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National Research Council report outlining possible approaches to cataloging
all asteroids near Earth.
Once the asteroids are tallied, selection criteria such as those proposed by
Elvis can be considered. (Regardless of
choice, it is unlikely that the asteroid
will have enough gravity to allow a landing. Rather, astronauts would probably
tether their spacecraft to the asteroid
and move as it moves, possibly zipping
to the rock in a smaller vehicle.)
Planetary scientist Paul Abell of
NASA’s Johnson Space Center in Houston says an asteroid’s composition might
also affect its desirability. Visiting an
asteroid that holds water-ice, for example, might help astronauts figure out how
to extract water for drinking and for fuel,
a technique that could come in handy
during pit stops on a long trip to Mars.
Of course, a crewed mission to an asteroid would garner rich scientific rewards
in its own right. Visiting an asteroid “tells
you about what existed back when planets were forming,” Bottke says. Asteroids
may host carbon-containing molecules,
which could hold clues to the beginning
of life on Earth. So far, scientists have
gleaned much of their information about
the early solar system from meteorites
that have landed on Earth, but these samples lose a lot of material as they flame
through the atmosphere, he says.
Though robots have successfully
landed on two asteroids so far — Eros
and Itokawa — people could accomplish
experiments that robots couldn’t. “
Having humans in the mix gives you a lot of
flexibility,” Abell says. A human with a
hammer could pick up a rock and then
choose to discard it in favor of a more
intriguing rock somewhere else.
But having “non-artificial intelligence,”
as planetary astronomer Andrew Rivkin
of Johns Hopkins University’s Applied
Physics Laboratory in Laurel, Md., puts
it, doesn’t mean a thing unless the astronauts survive the trip. Keeping them safe
on a long flight to an asteroid, as well as to
Mars, will pose new challenges.
The NEAR spacecraft (artist’s illustra-
tion shown) landed on Eros in 2001.
“Going to an asteroid is a new idea,
but I don’t think all of the complications
have been thought through,” Bottke says.
“I think everyone’s being a little cavalier
about jumping on the bandwagon.”
For instance, researchers will need
to quantify the doses of radiation that
astronauts will experience on the jour-
ney. An inopportune solar flare could
be deadly, and the requisite protective
shielding could be too heavy to carry.
Back Story | AS TEROIDS TO WATCH
More than 6,500 asteroids are known to enter Earth’s neighborhood. Of these,
1,100-plus are classi;ed as “potentially hazardous” —meaning they can approach
Earth relatively closely and have diameters larger than 150 meters. The orbits of a
few of these asteroids are shown below.
March 6, 2030
Nov. 8, 2011
25143 Itokawa grabbed public attention when it
became the target of the Japanese Hayabusa mission, which launched in 2003, imaged the asteroid and attempted to collect soil samples. (The
recovery capsule is expected to land in Australia
in June.) The asteroid’s next close approach will
be in March 2030, when it will pass within 56.3
million kilometers of Earth.
FROM TOP: SPL/PHOTO RESEARCHERS, INC.; BACK STORY: NEO.JPL.NASA.GOV/NEO/PHA.HTML
Recent observations suggest asteroid 2005
YU55 is 400 meters long, twice as large as previ-
ously thought. The measurements were taken
in April as the Arecibo telescope in Puerto Rico
tracked the asteroid passing within 2. 3 million
kilometers of Earth. On its next approach, in
November 2011, the body is expected to get
much closer —a mere 325,000 kilometers away.
Nov. 9, 2040
6344 P-L was ;rst discovered in 1960, but then
researchers lost track of it. The asteroid was
rediscovered in 2007 and given the name 2007
RR9 before it was recognized. The asteroid has
a highly elongated orbit that takes 4. 7 years to
traverse, and its next close approach to Earth will
be in November 2040, when it will pass within
11 million kilometers.