After a six-year odyssey, the Galileo Probe plunged into Jupiter's atmosphere at 2:04 p.m. PST on December 7, 1995. During the first two minutes of entry, the craft experienced temperatures twice as hot as the Sun's surface and deceleration forces as great as 230 times Earth gravity as it was slowed by the atmosphere. The Galileo Orbiter, which entered orbit around Jupiter a few hours after the Probe's descent, recorded 57.6 minutes of data from instruments before the Probe fell silent.

Launched October 18, 1989, Galileo has traveled 3.7 billion kilometers (2.3 billion miles) in a looping path through the solar system to reach Jupiter, which is 934 million kilometers (580 million miles) away from Earth. Along the way, Galileo flew by Venus, the Earth and moon, the asteroid Gaspra, again by the Earth and Moon, and the asteroid Ida, discovering its moon Dactyl.

Having Galileo take pictures of Io and Europa isn't the problem--the difficulty is in storing the images so that they can be sent down to Earth at some later time.

Although the tape recorder is working, the Project wants to limit use of the tape recorder until we 1) better understand the anomaly and 2) identify what are safe modes of operation for the recorder, because there is a chance that we could, unknowingly, further damage the recorder. Engineers are still analyzing exactly why there was an anomaly, as well as identifying exactly what activities the tape recorder can perform. How fast can the tape safely move? Can the tape move in both directions? Until these questions, and others like them, are answered, the project wants to use the tape recorder as little as possible.

The tape recorder will be used on December 7th-- to store probe data, the number one scientific priority of the entire mission. The spacecraft will also record over 3 hours of Io plasma torus observations, as well as recording engineering data during the Jupiter Orbit Insertion burn.

What data can we expect to see on December 7, when the spacecraft arrives at Jupiter?

Unlike the Voyager flybys of Jupiter, Saturn, Uranus and Neptune, Galileo won't be sending back pictures "live" on arrival day. The atmospheric probe's data, and fields and particles observations of Io's plasma torus, will be stored on board the spacecraft for later transmission to Earth.

So, what will we see in the "real time" data? For starters, we'll get confirmation that the orbiter is "in lock" with the probe, and that the probe relay is proceeding as planned. Although we won't be seeing the actual data, this will still be a tremendous reassurance to the project and to the probe's scientists--keep in mind that there has been no communication with the probe since its release last July! We'll also be seeing engineering and tracking data that will show us that Galileo's 400-Newton main engine is performing as scheduled, sending the craft into orbit around Jupiter. You can be sure that this will also bring forth major sighs of relief from the flight team, since the orbiter's mission is completely dependent on orbiting Jupiter, and not flying by it!

Will there be any images released prior to Dec. 7?

No. On October 11, 1995, Galileo's Solid State Imaging camera took a Jupiter Approach Global Image, designed to give scientists a closer look at the Probe Entry Site just prior to arrival. Because of the tape recorder anomaly, this image will not be sent down to Earth.

When can I see images from the Probe's plunge into Jupiter's atmosphere?

Most people are surprised to learn that the Probe doesn't have a camera at all (so there aren't going to be any images from the Probe at all). Keep in mind that the Probe sends data to the Orbiter at 128 bits per second per channel, and that the Probe mission only lasts 75 minutes at most. A single picture from the Solid State Imaging camera on the Orbiter can easily run around 160 kilobytes, so there wouldn't have been time to send up very many pictures from the Probe before the end of its mission.

A partial "quick look" set of the Probe data will be sent back to Earth December 10-13 (investigators will be announcing their preliminary results at a December 19 press conference). A full playback of the entire Probe data set will start in January 1996, following the end of the solar conjunction period (where the Sun lies almost directly between the Earth and Jupiter), and end in March.

Will Earthbound observers be able to see the "flash" from the Probe's entry?

As seen from Earth, Probe entry will occur such that the Probe crosses the dusk terminator (the line dividing day from night) during its mission. The 15,500 degree C (28,000 degree F) incandescent plasma envelope generated ahead of the Probe, which is produced by hypersonic compression and friction with the atmosphere, will briefly be brighter than the Sun's surface.

However, will the high-temperature streak generated by the Probe be detectable?

Unfortunately the answer to this question is NO. Although the length of the streak may be several degrees long in the night sky, the width of the streak is WELL below the resolution of any Earth-based telescope imaging system. Keep in mind, too, that Jupiter is quite near the Sun in the sky, adding another observing difficulty.

Is there a chance that Galileo could return to Io later in the mission?

It is not feasible for the spacecraft to return to Io during Galileo's primary mission, which runs through the end of 1997. However, NASA is currently considering a follow-on mission with the Galileo spacecraft which is called the Galileo Europa Mission, or GEM. GEM would start immediately after the end of the primary mission of Galileo in December 1997 and would continue until late in 1999. Its objectives would be an intensive study of Europa, followed by in-situ study of the Io Plasma Torus, and ending with a spectacular close encounter with Io.

The key resources that Galileo must have to accomplish the GEM are money, propellant, radiation tolerance and general good health, and power, more or less in that order. If Galileo is healthy, and GEM is funded, there is a good prospect of there being enough propellant to navigate the return to Io; don't forget that gravity assists provide the majority of the trajectory change required! There is enough power left in the spacecraft for the required operations. While the spacecraft has been designed to survive Jupiter's hostile environment, returning multiple times to the high radiation environment near Jupiter during GEM could prove fatal to Galileo. Also, given NASA's limited resources, funding for GEM is by no means assured!