Monday, January 30, 2023

3852 - ASTEROIDS - threaten our planet?


            -  3852  -      ASTEROIDS  -  threaten our planet?    Asteroids hanging around Earth?   Scientists are discovering new near-Earth asteroids practically daily, with more than 27,000 identified to date.

           


            --------------------  3852  -   ASTEROIDS  -  threaten our planet?

            -    Just how many space rocks out there actually threaten our planet?  NASA knows of zero asteroids large enough to do meaningful damage on Earth and currently on track to collide with our planet in the foreseeable future.

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            -    But large asteroids hanging around Earth?   Scientists are discovering new near-Earth asteroids practically daily, with more than 27,000 identified to date.

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            -     There is no known threat right now to Earth.   And while it may seem paradoxical, the constant rise in near-Earth asteroid tallies turns out to be the best news possible if you're worried about a potential asteroid impact.

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            -  The art of protecting Earth from an asteroid impact is called planetary defense, and there are two key stages to the process. NASA's Double Asteroid Redirection Test (DART), launching in Feruary, 2023, is a mission designed to test the second stage of planetary defense, diverting a threatening asteroid from crossing paths with Earth.

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            -    But before anyone can even try to divert an asteroid, scientists have to find the space rock and map out its orbit many years into the future to realize that it will or may hit Earth.

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            -    Keeping track of the actual asteroids, identifying them and finding them is really crucial toward being able to do anything about them in the future. Scientists have identified some 750,000 asteroids to date, but suspect there are millions of space rocks ricocheting through the full solar system.

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            -    Near  Earth that number comes down somewhat: Scientists have identified more than 27,000 near-Earth asteroids, with new ones spotted daily.  Those discoveries are thanks to a team of instruments on Earth and in space that dedicate some or all of their time to spotting and cataloging asteroids. The vast majority of these discoveries have come since the late 1990s.

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            -    The Catalina Sky Survey based in Arizona specializes in catching smaller asteroids, the Pan-STARRS observatory in Hawaii that excels at spotting faint objects, the NEOWISE space telescope that can see the whole sky and the ATLAS telescopes in Hawaii that are tuned to the fastest-moving objects.

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            -    Wide-field survey telescopes are set up for other purposes like for astrophysics investigations for instance, and then they end up getting the asteroids that photobomb them.

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            -    The Vera C. Rubin Observatory in Chile begin observing in 2023; a space-based mission called NEO Surveyor is also in development and scheduled to launch later this decade.

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            -    Potentially hazardous asteroid identified by early 2013, more than 1,400 objects in total. Today, scientists track more than 2,000 potentially hazardous asteroids.

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            -     If all those observations find that an asteroid is over a certain brightness  and will come within 4.65 million miles of Earth, the object is automatically dubbed a "potentially hazardous asteroid." (The distance works out to one-twentieth of the average distance between Earth and the sun.)

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            -    But in most cases, despite the ominous terminology, "potentially hazardous asteroids" may as well be called "not currently hazardous asteroids." After all, these are the objects that scientists have already found, and followed, and mapped, and forecast into the future.

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            -    Scientists believe they've found nearly all the largest asteroids, those larger than 3,300 feet (1 km) across. and know that these are the easiest to find anyway. And while tiny near-Earth asteroids are plentiful and difficult to find, they are also the most likely to fall apart harmlessly in Earth's atmosphere.

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            -    So it's the middle size category of asteroids, those more than 460 feet but less than 3,300 feet wide that most worries planetary defense experts.  As of the end of 2020, estimates suggested scientists have found just 40% of near-Earth objects of this size; this year has added 500 to the tally.

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            -    NASA's planetary defense office estimates that at the current pace, it will take scientists 30 more years to have identified 90% of objects this size.

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            -    The asteroid Itokawa is a pile of rocky debris 1,640 feet long.  It is peanut-shaped.  Astronomers have found that Itokawa is like a giant space cushion, and very hard to destroy.   They calculated Itokawa's age using specks of asteroid dust that were scooped by the Japanese Hayabusa spacecraft and brought back to Earth in 2010.

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            -    Itokawa is almost as old as the solar system itself. Itokawa has survived countless asteroid collisions over 4.2 billion long years. 

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            -    The scientists used a radioactive dating method called argon-argon dating to measure Itokawa's age, which they clocked at 4.2 billion years.  They measured how much the dust particles had been affected by shocks from asteroid collisions. For this, the researchers used another method called electron backscatter diffraction to measure the structures and orientations of crystals embedded inside the dust particles.

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            -    The team found that the dust particles were mostly pristine, suggesting that they were excavated from deep within the parent asteroid, likely when it broke apart during the catastrophic collision. The scientists concluded that Itokawa is extremely resilient to collisions, thanks to the asteroid's highly porous nature.

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            -    Itokata hosts boulders of different shapes and sizes that have blended under gravity. The rubble pile is entirely made of loose boulders and rocks, with almost half of it being empty space.

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            -    When asteroids impact Itokawa, large cavities or pores between these boulders absorb much of the resulting energy surge, protecting the asteroid's structure from fractures. In this way, the pores help rubble piles like Itokawa survive asteroid collisions for at least 10 times longer than conventional, single-body asteroids, also known as monoliths.

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            -    Analysis of Itokawa suggests that thanks to their resilience in the face of impacts, rubble-pile asteroids may be more common, both in the asteroid belt and near-Earth.

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            -     And the structure of an asteroid may make a difference if humans need to choose a strategy for deflecting a threat. For example, NASA's Double Asteroid Redirection Test (DART) mission rammed into Dimorphos, a similar rubble pile that was not on a collision course with Earth, but that was a convenient target to test how humans might respond to a future threatening asteroid. The impact shortened Dimorphos' orbit around the larger asteroid Didymos by 33 minutes, a major success for the mission.

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            -    When it collided with Dimorphos, DART transferred its energy and momentum to the asteroid. Although this kinetic impact was successful with DART,  it may be less efficient at deflecting shock-absorbent porous asteroids.

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            -    The kinetic impactor method is also most effective when we spot asteroids on collision courses with Earth well in advance, leaving enough time for a small change in orbit to build up.

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            -    If a threatening asteroid is spotted too late for the kinetic impactor approach, we can then potentially use a more aggressive approach like using the shockwave of a close-by nuclear blast to push a rubble-pile asteroid off course without destroying it.

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            -   This is the stuff that movies re made from. 

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            January 30, 2022       ASTEROIDS  -  threaten our planet?              3852                                                                                                                            

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