- 3630 - ASTEROID BENNU - learn from a visit? - We sent a satellite to visit the asteroid “Bennu“. It was not the space rock we expected to find. When the satellite arrived it unleashed an unexpected explosion trying to touch down on asteroid.
--------------------- 3630 - ASTEROID BENNU - learn from a visit?
- This is the mission to asteroid Bennu launched in October 2020. It was to collect a sample from the asteroid and carry it home to Earth for analysis.
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- The researcher’s findings might have implications for a possible future deflection mission. The 1,640-feet-wide Bennu is one of the riskiest known near-Earth asteroids ever threaten to impact the planet.
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- Researchers 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. Instead the images after the event saw a giant wall of debris flying away from the sample side.
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- The impact aftermath was so unexpected that researchers wanted the spacecraft to revisit the area to understand what happened. Six months after sample collection, in April 2021, the researchers got another glimpse of this OSIRIS-REx touchdown site.
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- 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.
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- 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 we sunk in with no resistance whatsoever. The surface was soft and flowed away like a fluid.
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- 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.
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- From the measurements acquired during this repeat visit researchers 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.
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- The surface boulders were very porous and there was a lot of void space between them. Researchers 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.
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- 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.
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- Scientists now 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.
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- 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.
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- 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.
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- 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.
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- This “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.
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- What interesting times we live in. There is so much to learn. We humans should focus on that instead of destroying each other. This is the only planet we have to live on.
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July 17, 2022 ASTEROID BENNU - learn from a visit? 3630
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