- 4179 -
BENNU ASTEROID -
visited by spacecraft.
Dramatic sampling shows asteroid Bennu is nothing like scientists
expected. The surface was soft and
flowed away like a fluid. NASA's
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.
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---------------------
4179 - BENNU
ASTEROID - visited by spacecraft.
-
- These 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.
-
- They expected the
surface to be pretty rigid, kind of like if you touch down on a gravel pile: a
little bit of dust flying away and a few particles jumping up. But as they were bringing back the images
after the event they saw a giant wall of debris flying away from the sample
side.
-
- The impact
aftermath was so unexpected that the decided to have the spacecraft revisit the
area to understand what happened. 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.
-
- But the spacecraft
sunk in. 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.
-
- The surface
boulders are very porous and there is a lot of void space between them. They
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.
-
- Scientists assume
that many asteroids sport a similar "rubble pile" structure. They are 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. And, 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
get theur OSIRIS-REx's samples delivered in September, 2023. 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.
-
-
October 5, 2023 BENNU
ASTEROID - visited by spacecraft. 4179
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