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(CNN) --
Astronomers have spotted three near-Earth asteroids hidden behind the sun's glare. One of them is the biggest potential hazard object to Earth discovered in the past eight years.
Asteroids are part of a group that lies within the orbits of Earth and Venus, but they are very difficult to detect because the brightness of the Sun shields them from observations with telescopes.
To avoid the Sun's glare, astronomers took the opportunity to make their observations during the brief window of twilight.
An international team observed the space rocks using the Dark Energy Camera (DECam) of the 4-meter Victor M. Blanco telescope, which is located at the Cerro Tololo Inter-American Observatory in Chile.
Their findings were published Monday in the academic journal
The Astronomical Journal.
One of the asteroids, called 2022 AP7, is 1.5 kilometers wide and has an orbit that could bring it closer to Earth's path in the future.
But it's hard for scientists to know when that would happen.
This artist's illustration shows an asteroid orbiting closer to the Sun than Earth's orbit.
(Credit: NSF/DOE/FNAL/DECam/CTIO/NOIRLab NOIRLab)
"Our twilight survey looks for asteroids in the orbits of Earth and Venus," explained study lead author Scott S. Sheppard, an astronomer with the Earth and Planets Laboratory at the Carnegie Institution for Science in Washington, in a statement. .
"So far we have found two large near-Earth asteroids that are around 1 kilometer in diameter, a size for which we call them 'planet killers'."
Scientists determined that the asteroid crosses Earth's orbit, but it does so when our planet is on the opposite side of the Sun. A pattern that will continue for centuries, as the asteroid takes five years to complete one orbit around the Sun. But , over time, the asteroid's orbital motion will become more synchronized with that of Earth.
Scientists don't know the asteroid's orbit precisely enough to say how dangerous it could become in the future.
For now, however, "it will stay well away from Earth," Sheppard said.
A near-Earth asteroid measuring 1 kilometer or more "would have a devastating impact on life as we know it," he added.
Dust and pollutants would fill the atmosphere for years, cooling the planet and preventing sunlight from reaching Earth's surface.
"It would be a mass extinction event the likes of which has not been seen on Earth in millions of years," Sheppard said.
The team expects to find more "planet killer" asteroids in their observations over the next few years.
Scientists believe there are about 1,000 near-Earth objects larger than a kilometer in size, and studies in the last decade have found about 95% of them.
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The other two asteroids, 2021 LJ4 and 2021 PH27, are in much safer orbits that pose no risk to Earth.
However, astronomers are intrigued by 2021 PH27, because it is the closest known asteroid to the Sun.
As the space rock approaches our star, its surface reaches temperatures high enough to melt lead.
Asteroid-hunting astronomers face a major challenge in finding them in the inner solar system, which includes Mercury, Venus, Earth, Mars, and the main asteroid belt.
To avoid the strong sunlight, they only have two 10-minute windows each night to survey the area with ground-based telescopes.
During twilight, astronomers still face the complications of having the Sun shine as a backdrop.
And to search the inner solar system, their telescopes must focus near the horizon, which means they have to peer through Earth's thick atmosphere and its blurring effects.
If things seem complicated for ground-based telescopes, observations of the inner solar system are impossible for space telescopes like Hubble and James Webb because the heat and intense light from the Sun could burn out their instruments.
For that reason, both space observatories point far from the star.
The wide-field capability of the Dark Energy Camera helped astronomers overcome their observing challenges and were able to examine vast expanses of the night sky in detail.
"Large areas of sky are needed because inner asteroids are rare, and deep imaging is needed because asteroids are faint and you're fighting against the bright twilight sky near the Sun, as well as the distorting effect of Earth's atmosphere." Sheppard explained.
"DECam can cover large areas of the sky at depths that smaller telescopes can't reach. This allows us to go deeper, cover more sky and probe the inner Solar System in ways never before possible."
Near-Earth objects are asteroids and comets with an orbit that places them within 30 million miles of Earth.
Detecting the threat of objects close to our planet, which could cause serious damage, is one of the main objectives of NASA and other space organizations around the world.
No asteroid is currently on a direct impact course with Earth.
But there are more than 27,000 near-Earth asteroids of all shapes and sizes.
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Although NASA has recently shown that it can successfully alter the trajectory of an asteroid with the Double Asteroid Redirection Test (DART) mission in September, astronomers must first find the space rocks that pose a threat to our planet.
Instruments like the Dark Energy Camera, as well as future space observatories like the Near Earth Object Surveyor, can locate hitherto unknown asteroids.
Studying and understanding asteroid populations will also help scientists understand the distribution and dynamics of space rocks, such as how heat from the Sun can fracture and fragment them over time.
"Our DECam survey is one of the most extensive and sensitive searches ever conducted for objects within Earth orbit and near the orbit of Venus," said Sheppard.
"This is a unique opportunity to understand what types of objects lurk in the inner Solar System."