It would have been terrifying to be a citizen of Botswana on early Saturday evening. A blindingly white orb suddenly streaked down the sky toward the horizon, appearing larger and brighter with every second. Just as it looked ready to crash into the Earth, it exploded into a huge dome of light, illuminating the sky. Unless you worked for NASA, you probably wouldn’t have known what happened. Even NASA only sort of knew what was going on, but the space agency stayed cool.
In a news release on Sunday, NASA’s Jet Propulsion Laboratory stated that the six-foot-wide asteroid, named 2018 LA, was discovered on Saturday morning to be on a collision course with Earth. There weren’t enough data to determine exactly where it’d hit: Scientists sketched out a very rough map covering South Africa, the Indian Ocean, and New Guinea, comprising a very large swath of Earth. But they weren’t too worried because the asteroid, being so small, was “expected to safely disintegrate in Earth’s atmosphere.”
NASA was right, fortunately, and the asteroid disintegrated several miles above the surface of Botswana, which is what created the bright white fireball. Paul Chodas, manager of the Center for Near-Earth Object Studies at JPL and seemingly chill guy, reassured the public in a statement that NASA and its network of international space agencies are on top of planet’s asteroid watch, even though this most recent one may have seemed like a close call.
“The discovery of asteroid 2018 LA is only the third time that an asteroid has been discovered to be on an impact trajectory,” he said. “It is also only the second time that the high probability of an impact was predicted well ahead of the event itself.”
NASA and its affiliates keep track of potential Armageddon scenarios using an array of survey telescopes that are constantly taking pictures of the sky. If something is moving, images taken successively of the same patch of sky will reveal an object slowly changing position. An array of computers are tasked with finding these moving anomalies, and if they do, they check it against a database of “known objects” — bodies like comets and periodic meteor showers, which aren’t cause for alarm. If they can’t find the object in the database, then it gets placed on NASA’s radar as an “object to confirm” — and gets top priority if its calculated trajectory puts it on a collision course with Earth.
That seems to be what happened in the case of LA 2018. It was first detected by telescopes near Tucson, Arizona operated by the Catalina Sky Survey when it was far away near the Moon’s orbit. The Minor Planet Center in Cambridge, Massachusetts and Center for Near-Earth Object Studies in Pasadena, California took that data and calculated the asteroid could indeed hit Earth. Sending alerts to citizen asteroid observers as well as the Planetary Defense Coordination Office at NASA Headquarters in Washington, they put all interested parties on Asteroid Watch. “However, since the asteroid was determined to be so small and therefore harmless,” NASA writes, “no further impact alerts were issued by NASA.”
As space rocks enter the Earth’s atmosphere at blisteringly fast speeds — LA 2018 entered at 38,000 miles per hour — they break apart, and all the fragments heat up and burn away, creating the bright lights we see in the sky. At only six feet across, LA 2018 was deemed unworthy of a closer look: It would certainly burn up before it touched down. For comparison, the meteor that exploded over Chelyabinsk, Russia in 2013 and injured 950 people, was 65 feet wide; as a 2017 study on the explosion showed, it might have actually exploded from the inside out.
Fortunately, nobody was hurt in Botswana or in South Africa, where LA 2018’s trajectory came to an end, though it’s probably safe to say local residents weren’t nearly as chill as NASA.