On a collision course with Earth, a 2-meter-wide (six-foot-wide) asteroid was detected 2 June by the NASA-funded Catalina Sky Survey near Tucson, Arizona, just hours before impact in the atmosphere. With little tracking data to work with – the body was as close as the Moon when it was first detected – researchers predicted the boulder would hit the atmosphere somewhere along a path stretching from South Africa across the Indian Ocean to New Guinea.
Early that evening, at 16:44 UTC, witnesses reported a brilliant fireball above Botswana, Africa, that matched up with the predicted trajectory. Later calculations showed the rock, dubbed 2018 LA, hit the top of the discernible atmosphere at a blistering 17 kilometres per second (38,000 mph) and broke apart several miles above the surface.
The event was witnessed by multiple observers and caught in a webcam video.
“The discovery of asteroid 2018 LA is only the third time that an asteroid has been discovered to be on an impact trajectory,” said Paul Chodas, manager of the Center for Near-Earth Object Studies at the Jet Propulsion Laboratory in Pasadena, California. “It is also only the second time that the high probability of an impact was predicted well ahead of the event itself.”
As with all such observations, the object was catalogued by the Minor Planet Center in Cambridge, Massachusetts, which determined the possibility of an impact. Those data were passed along to the Center for Near-Earth Object Studies where an automated program known as Scout confirmed the impact trajectory. Additional analysis showed the asteroid posed no threat to Earth and no additional alerts were issued.
But in a nice bit of detective work, two additional observations were obtained by the ATLAS asteroid survey that were used by the Scout system to narrow down the predicted impact points in southern Africa. The International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty then picked up infrasound data just after the event that was consistent with an impact over Botswana.
“This was a much smaller object than we are tasked to detect and warn about,” said Lindley Johnson, Planetary Defence Officer at NASA Headquarters in Washington. “However, this real-world event allows us to exercise our capabilities and gives some confidence our impact prediction models are adequate to respond to the potential impact of a larger object.”