Want to know if that meteor that just struck Earth has a companion? Take a look at its trail. A new study shows that images of a meteor’s streak through the atmosphere taken by Earth-gazing probes, including weather satellites, can pin down the object’s orbit, enabling scientists to check and see whether another planet-threatening object is traveling in the same trajectory. The finding comes thanks to the almost-20-meter-wide meteoroid that blazed into Earth’s atmosphere in February and exploded over Chelyabinsk, Russia, damaging buildings there and injuring hundreds. Soon after it streaked over the country (main image)—in some cases, mere minutes later—a number of satellites snapped views of the trail from on high (example, inset). Analyses of those images enabled researchers to confirm the trail’s location, height, and orientation, which in turn allowed them to determine the orbit that the object had been following before it slammed into the atmosphere. The orbit estimated using satellite data alone reasonably matched the one estimated via ground-based videos, the team reports online today in the Proceedings of the National Academy of Sciences. In situations where objects enter Earth’s atmosphere in more remote locations—over the ocean far from land, for example—satellites may be the only sources of data that could be used to determine an object’s orbit. The threat to our planet from an object’s orbital companions isn’t merely an abstract concern, the researchers contend: One recent study suggests that about 15% of the asteroids that cross Earth’s path may be part of double or triple asteroid systems.

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