Universe Today
It’s amazing how much one movie can act as a cultural touchpoint for an entire topic - even a topic as serious as defense of a planet. Popular media consistently use the 1998 movie Armageddon as a reference when talking about how we would destroy a civilization-ending asteroid. That’s despite the movie’s glaring scientific flaws, not the last of which is the likely size of the rogue comet that threatens the Earth. Planetary defense researchers at MIT were recently interviewed by the university’s media department as part of their “3 Questions” series. One of the most important takeaways is that the size of any likely planetary impactor in our lifetime is going to be much smaller than the kilometer-sized behemoth that did in Bruce Willis’ character.
These smaller objects, known as decameter-scale asteroids because they typically have a diameter of 10s of meters, aren’t the civilization-destroying kind—those are typically kilometer scale and above. But they are much more common. The MIT researchers believe they impact the Earth-Moon system roughly every couple of decades, compared to the once in ten million years a larger impactor would hit us.
To be clear, these decameter sized objects are bigger than the ones that have been causing a significant amount of fireballs over US cities. For example, the one that burst over my home city of Cleveland a few weeks ago, which was loud enough to shake houses in the area, was only around 2 meters in diameter.
One recent example of an asteroid in this size is 2024 YR4, which was discovered a little more than a year ago, and comes in at between 53 and 67 meters - roughly the size of a 15 story building. According to the MIT researchers, this class of objects isn’t likely to cause human casualties. However, if they strike a populated area, they certainly could, as they could release an airburst equivalent to 8 to 10 megatons of TNT.
But what they are sure to do is disrupt space infrastructure - including the satellites used for GPS and communications. In really bad scenarios, they could potentially be the spark that ignites Kessler syndrome - the orbital debris cascade that could lock us out of space access for decades or longer. So even if all this type of asteroid did was knock out a few satellites, its best if we knew it was coming and could potentially do something about it.
The problem is they are really hard to see. At this scale, these asteroids don’t reflect much light, and ground-based observatories have a hard time tracking them. Some space-based observatories, such as the James Webb Space Telescope, fare better. It was used by some members of the MIT team to track 2024 YR4 and recently definitively rule out an impact on the Moon in 2032. But, since the JWST is our most capable deep-space telescope, demands on its time are so frequent it can’t constantly be used to watch for decameter scale asteroids.
Another ground-based telescope that is coming online shortly should be able to help, though. The Vera Rubin Observatory is expected to find up to 10 times more decameter-scale asteroids than we have previously found. However, while it's great at detecting very faint objects like these small asteroids, it is not great at tracking them, making it hard to determine either the asteroid’s size or trajectory.
To make up for this shortfall, the MIT team is developing a pipeline of other telescopes, such as the MIT Haystack and Wallace Observatories, that should be able to track the asteroids that Vera Rubin finds. That pipeline will also include data analysis to make sure they are tracking actual objects and not artifacts from the telescope or other noise.
Figuring out what to do when they inevitably find a decameter sized asteroid that will actually hit the Earth (or the Moon) is a different matter entirely. It’s almost inevitable that we will though. The MIT researchers expect that, within the next decade, astronomers will identify several small objects on a course to impact the Earth-Moon system this century. As of now, there’s still no framework for the nations of the world to deal with this possibility. But what planetary defenders can be sure of is simply sending Bruce Willis and his hand picked team to take care of it definitely won’t help.
Learn More:
MIT - 3 Questions: Fortifying our planetary defenses
UT - We Need a Rapid Asteroid Response Mission
UT - Should Planetary Defence Take Center Stage?
UT - Roman Space Telescope Joins Earth's Asteroid Defence Team
