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DART mission: dress rehearsal for world rescue successful

27.9.2022

Translation: machine translated

As planned, the DART probe crashed on the asteroid moon Dimorphos. The test is to show whether potentially dangerous asteroids can be steered away from Earth.

At first, only a blurred bright spot was seen in the centre of the image sent to Earth by NASA's DART probe. Later, a second point of light appeared to the right above the object, which was now recognisable as a grey, irregular lump - the actual target of the mission. While Didymos, the larger of the two bodies, slowly slipped out of the picture, the asteroid moon Dimorphos remained in the centre of the image as if in crosshairs. Target is meant quite literally here. DART, short for "Double Asteroid Redirection Test" , was a kinetic impactor. A projectile designed to hit the rock with as much force as possible and divert it from its trajectory.

The minutiæ of the DART test were the most powerful.

The meticulously planned collision with the celestial body, which measures only 163 metres, is part of the AIDA mission, a research project of the US space agency NASA in cooperation with the Applied Physics Laboratory (APL) of Johns Hopkins University in Maryland to ward off asteroids that may pose a threat to Earth. Because our planet is a cosmic target: Bits of rock from space pelt the Earth every second. The vast majority are only fractions of a millimetre in size and burn up completely when they enter the Earth's atmosphere. But there are about 210 known craters on Earth that bear witness to the force of the impact of a larger celestial body.

For example, the Chicxulub crater on Mexico's Yucatán Peninsula shows what a real projectile can do: Around 66 million years ago, an asteroid measuring a good ten kilometres struck here, presumably triggering the great mass extinction that also claimed the lives of the dinosaurs. Statistically, such an impact must be expected every 100 million years. So it is not a question of whether we will be hit by a chunk from space, but rather when, said NASA science chief Thomas Zurbuchen to Der Spiegel in advance .

Practical test for saving the world

But doom is avoidable - as long as the potential planet killer is spotted in time. Even a minimal change in orbit adds up to millions of kilometres, so a relatively small impact is enough to protect life on Earth. DART is the first practical test of this idea. Dimorphos was chosen because it was comparatively easy to reach despite its huge distance - not because it poses a real threat to our planet.

The test was successful. About half an hour before impact, the control centre confirms: DART has its target in sight. When the surface of Dimorphos, littered with angular boulders, finally takes up the entire image, the transmission abruptly breaks off - and in the Applied Physics Laboratory the blue-clad experts cheer and applaud. DART has hit the celestial body at a speed of almost 22 000 kilometres per hour. With the collision at 1.14 a.m. Central European Time, humans have for the first time deliberately influenced the orbit of a celestial body. This is because the impact is expected to slow Dimorphos down by a few millimetres per second.

This means that the smaller companion will need a few minutes less for its almost twelve-hour lap around Didymos. However, we won't know more precisely for a few weeks or months at the earliest, once all the data has been analysed. For while the basic physics is not complicated, the details of such a collision are as yet poorly understood.

Experts can only guess what effects the impact of the 570-kilogram probe will have on Dimorphos, which measures only 163 metres. They know too little about its structure. The asteroid can be anything between a compact object and a flying pile of rubble held together only by gravity. Accordingly, the impact of the probe can vary.

JWST and Hubble observe Dimorphos

The lack of such information is also due to a failed ESA exploration project that was supposed to be part of the mission. In 2015, NASA and the European Space Agency ESA agreed to jointly study the 1996 GT double asteroid, now christened Didymos, which collided some 11 million kilometres from Earth, and to target its trajectory. Didymos is orbited by the smaller asteroid Dimorphos. But after several years of development, the budget to carry out the ESA mission was cancelled. In June 2017, NASA finally approved the concept for DART and initiated the design phase. On 24 November 2021, a Falcon 9 rocket from the private spaceflight company SpaceX put the probe on course towards Dimorphos.

By its very nature, DART can no longer provide information about what happened after the impact. But the aftermath of the direct hit is being recorded in detail. The Italian mini-satellite "LICIACube", which was launched by the DART probe a good a fortnight ago and flew past Dimorphos during the crash, will provide close-up images. In addition, the "Webb" and "Hubble" space telescopes will try to track the impact from a distance, as will numerous other observatories on Earth. In two years' time, the European probe "Hera" will set off for the asteroid pair and, after its arrival in 2026, study the composition, mass and trajectory of the pair in more detail.

The DART mission's progress according to plan is a small ray of hope for NASA. Recently, they had little to cheer about. The launch of the prestigious Artemis moon mission has been plagued by glitches and is being pushed back further and further. Private space companies are increasingly outpacing the state space agency. At the Applied Physics Laboratory, however, where the DART mission centre is located, the success is now being enjoyed for the time being. Mission accomplished.

Spectrum of Science

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Originalartikel auf Spektrum.de
Titelbild: NASA/Johns Hopkins APL

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