The
asteroid belt's largest bodies have drifted virtually alone since their
creation about 4.5 billion years ago, but each will soon receive a visit from
NASA's Dawn spacecraft.
Mission
scientists hope to use Dawn's
observations of the dwarf planet Ceres and asteroid Vesta to investigate
the solar system's structure and evolution, as well as shed new light on secrets
of planet formation.
"We
truly are going back in time, back to the dawn of the solar system," said
David Lindstrom, NASA's Dawn
program scientist at the
agency's Washington, D.C., headquarters, during a July mission briefing.
Dawn is set
to rocket into space from Florida's Cape Canaveral Air Force Station on Thursday at 7:20 a.m. EDT
(1120 GMT) aboard a Delta 2 booster. The launch will send the 2,685-pound
(1,218-kilogram) Dawn spacecraft on
an eight-year journey to the asteroid-rich zone between Mars and Jupiter.
Its launch
was scheduled for Wednesday, but bad weather prevented crews from fueling the second stage of the
probe's Delta 2
rocket on Sunday, prompting the 24-hour delay. Delays launching Dawn's $449 million mission
earlier this summer were expected to add about $25 million to the probe's total
cost, mission managers have said.
Sibling
satellites
Together,
Ceres and Vesta make up more than a third of the asteroid belt's mass. During Dawn's total 3-billion-mile
(4.9-billion-kilometer) trip, it will make an orbital pit stop at each of the two
rocky bodies before the mission ends in July 2015.
The
spacecraft's first visit is set for August 2011, when it will park itself
around Vesta--an oblong asteroid 330 miles (530 kilometers) in diameter that
hides an iron core beneath its rocky surface. The spacecraft will gradually
scan the dry rock's exterior during a 10-month visit, helping scientists to
investigate how planets like Mars might have looked early in their
formation.
"It's
sort of like an archaeological trip where we're going to the ruins of an
ancient civilization," said Chris Russell, Dawn's principal investigator
at the University of California, Los Angeles.
Once Dawn
has fully scoped out the arid asteroid, it will put its lightweight ion drive
in full gear to reach the Ceres, a Texas-sized dwarf planet roughly 585 miles
(942 kilometers) in
diameter, by February 2015.
Based on
observations made by the Hubble Space Telescope, astronomers think Ceres may harbor not
only a thin atmosphere, but also a thick layer of water ice beneath its
surface. If true, Ceres may boast nearly six times as much fresh water than is
found on Earth.
"If we
discover evidence of a subsurface ocean, than certainly it would be a high
priority to go back and explore in more detail," said Mark Sykes, a Dawn
co-investigator at the Planetary Science Institute in Tucson, Ariz.
In addition
to providing for life on Earth, astronomers think such sources of water could
have played integral roles in planet formation.
To study
the asteroid belt's two biggest satellites, Dawn will use three different
instruments: a large optical camera, a mapping spectrometer and a neutron and
gamma-ray detector (GRaND).
The optical
camera will create detailed maps of each body down to 230 feet (70 meters) per pixel for Vesta and 410 feet (125 meters) per
pixel for Ceres. Working in less detail, Dawn's mapping spectrometer will scan
each object's surface for patches of minerals.
The GRaND
instrument will use celestial radiation to deduce the basic elements present in
both Ceres and Vesta. If the instrument can peer deep enough below Ceres'
surface, signs of frozen or liquid water may be detected.
Highs
and lows
NASA first
approved the Dawn mission in 2001, but the program has since suffered
cancellations, postponements and several launch delays. Attempts to launch the probe in July went without
success due to bad weather, rocket booster glitches and difficulties arranging
tracking aircraft and ships to monitor the planned liftoff.
Technical and financial woes prompted
NASA to order the mission to stand in October 2005 and ultimately scrap the
flight in March 2006. But a reevaluation of the Dawn mission's difficulties by
the space agency led
to its reinstatement a few weeks after its cancellation.
In spite of
recent accidental damage to the spacecraft's solar panel array and several
delays this year, mission managers are confident Dawn will successfully begin
its journey on Thursday.
Should mission managers delay the probe's launch again, they will have until
late October to send Dawn spaceward; otherwise, the first launch opportunity to
visit both Ceres and Vesta won't open again until about 2022.
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