The most likely way that the universe could eliminate life on planet Earth has to be with an asteroid; the planet won’t be swallowed by the Sun or destroyed in some other astronomical catastrophe anytime soon. In his book Death From The Skies!, Bad Astronomy blogger Phil Plait writes:
The American astronomer Alan Harris has composed a table of risks from impacts, and the results are surprising: if you live in the United States, the overall risk of dying from an impact in your lifetime is only 1 in 700,000, somewhat less than being killed in a fireworks accident, but still more probably than being killed on an amusement park ride or by an act of terrorism.
The odds of a truly horrible impact along the lines of the one that killed off the dinosaurs 65 million years ago are even more remote. And, as Plait notes, these impacts are, theoretically at least, preventable. But blowing up an asteroid, a la the movie Armageddon, isn’t the best option—it only creates multiple asteroids still headed towards Earth. Deflection, though, might work—just give the rock a little nudge and it should pass safely by.
Scientists began preparing for a practice run of this deflection technique with a mission from the European Space Agency called Don Quijote. The plan calls for two spacecraft to head to an asteroid (possible targets are 2002 AT4 and (10302) 1989 ML). One of those spacecraft would be an impactor, named Hidalgo. Its duty would be simple—hit the asteroid within 50 meters of a target. The second spacecraft, named Sancho, would be loaded up with equipment for imaging and monitoring the asteroid. Sancho would orbit the asteroid during the impact and for months afterwards to record any changes in the asteroid’s direction.
A minor worry comes from the fact that both potential targets are not that far away from Earth. Could changing the path of one ultimately send it hurtling towards our own planet? Could we be our own downfall? Such an impact, with an origin of our own making, would be ironic, to say the least.
But ESA says it’s not a problem:
Even a very dramatic impact of a heavy spacecraft on a small asteroid would only result in a minuscule modification of the object’s orbit. In fact the change would be so small that the Don Quijote mission requires two spacecraft—one to monitor the impact of the other. The second spacecraft measures the subtle variation of the object’s orbital parameters that would not be noticeable from Earth.
Target objects can also be selected so that all possible concerns are avoided altogether, by looking into the way the distance between the asteroid’s and the Earth’s orbits changes with time. If the target asteroid is not an ‘Earth crosser’…testing a deflection manoeuvre represents no risk to the Earth.
Anyway, planning for Don Quijote is still ongoing—for example, researchers just published a paper about what kind of measurements such a mission would require—and an actual impact is years in the future, if it ever occurs. And surely we’ll have worked out how to protect our planet from such an impact by the time any such danger becomes imminent, right?