It’s not a matter of if a large asteroid hits Earth — it’s when. Space rocks have rained down on Earth long before humans were here, and they’re not going to stop now. However, a team from MIT has conducted a study of all the current plans for deflecting an asteroid and developed a model to determine the best course of action based on several crucial variables. We might not have much chance if we spotted a large asteroid on a collision course tomorrow, but the new study provides a path to potential salvation.
The analysis points out there are two points at which we could attempt to stop an asteroid destined to hit Earth, one of which would be much easier but requires additional planning. We could try to deflect an asteroid as it hurtled toward us, but that would require much more force. Alternatively, we could nudge a space rock aside as it passed through a gravitational “keyhole.” That’s simply a location in Earth’s gravity field that pushes an asteroid into a collision course on its next orbit.
Lead author Sung Wook Paek notes that a “last-minute” deflection is where most research has focused. However, intercepting an object before it passed through a keyhole could be much smarter. The main drawback here is that we need more data about the asteroid and its orbit. The study used two near-Earth asteroids about which we know a great deal: 99942 Apophis and 101955 Bennu. Apophis will pass near a keyhole in 2029, but it’s not currently predicted to hit us. Bennu is even less likely to find its way into a keyhole, but we have good data on this object as it’s the target of NASA’s OSIRIS-REx mission.
Paek and his team considered three basic mission profiles to deflect asteroids from a keyhole. The simplest is a single kinetic impactor, which we would fire into the object shortly before it reaches a keyhole to push it off course. Another option is to send a scout to inspect the asteroid to zero in on how a second spacecraft could knock it off course. The third consists of two halves: a scout and small impactor to potentially deflect the asteroid in the first phase, and then a second larger impactor to make completely sure the asteroid is no threat.
Based on the test cases, the team determined five years is enough time to go for the most elaborate mission profile. If we knew five or more years in advance that Apophis was headed for a keyhole, we could send a scout and small impactor, followed later by a large impactor. With two to five years, we could still send a scout to hone the eventual impactor mission. Less than that, and we’d have to send a single impactor. With less than one year of notice, it’s unlikely we could do anything to stop an asteroid from passing through a keyhole.
For an object like Bennu, we might be able to skip the scout missions. NASA will soon have a very good understanding of its composition thanks to the OSIRIS-REx mission. It all goes as planned, a sample of Bennu will arrive on Earth in 2023.
Top photo credit: NASA
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