Tiny, Earth-bound asteroid has disintegrated over Africa: NASA

A boulder-sized asteroid on a collision course with Earth reportedly disintegrated in the atmosphere - lighting up the sky over Botswana, according to NASA.

The asteroid, estimated to be only about two metres across, was first discovered on June 2 by the Catalina Sky Survey, operated by the University of Arizona.

Designated 2018 LA, the asteroid was small enough that it was expected to safely disintegrate in Earth's atmosphere.

Although there was not enough tracking data to make precise predictions ahead of time, a swath of possible locations was calculated stretching from Southern Africa, across the Indian Ocean, and onto New Guinea.

Reports of a bright fireball above Botswana, Africa, early Saturday evening match up with the predicted trajectory for the asteroid.

The asteroid entered Earth's atmosphere at the high speed of 17 kilometres per second at about 6:44 pm local Botswana time and disintegrated several miles above the surface, creating a bright fireball that lit up the evening sky.

When it was first detected, the asteroid was nearly as far away as the Moon's orbit, although that was not initially known. The asteroid appeared as a streak in the series of time-exposure images taken by the Catalina telescope.

As is the case for all asteroid-hunting projects, the data were quickly sent to the Minor Planet Center in Cambridge, Massachusetts, which calculated a preliminary trajectory indicating the possibility of an Earth impact.

The data were in turn sent to the Center for Near-Earth Object Studies (CNEOS) at NASA's Jet Propulsion Laboratory in Pasadena, California, where the automated Scout system also found a high probability that the asteroid was on an impact trajectory.

Automated alerts were sent out to the community of asteroid observers to obtain further observations, and to the Planetary Defense Coordination Office at NASA Headquarters in Washington.

However, since the asteroid was determined to be so small and therefore harmless, no further impact alerts were issued by NASA.

"This was a much smaller object than we are tasked to detect and warn about. 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," said Lindley Johnson, Planetary Defense Officer at NASA Headquarters.

The ATLAS asteroid survey obtained two additional observations hours before impact, which were used by Scout to confirm the impact would occur, and narrowed down the predicted location to southern Africa.

Infrasound data collected just after the impact clearly detected the event from one of the listening stations deployed as part of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty. The signal is consistent with an atmospheric impact over Botswana.