Hamburg (dpa) – Scientists in the United States are debating what to do with
the Galileo space probe once it finishes exploring Jupiter and its moons by
the year 2002.
Among the options under consideration by the U.S. space agency NASA is to
deliberately crash the 1.5-billion-dollar spacecraft in order to avoid it
hitting the moon Europa.
Astronomers believe that simple forms of extraterrestrial life might exist
beneath Europa’s icy crust and fear that they could be contaminated by
Galileo with microbes from Earth.
Other alternatives are to allow the spacecraft to orbit Jupiter endlessly or
to aim it away from the planet’s gravitational pull and send it hurtling
deep into outer space.
If it is allowed to remain within Jupiter’s planetary system, Galileo could
be dragged towards Europa, hence the considerations to crash it on the
Jupiter moon Io, or another icy satellite.
The spacecraft, which was launched in October 1989 from the U.S. shuttle
Atlantis, travelled 4.3 billion kilometres before entering orbit around
Jupiter in December 1995.
Its two-year mission provided breathtaking photographs of the largest planet
in the solar system and was followed by an extension of two years that
focused on Europa.
The extended mission ended in January, but since then the aging probe has
embarked on a new project called the Galileo Millennium Mission.
The new adventure saw Galileo pass just 200 kilometres above the surface of
Io in February. Io, the third biggest of Jupiter’s moons, is the most
volcanic body in the solar system.
Io has volcanic vents that spew plumes of sulphur more than 100 kilometres
into space. The sulphur eventually falls back to the moon’s surface,
creating a red, yellow and black landscape.
“Io’s volcanoes are so active that the moon’s surface is always changing,
and with each new flyby we get new and different observations,” says Dr
Torrence Johnson, Galileo project scientist at the Jet Propulsion Laboratory
in Pasadena, California.
The Millennium Mission is expected to last until at least February 2001 and
include two close flybys of Ganymede, the biggest of Jupiter’s frozen moons.
During this mission, the space probe will monitor conditions along the
perimeter of Jupiter’s magnetic field in a region where it comes into
contact with solar winds – high energy particles blown from the sun.
NASA’s plans envisage another spacecraft being launched in November 2003 to
explore Europa. The craft, much smaller than the 340-kilogram Galileo, is
expected to take between 2.7 and 3.4 years to reach its target.
Experts hope the mission will be able to shed light on whether there is a
liquid water ocean beneath the moon’s ice shell. If there is, it could
contain the ingredients needed to support primitive life.
A more adventurous mission, planned for an unspecified later date, envisages
a probe burrowing its way through Europa’s icy crust by taking advantage of
a melting process.
Once it reaches the liquid area, the probe will convert to a submarine or
hydrobot and guide itself through the ocean’s depths by measuring the
water’s temperature.
