APOD: 2020 September 16 – Gravel Ejected from Asteroid Bennu




APOD: 2020 September 16 – Gravel Ejected from Asteroid Bennu<br />

Discover the cosmos!
Each day a different image or photograph of our fascinating universe is
featured, along with a brief explanation written by a professional astronomer.

2020 September 16


See Explanation.  Clicking on the picture will download
the highest resolution version available.


Gravel Ejected from Asteroid Bennu
Image Credit:
NASA‘s
GSFC,
U. Arizona,
OSIRIS-REx
Lockheed Martin

Explanation:
Why does asteroid Bennu eject gravel into space?

No one is sure.

The discovery,
occurring during several episodes by
NASA‘s visiting
OSIRIS-REx spacecraft, was unexpected.

Leading ejection hypotheses include impacts by Sun-orbiting
meteoroids,
sudden thermal fractures
of internal structures, and the
sudden release of a water vapor jet.

The
featured two-image composite shows an ejection event that occurred in early 2019,
with sun-reflecting ejecta seen on the right.

Data and simulations show
that large gravel typically falls right back to the rotating 500-meter asteroid,
while smaller rocks skip around the surface,
and the smallest rocks completely escape the low gravity of the Earth approaching, diamond-shaped asteroid.

Jets and surface ejection events
were thought to be predominantly the domain of comets,
responsible for their
tails,
comas, and later
meteor showers on Earth.

Robotic OSIRIS-REx arrived at
101955 Bennu in late 2018, and is
planned to touchdown
to collect a surface sample in October 2020.

If all goes well, this sample will then be returned to Earth for a
detailed analysis during 2023.

Bennu was chosen as the destination for
OSIRIS-REx in part because its surface shows potential to reveal
organic compounds from the
early days of
our Solar System, compounds that could have been the building blocks for
life on Earth.


Experts Debate:
How will humanity first discover extraterrestrial life?
Tomorrow’s picture: cycle 25


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Authors & editors:
Robert Nemiroff
(MTU) &
Jerry Bonnell (UMCP)
NASA Official: Phillip Newman
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A service of:
ASD at
NASA /
GSFC

& Michigan Tech. U.



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