The six-year-long wait for the Galileo trip to Jupiter started paying off scientific returns last fortnight, as the data sent by the probe was analysed and NASA scientists released the first results
THE plucky American spacecraft Galileo,
which went into orbit around Jupiter
after successfully delivering a 'suicide
probe' in December last year, has gradually begun to unveil the mysteries surrounding the planet's atmosphere.
, After a reasonably long wait, scientists at the us National Aeronautics and
Space Administration (NASA) have now
begun receiving the data collected by the
'suicide probe' following its 57-minute
sojourn in the Jovian atmosphere. They
say that the probe's measurements may
necessitate a re-evaluation of existing
views on how Jupiter evolved from the
solar nebula.
The composition of the Jovian
atmosphere offered some surprises to
the Galileo project scientists. The 'suicide probe' found significantly lower levels of helium, neon, and certain other
heavy elements, such as carbon, oxygen
and sulphur. It also did not encounter
any solid objects or surfaces during its
entire 600 km descent; this was expected
in the case of a, giant gas-planet such as
Jupiter, say scientists.
"The probe detected extremely
strong winds and intense turbulence
during its descent through Jupiter's
thick atmosphere. This provides evidence that the energy source driving
much of Jupiter's distinctive circulation
phenomena, is probably the heat escaping from the interiors of the planet,"
said one scientist with the Galileo
project. "The probe also discovered an
intense new radiation belt approximately 49,879 km above the planet's
cloud tops and a veritable absence of
lightning," he observed.
What are the implications of the information disclosed by the 'suicide probe'?
Most researchers at NASA
believe that Jupiter has a
bulk composition similar to
that of the, gas and dust
cloud of the primitive nebula
from which other planets
and the sun were formed.
The. lower-than-expected
levels of helium and neon on
Jupiter compared to the sun,
influence scientific understanding of the process of
fractionation - the 'raining
out' of helium and neon
during planetary evolution.
During the probe's high-
speed atmospheric entry
phase, deceleration measurements high in the Jovian
atmosphere revealed that the
density was much higher
than previously believed.
Corresponding temperatures were also much higher
than predicted. The high
temperatures appear to require an unidentified heating mechanism for this region of the planet's atmosphere, say NASA scientists.
During the parachute deployment
phase, six scientific instruments onboard the probe collected data throughout the 156 km of its descent. During
this phase the probe endured extreme
winds, periods of intense cold and heat
and strong turbulence. The extreme
pressure and temperature in the planet's
environment caused the probe's communication subsystem to terminate the
data transmission operations to the
mother craft.
Earth-based telescopic observations
suggest that the probe's -entry sight may
well have been in one of the least cloudy
areas on Jupiter. At this location, the
probe did not explicitly detect the three
distinct layers of clouds - a top layer of
ammonia crystals, a middle layer of
ammonium hydrosulfide, and finally a
thick layer of water and ice crystals -
that the researchers had anticipated. But
there are some indications of a high-
level ammonia ice cloud being detected
by the net flux radiometer. Evidence of a
thin cloud, 'suspected to be that of
ammonium hydrosulfide, was also provided by
the scientific instruments onboard the space probe.
The data flow from the space probe
has provided new impetus to the ongoing debate on the nature of the Jovian
system. A clearer picture is expected to
emerge after the mother craft completes
its two-year study mission around the
giant planet and its retinue of moons.
On the day of Galileo's rendezvous
with Jupiter, NASA chief David S Goldin
had predicted that by the turn of the
century or soon afterwards, the agency
would be launching a spacecraft once
every month - small cheap machines
designed to explore the solar system,
and search for earth-sized planets
around other stars. "The best is yet to
come," he asserted.
Plans are underway to dispatch two
spacecrafts to Mars late this year - one
to orbit the planet and other to land an
automated rover on the surface.
Another ambitious mission, christened
'Cassini', is set for launch in 1997 to
Saturn and its gaint moon Titan. NASA
scientists have already begun work for a
flight to the moon, more missions to
Mars in 1998, and still another designed
to fetch some dust from a comet.
Progress is also being made in devising
an affordable mission to Pluto, the only
planet in the solar system yet to welcome a spacecraft from earth.
Goldin's optimistic observations
about the future of planetary exploration probably came as a surprise to
many NASA Sceptics for whom the days
of extensive planetary scouting seems to
have become a thing of the past. The
Pioneers and Voyagers are coasting to
the edge of the solar system, with their
discoveries behind them. The Vikings
have been relegated to the dustbin of
history. Galileo, which was launched six
years ago, is the only spacecraft actively
engaged in studying a planet.
Notwithstanding the scepticism, the
agency has managed to sectire the White
House's approval on its philosophy of
smaller, better and less expensive missions. But congressional support may
be very difficult to come by. Growing
demand for reduction in federal spending could jeopardise these and other
NASA programmes.
Wesley T Huntress Jr, NASA's associate administrator for space science ,
says there is hope for new plans as long
as they are achieved without increasing
the agency's annual budget devoted to
science. In the current budget, the allotment for new plans is us $2 billion out
of the total us $13.8 billion. With
Galileo at its destination and Cassini
near completion, expenditure on two
high priced projects is sharply diminished, leaving room for embarking on
new missions.
To evolve a new approach to space
exploration that is less expensive and
focused in nature, NASA planners have
come out with a concept called the
Pluto Express, at an estimated cost of us $400
million, which the agency
officials presume, will be
affordable. Instead of
packing several instruments in a single craft
weighing several tonne,
engineers have designed
two light-weight spacecrafts weighing
as little as 137 kg (approximately) each.
This was made possible by incorporating new microelectronic technology
and limiting the number of scientific
instruments on board. Further, a high
degree of automation is expected to
reduce the costs of operating the craft in
flight.
The Pluto Express involves launching of two crafts seperately, -perhaps by
Russian Proton rockets, on 'fast' trajectories. They should be able to reach
Pluto in six to eight years compared to
Voyager-2's travel to Neptune in 12
years.
The Discovery programme of NASA
is a starter in the direction of small, low-cost projects. The idea is to develop
spacecraft with narrowly focused and
precise goals for flight in less than three
years at a cost of less than US $150 million, including the cost of launching
four such missions. The first mission
craft is Stipulated to orbit and study an
asteroid, Eros.
Another approach to the future is
being studied at the Jet Propulsion
Laboratory (JPL) in Pasadena, under
what is called the New Millennium
Programme - aimed at identifying the
likely science missions of the next
century and determining the new technology that would be required to
accomplish the objectives at reasonable
costs. The first New Millennium flight,
scheduled for 1998, would involve a 100
kg (approximately) spacecraft equipped
with miniaturised antenna and automated controls. It will be the first spacecraft that would depend on solar electric
propulsion for its main source of thrust,
instead of conventional solid or liquid
propellents. With electric propulsion,
the craft can get continuous thrust,
rather than coasting, and this would
reduce the time of flight substantially,
Say JPL scientists.
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