Sidereal Messenger: Dart and Brazilian study animate chance to save Earth from asteroids

The scenario for humanity escaping a killer asteroid in the future has greatly improved in the past week. For starters, the first test on the deflection of a celestial object, carried out by NASA with the Dart probe last Monday (26), was a great success.

It is not yet known exactly how much the trajectory of the asteroid Dimorph, with its about 160 meters in diameter, has changed. But the bet, based on the images taken by telescopes, is that it was a lot. That’s because what was seen was a spectacular and profuse ejection of material from the bolide just after the full impact of the half-ton spacecraft, at more than 21,000 km/h. The precise result can only be checked over the weeks, as the dust settles and astronomers can observe the Dimorph’s orbital period around the system’s largest asteroid, Didymus.

At this point, it is quite possible that this technique of deflecting asteroids by kinetic impact (the simplest possible, basically a cosmic billiard shot) will prove adequate to deflect stars the size of the Dimorph, capable of local damage in the event of a collision. But what about larger objects, which exceed 1 km in diameter, and would have the potential to cause the end of civilization?

A study recently published by a trio of Brazilian researchers in the scientific journal Simmetry suggests that a kinetic impact deflection can take care of even these big guys, with the addition of a trick well known to space mission planners: a gravitational slingshot.

The procedure is familiar: probes graze past planets and, thanks to their gravity, gain speed and change their trajectory towards their final destination. New Horizons, which went to Pluto, for example, grazed Jupiter to get there faster.

The idea of ​​Bruno Chagas and Othon Winter, from Unesp (Universidade Estadual Paulista), and Antonio Fernando de Almeida Prado, from Inpe (National Institute for Space Research), is that a well-placed shot at an asteroid at a time when it is approaching Earth, but not yet on a collision course, could change the distance of the passage by the planet, which would end up generating much greater deflection than just the hit, without the slingshot that Earth’s gravity would give it.

In practice, it’s choosing the best time to get the biggest effect with the least possible action. “This would make it possible to deflect bodies larger than 1 km, depending on how many orbits before the collision with Earth we perform the kinetic impact”, explains Winter.

Success, therefore, requires us to have a few years or decades’ notice (and orbits) – which is to be expected, by the way, as we map all the potentially dangerous asteroids out there. The key is to stay focused on this work of discovery and cataloguing, so we don’t get caught off guard.

This column is published on Mondays, in Folha Corrida.

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