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Why does the asteroid Bennu eject particles into space?




The asteroid, which is being studied by NASA’s OSIRIS-REx, exhibits surprising activity on its surface and scientists are beginning to understand what could be causing it.


When NASA’s OSIRIS-REx
the probe arrived at the asteroid (101955) Bennu, the mission scientists knew
their spaceship was orbiting something special. Not only was the boulder strewn with boulders
asteroid shaped like a rough diamond, its surface crackled with activity, falling
small pieces of rock in space. Now, after more than a year and a half
near Bennu, they are starting to better understand these dynamic particle ejections
events.

A collection of studies in a special edition of the Journal of
Geophysical Research: The planets are located on the asteroid and these are enigmatic
particles. The studies provide a detailed look at how these particles act when
in space, possible clues as to how they are ejected and even how their trajectories
can be used to approximate Bennu̵

7;s weak gravitational field.

Generally, we consider comets,
not asteroids, to be the active ones. Comets are made up of ice, rock and
dust. When those ices are heated by the sun, the vapor sizzles from the surface,
dust and pieces of the comet’s core are lost in space and a long dusty tail
forms. Asteroids, on the other hand, are composed mostly of rock and dust (and possibly
less ice), but it turns out that some of these space rocks can be surprisingly
also lively.

“We thought that of Bennu
the boulder-covered surface was the asteroid’s wild card discovery, but these
the particle events definitely surprised us, “said Dante Lauretta, OSIRIS-REx
principal investigator and professor at the University of Arizona. “We have
we have spent the last year investigating the Bennu active area, and it has been provided to us
with a remarkable opportunity to expand our knowledge of how active asteroids are
to behave.”

Cameras on OSIRIS-REx
(abbreviation of Origins, Spectral Interpretation, Resource Identification and Security-Regolith
Explorer) spotted rock particles repeatedly launched into space during a January 2019 investigation of the asteroid, which involves
one third of a mile (565 meters) wide at its equator.

One of the studies, led by NASA senior researcher Steve Chesley
Jet Propulsion Laboratory in Southern California found that most of these
pieces of rock about the size of a pebble, typically measuring about a quarter inch (7 millimeters),
were returned to Bennu under the asteroid’s weak gravity after a short jump,
sometimes even bouncing into space after colliding with the surface. Others
it took longer to return to the surface, remaining in orbit for a few days or more
at 16 turns. And some were expelled with enough grit to escape completely
from the surroundings of Bennu.

Using data collected by NASA’s OSIRIS-REx mission, this animation shows the trajectories of rock particles after they are ejected from the surface of the asteroid (101955) Bennu. Credit: M. Brozovic / NASA / JPL-Caltech / University of Arizona

Tracing the file
voyages of hundreds of ejected particles, including Chesley and his collaborators
able to better understand what could cause the launch of the particles
the surface of Bennu. The particle size corresponds to what is expected for the thermal
fracturing (as the surface of the asteroid is repeatedly heated and cooled as you
wheel), but the locations of the eject events also match the pattern
impact positions of meteoroids (small rocks that hit the surface of Bennu while
orbit around the Sun). It could also be a combination of these phenomena, he added
Chesley. But to arrive at a definitive answer, further observations are needed.

While their
the very existence raises numerous scientific questions, even the particles were needed
as high-fidelity probes of Bennu’s gravitational field. Many particles were orbiting
Bennu much closer than would be safe for the OSIRIS-REx probe, and so on
the trajectories were highly sensitive to Bennu’s irregular gravity. This
allowed researchers to estimate Bennu’s gravity even more precisely than
it was possible with the tools of OSIRIS-REx.

“The
particles have been an unexpected gravity science gift to Bennu ever since
it allowed us to see tiny variations in the gravity field of the asteroid that we would see
I didn’t know otherwise, ”Chesley said.

On average,
only one or two particles are excreted per day, and since they are found so much
low gravity environment, most moving slowly. As such, they pose little
threat to OSIRIS-REx, which will attempt to briefly land on the asteroid on October 20 to collect surface material, which
it can also include particles that were ejected before falling back into the file
surface.

If all goes as planned,
the spacecraft will return to Earth in September 2023 with a cache of Bennu’s material
for scientists to study further.

NASA’s Goddard space flight
The Greenbelt, Maryland center provides systems and general mission management
safety and mission engineering and assurance for OSIRIS-REx. Dante
Lauretta of the University of Arizona at Tucson is the principal investigator,
and the University of Arizona also leads the science and mission teams
scientific observation planning and data processing. Lockheed Martin Space in
Denver built the spacecraft and provides flight operations. Goddard and KinetX
Aerospace is responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx
it is the third mission of NASA’s New Frontiers program, which is managed by NASA
Marshall Space Flight Center in Huntsville, Alabama, for the Science agency
Directorate of the mission in Washington.

For more information on NASA
OSIRIS-REx, visit:

https://www.nasa.gov/osiris-rex

https://www.asteroidmission.org

Media contact

Ian J. O’Neill / DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-2649 / 818-393-9011
ian.j.oneill@jpl.nasa.gov / agle@jpl.nasa.gov

2020-174


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