YOU might as well go out in style. At least that鈥檚 the philosophy of
researchers controlling NASA鈥檚 Near Earth Asteroid Rendezvous spacecraft, also
known as NEAR-Shoemaker. On 12 February they will let the dying craft fall onto
the surface of asteroid 433 Eros, the lump of rock it has been waltzing around
since last Valentine鈥檚 Day.
Launched in 1996, NEAR has spent the past year orbiting the potato-shaped
rock, which measures roughly 33 by 13 by 13 kilometres and is currently more
than 300 million kilometres from Earth between the orbits of Mars and Jupiter.
In that time NEAR has returned hundreds of thousands of pictures, and reams of
other data that have transformed researchers鈥� understanding of asteroids.
At first, says Andrew Cheng, a planetary scientist at Johns Hopkins
University Applied Physics Laboratory in Laurel, Maryland, they had expected
Eros to be a collection of many boulders and rocks loosely held together by
gravity. Instead, it turned out to be one large rock with a rubble-strewn
surface. Eros also appears never to have melted, indicating that it hasn鈥檛 been
compressed. That means it is not a fragment of a long-dead planet and has been
hanging around largely unchanged since the earliest days of the Solar
System.
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But now NEAR has spent almost all the fuel for its thrusters and will soon
become uncontrollable. That would mean a dreary drift into oblivion, so NEAR
researchers decided to use what fuel is left to bring the affair to a dramatic
climax: they will 鈥済ently鈥� drop NEAR onto Eros, taking pictures all the way
down. 鈥淲e鈥檝e been trying to come up with a fitting end,鈥� says Robert Farquhar,
NEAR mission director at Johns Hopkins. 鈥淲e decided to do some bonus science,
and to try some new things with a spacecraft.鈥�
While NEAR falls, researchers hope to take pictures revealing rocks just 5 to
10 centimetres across, about one-tenth the size of those in pictures taken from
NEAR鈥檚 latest orbit 35 kilometres from the centre of Eros. They will try to ease
the spacecraft down at no more than 11 kilometres per hour.
But even at that speed the delicate machine probably won鈥檛 survive its
鈥渃ontrolled descent鈥� onto the boulder-strewn surface, says Edward Weiler,
associate administrator for space science at NASA. 鈥淣ote that I didn鈥檛 say
landing,鈥� he adds. 鈥淚t is not a landing.鈥�
While NASA hasn鈥檛 scheduled any more missions to asteroids, Cheng hopes
someday to be able to answer some of the questions raised by NEAR. 鈥淚n the
future, we鈥檇 like to land a space package on an asteroid and maybe bring back a
sample,鈥� he says.