Nearly 1,000 bright fireballs – large meteors that (mostly) burn up in Earth’s atmosphere – have hit our planet since 1988. We know this because the US Department of Defense has tracked them.
For years, the Department of Defense (DoD) released only basic information about these events. Now, through a collaboration between NASA and the US Space Force, the DoD is releasing additional data on the brightest fireballs to aid basic research and planetary defense.
If you have observed meteor showers, you may have seen a fireball. These meteors are the brightest, brighter than Venus, which occur when a larger-than-usual space rock crashes into our upper atmosphere. Cars represent the brightest fireballs (although in practice the terms are often used interchangeably).
Here’s what’s really happening when you see that bright flash for a few seconds: When a meteoroid enters the atmosphere, air friction pulls its surface away. The extreme pressure on the front end often breaks the body, which can exceed one meter in size. These pieces then make surface contact with the atmosphere until all of the meteor has vaporized into the upper atmosphere, usually in the mesosphere, about 50 to 85 km (31 to 53 miles) above the Earth’s surface. The whole event only takes a few seconds.
Until now, researchers had to rely on publicly available data: usually the time, location, and altitude of the impact, along with the estimated velocity, along with occasional estimates of the total energy of the fireball. Now, for the first time, scientists will have access to crucial information: how these explosions vary in brightness over the few seconds it takes them to break apart.
The energy released by a typical atmospheric impact is on the order of a few hundred tons of TNT. A few freed a couple thousand tons, however, and the Chelyabinsk meteor that exploded over Russia in 2013 released the energy of 440,000 tons of TNT, slightly less than the Tunguska explosion of 1908.
Much of these fireworks occur at infrared wavelengths, but US government sensors register visible light. Consequently, the light curves can only be built for the brightest fireballs. Check out the database here: Fireball Light Curve Database
By observing the light emitted when a meteor smashes, scientists can learn more about the meteors themselves. “[Meteors’] The response to increasing atmospheric pressure, represented by the light curves, is an indirect probe of their strength and structure,” says Peter Brown (University of Western Ontario, Canada), a planetary scientist who has used publicly available fireball data in its own search. “By studying light curves, we can indirectly infer the overall strength of near-Earth objects ranging in size from a meter to a decametre.”
Such data can, for example, shed light on whether an incoming meteor is a fragment of an asteroid or a comet. Understanding meteor structures is key to defending the planet against future impacts.
An interstellar object before ‘Oumuamua?
An unexpected result to come from the fireball data analysis is the identification of a possible interstellar bolide – that is, an impactor originating from outside the solar system. It should be noted from the outset, however, that not everyone is convinced of the claim.
In 2019, Amir Siraj and Abraham Loeb (both of Harvard University) reported that a half-meter meteor detected on January 8, 2014 was heading towards Earth on a hyperbolic orbit, one not related to the Sun. They based the object’s trajectory on the high impact velocity recorded at the Center for Near-Earth Object Studies (CNEOS): 44.8 kilometers per second (100,000 mph).
If this materializes, it would precede the discovery of ‘Oumuamua, believed to be the first interstellar object, by three years. Joel Mozer, the US Space Operations Command’s chief scientist, believes the velocity data is accurate enough to point to the origin of the meteor from outside the solar system. However, others do not think the evidence merits such an extraordinary claim.
“The data referred to relates to only a very brief period as the fireball is detected passing through the Earth’s atmosphere,” says NASA planetary defense officer Lindley Johnson. “The duration of the data is less than 5 seconds and there are no other known sources of independent detection.”
“Although further analysis by our US Space Force source confirms a relatively high speed for this bolide,” he adds, “it is very difficult to be conclusive as to the origin of a object based on this sparse and short data scope.”