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\u2014it was a meteor falling from outer space that caused a shockwave as it sped through the atmosphere at about 75,000 miles per hour.<\/p>\n
It turns out that meteors are regularly falling to Earth\u2014it\u2019s just that most don\u2019t come anywhere near population centers to see or hear them, says David Martin<\/a>, assistant professor of astronomy and physics.\u00a0<\/p>\n 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.\u00a0<\/p>\n What exactly are meteors?<\/p>\n A meteor is the streak of fire across the sky\u2014a \u201cshooting star\u201d\u2014caused 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 \u201cfireball\u201d 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\u2019s atmosphere after coming from the Moon.<\/p>\n How often do meteors end up coming near to or hitting Earth?<\/p>\n We largely think of our solar system as a Sun plus eight (or nine, depending how retro you\u2019re feeling) planets, but there are many more smaller bodies around\u2014roughly called meteoroids for the smaller ones and asteroids for the bigger ones.\u00a0<\/p>\n 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\u2019t make it into planet formation.\u00a0<\/p>\n 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.\u00a0<\/p>\n If you look at a clear sky far from the city, you\u2019ll typically see shooting stars at least once an hour, typically more. Most of those aren\u2019t big enough to cause a boom. Ones like the recent New England one fall pretty regularly\u2014I believe you get something like that every month or so\u2014but to have it so close to a populated area is super rare.<\/p>\n Can they be tracked from Earth?<\/p>\n 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.\u00a0<\/p>\n However, something as small as a few meters wide would be impossible to track, and indeed the New England one wasn\u2019t tracked. Meteoroids (and asteroids) do not produce their own light\u2014they merely reflect that of the Sun. And a tiny body just isn\u2019t going to reflect much, so they are hard to see.<\/p>\n How does a sonic boom from a meteor happen?<\/p>\n The meteor off of Massachusetts was going at tens of thousands of meters per second, which is much faster than the speed of sound\u2014300 meters per second. This means it was \u201chypersonic.\u201d The sound waves get compressed together into a shockwave, since the object is now traveling faster than the sound waves propagate.\u00a0<\/p>\n 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.<\/p>\n 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\u2014it was this shockwave.\u00a0<\/p>\n Is there any danger from meteors hitting Earth?<\/p>\n 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<\/a>, 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\u2019t know well in advance.<\/p>\n