by A frequent idea in sci-fi and apocalyptic movies is an asteroid hitting Earth and causing global destruction. Although the odds of this type of mass extinction happening on our planet are extremely small, they are not zero.
The results of NASA’s Dart mission to the asteroid Dimorphos have now been published. They contain interesting details about the composition of this asteroid and whether we can protect the Earth from incoming space rocks.
The Double Asteroid Redirect Test (Dart) was a spacecraft mission launched in November 2021. It was sent to an asteroid called Dimorphos and directed to collide with it, in September 2022.
Dimorphos was not a threat to Earth in the near future. But the mission was designed to see if an asteroid could be deflected off a collision course with Earth by “kinetic” means – in other words, the direct impact of a man-made object on its surface.
Asteroid missions are never easy. The relatively small size of these objects (compared to the planets and moons) means that there is no significant gravity to enable spacecraft to land and collect a sample.
Space agencies have sent several spacecraft to asteroids in recent years. For example, the Japanese space agency’s (Jaxa) Hayabusa-2 mission reached the asteroid Ryugu in 2018, the same year that Nasa’s Osiris-Rex mission rendezvoused with the asteroid Bennu.
The Japanese Hayabusa missions (1 and 2) fired a small projectile at the surface as they approached. They would then collect the debris as it flew.
High speed collision
However, the Dart mission was special in that it was not launched to deliver samples of asteroid material to laboratories on Earth. Instead, it was flown at high speed into the space rock and destroyed in the process.
A high-speed collision with an asteroid requires incredible precision. Dart’s target of Dimorphos was part of a double asteroid system, called a binary because the smaller object orbits the larger one. This binary contained Didymus – the larger of the two objects – and Dimorphos, which effectively behaves like a moon.
The simulations of what happened to Dimorphos show that while we would expect to see a very large crater on the asteroid from Dart’s impact, it is more likely that it changed the shape of the asteroid instead.
An ant hitting two buses
The collision with an asteroid of around 5 billion kg mass was 580kg. By comparison, this is the equivalent of an ant hitting two buses. But the spacecraft is also traveling at about 6 kilometers per second.
The simulation results based on observations of the asteroid Dimorphos have shown that the asteroid is now orbiting its larger companion, Didymus, 33 minutes slower than before. Their orbit has gone from 11 hours, 55 minutes to 11 hours, 22 minutes.
The momentum change at the core of Dimorphos is also higher than one would predict from the direct impact, which may seem impossible at first. However, the asteroid is quite weakly constructed, consisting of loose debris held together by gravity. The impact caused many objects to be blown off Dimorphos.
This material is now traveling in the opposite direction for impact. This acts like recoil, slowing down the asteroid.
By looking at all the highly reflective material lost from Dimorphos, scientists can estimate how much of it was lost from the asteroid. The result is about 20 million kilograms – the equivalent of six Apollo-era Saturn V rockets fully loaded with fuel.
By combining all the parameters (mass, speed, angle and amount of material lost) and simulating the impact the researchers are quite confident about the answer. Confident, not only about the grain size of the material coming from Dimorphos, but also that the asteroid has limited cohesion and the surface must constantly be changed, or reshaped, by minor impacts.
But what does this tell us about protecting ourselves from an asteroid impact? Notable recent Earth impacts include the meteor that broke up in the sky above the city of Chelyabinsk, Russia, in 2013, and the infamous Tunguska impact on a remote part of Siberia in 1908.
Although these were not the types of events capable of causing a mass extinction – like the 10km object that wiped out the dinosaurs when it hit our planet 66 million years ago – larger objects could have caused damage and loss of life. less like those at Chelyabinsk and Tunguska are very high.
The Dart mission cost US$324 million (£255 million), which is low for a space mission, and once its development phase was completed, a similar mission could be launched more cheaply to deflect an asteroid heading our way.
The big variable here is how much warning we’ll have, because a 30 minute change in orbit – as observed when Dart hit Dimorphos – won’t make much of a difference if the asteroid is already very close to Earth. However, if we can predict the object’s path further out – preferably outside the Solar System – and make small changes, this could be enough to divert an asteroid’s path away from our planet.
We can expect to see more of these missions in the future, not only because of scientific interest in asteroids, but because the ease of extracting material from them means that private companies may want to add with their ideas for mining these space rocks. precious metals.
This article from The Conversation is republished under a Creative Commons license. Read the original article.
Ian Whittaker does not work for, consult with, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
