Dec. 12, 2012: This week, NASA's Goldstone radar is tracking a
large asteroid as it passes by Earth, and obtaining unusually clear images of
the tumbling space rock.
"There is no danger of a collision with Earth," says Lance Benner of NASA's
Near Earth Object Program. "At closest approach on Dec. 12th, asteroid 4179
Toutatis will be 7 million km away or 18 times farther than the Moon."
Asteroid Toutatis is well known to astronomers; it passes by Earth’s orbit
every 4 years. Measuring 4.5 km in length, it is one of the largest known
potentially hazardous asteroids (PHAs), and its orbit is inclined less than
half-a-degree from Earth's. No other kilometer-sized PHA moves around the Sun in
an orbit so nearly coplanar with our own. This makes it an important target for
radar studies.
NASA's Goldstone radar in the Mojave Desert will be pinging the space rock
every day from Dec. 4th through 22nd. The echoes highlight the asteroid's
topography and improve the precision with which researchers know the asteroid's
orbit.
"We already know that Toutatis will not hit Earth for hundreds of years,"
says Benner. "These new observations will allow us to predict the asteroid's
trajectory even farther into the future."
Benner and colleagues are particularly excited about a new digital imaging
system at Goldstone that could reveal never-before-seen details on the
asteroid's surface. "Using the new system, we can now image the asteroid's
surface with 2 to 5 times finer resolution than previous flybys," he says. "We
may we see something new on Toutatis."
The asteroid is already remarkable for the way that it spins. Unlike planets
and the vast majority of asteroids, which rotate in an orderly fashion around a
single axis, Toutatis travels through space tumbling like a badly thrown
football (movie).
One of the goals of the radar observations is to learn more about the asteroid’s
peculiar spin state and how it changes in response to tidal forces from the Sun
and Earth.
It's probably no coincidence that the tumbling asteroid is elongated and
lumpy.
"Toutatis appears to have a complicated internal structure," says radar team
member Michael Busch of the National Radio Astronomy Observatory. "Our radar
measurements are consistent with the asteroid's little lobe being ~15% denser
than the big lobe; and they indicate 20% to 30% over-dense cores inside the two
lobes."
This raises the interesting possibility that asteroid Toutatis is actually a
mash up of smaller space rocks. "Toutatis could be re-accumulated debris from
an asteroid-asteroid collision in the main belt," he says. The new
observations will help test this idea.
Busch points out that the upgraded Goldstone imaging system will produce data
with a resolution of 3.75 meters per pixel. "We'll be putting hundreds of
thousands of pixels across the asteroid's surface."
What will so much resolution reveal? Stay tuned for updates from
Science@NASA.
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