An astronomer explains where meteors come from, if we can stop them, and how their shockwaves create sonic booms
A meteor streaks across the sky during the annual Perseid meteor shower in 2021, viewed from Spruce Knob, West Virginia. Photo: NASA/Bill Ingalls
On Saturday, May 30 at about 2 p.m., many residents in eastern Massachusetts heard a loud bang, which some said sounded like a tree falling on their house. Soon the explanation came—it was a meteor falling from outer space that caused a shockwave as it sped through the atmosphere at about 75,000 miles per hour.
It turns out that meteors are regularly falling to Earth—it’s just that most don’t come anywhere near population centers to see or hear them, says David Martin, assistant professor of astronomy and physics.
To learn more about meteors, whether they can be tracked, and what we can do about them as they head to planet Earth, Tufts Now recently spoke with Martin.
What exactly are meteors?
A meteor is the streak of fire across the sky—a “shooting star”—caused by a small rocky body on the scale of several meters dimension, which we call a meteoroid, entering the atmosphere at tens of kilometers per second. The “fireball” you see is typically ionization of the atmosphere due to the crazy high kinetic energy from the movement of the object. We saw practically the same effect when the Artemis II mission entered Earth’s atmosphere after coming from the Moon.
How often do meteors end up coming near to or hitting Earth?
We largely think of our solar system as a Sun plus eight (or nine, depending how retro you’re feeling) planets, but there are many more smaller bodies around—roughly called meteoroids for the smaller ones and asteroids for the bigger ones.
Indeed, we believe that planets were created from the ground up by sticking together lots of smaller bodies, so any of those small bodies that are still around are the leftovers that didn’t make it into planet formation.
Now, with all of this stuff around, the entire solar system becomes a bit of a gravitational pinball. Meteoroids passing near planets or moons can be deflected in their path, and indeed, that can send them towards Earth.
If you look at a clear sky far from the city, you’ll typically see shooting stars at least once an hour, typically more. Most of those aren’t big enough to cause a boom. Ones like the recent New England one fall pretty regularly—I believe you get something like that every month or so—but to have it so close to a populated area is super rare.
Can they be tracked from Earth?
Yes, but with caveats. Planetary defense is a big thing. A basic component is taking images of the sky on a high cadence (e.g., every night) and seeing if a foreground object (e.g. an asteroid) moves relative to the background (e.g., stars). By tracking its motion and extrapolating forward using what we know about gravity, we can predict its path forward.
However, something as small as a few meters wide would be impossible to track, and indeed the New England one wasn’t tracked. Meteoroids (and asteroids) do not produce their own light—they merely reflect that of the Sun. And a tiny body just isn’t going to reflect much, so they are hard to see.
How does a sonic boom from a meteor happen?
The meteor off of Massachusetts was going at tens of thousands of meters per second, which is much faster than the speed of sound—300 meters per second. This means it was “hypersonic.” The sound waves get compressed together into a shockwave, since the object is now traveling faster than the sound waves propagate.
When this shockwave hits something, it creates a loud boom, because everything is compressed. The shockwave is continuous as long as the meteor is still traveling faster than the speed of sound.
Note that even though the meteor exploded in the atmosphere, rather than making it all the way to the ground, the boom was not an explosion boom—it was this shockwave.
Is there any danger from meteors hitting Earth?
Yes, the Earth gets hit all the time, but there is a wide range of possible effects. Something that would wipe out civilization would have to be in the several kilometers size range, and I think particularly with the new Vera Rubin survey, we are close to knowing if anything like that is coming. Smaller objects (10s of meters across) might do significant damage if they hit a city, and we probably wouldn’t know well in advance.
Can we stop these things? The NASA DART mission a few years ago tested the ability to deflect an asteroid by ramming a spacecraft into it. It was a successful demonstration. If a dangerous body were discovered significantly far in advance, then a small nudge a long time in advance could be enough to deflect it from hitting Earth. We don’t quite have the survey technology yet to find all the dangerous objects yet, though.
