Scientists study the rugged surface of near-Earth asteroid Bennu

Date:
October 8, 2020
Source:
Southwest Research Institute
Summary:
As the days count down to NASA's OSIRIS-REx spacecraft's
Touch-And-Go asteroid sample collection attempt, scientists
have determined what the spacecraft can expect to return from
the near-Earth asteroid Bennu's surface. Three papers discuss the
color, reflectivity, age, composition, origin and distribution of
materials that make up the asteroid's rough surface.



FULL STORY ==========================================================================
As the days count down to NASA's OSIRIS-REx spacecraft's Touch-And-Go
asteroid sample collection attempt, Southwest Research Institute
scientists have helped determine what the spacecraft can expect to
return from the near-Earth asteroid Bennu's surface. Three papers
published online by Science on Oct. 8 discuss the color, reflectivity,
age, composition, origin and distribution of materials that make up the asteroid's rough surface.


==========================================================================
On October 20, the spacecraft will descend to the asteroid's
boulder-strewn surface, touch the ground with its robotic arm for a
few seconds and collect a sample of rocks and dust -- marking the first
time NASA has grabbed pieces of an asteroid for return to Earth. SwRI scientists played a role in the selection of the sample sites. The first attempt will be made at Nightingale, a rocky area 66 feet in diameter in Bennu's northern hemisphere. If this historic attempt is unsuccessful,
the spacecraft will try again at a secondary site.

Since the spacecraft arrived at Bennu in 2018, scientists have been characterizing the asteroid's composition and comparing it to other
asteroids and meteorites. The mission discovered carbon-bearing compounds
on Bennu's surface, a first for a near-Earth asteroid, as well as minerals containing or formed by water. Scientists also studied the distribution
of these materials, globally and at the sample sites "Our recent studies
show that organics and minerals associated with the presence of water
are scattered broadly around Bennu's surface, so any sample returned to
Earth should contain these compounds and minerals," said SwRI's Dr.

Vicky Hamilton, a coauthor on all three papers. "We will compare the
sample's relative abundances of organics, carbonates, silicates and other minerals to those in meteorites to help determine the scenarios that
best explain Bennu's surface composition." Asteroid Bennu is a dark,
rubble pile held together by gravity and thought to be the collisional
remnant of a much larger main-belt object. Its rubble-pile nature and
heavily cratered surface indicates that it has had a rough-and- tumble
life since being liberated from its much larger parent asteroid millions
or even billions of years ago.

"Boulders strewn about near the Nightingale site have bright carbonate
veins," Hamilton said. "Bennu shares this compositional trait with
aqueously altered meteorites. This correlation suggests that at least
some carbonaceous asteroids were altered by percolating water in the
early Solar System." The boulders on Bennu have diverse textures and
colors, which may provide information about their variable exposure to micrometeorite bombardment and the solar wind over time. Studying color
and reflectance data provide information about the geologic history of planetary surfaces.

"Bennu's diverse surface includes abundant primitive material
potentially from different depths in its parent body plus a small
proportion of foreign materials from another asteroid family littered
about its surface," said SwRI's Dr. Kevin Walsh, a coauthor of one of
the papers. "In addition, both the primary and back-up sample sites, Nightingale and Osprey, are situated within small spectrally reddish
craters that are thought to be more pristine, having experienced less
space weathering than most of Bennu's bluish surface." The OSIRIS-REx
team is also comparing Bennu to Ryugu, another near-Earth asteroid. Both asteroids are thought to have originated from primitive asteroid families
in the inner main belt. The Japan Aerospace Exploration Agency launched Hayabusa2 in 2014 and rendezvoused with near-Earth asteroid Ryugu in
2018. After surveying the asteroid for a year and a half, the spacecraft collected samples and is expected to return to Earth December 6, 2020.

The sample returned by OSIRIS-REx, combined with the surface context maps OSIRIS-REx has collected, will improve interpretations of available ground
and space telescope data for other primitive dark asteroids. Comparing
returned Bennu samples with those of Ryugu will be instrumental for understanding the diversity within, and history of, asteroid families
and the entire asteroid belt.


========================================================================== Story Source: Materials provided by Southwest_Research_Institute. Note:
Content may be edited for style and length.


========================================================================== Journal References:
1. D. N. DellaGiustina, K. N. Burke, K. J. Walsh, P. H. Smith,
D. R. Golish,
E. B. Bierhaus, R.-L. Ballouz, T. L. Becker, H. Campins,
E. Tatsumi, K.

Yumoto, S. Sugita, J. D. Prasanna Deshapriya, E. A. Cloutis,
B. E. Clark, A. R. Hendrix, A. Sen, M. M. Al Asad, M. G. Daly,
D. M. Applin, C.

Avdellidou, M. A. Barucci, K. J. Becker, C. A. Bennett,
W. F. Bottke, J.

I. Brodbeck, H. C. Connolly, M. Delbo, J. de Leon, C. Y. Drouet
d'Aubigny, K. L. Edmundson, S. Fornasier, V. E. Hamilton, P. H.

Hasselmann, C. W. Hergenrother, E. S. Howell, E. R. Jawin,
H. H. Kaplan, L. Le Corre, L. F. Lim, J. Y. Li, P. Michel,
J. L. Molaro, M. C. Nolan, J. Nolau, M. Pajola, A. Parkinson,
M. Popescu, N. A. Porter, B. Rizk, J.

L. Rizos, A. J. Ryan, B. Rozitis, N. K. Shultz, A. A. Simon,
D. Trang, R.

B. Van Auken, C. W. V. Wolner, D. S. Lauretta. Variations in color
and reflectance on the surface of asteroid (101955) Bennu. Science,
2020; eabc3660 DOI: 10.1126/science.abc3660
2. H. H. Kaplan, D. S. Lauretta, A. A. Simon, V. E. Hamilton, D. N.

DellaGiustina, D. R. Golish, D. C. Reuter, C. A. Bennett,
K. N. Burke, H.

Campins, H. C. Connolly, J. P. Dworkin, J. P. Emery, D. P. Glavin,
T. D.

Glotch, R. Hanna, K. Ishimaru, E. R. Jawin, T. J. McCoy, N. Porter,
S. A.

Sandford, S. Ferrone, B. E. Clark, J.-Y. Li, X.-D. Zou, M. G. Daly,
O. S.

Barnouin, J. A. Seabrook, H. L. Enos. Bright carbonate veins
on asteroid (101955) Bennu: Implications for aqueous alteration
history. Science, 2020; eabc3557 DOI: 10.1126/science.abc3557
3. Amy A. Simon, Hannah H. Kaplan, Victoria E. Hamilton, Dante
S. Lauretta,
Humberto Campins, Joshua P. Emery, M. Antonietta Barucci,
Daniella N.

DellaGiustina, Dennis C. Reuter, Scott A. Sandford, Dathon
R. Golish, Lucy F. Lim, Andrew Ryan, Benjamin Rozitis,
Carina A. Bennett. Widespread carbon-bearing materials on
near-Earth asteroid (101955) Bennu. Science, 2020; eabc3522 DOI:
10.1126/science.abc3522 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201008170643.htm

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