A small asteroid hit Earth on Saturday, June 2nd, exploding in the atmosphere over Botswana before it could reach the ground. The Catalina Sky Survey in Arizona had discovered the space rock only hours earlier as it hurtled toward our planet from inside the orbit of the Moon. Sensors used to monitor rogue nuclear explosions detected the asteroid and estimated its yield near ~500 tons of TNT.
The Catalina Sky Survey in Arizona discovered a small asteroid (2018 LA) near the orbit of the Moon. Hours later, it hit Earth.
The boulder-sized space rock entered the atmosphere traveling 38,000 mph (17 km/s) and exploded over Botswana at 6:44 p.m. local time. A video camera at a farm near Ottosda, South Africa, recorded the explosion. It was impressively bright even at a distance:
The explosion sent waves of low-frequency sound (infrasound) rippling through the atmosphere, and it was detected by an infrasound monitor in South Africa, deployed as part of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty. Meteor expert Peter Brown of the University of Western Ontario analyzed the signals and came to these conclusions about the explosion:
“The yield was in the range 0.3 to 0.5 kilotons of TNT,” he says. “That corresponds to a 2 meter diameter asteroid.”
As asteroids go, that’s very small. It posed no significant danger to objects on the ground as it disintegrated almost wholly in the atmosphere. Fragments may yet be found on the ground and recovered for sale or scientific study.
The real significance of this event is that it highlights the growing capability of modern sky surveys to discover asteroids targeting Earth. Even small faint space rocks are being caught in the net. Boulder-sized impactors have been discovered hurtling toward Earth three times in the past 10 years: 2008 TC3 exploded over northern Sudan on Oct. 7, 2008; 2014 AA burned up above the Atlantic Ocean on Jan. 1, 2014; and now 2018 LA. In each case, the warning was less than a day. Larger asteroids may be seen at a greater distance, however, allowing for more lead time. Learn more about the latest impact from NASA.
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 10 miles per second (38,000 mph, or 17 kilometers per second) at about 16:44 UTC (9:44 a.m. PDT, 12:44 p.m. EDT,6:44 p.m. 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,” said Lindley Johnson, Planetary Defense Officer at NASA Headquarters. “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.”
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.
“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 (CNEOS) at JPL. “It is also only the second time that the high probability of an impact was predicted well ahead of the event itself.”
The first event of this kind was the impact of asteroid 2008 TC3, which lit up the predawn sky above Northern Sudan on October 7, 2008. That was a slightly larger asteroid (about 13 feet, or 4 meters in size), and it was discovered a full 19 hours before impact, allowing for a large number of follow-up observations and a very precise trajectory to be calculated. The second predicted impact event was for asteroid 2014 AA, which was discovered only a few hours before impact on Jan. 1, 2014, in the Atlantic Ocean, leaving too little time for follow-up observations. The Catalina Sky Survey has been responsible for discovering all three of these small asteroids on impact trajectories, and all on the watch of the same observer, Richard Kowalski.
NASA’s Planetary Defense Coordination Office is responsible for finding, tracking and characterizing potentially hazardous asteroids and comets coming near Earth, issuing warnings about possible impacts, and assisting coordination of U.S. government response planning, should there be an actual impact threat. JPL hosts the Center for Near-Earth Object Studies for NASA’s Near-Earth Object Observations Program, an element of the Planetary Defense Coordination Office within the agency’s Science Mission Directorate.
For more information about NASA’s Planetary Defense Coordination Office, visit:
More information about asteroids and near-Earth objects can be found at: