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Astronomers have spotted three near-Earth asteroids lurking undetected in the sun’s glare. One of the asteroids is the largest potentially dangerous object for Earth discovered in the past eight years.
The asteroids belong to a group in orbit between Earth and Venus, but they’re incredibly difficult to observe because the Sun’s brightness shields them from telescopic observations.
To avoid glare from the sun, the astronomers took the opportunity to conduct their observations during the brief twilight window. An international team spied the space rocks while using the Dark Energy Camera located on the Victor M. Blanco 4-meter telescope, located at the Cerro Tololo Inter-American Observatory in Chile.
Their findings were published in Monday The Astronomical Journal.
One of the asteroids, called 2022 AP7, is 1.5 kilometers (0.9 miles) wide and has an orbit that could put it in Earth’s orbit in the future, but it’s difficult for scientists to know when.
“Our twilight survey scans the area inside the orbits of Earth and Venus for asteroids,” study lead author Scott S. Sheppard, an astronomer at the Carnegie Institution for Science’s Earth & Planets Laboratory, said in a statement.
“So far we have found two large near-Earth asteroids that are about 1 kilometer in diameter, a size we call planet killers.”
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 hot enough to melt lead.
Asteroid-hunting astronomers face quite a challenge when trying to find space rocks in the inner Solar System – which includes Mercury, Venus, Earth, Mars and the main asteroid belt. To avoid the sun’s glare, they only have two 10-minute windows each night to scan the area with ground-based telescopes.
At twilight, astronomers still face the complications of a bright background sky due to the sun. And to search the inner solar system, their telescopes have to focus close to the horizon, which means they have to see through Earth’s dense atmosphere and its blurring effects.
Even though things sound complicated to ground-based telescopes, observations of the inner Solar System are impossible for space-based telescopes like Hubble and James Webb, as the sun’s heat and intense light could fry their instruments, which is why both space observatories face away from the star.
The Dark Energy Camera’s wide-field capability helped astronomers overcome their observational challenges, and they were able to capture large parts of the night sky in detail.
“Large areas of sky are needed because the inner asteroids are rare, and deep images are needed because asteroids are faint and you have to contend with the bright twilight skies near the sun and the distorting effect of Earth’s atmosphere,” Sheppard said. “DECam can cover large areas of the sky to depths unattainable with smaller telescopes, allowing us to go deeper, cover more sky, and study the inner Solar System in a way never seen before.”
Near-Earth objects are asteroids and comets with an orbit that places them within 30 million miles (48.3 million kilometers) of Earth. Detecting the threat of near-Earth objects that could cause severe damage is a major focus for NASA and other space agencies around the world.
There are currently no asteroids on a direct impact course with Earth, but there are more than 27,000 near-Earth asteroids of all shapes and sizes.
While NASA recently did, it can successfully change the motion of an asteroid in space With September’s Double Asteroid Redirection Test, or DART mission, astronomers must first find space rocks that pose a threat to our planet. Instruments like the Dark Energy Camera as well as future space-based observatories like the Near Earth Object Surveyorcan locate previously unknown asteroids.
Studying and understanding asteroid populations will also help scientists understand the distribution and dynamics of space rocks — such as how the Sun’s heat can fracture and fragment them over time.
“Our DECam survey is one of the largest and most sensitive searches ever conducted for objects in Earth orbit and near Venus orbit,” said Sheppard. “This is a unique opportunity to understand what types of objects lurk in the inner solar system.”