[meteorite-list] Dawn Spacecraft Begins Approach to Dwarf Planet Ceres

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 29 Dec 2014 23:59:58 -0800 (PST)
Message-ID: <201412300759.sBU7xwv0015215_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?feature=4425

Dawn Spacecraft Begins Approach to Dwarf Planet Ceres
Jet Propulsion Laboratory
December 29, 2014

* Dawn has entered its approach phase toward Ceres
* The spacecraft will arrive at Ceres on March 6, 2015

NASA's Dawn spacecraft has entered an approach phase in which it will
continue to close in on Ceres, a Texas-sized dwarf planet never before
visited by a spacecraft. Dawn launched in 2007 and is scheduled to enter
Ceres orbit in March 2015.

Dawn recently emerged from solar conjunction, in which the spacecraft
is on the opposite side of the sun, limiting communication with antennas
on Earth. Now that Dawn can reliably communicate with Earth again, mission
controllers have programmed the maneuvers necessary for the next stage
of the rendezvous, which they label the Ceres approach phase. Dawn is
currently 400,000 miles (640,000 kilometers) from Ceres, approaching it
at around 450 miles per hour (725 kilometers per hour).

The spacecraft's arrival at Ceres will mark the first time that a spacecraft
has ever orbited two solar system targets. Dawn previously explored the
protoplanet Vesta for 14 months, from 2011 to 2012, capturing detailed
images and data about that body.

"Ceres is almost a complete mystery to us," said Christopher Russell,
principal investigator for the Dawn mission, based at the University of
California, Los Angeles. "Ceres, unlike Vesta, has no meteorites linked
to it to help reveal its secrets. All we can predict with confidence is
that we will be surprised."

The two planetary bodies are thought to be different in a few important
ways. Ceres may have formed later than Vesta, and with a cooler interior.
Current evidence suggests that Vesta only retained a small amount of water
because it formed earlier, when radioactive material was more abundant,
which would have produced more heat. Ceres, in contrast, has a thick ice
mantle and may even have an ocean beneath its icy crust.

Ceres, with an average diameter of 590 miles (950 kilometers), is also
the largest body in the asteroid belt, the strip of solar system real
estate between Mars and Jupiter. By comparison, Vesta has an average diameter
of 326 miles (525 kilometers), and is the second most massive body in
the belt.

The spacecraft uses ion propulsion to traverse space far more efficiently
than if it used chemical propulsion. In an ion propulsion engine, an electrical
charge is applied to xenon gas, and charged metal grids accelerate the
xenon particles out of the thruster. These particles push back on the
thruster as they exit, creating a reaction force that propels the spacecraft.
Dawn has now completed five years of accumulated thrust time, far more
than any other spacecraft.

"Orbiting both Vesta and Ceres would be truly impossible with conventional
propulsion. Thanks to ion propulsion, we're about to make history as the
first spaceship ever to orbit two unexplored alien worlds," said Marc
Rayman, Dawn's chief engineer and mission director, based at NASA's Jet
Propulsion Laboratory in Pasadena, California.

The next couple of months promise continually improving views of Ceres,
prior to Dawn's arrival. By the end of January, the spacecraft's images
and other data will be the best ever taken of the dwarf planet.

The Dawn mission to Vesta and Ceres is managed by JPL, a division of the
California Institute of Technology in Pasadena, for NASA's Science Mission
Directorate, Washington. UCLA is responsible for overall Dawn mission
science.

More information about Dawn:

http://dawn.jpl.nasa.gov

Media Contact
Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
Elizabeth.Landau at jpl.nasa.gov

2014-443
Received on Tue 30 Dec 2014 02:59:58 AM PST