The Galileo spacecraft's 14-year odyssey came to an end on Sunday,
Sept. 21, when the spacecraft passed into Jupiter's shadow then
disintegrated in the planet's dense atmosphere at 11:57 a.m. Pacific
Daylight Time. The Deep Space Network tracking station in Goldstone,
Calif., received the last signal at 12:43:14 PDT. The delay is due to
the time it takes for the signal to travel to Earth.
Hundreds of former Galileo project members and their families were
present at NASA's Jet Propulsion Laboratory in Pasadena, Calif., for a
celebration to bid the spacecraft goodbye.
"We learned mind-boggling things. This mission was worth its weight
in gold," said Dr. Claudia Alexander, Galileo project manager.
Having traveled approximately 4.6 billion kilometers (about 2.8
billion miles), the hardy spacecraft endured more than four times the
cumulative dose of harmful jovian radiation it was designed to
withstand. During a previous flyby of the moon Amalthea in November
2002, flashes of light were seen by the star scanner that indicated
the presence of rocky debris circling Jupiter in the vicinity of the
small moon. Another measurement of this area was taken today during
Galileo's final pass. Further analysis may help confirm or constrain
the existence of a ring at Amalthea's orbit.
"We haven't lost a spacecraft, we've gained a steppingstone into the
future of space exploration," said Dr. Torrance Johnson, Galileo
project scientist.
The spacecraft was purposely put on a collision course with Jupiter
because the onboard propellant was nearly depleted and to eliminate
any chance of an unwanted impact between the spacecraft and Jupiter's
moon Europa, which Galileo discovered is likely to have a subsurface
ocean. Without propellant, the spacecraft would not be able to point
its antenna toward Earth or adjust its trajectory, so controlling the
spacecraft would no longer be possible. The possibility of life
existing on Europa is so compelling and has raised so many unanswered
questions that it is prompting plans for future spacecraft to return
to the icy moon.
Galileo was launched from the cargo bay of Space Shuttle Atlantis in
1989. The exciting list of discoveries started even before Galileo
got a glimpse of Jupiter. As it crossed the asteroid belt in October
1991, Galileo snapped images of Gaspra, returning the first ever
close-up image of an asteroid. Less then a year later, the spacecraft
got up close to yet another asteroid, Ida, revealing it had its own
little "moon," Dactyl, the first known moon of an asteroid. In 1994
the spacecraft made the only direct observation of a comet impacting a
planet-- comet Shoemaker-Levy 9's collision with Jupiter.
The descent probe made the first in-place studies of the planet's
clouds and winds, and it furthered scientists' understanding of how
Jupiter evolved. The probe also made composition measurements designed
to assess the degree of evolution of Jupiter compared to the Sun.
Galileo made the first observation of ammonia clouds in another
planet's atmosphere. It also observed numerous large thunderstorms on
Jupiter many times larger than those on Earth, with lightning strikes
up to 1,000 times more powerful than on Earth. It was the first
spacecraft to dwell in a giant planet's magnetosphere long enough to
identify its global structure and to investigate the dynamics of
Jupiter's magnetic field. Galileo determined that Jupiter's ring
system is formed by dust kicked up as interplanetary meteoroids smash
into the planet's four small inner moons. Galileo data showed that
Jupiter's outermost ring is actually two rings, one embedded within
the other.
Galileo extensively investigated the geologic diversity of Jupiter's
four largest moons: Ganymede, Callisto, Io and Europa. Galileo found
that Io's extensive volcanic activity is 100 times greater than that
found on Earth. The moon Europa, Galileo unveiled, could be hiding a
salty ocean up to 100 kilometers (62 miles) deep underneath its frozen
surface containing about twice as much water as all the Earth's
oceans. Data also showed Ganymede and Callisto may have a
liquid-saltwater layer. The biggest discovery surrounding Ganymede
was the presence of a magnetic field. No other moon of any planet is
known to have one.
The prime mission ended six years ago, after two years of orbiting
Jupiter. NASA extended the mission three times to continue taking
advantage of Galileo's unique capabilities for accomplishing valuable
science. The mission was possible because it drew its power from two
long-lasting radioisotope thermoelectric generators provided by the
Department of Energy.
"The mission was a testimonial to the persistence of NASA even through
tremendous challenges. It was a phenomenal mission," said Sean
O'Keefe, NASA administrator.
JPL, a division of the California Institute of Technology in Pasadena,
manages the Galileo mission for NASA's Office of Space Science,
Washington, D.C. JPL designed and built the Galileo orbiter, and
operated the mission.
Additional information about the Galileo mission and its discoveries
is available online at:
http://www.jpl.nasa.gov/galileo-legacy and
http://galileo.jpl.nasa.gov .
For information about NASA, visit:
http://www.nasa.gov/ .
