Galileo Jupiter Atmospheric Probe

Launch Date	October 18, 1989
Launch Site	Kennedy Space Center, Pad 39-B
Destination	Jupiter
Type	Descent Probe
Status	Mission successfully completed; destroyed in Jupiter’s atmosphere
Nation	United States
Alternate Names	Galileo Probe

Goals

• Determine the chemical composition of the Jovian atmosphere
• Characterize the structure of the atmosphere to a depth of at least 10 bars
• Investigate the nature of cloud particles and the location and structure of cloud layers
• Examine the Jovian radiative heat balance
• Study the nature of Jovian lightning activity
• Measure the flux of energetic charged particles down to the top of the atmosphere

Accomplishments

• The probe was the first spacecraft to enter Jupiter's atmosphere.
• It detected wind speeds in excess of 400 mph (600 kilometers per hour).
• It detected far less water in Jupiter's atmosphere than estimated from earlier Voyager observations and from models of the Comet Shoemaker-Levy 9 impact. Scientists later determined the probe had entered an unusually dry “hot spot.”
• It found far less lightning activity (about 10 percent of that found in an equal area on Earth) than anticipated. The individual lightning events, however, are about 10 times stronger on Jupiter than the Earth.
• It found that Helium abundance in Jupiter is very nearly the same as its abundance in the Sun (24 percent compared to 25 percent).

Key Dates

• Released from Galileo spacecraft: July 13, 1995
• Penetrated Jupiter's atmosphere: December 7, 1995

In Depth

The Galileo spacecraft and probe traveled as one for almost six years. In July 1995, the probe was released to begin a solo flight into Jupiter.

Five months later, the probe sliced into Jupiter's atmosphere at 106,000 mph. It slowed, released its parachute, and dropped its heat shield. As the probe descended through 95 miles of the top layers of the atmosphere, it collected 58 minutes of data on the local weather. The data were sent to the spacecraft overhead, then transmitted back to Earth.

It appeared that Jupiter's atmosphere is drier than we thought. Measurements from the probe showed few clouds, and lightning only in the distance. It was only later that we discovered that the probe had entered an area called a "hot spot."

Towards the end of the 58 minute descent, the probe measured winds of 450 mph--stronger than anything on Earth. The probe was finally melted and vaporized by the intense heat of the atmosphere.

Spacecraft

Launch Vehicle: Space Shuttle Atlantis (and then carried to Jupiter by the Galileo spacecraft)

Spacecraft Mass: 746 pounds (339 kilograms)

Spacecraft Size: 4 feet (1.25 meters) in diameter and 2.8 feet (0.86 meters) in height

Spacecraft Instruments:

• atmospheric structure group of sensors for measuring temperature, pressure and deceleration
• neutral mass spectrometer supporting atmospheric composition studies
• helium-abundance detector supporting atmospheric composition studies
• nephelometer for cloud location and cloud-particle observations
• net-flux radiometer measuring the difference, upward versus downward, in radiant energy flux at each altitude
• lightning/radio-emission instrument with an energetic-particle detector

Additional Resources

NASA Space Science Data Coordinated Archive https://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1989-084E

Selected References

Siddiqi, Asif A. Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, NASA, 2002.