Dinosaurs had no warning and no way to defend themselves when an asteroid suddenly destroyed their existence 65 million years ago. Humans, understandably, want to avoid the same fate.
A space program might protect humans from space-based threats, like massive asteroids headed toward Earth. With this in mind, NASA wants to smash a spacecraft into an asteroid in a rehearsal of saving Earth from a hypothetical asteroid catastrophe. But, according to MIT Technology Review, it could have chaotic results.
The Mission
NASA will launch a mission dubbed the Double Asteroid Redirection Test (DART) to test out methods of potentially deflecting any future Earthbound asteroid.
DART is slated to launch on November 24 (or as late as February 2022) and will take a year in transit to reach its target: Dimorphos. This stadium-size asteroid orbits a much more giant asteroid called Didymos.
This mission involves slamming Dimorphos at a ridiculous speed of around 6.5 kilometers per second (4 m/s) with the car-sized DART spacecraft, weighing about a third of a ton. If all goes well, Dimorphos’ almost 12-hour orbit around Didymos will be modified on the scale of a few minutes.
Another mission from the European Space Agency, dubbed Hera, will arrive five years later to examine the aftermath to see if the mission worked. “We’re doing this to have the ability to prevent a truly catastrophic natural disaster,” explained Tom Statler, DART program scientist at NASA’s Washington-D.C. headquarters.
The impact of the DART spacecraft will have only a minor effect on the asteroid, but that should be enough to divert an asteroid from Earth’s path in the future. However, this plan only works if we detect the threat well in advance.
A Chaotic Outcome
While scientists have thoroughly researched what to expect from this shift in Dimorphos’ path, they have no way to fully predict or document how the asteroid will behave after the impact. A study, published in the journal Icarus, investigates this question and creates what the authors describe as the first-ever simulations attempting to draw an image of a post-impact Dimorphos.
The researchers, led by Harrison Agrusa from the University of Maryland, modeled how much DART could accelerate or slow the rotation or spin of Dimorphos by calculating how the impact momentum would alter the asteroid’s yaw, pitch, and roll. Their conclusion indicates a chaotic outcome. Agrusa points out that “it could start tumbling and enter a chaotic state.”
The spinning behavior poses some notable challenges. For example, this would make it more challenging to land on the asteroid, which ESA hopes to attempt with two tiny spacecraft on its Hera mission. And, most significantly, the chaotic result could complicate further attempts to deflect the asteroid, as any slight rotation can affect an asteroid’s route through space.
Once DART slams into Dimorphos, the impact energy will be about the same as three tons of TNT exploding – resulting in thousands of bits of debris dispersing up and outward into space. In the MIT report, Statler likens this effect to a golf cart flying at 15,000 miles per hour then smashing into the edge of a football stadium.
The impact won’t immediately alter Dimorphos’ spin, but this will change in the following days. First, the asteroid will display a subtle wobble, which will grow more intense as the momentum from the impact starts to push the asteroid’s rotation out of balance.
Since there’s no friction between outer space and the asteroid, this wobble will only accelerate until all of the impact energy is converted into the asteroid’s motion (once the initial disperse of bits and pieces is finished). As a result, Dimorphos could spin in multiple ways, including along its axis, like a rotisserie.
The result will require studying highly complex phenomena to understand everything from a chaotic spin state to the effect of sunlight and heat dispersal. “There’s a lot of physics you need to understand. It’s not as simple as just crashing a spacecraft into the asteroid,” said astronomer Paul Wiegert from the University of Western Ontario.
