A VIRTUAL game of interplanetary pool has revealed the best way to knock an asteroid off course and prevent it colliding with the Earth.
Several earlier studies have simulated the effects of firing a projectile at a menacing asteroid to change its orbital velocity and hence its trajectory. But they all included simplifications, for instance that the projectile would hit the rock head-on or from behind, a so-called parallel attack, rather than at an oblique angle.
Now Ekkehard K眉hrt, Ralph Kahle and Gerhard Hahn from the German Aerospace Center in Berlin have designed a more sophisticated mathematical model. It takes account of the gravitational influence of the moon and all the planets, including the Earth, and selects the best angle of attack to make sure an asteroid passes the Earth at a safe distance of twice the planet鈥檚 radius. 鈥淚t鈥檚 a very complex simulation,鈥� says K眉hrt.
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The team applied the model to 100 hypothetical asteroids and one real one, 99942 Apophis, which has a tiny chance of colliding with Earth in the mid-2030s. 鈥淚n 2029, it will pass about 30,000 kilometres away from Earth, which is very close. We can definitely rule out a collision then. But we can鈥檛 rule out a collision in the mid-2030s. Maybe in 2034 or 2036, it could impact the Earth. And in this case, we would have to design a mission to push it away,鈥� says K眉hrt.
The results show that if an asteroid is only two or three orbits away from an Earth impact, an oblique strike can nudge it into a safe orbit much more efficiently than a parallel attack because it requires much less force.
K眉hrt announced the results last week at the American Astronomical Society鈥檚 Division for Planetary Sciences meeting in Cambridge, UK. He thinks we could easily head off an asteroid such as 99942 Apophis. The rock is only about 320 metres wide, but if it hit Earth, it could devastate an entire country and trigger earthquakes and tsunamis.
Earlier this year, the NASA spacecraft Deep Impact fired a projectile into comet Tempel 1. K眉hrt says the impact changed its speed by about 10-7 metres per second. To deflect an asteroid safely, he says you would need to change the speed by about 10-6 metres per second. 鈥淲e have a very good chance of deflecting an object like [99942 Apophis],鈥� says K眉hrt. 鈥淚t could be done with technology available today.鈥�
