- 3345 - ASTEROID IMPACT - deflect it before it hits? Scientists are tracking more than 27,000 asteroids circling around Earth's neighborhood of space. Experts in the field they call planetary defense know that just such an object killed off most of the dinosaurs, and they're determined to see to it that humans don't meet the same fate.
--------------------- 3345 - ASTEROID IMPACT - deflect it before it hits?
- Tucked away gathering dust in a nondescript warehouse, there will be a spacecraft waiting to be called to the launch pad, even as its builders pray it never flies. Seems odd? What is it for?
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- It wouldn't be a typical spacecraft, it would be assigned a far more somber task: to deflect an asteroid on course to hit the Earth.
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- The solution is to nudge any threatening asteroid just enough to avoid the collision. Now, the first-ever planetary defense spacecraft is at Vandenberg Space Force Base in California, waiting for its first launch opportunity early on November 24, 2021.
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- That mission, NASA's “Double Asteroid Redirection Test”, or, DART, is doomed to spend less than a year in space and make a stunning exit by slamming into the moonlet of an asteroid called “Didymos“.
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- If all goes well, it will give planetary defense specialists their first real-world data about deflecting space rocks.
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- It's not a new problem: people have known this is something that is a potential hazard, and people have been wanting to take steps to prevent this in the future.
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- There's more than one way to deflect an asteroid, but DART is testing the kinetic impactor technique. If you slam an orbiting asteroid head-on with something massive enough at a fast enough speed, the asteroid's orbit changes. First, it slows down, but that means it falls toward the object it's orbiting. Through a nifty trick of physics, the closer orbit makes for a slightly faster orbit than the rock's original path.
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- DART will crash all of its 1,210 pounds into an object called “Dimorphos“, which is a small moonlet orbiting its parent asteroid “Didymos“.
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- Scientists believe that both rocks in the system are the most common flavor of near-Earth asteroid, stony or S-type. At 2,560 feet, Didymos is about as wide as a particularly lofty skyscraper is tall; Dimorphos is more like the size of the Great Pyramid in Egypt, at about 530 feet across.
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- Asteroids come in three categories. The largest ones, more than 3,300 feet wide, could cause the most damage, but they're also the easiest to find, so scientists are pretty confident they've seen most of them. None are a threat.
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- The smallest asteroids aren't hefty enough to cause much damage; some don't even survive the trek through Earth's atmosphere.
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- The middle category, of rocks more than 460 feet but less than 3,300 feet across is what worries planetary defense experts. These asteroids are harder to spot than the largest ones, but could still cause regional devastation if one hit Earth. Dimorphos matches that size.
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- All the near-Earth asteroids discovered through 2018 number more than 18,000 objects. As of November 2021, the tally has reached 27,000.
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- The DART team also wanted to target a moonlet orbiting a larger asteroid instead of an asteroid orbiting the sun. That choice was in part for convenience and in part out of caution. For one, the DART leaders are confident that nudging this object isn't going to accidentally send anything hurtling toward Earth, worsening the very problem the team is trying to work toward solving.
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- A single asteroid orbits every few years perhaps, Dimorphos orbits Didymos once every 12 hours or so. The DART team expects the impact will shave perhaps 10 minutes or so off that rhythm, a difference that is much more noticeable against a 12-hour orbit and can be clocked more quickly.
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- DART's observations will be the first real-world data that would-be planetary defenders can feed into the models that tell them just how big a spacecraft going just how fast might be enough to ward off an asteroid.
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- Scientists in the planetary defense community are quick to note that no one can deflect a threat that isn't detected, and the more warning time Earthlings have, the better the situation will turn out for us.
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- Warning time is vital for an approach like DART's kinetic impactor because the change expected in an asteroid's orbit is fairly small, so the asteroid needs to make a few loops of the sun to build up a difference from its original position's impact with Earth.
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- With enough warning, even more possibilities open up. Like sending a spacecraft to scout out the threat and hone the deflection mission. This would make a good Hollywood movie.
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- Scientists can only learn so much about any given space rock from Earth: its orbit, a vague size estimate, perhaps an idea of its shape and composition. All of those factors affect the design of an optimal planetary defense mission.
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- In a real planetary defense scenario, a particularly crucial use of warning time old be critical. Some countries may be hit, some countries may be able to act to stop the impact, some countries may see collateral effects, and all countries ought to be involved in the planet's response, planetary defense experts emphasize.
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- Planetary defense is particularly tricky because one potential deflection technique relies on nuclear explosives, yet nuclear weapons are not permitted in space. Laying the groundwork for conversations that could work around such rules and international nuclear fears is a key focus.
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- The kinetic impactor approach is only one technique that planetary defense specialists consider for moving an asteroid's path. Other options may be to use lasers, a companion spacecraft's gravity or a nuclear explosion. Which option makes the most sense when needed will depend on the warning time Earth has and the size of the asteroid.
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- Engineers lower the DART spacecraft into place in SpaceX's processing facility at Vandenberg Space Force Base, where the mission will launch no earlier than November 24, 2021.
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- The logistical problems multiply if a deflection were to require a series of launches. A host of nightmare scenarios can unfold. A partial deflection, one that moves the asteroid but not enough to clear Earth. "It's still heading toward the Earth, but now the impact point is somewhere other than where it was before. Now we've artificially created a different version of the disaster, different from what the natural version was going to be.
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- Or if a mass estimate is off, or the asteroid doesn't respond as predicted. It's plausible that you could inadvertently break off a chunk of the asteroid when you hit it rather than just deflecting it as a whole unbroken object. Those fragments would then pose their own threats.
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- So that spacecraft in a warehouse had better have a companion. The $330 million DART mission does have a successor that plans to visit the scene. The European Space Agency will launch a spacecraft named “Hera” in 2024, after the dust has settled, to allow scientists to understand in even more detail the factors that a real planetary defense mission may need to consider.
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- DART is the start; it is the first step. Don’t miss it!
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- November 19, 2021 ASTEROID IMPACT - deflect it before it hits? 3345
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