Oh, great. By peering into twilight, boffins find 'planet killer' asteroids in our system

One may hit Earth, but unlikely. One could whack Venus. This is good or bad news, depending on your outlook

Astronomers have spotted an asteroid of sufficient size and orbit to cause Earth-wide destruction – if it were to ever strike our planet. And that's a mighty big if.

2022 AP7 was discovered alongside two other large asteroids – 2021 LJ4 and 2021 PH27 – by a team of scientists looking for objects within the inner Solar System during observations at the Cerro Tololo Inter-American Observatory in Chile.

Over 30,000 near-Earth asteroids have been cataloged so far, and thousands of new entries are added each year. The latest trio of space rocks, however, are notable for their size and location.

At less than a kilometre in diameter, 2021 LJ4 is the smallest of the three.

2021 PH27 is over a kilometre wide, is the nearest known asteroid to the Sun, and offers the hellish prospect of surface temperatures hot enough to melt lead when it's closest to our star.

And 2022 AP7, also just over a kilometre wide and with a five-year orbit of the Sun, is the largest potentially hazardous asteroid to be found in our system in the past eight years, according to a paper published lately in The Astrophysical Journal.

Currently, there are no dates that would have 2022 AP7 collide with Earth and it is highly unlikely it ever will

"Currently, 2022 AP7 crosses Earth orbit, which means it is a potentially hazardous asteroid as it could one day collide with Earth, if Earth happened to be in its orbit at the exact spot the asteroid crosses it," Scott Sheppard, an astronomer at the Earth and Planets Laboratory of the Carnegie Institution for Science and the lead author of the paper, told The Register on Monday.

"Currently there are no dates that would have 2022 AP7 collide with Earth and it is highly unlikely it ever will.

"If 2022 AP7 were to collide with Earth, it would be a mass extinction event as dust would be blown up into the Earth's atmosphere for years, blocking out the precious needed sunlight."

These inner-system asteroids are difficult to spot because observing them requires staring at the Sun – which is so bright its glare obscures small objects. The team only discovered the trio when they observed the night sky in short bursts during twilight hours when the Sun's glare was at its lowest. 

"Our twilight survey is scouring the area within the orbits of Earth and Venus for asteroids," Sheppard said in an earlier statement. "So far we have found two large near-Earth asteroids that are about one kilometer across – a size that we call planet killers."

Astronomers only had two brief ten-minute windows to observe the space rocks using the observatory's Dark Energy Camera (DECam) mounted on the Víctor M. Blanco four-metre telescope, and even with that fine instrument at their disposal, the asteroid boffins don't have it easy. 

"Large areas of sky are required because the inner asteroids are rare, and deep images are needed because asteroids are faint and you are fighting the bright twilight sky near the Sun as well as the distorting effect of Earth's atmosphere," said Sheppard. "DECam can cover large areas of sky to depths not achievable on smaller telescopes, allowing us to go deeper, cover more sky, and probe the inner solar system in ways never done before."

If you're wondering about 2021 LJ4 and 2021 PH7: they are not dangerous and will not trouble us Terrans as the rocks circle the Sun at distances within Venus' orbit. There is a 0.7 percent chance 2021 PH27 may collide with Earth's neighbor in the next million years, the researchers calculated.

The scientists believe there are a few more potentially hazardous undiscovered objects within the Solar System, and pledged that the search would go on.

"There are likely only a few near-Earth asteroids with similar sizes left to find, and these large undiscovered asteroids likely have orbits that keep them interior to the orbits of Earth and Venus most of the time. Only about 25 asteroids with orbits completely within Earth's orbit have been discovered to date because of the difficulty of observing near the glare of the Sun," Sheppard concluded. ®

More about


Send us news

Other stories you might like