Galileo Flyby: Extreme Explorers Hall of Fame


Extreme Explorers' Hall of Fame
Highlighting the visual benefits of a close-up view of Jupiter’s moons, this glimpse into an active volcano on the moon Io, shows hot black lava, warm red sulfur deposits likely deposited from vented gas, and hilly yellow terrain also high in sulfur. This caldera called Tupan Patera is actually a volcanic depression, surrounded by cliffs nearly a kilometer high. The width of the depression is about 75 kilometers. Inset upper right shows the Galileo spacecraft, and inset lower left shows a view of the Nov.5 close flyby of the reddest object in the solar system, Jupiter’s moon, Amalthea. Not to scale in perspective or orientation.
Credit: Montage of related Galileo images NASA/JPL

The spectacular Galileo flybys of Europa and Io are largely credited with the discovery of frozen water ice and some of the earliest examples of non-solar (tidal) heating anywhere in our solar system. For the next 10 days, Galileo scientists are preparing for their next target: probing one of Jupiter’s moons, Amalthea, at close-up ranges of <100 miles. Amalthea is one of the most unusual moons in the solar system, because it gives off more heat than it receives from the Sun.

On-orbit mass: 2380 Kg
Power System: Radioisotope Thermal Generators (RTGs) of 570 W
Dimensions: The length of the spacecraft is 9 m and, with the high-gain antenna (HGA) deployed, is 4.6 m in diameter.
Gravity Assist: The trajectory which the spacecraft followed was called a VEEGA (Venus-Earth-Earth Gravity Assist), traveling first in toward the Sun for a gravity assist from Venus before encountering the Earth two times (spaced two years apart). These encounters with Venus and the Earth allowed Galileo to gain enough velocity to get it out to Jupiter.

Launch Date: 18 October 1989 at 22:23 UTC
Launch Vehicle: Shuttle/Inertial Upper Stage

Milestone Science:

  • First mission to make a close flyby of an asteroid (Gaspra).
  • First mission to discover a satellite of an asteroid (Ida’s satellite Dactyl).
  • First multispectral study of the Moon.
  • First atmospheric probe to enter Jupiter’s atmosphere.
  • First spacecraft to go into orbit around Jupiter.
  • First direct observations of a comet impacting a planet (Shoemaker-Levy 9).
  • The discovery of a satellite (Dactyl) of an asteroid (Ida).
  • Confirmation of the existence of a huge ancient impact basin in the southern part of the Moon’s far side (inferred from Apollo data but never before mapped).
  • Evidence of more extensive lunar volcanism than previously thought.
  • Discovery of an intense interplanetary dust storm (the most intense ever observed).
  • Discovery of an intense new radiation belt approximately 50,000 km (31,000 miles) above Jupiter’s cloud tops.
  • Jovian wind speeds in excess of 600 kilometers per hour (> 400 mph) were detected.
  • Far less water was detected in Jupiter’s atmosphere than estimated from earlier Voyager observations and from models of the Comet Shoemaker-Levy 9 impact.
  • Far less lightning activity (about 10% of that found in an equal area on Earth) than anticipated. The individual lightning events, however, are about ten times stronger on Jupiter than the Earth.
  • Helium abundance in Jupiter is very nearly the same as its abundance in the Sun (24% compared to 25%).
  • Extensive resurfacing of Io’s surface due to continuing volcanic activity since the Voyagers flew by in 1979.
  • Preliminary data support the tentative identification of intrinsic magnetic fields for both Io and Ganymede.
  • Evidence for liquid water ocean under Europa’s surface.

This week’s events for the Amalthea flyby:

Scientific significance: In 10 days, the next satellite flyby will occur on November 5, 2002 when Galileo flies by Amalthea.

This encounter is referred to as Amalthea 34 since it will occur on the 34th orbit since Galileo entered orbit around Jupiter in December 1995. It is the reddest object so far seen within in the solar system and appears to give out more heat than it receives from the Sun, perhaps from either radiation bands around Jupiter or tidal heating.

This flyby should yield an estimate of the mass and, correspondingly, the bulk density for the satellite–an important finding to understand how the many Jovian moons formed.

Mass determination requires no functional instruments, only tracking of the spacecraft’s trajectory through monitoring of its downlinked radio signals.

Engineering events:

On Monday, October 21, the Fields and Particles suite of instruments were turned on and configured to collect continuous data for the next three weeks. During this time, the spacecraft passed the tiny inner moon Amalthea, and passed closer to Jupiter than any spacecraft since Pioneer 10 and 11 sped by nearly three decades ago. The instruments participating in the Galileo data collection were the Dust Detector, the Energetic Particle Detector, the Heavy Ion Counter, the Magnetometer, the Plasma Subsystem, and the Plasma Wave Subsystem.

While these data were being collected, occasional gaps in the ground communications antenna coverage required the data to be stored in an on-board computer memory buffer, and when that buffer filled, the data are copied onto the tape recorder for later playback. To prepare for these buffer dumps, the tape was moved on Monday to the correct position to begin recording. Over the next two weeks the buffer is dumped to tape 14 times.

On Thursday, October 24, a test of the gyroscopes that help determine the spacecraft attitude was performed. This test helped engineers decide if any of the software parameters that are used to process the gyro data needed to be updated before the maneuver that will occur next week.

On Friday, October 25, routine maintenance of the propulsion system is performed. Also on that day the spacecraft closes to within 100 Jupiter radii (7.1 million kilometers or 4.4 million miles) of the giant planet.

Finally, on Sunday, October 27, the sequence of commands that will govern spacecraft activity during the week of the close Amalthea flyby will be transmitted to Galileo.

Torrence Johnson is chief scientist for Galileo at the Jet Propulsion Laboratory (JPL) in Pasadena, California

Related Web Sites

  • Amalthea Backgrounder
  • Scientific Assessment for Galileo Disposal
  • Amalthea Viking Images
  • Galileo Home