- 4186 - ASTEROID - mission to sample Bennu? Asteroid Bennu is nothing like scientists expected. The surface was soft and flowed away like a fluid. 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.
---------------------
4186 - ASTEROID
- mission to sample Bennu?
-
- The researchers say
that the findings from Bennu 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 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 we were bringing back the images after
the event saw 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.
-
- 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 scientists 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 with 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.
-
- 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.
-
- Samples of asteroid
Bennu delivered by the OSIRIS-REx mission include carbon, water and other
ingredients of the primordial Solar System.
Pieces of the asteroid Bennu, brought back to Earth in September by
NASA’s OSIRIS-REx spacecraft, include crumbly rocks and dust that contain water
and carbon, some of the building blocks of life on Earth.
-
- The Bennu sample
includes clay minerals with water trapped inside their crystal structure,
bright and dark dust grains that look like flecks of salt and pepper, and
sulfur-rich minerals like those that might have played a key part in planetary
evolution. The pristine sample material
from Bennu represents a valuable resource providing a window into the early
Solar System.
-
- This bounty of
materials comes from the outer surface of OSIRIS-REx’s sample canister. Researchers are particularly excited about
the Bennu sample because the spacecraft’s heat shield kept the material cold on
its journey back to Earth. Otherwise the heat of passing through the Earth’s
atmosphere might have altered the sample’s chemistry, just as it can distort
the chemical record contained within meteorites.
-
- Scientists had
known that Bennu is a carbon-rich asteroid, but early analysis suggests that
some of the returned sample is as much as 4.7% carbon, among the highest
percentages of extraterrestrial carbon ever measured. Some of that carbon is
bound up in carbonate minerals, which are made primarily of carbon and oxygen
and are common in geological samples on Earth.
-
- Bennu also contains
organic material made of compounds incorporating carbon and hydrogen. On Earth,
organic compounds are found in living organisms, but, also in the absence of
life. Under ultraviolet light, organic patches in the Bennu samples light up
like a holiday tree.
-
- The clay samples
from Bennu look like tiny fibers in electron microscopy images. Water locked
inside those clay minerals might be ancient water from the dawn of the Solar
System. Asteroids might have carried such water to the early Earth and helped
to make it habitable.
-
- Other microscopy
images show hexagonal crystals that are likely sulfur-rich. Sulfur compounds
play a crucial role in determining the rate at which rocks melt, as well as
being involved in biologically interesting chemical reactions. The Bennu
samples also contain iron-rich minerals with large flat surfaces, which might
have helped catalyze chemical reactions early in the asteroid’s history.
-
- At least one of the
rocks in the Bennu sample is crumbly and hummocky-looking, similar to the
boulders that dominate Bennu’s rubbly surface. There are also examples of both
dark-colored and light-colored rocks, as scientists had suspected might be on
Bennu. The light colors might represent areas altered by water early in Bennu’s
history.
-
- When OSIRIS-REx
stretched out its robotic arm in 2020 to collect material from the asteroid’s
surface, it came away with so much material that it overflowed the collecting
mechanism.
-
- However much it
ultimately ends up being, it will be the most material to come back from outer
space since the Apollo astronauts brought Moon rocks to Earth in the 1960s and
1970s. Japan’s two Hayabusa missions, which both flew to asteroids and came
back with samples, together brought back a teaspoon of material at most.
-
-
October 12, 2023 ASTEROID -
mission to sample Bennu? 4186
------------------------------------------------------------------------------------------
-------- Comments
appreciated and Pass it on to whomever is interested. ---
--- Some reviews are
at: -------------- http://jdetrick.blogspot.com -----
-- email feedback,
corrections, request for copies or Index of all reviews
--- to: ------
jamesdetrick@comcast.net
------ “Jim Detrick” -----------
--------------------- ---
Saturday, October 14, 2023 ---------------------------------
No comments:
Post a Comment