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Latest news in Yorkshire: Published March 20, 2019 09:26:45 AM
A NASA spacecraft that will return a sample of a near-Earth asteroid
named Bennu to Earth in 2023 made the first-ever close-up observations
of particle plumes erupting from an asteroid’s surface. Bennu also
revealed itself to be more rugged than expected, challenging the mission
team to alter its flight and sample collection plans, due to the rough
terrain.
Bennu is the target of NASA’s Origins, Spectral Interpretation, Resource
Identification, Security-Regolith Explorer (OSIRIS-REx) mission, which
began orbiting the asteroid on Dec. 31. Bennu, which is only slightly
wider than the height of the Empire State Building, may contain
unaltered material from the very beginning of our solar system.
“The discovery of plumes is one of the biggest surprises of my
scientific career,” said Dante Lauretta, OSIRIS-REx principal
investigator at the University of Arizona, Tucson. “And the rugged
terrain went against all of our predictions. Bennu is already surprising
us, and our exciting journey there is just getting started.”
Shortly after the discovery of the particle plumes on Jan. 6, the
mission science team increased the frequency of observations, and
subsequently detected additional particle plumes during the following
two months. Although many of the particles were ejected clear of Bennu,
the team tracked some particles that orbited Bennu as satellites before
returning to the asteroid’s surface.
The OSIRIS-REx team initially spotted the particle plumes in images
while the spacecraft was orbiting Bennu at a distance of about one mile
(1.61 kilometers). Following a safety assessment, the mission team
concluded the particles did not pose a risk to the spacecraft. The team
continues to analyze the particle plumes and their possible causes.
“The first three months of OSIRIS-REx’s up-close investigation of Bennu
have reminded us what discovery is all about – surprises, quick
thinking, and flexibility,” said Lori Glaze, acting director of the
Planetary Science Division at NASA Headquarters in Washington. “We study
asteroids like Bennu to learn about the origin of the solar system.
OSIRIS-REx’s sample will help us answer some of the biggest questions
about where we come from.”
OSIRIS-REx launched in 2016 to explore Bennu, which is the smallest body
ever orbited by spacecraft. Studying Bennu will allow researchers to
learn more about the origins of our solar system, the sources of water
and organic molecules on Earth, the resources in near-Earth space, as
well as improve our understanding of asteroids that could impact Earth.
The OSIRIS-REx team also didn’t anticipate the number and size of
boulders on Bennu’s surface. From Earth-based observations, the team
expected a generally smooth surface with a few large boulders. Instead,
it discovered Bennu’s entire surface is rough and dense with boulders.
The higher-than-expected density of boulders means that the mission’s
plans for sample collection, also known as Touch-and-Go (TAG), need to
be adjusted. The original mission design was based on a sample site that
is hazard-free, with an 82-foot (25-meter) radius. However, because of
the unexpectedly rugged terrain, the team hasn’t been able to identify a
site of that size on Bennu. Instead, it has begun to identify candidate
sites that are much smaller in radius.
The smaller sample site footprint and the greater number of boulders
will demand more accurate performance from the spacecraft during its
descent to the surface than originally planned. The mission team is
developing an updated approach, called Bullseye TAG, to accurately
target smaller sample sites.
“Throughout OSIRIS-REx’s operations near Bennu, our spacecraft and
operations team have demonstrated that we can achieve system performance
that beats design requirements,” said Rich Burns, the project manager of
OSIRIS-REx at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
“Bennu has issued us a challenge to deal with its rugged terrain, and we
are confident that OSIRIS-REx is up to the task.”
The original, low-boulder estimate was derived both from Earth-based
observations of Bennu’s thermal inertia – or its ability to conduct and
store heat – and from radar measurements of its surface roughness. Now
that OSIRIS-REx has revealed Bennu’s surface up close, those
expectations of a smoother surface have been proven wrong. This suggests
the computer models used to interpret previous data do not adequately
predict the nature of small, rocky, asteroid surfaces. The team is
revising these models with the data from Bennu.
The OSIRIS-REx science team has made many other discoveries about Bennu
in the three months since the spacecraft arrived at the asteroid, some
of which were presented Tuesday at the 50th Lunar and Planetary
Conference in Houston and in a special collection of papers issued by
the journal Nature.
The team has directly observed a change in the spin rate of Bennu as a
result of what is known as the Yarkovsky-O’Keefe-Radzievskii-Paddack
(YORP) effect. The uneven heating and cooling of Bennu as it rotates in
sunlight is causing the asteroid to increase its rotation speed. As a
result, Bennu’s rotation period is decreasing by about one second every
100 years. Separately, two of the spacecraft’s instruments, the MapCam
color imager and the OSIRIS-REx Thermal Emission Spectrometer (OTES),
have made detections of magnetite on Bennu’s surface, which bolsters
earlier findings indicating the interaction of rock with liquid water on
Bennu’s parent body.
Goddard provides overall mission management, systems engineering, and
the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the
University of Arizona, Tucson, is the principal investigator, and the
University of Arizona also leads the science team and the mission’s
science observation planning and data processing. Lockheed Martin Space
in Denver built the spacecraft and is providing flight operations.
Goddard and KinetX Aerospace are responsible for navigating the
OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New
Frontiers Program, which is managed by NASA’s Marshall Space Flight
Center in Huntsville, Alabama, for the agency’s Science Mission
Directorate in Washington.
To find out more about the OSIRIS-REx mission, visit:
https://www.nasa.gov/osiris-rex
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[tags nasa, space, asteroid]