Just before he passed in 2018, famed physicist Stephen Hawking gave some last precious insights into some of the universe's greatest mysteries with his posthumously published book "Brief Answers to the Big Questions." In response to "What is the greatest threat to the future of this planet?" Hawking listed both man-made climate change and a catastrophic strike from a near-Earth object.
While Hawking thought humanity could still offer a response to fight climate change, he was less bullish on our species surviving a direct hit from above.
"An asteroid collision would be a threat against which we have no defense," he wrote.
In 2022, NASA and the European Space Agency (ESA) hope to craft the beginning of an answer to Hawking's challenge with the launch of the DART (Double Asteroid Redirection Test) mission. As shown in the brief animation below, the DART probe is intended as a proof-of-concept demonstration to see if a man-made "interstellar bullet" can create enough force to nudge an asteroid off-course.
"DART would be NASA's first mission to demonstrate what's known as the kinetic impactor technique — striking the asteroid to shift its orbit — to defend against a potential future asteroid impact," planetary defense officer Lindley Johnson said in a statement.
Throwing a punch at 'Didymoon'
In 2020, NASA intends to launch DART on a two-year, 6.8-million-mile mission to a binary asteroid system called Didymos. Instead of aiming for its parent body, a large asteroid measuring nearly 2,600 feet across, NASA will direct DART on a collision course with an orbiting satellite, a 500-foot-wide object nicknamed "Didymoon." If successful, the 1,100-pound probe will slam into Didymoon at a speed of 13,500 mph and create a very small velocity change (estimated at less than a fraction of 1 percent) that, over a long period of time, will have a much larger impact on the moonlet's orbit.
"With DART, we want to understand the nature of asteroids by seeing how a representative body reacts when impacted, with an eye toward applying that knowledge if we are faced with the need to deflect an incoming object," Andrew Rivkin, a researcher at Johns Hopkins Applied Physics Laboratory in Laurel, Maryland and a co-leader on the DART investigation, said in a statement. "In addition, DART will be the first planned visit to a binary asteroid system, which is an important subset of near-Earth asteroids and one we have yet to fully understand."
Despite all of this celestial drama taking place millions of miles away, ground-based telescopes and planetary radar on Earth will be utilized to measure any changes in momentum by the moonlet.
Autopsy of an asteroid collision
After DART completes its collision course with the moonlet, an event expected to take place in October 2022, the next mission phase will involve a visit some four years later by the ESA's Hera spacecraft. Its primary objective will be to use its array of high-resolution instruments to build detailed maps of Didymoon, the crater created by DART, and any dynamical changes present since the collision. It's hoped that the information gathered will better inform future versions of the DART weapon, in particular for deflecting much larger objects.
"This key data gathered by Hera will turn a grand but one-off experiment into a well-understood planetary defense technique: one that could in principle be repeated if we ever need to stop an incoming asteroid," Hera manager Ian Carnelli said in a statement.
Should DART prove successful, it could lead the way for what's expected to be a wide range of planetary defense options –– from nuclear explosive devices to solar sails that might attach and "pull" a near-Earth-object off-course. Either way, most astronomers agree that we'll need plenty of warning in the form of several years to even have a chance at altering a doomsday-sized object from colliding with Earth. With the last known major impact occurring roughly 35 million years ago, researchers are hopeful we'll still have time to plan accordingly.
As Danica Remy, president of the B612 Foundation's Asteroid Institute program, said last year: "It's 100 percent certain we'll be hit, but we're not 100 percent certain when."