Orbit Around Second-Most Massive Object In Asteroid Belt
Achieved Friday Night
NASA's Dawn spacecraft has returned the first close-up image
after beginning its orbit around the giant asteroid Vesta. On
Friday, July 15, Dawn became the first probe to enter orbit around
an object in the main asteroid belt between Mars and Jupiter.
Vesta Asteroid From Orbit
The image taken for navigation purposes shows Vesta in greater
detail than ever before. When Vesta captured Dawn into its orbit,
there were approximately 9,900 miles between the spacecraft and
asteroid. Engineers estimate the orbit capture took place at 2000
PDT.
Vesta is 330 miles in diameter and the second most massive
object in the asteroid belt. Ground- and space-based telescopes
have obtained images of Vesta for about two centuries, but they
have not been able to see much detail on its surface. "We are
beginning the study of arguably the oldest extant primordial
surface in the solar system," said Dawn principal investigator
Christopher Russell from the University of California, Los Angeles.
"This region of space has been ignored for far too long. So far,
the images received to date reveal a complex surface that seems to
have preserved some of the earliest events in Vesta's history, as
well as logging the onslaught that Vesta has suffered in the
intervening eons."
Vesta is thought to be the source of a large number of
meteorites that fall to Earth. Vesta and its new NASA neighbor are
currently approximately 117 million miles (188 million kilometers)
away from Earth. The Dawn team will begin gathering science data in
August. Observations will provide unprecedented data to help
scientists understand the earliest chapter of our solar system. The
data also will help pave the way for future human space
missions.
After traveling nearly four years and 1.7 billion miles, Dawn
also accomplished the largest propulsive acceleration of any
spacecraft, with a change in velocity of more than 4.2 miles per
second (6.7 kilometers per second), due to its ion engines. The
engines expel ions to create thrust and provide higher spacecraft
speeds than any other technology currently available. "Dawn slipped
gently into orbit with the same grace it has displayed during its
years of ion thrusting through interplanetary space," said Marc
Rayman, Dawn chief engineer and mission manager at NASA's Jet
Propulsion Laboratory (JPL) in Pasadena, Calif. "It is
fantastically exciting that we will begin providing humankind its
first detailed views of one of the last unexplored worlds in the
inner solar system."
Although orbit capture is complete, the approach phase will
continue for about three weeks. During approach the Dawn team will
continue a search for possible moons around the asteroid; obtain
more images for navigation; observe Vesta's physical properties;
and obtain calibration data. In addition, navigators will measure
the strength of Vesta's gravitational tug on the spacecraft to
compute the asteroid's mass with much greater accuracy than has
been previously available. That will allow them to refine the time
of orbit insertion.
Dawn will spend one year orbiting Vesta, then travel to a second
destination, the dwarf planet Ceres, arriving in February 2015.