A common idea in science fiction and apocalyptic movies is that an asteroid hitting Earth will cause global destruction. Although the probability of such a mass extinction occurring on our planet is incredibly small, it is not zero.
The results of NASA’s Dart mission to the asteroid Dimorphos have now been published. They contain fascinating details about the composition of this asteroid and whether we can defend Earth against incoming space rocks.
The Double Asteroid Redirection Test (Dart) was a spacecraft mission launched in November 2021. In September 2022, it was sent to an asteroid called Dimorphos and was ordered to collide with it head-on.
Dimorphos has not and will not pose any threat to Earth in the near future. But the mission was designed to see whether it was possible to divert an asteroid from its collision course with Earth by “kinetic” means, that is, by directly striking the surface of a human-made object.
Asteroid missions are never easy. The relatively small size of these objects (compared to planets and moons) means that there is no significant gravity to force the spacecraft to land and collect samples.
Space agencies have launched numerous spacecraft to asteroids recently. For example, the Japanese space agency’s (Jaxa) Hayabusa-2 mission reached asteroid Ryugu in 2018; That same year, NASA’s Osiris-Rex mission rendezvoused with the asteroid Bennu.
The Japanese Hayabusa missions (1 and 2) fired a small projectile at the surface on approach. They would then fly away and collect debris as they flew away.
high speed collision
But the Dart mission was special in that it was not sent to deliver samples of asteroid material to laboratories on Earth. Instead it was to fly towards the space rock at high speed and get destroyed in the process.
Colliding with an asteroid at high speed requires incredible precision. Dart’s target on Dimorphos was actually part of a binary asteroid system; this system was known as a binary system because the smaller object orbited the larger one. This duo included both Didymus, the larger of the two objects, and Dimorphos, which effectively acted as the moon.
Simulations of what happened to Dimorphos show that while we might expect to see a very large crater on the asteroid from Dart’s impact, it’s more likely that it actually changed the shape of the asteroid.
Ant hit two buses
The collision occurred when a mass of 580 kg hit an asteroid weighing approximately 5 billion kg. For comparison, this is equivalent to one ant hitting two buses. But the spacecraft is also traveling at about 6 kilometers per second.
Simulation results based on observations of the asteroid Dimorphos showed that the asteroid now orbits its larger companion Didymus 33 minutes slower than before. Its orbit increased from 11 hours 55 minutes to 11 hours 22 minutes.
The momentum change in Dimorphos’ core is also higher than would be predicted by direct impact, which may seem impossible at first. However, the asteroid has a very weak structure and consists of loose debris held together by gravity. The impact caused a lot of material to fly away from Dimorphos.
This material now moves in the opposite direction of the impact. This acts like a rebound, slowing the asteroid down.
Observing all of the highly reflective material shed from Dimorphos allows scientists to estimate how much has been lost from the asteroid. Their result is roughly 20 million kilograms; This is equivalent to six fully fueled Saturn V rockets of the Apollo era.
Putting all the parameters together (mass, speed, angle, and amount of material lost) and simulating the impact allowed the researchers to be quite confident in the answer. He is confident not only about the grain size of the material from Dimorphos, but also that the asteroid has limited adhesion and the surface must be constantly changing or reshaping by small collisions.
So what does this tell us about protecting ourselves from asteroid impact? Recent significant impacts on Earth include the meteor that ripped apart in the sky over Chelyabinsk, Russia, in 2013, and the infamous Tunguska impact in a remote part of Siberia in 1908.
While these were not the type of events that could cause mass extinctions like the 10 km object that wiped out the dinosaurs when it crashed into our planet 66 million years ago, smaller objects did have the potential for damage and loss of life. Chelyabinsk and Tunguska are very high.
The Dart mission costs US$324 million (£255 million), which is a low figure for a space mission, and once the development phase is complete, a similar mission to deflect an asteroid heading towards us could be launched for less.
The big variable here is how much warning we’ll get, because a 30-minute change in orbit will make little difference if the asteroid is already so close to Earth, as was observed during Dart’s impact with Dimorphos. But if we can predict the object’s path from further away (preferably from outside the Solar System) and make small changes, this could be enough to shift an asteroid’s path away from our planet.
We can expect to see more of these missions in the future, not only because of the interest in the science surrounding asteroids but also because the ease of extracting material from them means private companies may want to accelerate their ideas for mining these space rocks. precious metals.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Ian Whittaker does not work for, consultancy, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond his academic duties.