Meet asteroid 1999 RQ36, a chunk of rock and dust about 1,900
feet in diameter that could tell us how the solar system was born,
and perhaps, shed light on how life began. It also might hit us
someday.
"This asteroid is a time capsule from before the birth of our
solar system," said Bill Cutlip of NASA's Goddard Space Flight
Center in Greenbelt, Md., one of the leaders of Goddard's effort to
propose a mission called OSIRIS-REx that will return a sample from
RQ36.
If selected, Goddard will provide overall mission management for
OSIRIS-REx, working with the Principal Investigator, Dr. Michael
Drake, Director of the Lunar and Planetary Laboratory at the
University of Arizona, who will lead the OSIRIS-REx team. Lockheed
Martin Space Systems will build the spacecraft.
"You can't underestimate the value of a pristine sample," Cutlip
added. Meteorites, pieces of asteroids that break away and plunge
to Earth, are "toasted on their way through Earth's atmosphere,"
Cutlip explained. "Once they land, they then soak up the microbes
and chemicals from the environment around them."
"With a pristine sample - especially one from an asteroid type
not available in NASA's meteorite collections - scientists will
learn more about the time before the birth of our solar system, the
initial stages of planet formation, and the source of organic
compounds available for the origin of life," said Dr. Joseph Nuth
of NASA Goddard, OSIRIS-REx Project Scientist.
Asteroids are leftovers from the cloud of gas and dust –
the solar nebula -- that collapsed to form our sun and the planets
about 4.5 billion years ago. As such, they contain the original
material from the solar nebula, which can tell us about the
conditions of our solar system's birth.
In some asteroids, this material got altered by heat and
chemical reactions, either because they collided with other
asteroids, or because they grew so large that their interiors
became molten. That's what makes RQ36 special. It's small and
appears to have been altered very little, preserving the snapshot
of our solar system's infancy. It's also rich in carbon, an element
used in many of the organic molecules necessary for life. Organic
molecules have been found in meteorite and comet samples,
indicating that some of life's ingredients can be created in space.
Scientists want to see if they are also present in RQ36.
Sample return, however, isn't the only objective for the
mission. This asteroid crosses Earth orbit, and the International
Astronomical Union's Minor Planet Center has officially classified
RQ36 as a "potentially hazardous asteroid," with a slight chance
– one in 1,800 – of an impact in the year 2170.
"We'll orbit RQ36 for about a year to analyze its surface and
select a sample site. This will give us experience with operating
spacecraft in the vicinity of an asteroid, experience that will be
useful if we ever have to send a mission to deflect one," said
Nuth.
Piloting a spaceship near an asteroid is not easy. Most are
lumpy and rotate more rapidly than planets, which makes for
challenging landings. These small objects have feeble gravity, so
other forces can significantly influence the spacecraft's
position.
"Gravity on this asteroid is so weak, if you were on the
surface, held your arm out straight and dropped a rock, it would
take about half an hour for it to hit the ground. Pressure from the
sun's radiation and the solar wind on the spacecraft and the solar
panels is about 20 percent of the gravitational attraction from
RQ36. It will be more like docking than landing," adds Nuth.
The mission will also help to better track the orbits of
asteroids that might hit Earth by accurately measuring the
"Yarkovsky effect" for the first time. The Yarkovsky effect is a
small push on an asteroid that happens when the asteroid absorbs
sunlight and emits heat. The small push adds up over time, and it
is uneven due to an asteroid's various surface materials, wobble,
and rotation. There's no sure way to predict an Earth-approaching
asteroid's orbit unless you can factor in how the Yarkovsky effect
will change that orbit, according to the team. "It's like trying to
make a complex, banking shot in a game of pool with someone shaking
the table and kicking the legs," said Nuth.
"OSIRIS-REx" spells out what the mission will do. "O" stands for
the scientific theme, origins, as in the origin of life. "SI" is
for spectral interpretation, or taking images of the RQ36 at
wavelengths that will reveal its composition. "RI," or resource
identification, is surveying the asteroid for such useful resources
as water and metals. "S" stands for security, learning how to
predict the detailed motion of Earth-approaching asteroids. REx
stands for "Regolith Explorer". Regolith is a layer of broken-up
rock and dust, formed by meteorite impacts, which covers the
surface of many asteroids and moons in our solar system.
If approved, the mission will be significantly more capable than
the original OSIRIS proposal. "OSIRIS was a basic sample return
mission," says Nuth. "OSIRIS-REx adds more instruments to give us a
complete map of the surface composition and 3-D shape, or
topography, of the asteroid. It will allow us to put our sample in
the proper geologic context, so we'll have a much better idea of
what we're really sampling," says Nuth.
Additional instruments include a mass spectrometer, which
separates and identifies atoms and molecules based on their weight
and electric charge. The mass spectrometer will be built at NASA
Goddard.
Two infrared spectrometers will also be added. Infrared light is
invisible to the human eye, but we perceive it as heat, and it can
be measured by special instruments. These spectrometers will
separate the infrared light into its component "colors," or
wavelengths, like a prism separates white light into a rainbow.
Each element and molecule on the asteroid will emit or absorb a
unique combination of infrared wavelengths, creating a specific
signal in the spectrometer that will be used to identify it.
Goddard will provide one of the spectrometers, the Visible to
Near-Infrared spectrometer, and Arizona State University will
provide the other, called the OSIRIS Thermal Emission
Spectrometer.
The mission will also feature a more precise and accurate LIDAR
(Light Detection And Ranging) instrument. This instrument will
bounce laser pulses off the surface of the asteroid to measure its
topography. The OSIRIS Laser Altimeter will be provided by
MacDonald, Dettwiler and Associates Ltd., Richmond, British
Columbia, Canada, and funded by the Canadian Space Agency.
Once the asteroid has been completely analyzed from orbit, the
science team will pick the location to take a sample. OSIRIS-REx
will be gradually brought closer to the site, and an arm with a
sampling mechanism at the end will be extended to touch the surface
and collect the sample.
The sample will be stored in a capsule and returned to Earth,
slowing its final descent through the lower atmosphere with a
parachute like the successful Stardust capsule that returned
samples of comet Wild 2 on January 15, 2006.
"Like the Moon rocks from the Apollo missions, samples of RQ36
will keep on giving. They'll be analyzed for decades after mission
is complete, using new techniques we can't even imagine now, to
test new theories of how we came to be," said Nuth.
OSIRIS-REx was one of three proposals selected by NASA on
December 29, 2009 for more study under its New Frontiers program.
NASA Goddard received $3.3 million for a 12-month study to develop
the concept in more detail, called the "Phase A Concept Study
Effort". After the detailed mission concept studies are completed
and reviewed, NASA will select one of the three to be built. The
selected mission must be ready for launch no later than December
30, 2018 and must not exceed $650 million, excluding the cost of
the launch vehicle. In addition to the two instruments mentioned
above, Goddard will also provide overall mission management,
systems engineering, and safety and mission assurance.
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