Planetary Defense Test

[ilan]

A plan to knock an asteroid off course
Deborah Byrd in SPACE | February 5, 2019

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.

NASA’s Deep Impact spacecraft struck a 4-mile-wide (6-km-wide) comet – called Tempel 1 – on July 4, 2005. This image was acquired 67 seconds after impact. Image via ESA.

In the past several decades, astronomers woke up to the reality that asteroids orbiting our sun do sometimes strike the Earth. It’s now known 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 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? How?

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, Hera 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 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.