GOODBYE GALILEO!
On September 21,
2003 one of the most successful missions of NASA that had fruitful
encounters with Jupiter’s planets – the Galileo spacecraft - will
be made to plunge into its atmosphere to end its life. This is
to prevent any chance of contaminating possible microbial life
in the subsurface regions of Europa, the icy Moon of the solar
system’s largest planet.
Galileo was
launched by the sapce shuttle, Atlantis, in 1989. In October,
1989, the Galileo spacecraft was deployed and the rocket booster
fired, to trigger its six-year journey towards Jupiter.
The mission’s primary
goals ended six years ago. But it had three extensions of life,
until it was decided in February this year, to terminate the mission
on September 21, 2003. The spacecraft has nearly depleted its
onboard supply of propellant and would soon be unable to point
its antenna towards the Earth and adjust its trajectory. Since
its launch in 1989, Galileo has had unprecedented success in observing
Jupiter and its Moons, several asteroids, the Jovian atmosphere
and its magnetic environment.
In July 1994, when
the comet Shoemaker-Levy was captured by the mighty gravitational
tug of Jupiter and its fragments crashed onto the surface of this
giant planet, Galileo was fortuitously placed to study this in
detail.
Galileo Galilei
of Italy was the first to observe Jupiter through a telescope
and in January 1610, he first discerned four star-like objects
orbiting the planet Jupiter. These are now known as the Galilean
moons – Io, Europa, Gannymede and Callisto. Extensive studies
of these moons and their parent planet, Jupiter, were the primary
responsibilities of the aptly named Galileo mission. There are
many firsts credited to this mission. This was the first mission
to orbit Jupiter. All the earlier missions to Jupiter were flybys.
It was the first mission to drop a probe into the atmosphere of
Jupiter and to make a close flyby of an asteroid called Gaspra.
It was the first mission to discover a satellite of an asteroid,
Ida’s satellite Dactyl, as also to directly study a comet impacting
a planet and now it will be the first mission to be guided to
crash onto a Jovian planet.
This is not the
first close encounter of the Galileo mission with Jupiter’s atmosphere.
In 1995, the Galileo mission dropped a probe into the atmosphere
of Jupiter which successfully radioed back information about the
temperature structure, winds, lightening and chemistry inside
the mighty planet’s atmosphere.
Among the many
successes of the Galileo mission had been the serendipitous discovery
of about 9 new moons of Jupiter, when the spacecraft had a close
encounter with Amalthea, an inner moon of Jupiter, in November
2002. This was the last fly of Galileo over any Jovian satellite.
There seems
ample evidence indicating that beneath the icy, cracked surface
of Europa, one of the Galilean moons of Jupiter, a salty liquid
water ocean exists. This is currently the one location in the
solar system, outside the Earth, where there seems to be the possibility
of some life forms, even if just microbial. While this possibility
exists, no scientific exploration of the solar system would like
to endanger this possible microbial life forms on Europa. It is
to prevent a possible crashing onto the surface of Europa, that
the Galileo spacecraft is being guided to crash onto Jupiter instead,
before its fuel is completely exhausted. Galileo may be carrying
with it single-celled organisms from home. Some Earth microbes
are known to have survived for years in space in a dormant state.
Terrestrial micro-organisms could conceivably pose a threat to
microbes that may exist on Europa.
The proposed crash
of Galileo on the planet Jupiter, will be towards the face of
the planet turned away from us. So there will be no excitement
of trying to view the event from Earth.(PIB Features)
Contributed
by Dr. N. Rathnasree, Director, Nehru Planetarium, New Delhi
