[meteorite-list] Countdown to Vesta

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 19 Aug 2010 13:40:18 -0700 (PDT)
Message-ID: <201008192040.o7JKeI9U029020_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2010/19aug_dawn2/

Countdown to Vesta
NASA Science News
August 19, 2010

Let the countdown begin. NASA's Dawn spacecraft is less than one year
away from giant asteroid Vesta.

"There's nothing more exciting than revealing an unexplored, alien
world," says Marc Rayman, Dawn's chief engineer at the Jet Propulsion
Laboratory. "Vesta," he predicts, "is going to amaze us."

Dawn is slated to enter orbit around Vesta in late July 2011. As the
first breathtaking images are beamed back to Earth, researchers will
quickly combine them into a movie, allowing us all to ride along.

"It will look as though the spacecraft is hovering in one place while
Vesta rotates beneath it," says Rayman.

Previous missions have shown us a handful of asteroids, but none as
large as this hulking relic of the early solar system. Measuring 350
miles across and containing almost 10% of the mass of the entire
asteroid belt, Vesta is a world unto itself.

"It's a big, rocky, terrestrial type body - more likely similar to the
moon and Mercury than to the little chips of rocks we've flown by in the
past," continues Rayman. "For example, there's a large crater at Vesta's
south pole, and inside the crater is a mountain bigger than asteroid Eros."

Dawn will orbit Vesta for a year, conducting a detailed study and
becoming the first spacecraft to ever orbit a body in the asteroid belt.
Later, Dawn will leave Vesta and go on to orbit a second exotic world,
dwarf planet Ceres--but that's another story.

Many scientists consider Vesta a protoplanet. The asteroid was in the
process of forming into a full fledged planet when Jupiter interrupted
its growth. The gas giant became so massive that its gravity stirred up
the material in the asteroid belt so the objects there could no longer
coalesce.

"Vesta can teach us a lot about how planets formed," says Christopher
Russell of UCLA, the mission's Principal Investigator. "There is a whole
team of scientists sitting on the edge of their seats waiting for that
first glimpse of Vesta."

Dawn's official Vestian approach, which Rayman also calls the "oh man
this is so cool phase" of the mission, begins next May. Unlike most
orbital insertions, however, this one will be comparatively relaxing.

"This may be the first planetary mission that doesn't cause its mission
team members to bite their nails while their spacecraft is getting into
planetary orbit," says Rayman.

A conventional spacecraft's entry into a flight path around a celestial
body is accompanied by crucial periods during which maneuvers must be
executed with pinpoint precision. If anything goes wrong, all can be
lost. But Dawn, with its gentle ion propulsion, slowly spirals in to its
target, getting closer and closer as it loops around.

"Dawn's entire thrust profile for its long interplanetary flight has
been devoted largely to the gradual reshaping of its orbit around the
Sun so that by the time the spacecraft is in the vicinity of Vesta, its
orbit will be very much like Vesta's."

With just a slight change in trajectory, the spacecraft will allow
itself to be captured by Vesta's gravity.

"Even that gentle ion thrust will be quite sufficient to let the craft
slip into orbit. It's like merging into traffic on an interstate - only
gradual acceleration is needed. Dawn won't even notice the difference,
but it will be in orbit around its first celestial target."

Dawn's first survey orbits will be high and leisurely, taking days to
loop around Vesta at altitudes of about 1700 miles. After collecting a
rich bounty of pictures and data from high altitude, Dawn will resume
thrusting, spiraling down to lower and lower orbits, eventually settling
in a little more than 100 miles high--lower than satellites orbiting Earth.

Parts of the surface may be reminiscent of features on Earth or the Moon
with craters and perhaps even volcanoes.

"We don't expect to see active volcanoes," notes Carol Raymond, the
mission's Deputy Principal Investigator at JPL, "but there could be
ancient volcanic features still recognizable among the craters."

Meanwhile, "other sights could be completely unlike anything we've
imagined," says Rayman. "It'll be pure excitement!"


Author: Dauna Coulter
Editor: Dr. Tony Phillips
Credit: Science at NASA
Received on Thu 19 Aug 2010 04:40:18 PM PDT