The fact that people are trying to ward off asteroids has so far only been known from Hollywood films. But NASA is now getting serious: the first attempt at planetary asteroid defense starts at night. How it will turn out, however, is still completely open.
About 66 million years ago, a massive asteroid impact wiped out the dinosaurs, according to a popular theory. And the danger from larger and smaller chunks from space still exists today. In 2013, for example, a relatively small asteroid exploded over Chelyabinsk in Russia – but the shock wave was felt in six cities. The US space agency NASA wants to counter the threat with something that has so far only been known from films like “Armageddon”: a planetary asteroid defence. The first test is now imminent.
The time has come on Tuesday at 1:14 a.m. CEST: The NASA probe “DART” is supposed to hit the asteroid Dimorphos at a speed of more than 23,000 kilometers per hour. This is about 160 meters tall and orbits like a moon around a larger chunk called Didymos. While the asteroid poses no threat to Earth, it makes an excellent test subject. The collision takes place eleven million kilometers from Earth. NASA will broadcast the event live on the Internet.
Kai Wünnemann from the Museum of Natural History in Berlin will also follow everything. The meteorite researcher is part of the international “DART” science team. “It’s exciting. I hope we meet,” said Wünnemann to ntv.de. Should the probe actually miss the asteroid, it will not have a chance to make a second attempt for another two years. But Wünnemann is confident that everything will work out.
During the planned impact, the approximately 600-kilogram cube-shaped probe will be completely destroyed. The “LICIACube” companion probe, which was launched about two weeks ago, is intended to determine whether it was actually successful. The Italian “LICIACube” flies past Dimorphos about three minutes after the collision and tries to photograph the dust cloud ejected by the impact – and in the best case also the resulting crater.
Whether the targeted collision will really succeed in diverting the almost five million tonne asteroid from its orbit will probably only be certain in a few weeks or months. Telescopes on Earth and satellites in space will observe Dimorphos and measure whether it orbits Didymos slightly faster than before after the experiment. If so, the orbit has been successfully modified. This can be observed well from Earth, as Dimorphos passes in front of the larger Didymos with each orbit, obscuring it somewhat.
How strong the change in orbit will be exactly is completely open. This is because so far little is known about Dimorphos. It is unknown whether it is a solid, hard rock or a porous, loosely connected heap of rubble. However, the nature of the asteroid has a major impact on how much the asteroid is deflected by the impact. “With a hard celestial body, it’s like playing billiards, a lot of momentum is transferred. If the asteroid is rather soft, however, then it’s like hitting a sponge,” explains Wünnemann.
It will probably be a few more years before the consequences of the crash can be precisely calculated. The European probe “HERA” should not make its way to the asteroid team until 2024 and arrive there in 2026. “HERA” then measures the mass of Dimorphos and the exact size of the impact crater on site. “Only with ‘HERA’ do we know how large the mass of the body is. And then we also know how much energy has affected how much change in orbit,” says Wünnemann, who is playing a leading role in the ‘HERA’ mission.
The researchers hope to gain important insights into future planetary defenses from the experiments. This could possibly be useful one day: after all, around 27,000 asteroids have been identified near our planet, around 10,000 of them with a diameter of more than 140 meters. However, experts assume that there will be no problems with larger chunks in the next 100 years. But if it does, NASA wants to be prepared.
According to Wünnemann, an important result of the “DART” mission will also be the size class of asteroids up to which this technology is effective. He estimates that chunks of up to 200 meters in size could be successfully deflected in this way to prevent an impact on Earth. Maybe even larger ones if the warning time is long enough. However, given the current state of technology, nothing can be done about an asteroid ten kilometers across, like the one that presumably wiped out the dinosaurs.
