Astronomers in Chile have discovered a "planet killer" asteroid lurking in the glare of the Sun. Using the Dark Energy Camera (DECam), placed on top of the Victor M. Blanco four-metre telescope at Cerro Tololo Inter-American Observatory in Chile, scientists came across not one but three asteroids.
The largest of the three may be the biggest potentially dangerous asteroid that has been discovered in the past eight years, at 1.5km wide. Spotting asteroids in this region is difficult because asteroid hunters have to compete with the Sun's light.
But during twilight, when the light conditions were the most favourable, astronomers discovered three NEAs - near Earth asteroids. The largest asteroid, called 2022 AP7, has an orbit that means it may end up in the Earth's path some day.
The other asteroids, called 2021 LJ4 and 2021 PH27, have orbits that safely remain completely interior to Earth's orbit. 2021 PH27 is the closest known asteroid to the sun, and during orbit, its surface can get hot enough to melt lead.
Scott S. Sheppard, astronomer at the Earth and Planets Laboratory of the Carnegie Institution for Science and lead author of the paper published in Astronomical Journal, said: "Our twilight survey is scouring the area within the orbits of Earth and Venus for asteroids. So far we have found two large near-Earth asteroids that are about one kilometre across, a size that we call planet killers.
"There are likely only a few NEAs 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."
It can be challenging for astronomers to spot asteroids within the Solar System. They generally only have ten minutes to get a look at this area, and the bright background of the sky can make it even more difficult. As well as this, asteroids are often spotted on the Earth's horizon, meaning that astronomers have to look at them through the thickness of the Earth's atmosphere. This can mean that their vision is blurred or distorted.
Discovering these three new asteroids despite these challenges was possible thanks to the unique observing capabilities of DECam: a state-of-the-art instrument that is one of the highest-performance, wide-field CCD (charge-coupled device) imagers in the world.
Mr Sheppard said: "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.
"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."
Discovering asteroids that are close to Earth not only offers protection, but is also a step forward in understanding the distribution of small bodies in the Solar System. Asteroids that are further from the sun than the Earth are the easiest to spot.
Because of that, these fawaray asteroids tend to dominate current theoretical models of the asteroid population. Detecting these small objects also allows experts to understand how asteroids are transported throughout the inner Solar System, and how certain factors can contribute to their breaking-up.
The study - 'A deep and wide twilight survey for asteroids interior to Earth and Venus' - is published in The Astronomical Journal, 164, 168.
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