- 3717 - ASTEROID - what we learn with a visit? Astronomers have found more than 30,000 Near-Earth Asteroid. Astronomers think that most planet-killing asteroids have been found and have worked their way down to much smaller but still devastating impactors. Over 30,000 Near Earth Asteroids (NEAs) officially discovered.
--------------------- 3717 - ASTEROID - what we learn with a visit?
- Over 15,000 NEA’s have been discovered in the last ten years alone. A new improved instruments helps with that. The “Catalina Sky Survey” (CSS) is the most prolific, having been responsible for approximately 47% of all NEOs discovered. It continues to find a few new asteroids every week, but even so, it has dramatically improved its capabilities in recent years. In 2005, it found 310 new asteroids, whereas, in 2019, it found 1,067.
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- With those sensing capabilities, the CSS has been even more effective at finding smaller asteroids. Scientists are pretty sure they’ve found all the large space rocks that fit the definition of an NEA, that its orbit takes it at least within 1.3 AU of the Sun. “Large,” in this case, is quantified as a few kilometers in diameter which is enough to cause an extinction-level event if it were to hit Earth. One AU is 93,000,000 miles.
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- CSS has been concentrating on smaller rocks on the order of a few hundred meters in diameter. Being much smaller, these are also much harder to detect as they aren’t as bright in the night sky as their larger cousins. While these could still cause significant damage if they were to impact Earth, none appear to be on an immediate collision course for the next 100 years.
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- However, there are over 1,400 that have a “non-zero” chance of hitting Earth in the future. A team asteroid hunters stress that there isn’t any immediate danger, and we will have plenty of time to summon up a mission like the recently successful DART to push any threatening asteroid out of the way well before it causes any issues.
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- ESA maintains an “Asteroid Risk List” that keeps track of their orbits and the chances they will impact Earth. Hopefully, that won’t be useful for anything other than to keep track of potential sites for asteroid mining.
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- There is still a chance that the planetary defenders at ESA and elsewhere missed one. Or there might be a long-period metallic comet with no tail that could literally come out of the black directly on a collision course. The only way we can eliminate that possibility is by continually monitoring the sky and, when necessary, by taking action. This 30,000 NEA milestone is another successful step on that journey.
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- If the asteroid is not coming to us maybe we should go visit one of them. 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.
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- The researchers say that 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.
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- We expected the surface to be pretty rigid, kind of like if you touch down on a gravel pile But as we were bringing back the images after the event, we were stunned as they saw a giant wall of debris flying away from the sample side.
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- The impact aftermath was so unexpected that the team 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 the 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. There clearly was 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, 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 per cubic meter.
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- 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.
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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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- 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.
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- 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.
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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.
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- 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.
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October 17, 2022 ASTEROID - what we learn with a visit? 3717
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