Deflecting an asteroid – Australian Geographic


By Fred Watson, Australia’s Astronomer-at-Large

September 21, 2022


Everywhere, space scientists are following the latest movements of a small spaceship in space on a mission that could profoundly affect the future of mankind.

The mission is called DART (Double Asteroid Redirection Test), which describes exactly what it aims to achieve – test if we can redirect an asteroid.

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Why a double asteroid? That’s what makes this ambitious project so clever. To explain, let me start with the basics. Our planet’s space environment is quite rocky, and astronomers are constantly on the alert for potentially hazardous asteroids (PHAs) whose orbits could one day bring them into contact with Earth.

Typically, astronomers are on the lookout for objects around 140 m in size, as these can cause nationwide devastation upon impact. (Fortunately, the larger, more dangerous ones are easier to find and are already well catalogued. None are on a collision course with us for at least the next 100 years.)

Suppose a PHA is spotted with an orbit that could result in an on-track collision – say in a decade or so. What you want to do is change the asteroid’s trajectory just enough to guarantee a miss, which means apply an acceleration to it. The sooner you can do this, the less force required. One way to achieve this could be to ram a half-ton spacecraft into the asteroid. But how would you know if you applied enough force?

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That brings us back to DART, which will actually impact an asteroid later this month on September 26, 2022. But it’s not just any ordinary asteroid. It is a 170 m high rock called Dimorphos, which is actually the moon of a larger asteroid called Didymos. Together they form a double asteroid.

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Dimorphos’ orbit around Didymos is known and can be measured again after impact, allowing scientists to accurately estimate the effect. That would be harder if you just hit an asteroid in orbit around the sun.

Once this sophisticated double asteroid test is performed, we will have a much better understanding of what it would take to deflect a dangerous single asteroid – something we may someday have to do in reality.

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