If the dinosaurs had a space program, it would have been a bad one.
Of course, they didn't, but some might say a space program that can't protect its people from space-based threats, like colossal asteroids, wasn't that great, after all. Taking on the challenge, NASA wants to intentionally smash a spacecraft into an asteroid in a dress rehearsal of saving the planet from a hypothetical asteroid apocalypse, according to a blog post in MIT Technology Review.
And it's going to be a chaotic ride.
NASA's asteroid-slamming spacecraft could have 'chaotic' results
Humans don't want to die like the dinosaurs, which is why NASA plans to launch a mission to test out methods of potentially deflecting an Earthbound asteroid, should one be detected in the future. Dubbed the Double Asteroid Redirection Test (DART), the program could launch on Nov. 24 (or, pending delays, by Feb. 2022). After a year in transit, it'll arrive in the neighborhood of its target: Dimorphos, which is a stadium-size asteroid that orbits a much larger asteroid, known as Didymos. This mission involves slamming the asteroid at an unconscionable speed of roughly 4 miles per second (6.5 km/s) with the DART spacecraft, which is the size of a car and weighs roughly one-third of a ton. If all goes well, Dimorphos' nearly 12-hour orbit around Didymos will be modified on the scale of minutes.
Five years later, another mission from the European Space Agency (called Hera) will examine the aftermath to see if the plan worked. While the impact should only have a minor effect on the asteroid, it should be a sufficient enough adjustment to deflect the asteroid from Earth's path in the future. But this method only works if we know that it's coming well in advance. "We're doing this to have the ability to prevent a truly catastrophic natural disaster," said DART Program Scientist Tom Statler, of NASA's Washington-D.C. headquarters, in the MIT report. Scientists have researched what to expect from this shift in Dimorphos' trajectory extensively, but they've had no way to document or fully predict how the asteroid will behave following the impact.
Investigating this question, a new paper published in the journal Icarus describes the first-ever simulations attempting to draw a picture of a post-impact Dimorphos. In the study, the researchers modeled the degree to which DART could hasten or slow the spin or rotation of Dimorphos via a calculation of the impact momentum, and how this will change the yaw, pitch, and roll of the asteroid. Their conclusion suggested a chaotic outcome. "It could start tumbling and enter a chaotic state," said Agrusa in the MIT post. "This was really quite a big surprise." The spinning behavior could also create some notable challenges. For example, this would raise the difficulty level of landing on the asteroid, a goal the ESA holds in store for two small spacecraft equipped on the Hera mission. And, most crucially, the chaotic outcome could substantially complicate further attempts to deflect the asteroid, should the first impact not achieve the desired effect.
A 'dress rehearsal' for saving the Earth
Once DART smashes into Dimorphos, the impact energy will be roughly the same as three tons of TNT exploding, which will spray thousands of bits of debris up and outward into space. In the MIT report, Statler said this effect will be like a golf cart moving at 15,000 miles per hour slamming into the side of a football stadium. While the impact itself won't create an immediately noticeable change in the spin of Dimorphos, this will change in the following days. First, Dimorphos will show a subtle wobble, which will grow more pronounced as the momentum from the impact begins to push the asteroid's rotation out of balance. Since there's no friction between the asteroid and outer space, this wobble will only hasten until all of the impact energy has been converted into the motion of the asteroid (once the initial spray of pieces is finished). Dimorphos could spin in multiple ways, perhaps along its axis, like a rotisserie.
And, anyone looking at Didymos' sky from its surface, the erstwhile sedentary satellite will take on a wild new behavior, swinging maddeningly to and fro, with its former "dark" side now showing face. As a dress rehearsal for saving the Earth from an asteroid apocalypse, this is pretty cool. But the result will require studying a litany of highly complex phenomena to understand, from a chaotic spin state to the impact of sunlight and heat dispersal. "It's not as simple as just crashing a spacecraft into the asteroid," said Paul Wiegert, an astronomer at the University of Western Ontario, in the report. "There's a lot of physics you need to understand." He's right.