's moons, Io and Ganymede. During playback, the spacecraft computer retrieves the data stored on its onboard tape recorder, then processes and packages the data, and subsequently transmits the data to Earth. The Io data were acquired in February, and the Ganymede data were acquired more recently, in mid-May. Data from three observations are returned this week. One contains Io data, and was made by the Near-Infrared Mapping Spectrometer (NIMS). The other two contain data describing Jupiter's and Ganymede's magnetospheres, and were made by Galileo's suite of Fields and Particles instruments. The Fields and Particles instruments are comprised of the Dust Detector, Energetic Particle Detector, Heavy Ion Counter, Magnetometer, Plasma Detector, and Plasma Wave instrument.
Return of the NIMS observation is actually a continuation from last week. The observation focused on the Amirani volcanic region, previously known as Amirani-Maui. The Amirani region was originally thought to contain two separate volcanoes, but Galileo data have shown that Maui is actually the leading edge of a 250-km (160-mile) long lava flow originating from Amirani.
The Fields and Particles data are the first sets returned from Galileo's May flyby of Ganymede. One observation contains the recorded portions of a month-long survey of Jupiter's magnetosphere. In most orbits, magnetosphere surveys are performed in real-time only, which means that the data are not stored on the spacecraft's tape recorder, but rather are directly transmitted to Earth after processing and packaging. The duration of this survey, however, made it necessary to record some portions of the observation to prevent data loss. This survey spanned from the inner to outer regions of the magnetosphere, and the transition from inside Jupiter's vast magnetic bubble into the solar wind.
The second observation returned by the Fields and Particles instruments contains portions of a 60-minute high-resolution recording of the plasma, dust, and electric and magnetic fields surrounding Ganymede. Ganymede is the only planetary moon that is known to have its own internally-generated magnetic field, and thus, its own magnetosphere. With the recorded data, scientists hope to obtain a far more complete understanding of how the magnetic field lines and magnetospheres of both Ganymede and Jupiter interact with one another.