- 3972 - BENNU ASTEROID - sample returns September, 2023. The OSIRIS-REx mission unleashed an unexpected explosion when it touched down on asteroid Bennu in October 2020 to collect a precious sample to carry home to Earth.
----------------- 3972 - BENNU ASTEROID - sample returns September, 2023.
- Mission
scientists have described the dramatic sample retrieval, which led to
surprising discoveries about the asteroid's nature. The findings might have implications for a
possible future deflection mission, should the 1,640-feet-wide Bennu one of the
riskiest known near-Earth asteroids ever threaten to impact the planet.
-
- We expected
the surface to be pretty rigid, like touching down on a gravel pile A little bit of dust flying away and a few
particles jumping up. But, the images
after the event showed a giant wall of debris flying away from the sample side.
-
- Six months
after sample collection, in April 2021, the researchers got another glimpse of
the OSIRIS-REx touchdown site. When the spacecraft first arrived at Bennu, that
site, called “Nightingale”, sat within a 65-foot-wide impact crater. After
touchdown, mission scientists found a brand new 26-foot-wide gaping hole in the
surface, with displaced rubble and boulders scattered around the site.
-
- That's a
surprisingly large scar; scientists had expected to scoop out a bit about as
wide as the sample collector itself, 12 inches. "But, there clearly was no
resistance whatsoever. The surface was soft and flowed away like a fluid.
-
- The probe
sank as deep as 30 inches, revealing pristine material that, unlike the
asteroid's surface, was unaltered by the steady battering of cosmic rays and
the solar wind, the streams of high-energy particles from the sun.
-
- From the
measurements acquired during this repeat visit, they calculated that the
density of the surface material was only about 31 to 44 pounds per cubic
foot. For comparison, "a typical
Earth rock" has a density about six times higher, more like 190 pounds per
cubic foot per cubic meter.
-
- A second
study, based on measurements of forces exerted on the probe during the impact,
confirmed those numbers. The surface
boulders are very porous and there is a lot of void space between them.We
expected that small, fine grains and dust would stick to the large boulders and
fill the void space and act as a glue to provide some strength, which would
allow the surface to push back against the spacecraft more. But it's not there.
-
- Bennu's
soft, fluffy nature may complicate a possible future deflection attempt, should
astronomers determine the rock threatens to hit Earth. At 1,640 feet wide, a
strike by Bennu would cause continent-wide disruption on our planet. And even
though NASA estimates the chance of collision at 1 in 2,700 between the years
2175 and 2199, Bennu is still one of the most dangerous asteroids currently
known.
-
- Moreover,
scientists assume that many asteroids sport a similar "rubble pile"
structure: essentially conglomerations of rock, gravel and dirt held together
by weak gravitational forces. The sampling experiment at Bennu shows that it's
almost impossible to predict how such a rubble pile might respond to an impact.
-
- The
touchdown did provide the first experience of really pressing something into
the surface. If we ever go and actually
try to deflect something like this, we would need to know what the surface is
like so that it doesn't just absorb the impact.
-
- The
underground material appeared more red compared to the bluish surface of Bennu,
which suggests that cosmic rays and other forms of space weather erode the
exposed space rocks. The reddish hues hint that organic molecules, like
hydrocarbons, may be present inside the asteroid, which greatly interests
researchers trying to understand the origins of life on Earth.
-
- The
scientists will have to wait until OSIRIS-REx's scheduled delivery in September
2023 to get their hands on the precious material. During the dramatic sampling
attempt, the probe collected almost 9 ounces of asteroid dust, which is
somewhat less than the teams had hoped for but still four times more than they
need to conduct the analysis.
-
- The
OSIRIS-REx mission was recently extended and after the spacecraft drops off its
cargo at Earth next year, it will head to Apophis, another high-risk asteroid,
which it will visit in 2029.
-
April 24, 2023 3972
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