For just the seventh time ever, astronomers spotted an asteroid in space hours before it came falling down to Earth in a blaze.
In images taken at 20:18:07 UTC on February 12, the asteroid 2023 CX1, also known as Sar2667, was spotted by astronomer Krisztián Sárneczky of Konkoly Observatory's Piszkéstető Station in Hungary. It appeared to be "nothing special at first", Sárneczky noted on Twitter – just a normal object in near-Earth space.
But then the telescope recorded the asteroid a second time, and the discovery was reported to the International Astronomical Union's Minor Planet Center.
Based on these and other follow-up observations, scientists were able to calculate the trajectory of 2023 CX1. Their results indicated a 100 percent impact probability, right down to the approximate time it would arrive and even where on the globe the asteroid – by then a meteor, an object that has entered Earth's atmosphere – would hit.
The discovery image of #2023 CX1 (aka #Sar2667) taken at #Konkoly Observatory's Piszkéstető Station with the 0.60-m Schmidt telescope. Three 4x25 sec stacked images. Nothing special at first. A normal 19.5 mag NEO. pic.twitter.com/1PaYtsv9tz— Krisztián Sárneczky (@sarneczky) February 13, 2023
Their estimates placed the time of the impact between 02:50 and 03:03 UTC, over the English Channel that separates France and the UK. And, sure enough, at 02.59 UTC, 2023 CX1 turned into a spectacular fireball lighting up the skies as it ruptured into a glowing rubble-pile of falling debris. Any of those smaller rocks that might have hit dry land would be most likely found on the coast of France, north to the city of Rouen.
There are a number of reasons why this detection is so amazing. Measuring just an estimated 1.1 meters (3.3 feet) across, 2023 CX1 is one of the smallest impactors detected prior to atmospheric entry yet. And although only seven such detections have ever been made, 2023 CX1 is the third in the last 12 months. This means that we're getting much better at spotting potential meteorites well before they hit.
The other six asteroids that were detected prior to entry, and whose names reflect the years they were discovered, were 2008 TC3, which was around 4 meters across; 2014 AA, at 3 meters across; 2018 LA, also three meters across; 2019 MO at 6 meters across; 2022 EB5, which was around 2 meters across, spotted 2.5 hours prior to impact and also discovered by Sárneczky; and 2022 WJ1, just 1 meter across, spotted 4 hours prior to impact.
There are actually a fair number of rocks on a path that risks them entering a space close to Earth as they orbit the Sun. These are called near-Earth asteroids, and at time of writing, astronomers have discovered and cataloged 31,291 of them. Most of them are pretty small, and not likely to pose a danger; like 2023 CX1, they will burn up as fireballs as they fall through the atmosphere, breaking up and raining down as much smaller pieces of debris.
Astronomers are confident they're aware of almost all the near-Earth asteroids that could cause some serious damage. None of these, known as potentially hazardous asteroids, are going to come close enough to Earth in the next century to cause concern.
There is always the possibility that we've missed a sneaky rock or two, or that new threats could be knocked our way, so it's only sensible to hone our potential impactor detection skills. In addition, having advance warning of meteor fireballs will mean more people will have the opportunity to observe these spectacular events.
Scientists can also be better prepared to take more detailed observations as fireballs streak across the sky and crumble into dust. Exactly how these rocks burn up and break apart isn't fully understood; learning more about the process will not only help us better understand asteroids and meteors, it will help conduct risk assessment for other inbound space rocks.