Rocky rendezvous

Eros beckons: a depiction of f (Credit: Shri Krishan)IN THE run up to knowing more about
outer space and its intricate components, especially the asteroids - rocky
leftovers of the birth of the solar system
4.6 billion years ago - the National
Aeronautics and Space Administration
(NASA) successfully launched the first
ever space probe to orbit an asteroid on
February 17. Called NEAR for Near Earth
Asteroid Rendezvous, it will journey
two billion kin to reach the asteroid
Eros, named after the Greek god of love,
that is circling the sun relatively close to
the earth. Eros is the second largest of
the nearly 250 known asteroids that
approach the earth.

The car-sized spacecraft was built
on a shoe-string budget of us $17 million at the Johns Hopkins University
Applied Physics Laboratory in Laurel,
Maryland. It will take three years to
reach the designated orbital path
around Eros and will be manoeuvered
by NASA's jet Propulsion Laboratory in
Pasadena.

The spacecraft will swing past earth
in January- 1998 and will change its
orbital plane to match that of Eros. The
probe's first encounter with Eros will
take place in February 1999, and in
March J999, it is expected to reach the
optimal orbital distance of 30-50 kni to
conduct its study. Hovering close to the
target for almost an,entir 'e year, NEAR
will collect data on the asteroid's
mineral content with the help of special
cameras installed in it. Scientists also
hope to obtain information on the
geology of the asteroid, whether it has a
moon/ 'moons, and the precise density of
the asteroid. The mission will terminate
in December that year when it will be
commanded to either crash-land on
Eros or will be ejected out of the
asteroid's orbit.

According to project scientist,
Andrew Cheng of the Johns Hopkins
University, the data on mineralogy and
chemistry of Eros will offer scientists
"the first really good, close-up look at an
object which may preserve materials
dating all the way back to the origins of
our solar system, to the time when the
planets, including earth, were first
forming." It is not known whether Eros,
which was first sighted in 1898 by scientists in Germany and France, is a primitive celestial body or a i@hunk of a ruptured former planef.'The asteroids are
found in abundance,betvieen the orbits
of Mars and Jupiter in an asteroid belt
which is between 10- 1,000 km thick.

The asteroid study will also help to
find a connection between asteroids and
meteorites, the small fragments of stone
and metal which burn and plummet
onto the earth's surface. Theories have it
that meteorites originate from asteroids,
but as yet no match has been found. But
to be parent material for the meteorites,
the asteroids would have to escape the
asteroid belt and cross the earth's orbit.
How do they. manage that? Scientists
believe that within the asteroid belt,
bodies sometimes collide With each
other, scattering asteroid fragments. into
a frenzied state of motion wher
they are further confused by theA
gravitational pull of the surrounding planets. The existent
chaos acts as an escape hatch, wherein
the asteroids sneak away, and end up
crossing the earth's orbit. Sometimes
they even faRinto the earth's atmosphere streaking down in what is known
as shooting stars.

According to results of computer
stimulations conducted by Patrick
Michel and Christiane Froeschle of the
Nice Observatory and Paolo Farinella at
the University of Pisa, Italy in 1995,
there is a 50-50 chance that Eros might
crash-land on earth, thus ending its
existence. But the - catastrophe is
expected to occur many million years
later. The impact will, however, be
greater than the one which is thought to
have ended the dinosaur reign 65 million years ago.

Studies have revealed that most
meteorites belong to the chondrite
family of rocks which are rich in metal
content and they contain innumerable
tiny spheres - chondrules, made up of
silica-group minerals. These silica-rich
a$teroids are termed s-type asteroids
which abound in the inner third region
of the asteroid belt where the chief
escape hatches to earth are found.

On conducting light spectrum
analysis on meteorite fragments and
asteroid s, scientists found that they did
not match. This, they theorised, was
because in the course of its
patb toward the earth the,
meteorite underwent
certain changes, which
an asteroid does not.
Tests were conducted
at the Vernadsky
Institute in Moscow,
where; ordinary chondritic meteorite was
crushed and zapped with
lasers to simulate the
effect of tiny meteor
bombardments. The results of spectral analysis
of the meteorite was
found to match that of an
s-type asteroid. Scientists
hope their hypothesis will
be proved correct and
that the NEAR mission
will solve the puzzling
connection between the
asteroid and the meteorites once and for all.