Deborah Byrd reports that in what’s being called humankind’s 1st planetary defense test, space scientists are planning to visit a double asteroid – Didymos and its tiny moon – and crash into the moon in attempt to change its orbit. Historically, NASA's Deep Impact spacecraft struck a 4-mile-wide (6-km-wide) comet – called Tempel 1 – on July 4, 2005. The image of the impact was acquired 67 seconds after impact.
In the past several decades, astronomers woke up to the reality that asteroids orbiting our sun do sometimes strike the Earth. It’s now know that the relatively little ones strike fairly often, mostly disintegrating in Earth’s protective atmosphere, and/or falling into the ocean. But larger asteroids have been known to pierce Earth’s atmosphere as well, such as the one that entered over Russia airspace in 2013, causing a shock wave that broke windows in several Russian cities. At present, astronomers do not expect any large, world-destroying asteroids to be on a collision course with Earth, in the foreseeable future. But smaller asteroids – those capable of causing destruction on a regional or city-wide scale, for example – are possible. And what if we learned that one was headed our way while there was still time to try to avert the collision? Could we deflect it?
Astronomers have been meeting and seriously talking about what might be needed to deflect an asteroid for at least a couple of years. Those talks have evolved into action; NASA and the European Space Agency (ESA) are now planning a joint space mission to test what’s needed to change an asteroid’s course. The mission is called the Asteroid Impact and Deflection Assessment (AIDA). The NASA portion of the mission – called DART – is planned to launch in 2021, with the goal of ramming an asteroid in 2022. An ESA mission called Hera would be sent to orbit the asteroid a few years later, to perform the minute measurements needed to reveal whether DART did its job. A February 4, 2019, statement from ESA explained:
The target of the mission is a double asteroid system, called Didymos, which will come a comparatively close 11 million km (about 7 million miles) to Earth in 2022. The 800-meter-diameter main body (about 2,600 feet) is orbited by a 160-meter-diameter moon (about 525 feet), informally called ‘Didymoon’. As DART is currently planned to launch in 2021, Hera would only arrive at Didymos a few years after DART’s impact.
In 2022, NASA’s DART spacecraft will first perform a kinetic impact on the smaller of the two bodies, and, later, the Hera spacecraft will follow-up with a detailed post-impact survey that will turn this grand-scale experiment into a well-understood and repeatable planetary defense technique. ESA also said the Hera mission will be the first spacecraft to explore a binary asteroid system – the Didymos pair. Also, the moon Didymoon will be the smallest asteroid ever visited by a spacecraft. It is about the same size as the Great Pyramid of Giza. Hera manager Ian Carnelli said:
Such a binary asteroid system is the perfect testbed for a planetary defense experiment but is also an entirely new environment for asteroid investigations. Although binaries make up 15 percent of all known asteroids, they have never been explored before, and we anticipate many surprises. The larger Didymos asteroid would form a modest dot, with its smaller moonlet struggling to make a single pixel. ESA said Didymoon’s small size was one reason it was chosen for a pioneering planetary defense experiment. As it happens, this little asteroid moonlet is also in the riskiest class of near-Earth asteroids because of its size: larger bodies can more easily be tracked, smaller bodies will burn up or do limited damage, while a Didymoon-sized impactor could devastate an entire region of our planet.
Bottom line: In what’s being called humankind’s 1st planetary defense test, space scientists are planning send a spacecraft to a double asteroid – Didymos and its tiny moon – and crash it into the moon in attempt to change its orbit.
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