Astronomers discover the largest potentially dangerous asteroid discovered in the last eight years

Twilight observations with the US Department of Energy-manufactured Dark Energy Camera at the Cerro Tololo Inter-American Observatory in Chile, a program of NSF’s NOIRLab, have allowed astronomers to spot three near-Earth asteroids (NEAs) hiding in the sun’s glare . These NEAs are part of an elusive population lurking in the orbits of Earth and Venus. One of the asteroids is the largest potentially dangerous object discovered in the last eight years.

An international team using the Dark Energy Camera (DECam) mounted on the Víctor M. Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile, a program of NSF’s NOIRLab, has three new low-Earth ones Asteroids (NEAs) discovered hiding in the inner solar system the region within the orbits of Earth and Venus. This is a notoriously challenging region for observation as asteroid hunters struggle with the harsh sunlight.

However, by taking advantage of the brief but favorable observing conditions during twilight, astronomers found an elusive trio of NEAs. One is a 1.5-kilometer-wide asteroid called 2022 AP7, which has an orbit that could one day bring it into Earth’s orbit. The other asteroids, named 2021 LJ4 and 2021 PH27, have orbits that are sure to remain entirely within Earth’s orbit. Also of particular interest to astronomers and astrophysicists is 2021 PH27, the closest known asteroid to the Sun. As such, it has the largest general relativity effects of any object in our solar system, and during its orbit its surface gets hot enough to melt lead.

“Our twilight survey is combing the area inside the orbits of Earth and Venus for asteroids,” said Scott S. Sheppard, astronomer at the Carnegie Institution for Science’s Earth and Planets Laboratory and lead author of the article describing this work. “So far we have found two large near-Earth asteroids that are about 1 kilometer in diameter, a size we call planet killers.”

“There are probably very few NEAs of similar sizes left to be found, and these large undiscovered asteroids likely have orbits that keep them within the orbits of Earth and Venus most of the time,” Sheppard said. “So far, only about 25 asteroids have been discovered whose orbits are entirely within Earth’s orbit because it’s difficult to observe them near the bright sunlight.”

Finding asteroids in the inner solar system is a daunting observational challenge. Astronomers have only two short 10-minute windows each night to survey this area, and must contend with a bright background sky resulting from the Sun’s glare. Additionally, such observations occur very close to the horizon, meaning astronomers must observe through a thick layer of Earth’s atmosphere, which can blur and distort their observations.

The discovery of these three new asteroids despite these challenges was possible thanks to DECam’s unique observational capabilities. The state-of-the-art instrument is one of the most powerful wide-field CCD imagers in the world, giving astronomers the ability to image large areas of the sky with high sensitivity.

Astronomers refer to observations as “deep” when they detect faint objects. When searching for asteroids within Earth orbit, the ability to acquire both deep and far field observations is essential.

“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.”

In addition to discovering asteroids that could pose a potential threat to Earth, this research is an important step in understanding the distribution of small bodies in our solar system. Asteroids farther from the sun than Earth are the easiest to spot. Because of this, these more distant asteroids tend to dominate current theoretical models of the asteroid population.

The discovery of these objects also allows astronomers to understand how asteroids are transported through the inner solar system and how gravitational interactions and the Sun’s heat can contribute to their fragmentation.

“Our DECam survey is one of the largest and most sensitive searches ever conducted for objects within 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.”

“After ten years of remarkable service, DECam continues to deliver important scientific discoveries while contributing to the defense of the planet, a critical service that benefits all humankind,” said Chris Davis, NSF program director for NOIRLab.

The results are published in The Astronomical Journal.