[meteorite-list] Rosetta Visits Asteroid Lutetia to Unlock Its Secrets

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sun, 11 Jul 2010 11:17:40 -0700 (PDT)
Message-ID: <201007111817.o6BIHesU018804_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/news/n1007/10rosetta/

Rosetta visits mysterious asteroid to unlock its secrets
BY STEPHEN CLARK
SPACEFLIGHT NOW
July 10, 2010

Europe's Rosetta spacecraft flew less than 2,000 miles from asteroid
Lutetia Saturday, snapping pictures of the new world and collecting
bonus science on a primitive relic of the solar system.

Lutetia was unknown before the flyby, and scientists hoped Rosetta would
refine estimates of its size, chemical composition and origin.

Rosetta took more than 400 pictures of Lutetia, and the craft's other
instruments were programmed to map the asteroid's chemical make-up,
probe its interior and search for an atmosphere.

The first results from the flyby were from Rosetta's OSIRIS camera.

Check out a gallery <http://www.spaceflightnow.com/news/n1007/10lutetia/>
of images from Saturday's encounter.

"I'm startled by the images," said Rita Schulz, Rosetta's project
scientist at the European Space Agency. "These are fantastic and
exciting pictures, and we should not forget that these are just a few
images of all the data that will come down from this instrument, the
OSIRIS camera, and this is just one of the many instruments that
actually measured during this flyby."

Saturday's encounter made Lutetia the largest asteroid ever studied
up-close by a spacecraft.

The sharpest pictures of Lutetia appear to show grooves, landslides and
boulder fields, according to Holger Sierks, OSIRIS principal
investigator at the Max Planck Institute for Solar System Research in
Lindau, Germany.

"It's a new world discovered by Rosetta, and it will keep scientists
busy for years," Sierks said.

Engineers inside the European Space Operations Center in Germany
confirmed the flyby went as planned at 1610 GMT (12:10 p.m. EDT) Earth
time. It took more than 25 minutes for radio signals to travel across
the solar system from Rosetta, meaning the closest approach actually
occurred at 1544 GMT (11:44 a.m. EDT).

Rosetta was aiming for a point 1,965 miles from Lutetia and a relative
velocity of 33,500 mph. The flyby occurred more than 280 million miles
from Earth.

ESA unveiled the first high-resolution images of Lutetia in a ceremony
at 2100 GMT (5 p.m. EDT).

Flight planners added the Lutetia flyby to Rosetta's $1.2 billion
mission as an opportunity to gather ancillary science as the probe flies
toward comet Churyuomov-Gerasimenko. Rosetta will orbit the periodic
comet for more than a year, observing the icy body from orbit and
dropping a small lander to its surface.

"This is just the beginning," said David Southwood, ESA's director of
science and robotic exploration. "If this is the way the thing begins,
try and imagine how it's going to end. It is an historic day, Europe,
once again, proving that it can do major steps in solar system
exploration."

Rosetta also visited asteroid Steins in 2008, but the much larger
Lutetia offered a chance for ground-breaking science.

"Of the two asteroid flybys that we were able to sneak in on the way to
the comet, Lutetia has always been our main asteroid target because we
believe this will provide us with the most precious information about
how the planets have formed, and what the status of the material was
like during the period of planet formation," Schulz said before the flyby.

Despite its maximum diameter of about 80 miles, Lutetia's exact shape
and mineral make-up was still a mystery to scientists before Rosetta's
visit. The probe confirmed Lutetia has a slightly elongated shape, but
it will be several more weeks before scientists know its chemical
composition.

Lutetia was discovered in 1852, but the best pictures of the asteroid
from telescopes on Earth and in space only show a pixelated object.

The best guess is Lutetia is a C-type asteroid, meaning it has stayed
relatively untouched through most of the violent 4.6-billion-year
history of the solar system.

C-type asteroids are dark and rich in carbon and organic molecules.
Scientists believe they are leftover relics from the formation of the
solar system.

"If it does turn out to be a C-type, which we all hope, then we have a
large object which is rather pristine showing us what the solar system
was like shortly after the planets formed," said Rita Schulz, Rosetta's
project scientist, before the Saturday's flyby.

But some measurements suggest Lutetia could harbor metals, a signature
of an M-type asteroid. Schulz said metallic M-type asteroids formed from
rock from the interior of a larger body after massive collisions
fractured the parent object.

"It can't be, at the same time, a C-type and an M-type asteroid because
they are so different that it is not possible," Schulz said. "This is a
riddle that we can solve only by visiting this object because the
indications from all the observations we have right now are not
conclusive enough that anyone would dare to say this is for sure a
C-type asteroid."

Rosetta's task Saturday was to shed light on these fundamental questions.

The spacecraft was supposed to collect visible images of Lutetia, map
its surface with mineral-sniffing spectrometers, look for a thin
atmosphere, and study temperature variations on the asteroid. Rosetta
was also expected to determine Lutetia's density and search for a weak
magnetic field.

"If it does turn out to be a C-type, which we all hope, then we have a
large object which is rather pristine showing us what the solar system
was like shortly after the planets formed," Schulz said.

The Lutetia flyby was the final waypoint for Rosetta on the 10-year
voyage from Earth to Churyuomov-Gerasimenko.

Since its launch in 2004, Rosetta completed four gravity assists to bend
the robot's trajectory toward the comet, including three flybys of Earth
and a single visit to Mars.

Gerhard Schwehm, Rosetta's mission manager, said teams will spend the
next year preparing to put the 6,261-pound spacecraft into hibernation,
a power-saving deep sleep scheduled to last two-and-a-half years.

Controllers will power up all of Rosetta's science instruments later
this year to ensure they are healthy before hibernation. Some payloads
will also receive software updates, according to Schwehm.

"Hibernating a spacecraft for something like two years is a big deal,
and you want to make sure you can wake it up again," Schulz said.

As Rosetta spirals into the outer solar system, ground teams will test
its large solar panels in low-intensity mode, a special feature that
boosts the efficiency of the probe's power-production system as the
arrays collect less sunlight.

Rosetta's sensitive solar wings stretch 105 feet tip to tip, providing a
large collecting area for solar cells to convert weaker sunlight into
electricity.

Engineers also plan a lengthy deep space maneuver in January to put
Rosetta on course for Churyuomov-Gerasimenko. Four of Rosetta's
thrusters will change the probe's velocity by roughtly 1,767 mph,
according to Schwehm.

"We will have afterwards a very quiet period for the spacecraft that we
can monitor all the subsystems to be sure everything is OK and working
properly, and in June we will put Rosetta in hibernation," Schwehm told
Spaceflight Now.

Officials do not plan to wake up Rosetta during hibernation, partially
because the spacecraft will not have enough electricity to power all of
its systems at one time.

"We can't do a lot as we wouldn't have enough power to run the
spacecraft with all systems on to correct possible problems," Schwehm said.

Another large thruster burn is on tap for the spring of 2014, just after
Rosetta awakes from hibernation in the last few months before arrival at
the comet.

Rosetta should arrive close to Churyuomov-Gerasimenko in May 2014 and
enter orbit around the 2.5-mile wide comet nucleus as it approaches the
sun.

The spacecraft will deploy Germany's Philae lander to the surface of the
comet in early Novemer 2014, where it will send back images and data for
up to a week.

Rosetta will stay with the comet through 2015 as it passes near the sun,
mapping its dark surface and observing its changing characteristics as
it heats up and outgasses volatile compounds like water ice.
Received on Sun 11 Jul 2010 02:17:40 PM PDT