Last Saturday afternoon, a tiny asteroid burned up through the atmosphere just off the coast of Puerto Rico. The event was captured by weather satellites but it was also spotted by astronomical observatories well before the asteroid actually came close to our planet.
The object, known as 2019 MO, is estimated to have been around 4 meters (13 feet) in diameter, which could take down a building if it hit Earth, but is actually too small to survive burning up in the atmosphere.
The ATLAS observatory in Hawaii spotted the object four times in just 30 minutes when the asteroid was 500,000 kilometers (310,000 miles) from our planet, or 1.3 times the distance from Earth to the Moon, before it entered our atmosphere. The detection happened at about midnight local time, and proves that the ATLAS and Pan-STARRS survey telescopes can detect asteroids with enough time to provide a sufficiant warning for evacuation of impact sites.
The observations were assessed automatically by the Jet Propulsion Laboratory (JPL) Scout impact analysis software, which only gave a modest 2 on the likelihood of it hitting our planet (4 is likely). Jump to 12 hours later, and a bolide was observed crossing the Caribbean ocean. After this, JPL’s Davide Farnocchia wondered if the two were the same and asked the community for more observations in the patch of sky where 2019 MO was discovered.
Another Hawaiian telescope, Pan-STARRS 2 was operating at the same time and imaging the same area of the sky. Despite the camera not being fully operational, the team was able to analyze the images and find the asteroid. With the combined data of ATLAS and Pan-STARRS 2, the Scout software changed its estimation to likely and drew a predicted entry path very close to where the space rocks actually exploded, roughly 380 kilometers (240 miles) south of San Juan.
Twelve hours notification might not seem a huge amount of time but if it was a more dangerous object, this could have been life-saving. The successful location and pathway prediction could mean that for larger objects, we may be able to make detections days in advance. Perhaps not enough time to launch a mission to deflect the object, but maybe enough to send people at risk of being in an object's path to safety.
ATLAS automatically scans the whole sky every couple of nights, looking in all directions. It currently discovers around 100 asteroids larger than a block of flats every year. These are considered "town killers", similar in size to the one that exploded over Chelyabinsk in Russia in 2013, which was about 20 meters (65 feet) across. Anything larger than 140 meters (460 feet) has the potential to devastate a country and it's estimated that only about one-third of them are known to us. This successful prediction of power is certainly needed.