In the News
for a worthy rock
Proximity and slow spin rate
are desirable for exploration
By laura Sanders
The Little Prince, who stood tall on his fictional house-sized asteroid B612, may soon have company. Since President Obama
announced last month that NASA plans to
send people to an asteroid by 2025 (SN:
5/8/10, p. 10), scientists have been scrambling to fill in the details. Before astronauts can embark on such a journey, they
need to choose a destination.
Already, researchers have begun
culling the list of potential candidates.
Martin Elvis of the Harvard-Smithsonian
Center for Astrophysics in Cambridge,
Mass., proposed criteria for identifying
“potentially visitable objects” on April 28
in Brookline, Mass., at a meeting of the
American Astronomical Society’s Division on Dynamical Astronomy.
Asteroids come in a menagerie of
sizes, shapes and trajectories. Some are
little more than giant loose rubble piles,
while others are densely packed. Though
Obama’s proposal didn’t point to any specific destinations, Elvis says that a worthy
asteroid ought to have a fe w key features,
including a slow spin rate, no problematic satellites and a solar orbit that allows
for a long and recurring launch window.
“Are they spinning rapidly? Are they
elongated? Is there strange, irregular
Scientists have begun working out what makes an asteroid, eros shown here,
suitable for a crewed mission. Size, shape and composition are a few considerations.
gravity?” Elvis asks. If the asteroid is
“lumpy and nasty, that’s not good.”
The most important consideration,
though, is that the asteroid is easy to get
to. While the majority of asteroids reside
in a belt between the orbits of Mars and
Jupiter, some come close to Earth. A
relatively nearby asteroid that circles
the sun at a speed similar to the Earth’s
would be ideal, Elvis reported. So far,
six of 6,699 known near-Earth asteroids
seem to have amenable orbits.
For many researchers, the visit will
be a mini–Mars-mission — a chance to
test strategies and equipment before
traveling to the Red Planet. A round-
trip journey to a nearby asteroid might
take about half a year. A mission to Mars
would take more than twice as long.