In a few weeks, Nasa controllers will intentionally crash their $330 million dart robot spacecraft into an asteroid. The Halfton Probe will be traveling at more than four miles per second when it hits its target, Dimorphos, and is destroyed.
The goal of this scientific kamikaze mission is simple: space engineers want to learn how to deflect asteroids if one is ever spotted on a collision course with Earth. Observations of Dart’s impact on Dimorphos’ orbit will provide crucial data on how well spacecraft can protect Earth from asteroid Armageddon, they say.
“We know that asteroids have hit us in the past,” said Professor Alan Fitzsimmons, an astronomer at Queen’s University Belfast. “These effects are a natural process and will occur in the future. We want to stop the worst of them.
“The problem is that we have never tested the technology that is needed to do this. That’s the purpose of Dart,” said Fitzsimmons, a member of the science team for the Double Asteroid Redirection Test (Dart) mission. Launched last November, the probe is expected to hit its target in the early hours of September 27 (BST). Scientists believe that by carefully studying the asteroid’s post-collision trajectory, they will better understand how similar collisions could be used to deflect Earth-bound asteroids and comets.
“Dart’s target was carefully chosen,” said Jay Tate, director of the National Near Earth Objects Information Center in Knighton, Powys. “Dimorphos is actually orbiting another, larger asteroid called Didymos, and the magnitude of the deflection caused by the crash will be easier to see as astronomers have carefully monitored its path around the larger asteroid.”
Asteroid and comet impacts have had major impacts on life on Earth in the past. The best-known collision occurred 66 million years ago when a 10 km wide asteroid struck Chicxulub on Mexico’s Yucatán Peninsula. The collision produced an explosion that had the energy of billions of atomic bombs and resulted in the destruction of 75% of all plant and animal species, including all land-based dinosaurs.
Since then, films such as Don’t look up, Armageddon and Deep Impact have depicted similar devastation caused by asteroid or comet impacts in modern times. However, astronomers believe it is unlikely that we will experience such catastrophic effects in real life in the near future.
“We know where the large asteroids are because we can see them with our current generation of telescopes, and we know that none of the asteroids that have been discovered will come anywhere near our planet for the next few hundred years. So we can rest easy in our beds,” Fitzsimmons added.
“However, many smaller ones have yet to be discovered, and they are still large enough to destroy entire cities and devastate large areas. We’re mapping these smaller objects with increasing accuracy, but we must be ready to act if we find one heading for Earth. Dart is the first step in ensuring we have the right technology to deal with the threat.”
This is a point supported by Lindley Johnson, Nasa’s planetary defense officer, who stressed the importance of developing asteroid deflection technology as soon as possible. “We don’t want to get into a situation where an asteroid is headed for Earth and then have to test that kind of ability.”
An example of the danger posed by small asteroids and comets is the rocky object that entered Earth’s atmosphere on February 15, 2013 near the Russian city of Chelyabinsk. It was 20 meters in diameter and exploded in the atmosphere, releasing a 400 kiloton blast injuring more than 1,500 people.
“Had this object entered the atmosphere just 20 km to the north, it would have done much more damage to the city,” Tate said. “We’ve been very fortunate not to have suffered any significant casualties from these things in living memory. We have to be aware that they will happen one day and be prepared to do something about it.”
Dart’s target, Dimorphos, is 160 meters in diameter and orbits its parent asteroid every 12 hours. Ten days before impact, the spacecraft will release a purse-sized Italian-built probe called the LiciaCub, equipped with two cameras that gave the war of stars-Inspired names of Luke and Leia. Images of Dart’s asteroid impact are recorded by Luke and Leia and beamed back to ground controllers.
Ground-based telescopes will then study the asteroid and note how its orbit has changed. “It gives us an idea of how easy it will be to deflect incoming asteroids or comets,” Tate said.
In addition, in 2024, the European Space Agency will send a robotic spacecraft, Hera, to Dimorphos to study the crater left by Dart and analyze its collision with the asteroid.
“Meeting Dimorphos isn’t going to be easy,” Fitzsimmons said. “It’s only 160 meters in diameter and the spacecraft will be traveling at four miles per second. Hitting the asteroid’s dead center — where the crash will have the greatest impact — will push Dart’s autonomous navigation devices to their limits.
“NASA engineers and scientists have done an excellent job and are confident that this should absolutely work. But you never really know until you do it,” Fitzsimmons said.