Astronomers just detected a potentially hazardous 0.9-mile-wide asteroid hiding in the Sun's glare

A special camera was used to detect the asteroid trio lurking in the Sun’s glare.
Deena Theresa
Artist’s impression of an asteroid that orbits closer to the Sun than Earth’s orbit.
Artist’s impression of an asteroid that orbits closer to the Sun than Earth’s orbit.


An international team of astronomers has discovered three near-Earth asteroids (NEAs) hiding in the inner Solar System, safely tucked in the glare of the Sun. One of them is an enormous asteroid, dubbed a "planet killer" that could someday collide with the Earth.

One does not have to worry, as currently there are no predicted approaches with the Earth.

Named 2022 AP7, the 0.9-mile-wide (1.5 kilometers) asteroid is the largest object that is potentially hazardous to Earth to be discovered in the last eight years. The asteroid trio remain undetected hitherto as they were lurking in the region interior to the orbits of Earth and Venus, enveloped in the Sun's blinding light. Astronomers have only two brief 10-minute windows each night to survey the area. The challenges do not stop with the Sun's glare; they have to observe through a rather thick layer of the Earth's atmosphere. This can distort their observations.

And so, the asteroid hunters had to wait for favorable observing conditions during twilight to spot space rocks.

"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," Scott S. Sheppard, an astronomer at the Earth and Planets Laboratory of the Carnegie Institution for Science and the lead author of the paper describing this work, said in a statement. "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,"

The astronomers detailed their work in The Astronomical Journal.

The Dark Energy Camera helped discover the trio of asteroids

The finding was made possible, thanks to the U.S Department of Energy-fabricated Dark Energy Camera located on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF's NOIRLab.

The Dark Energy Camera, or the DECam, comprises high-performance, wide-field CCD imagers, that can capture details of the sky with "great sensitivity".

"Large areas of the 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."

The discovery also included two other asteroids called 2021 LJ4 and 2021 PH27, that have orbits that safely remain completely interior to Earth’s orbit. 2021 PH27 is particularly interesting as it's the closest known asteroid to the Sun. Therefore, 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," as per the statement.

"Our DECam survey is one of the largest and most sensitive searches ever performed for objects within Earth’s orbit and near Venus’s orbit,” said Sheppard. "This is a unique chance to understand what types of objects are lurking in the inner Solar System.”

This research is particularly important for identifying and understanding the "distribution" of small bodies in the Solar System. As asteroids that are far from the Sun are easy to detect, they tend to dominate the existing theoretical models of space rocks.

Study Abstract:

We are conducting a survey using twilight time on the Dark Energy Camera with the Blanco 4 m telescope in Chile to look for objects interior to Earth's and Venus' orbits. To date we have discovered two rare Atira/Apohele asteroids, 2021 LJ4 and 2021 PH27, which have orbits completely interior to Earth's orbit. We also discovered one new Apollo-type Near Earth Object (NEO) that crosses Earth's orbit, 2022 AP7. Two of the discoveries have diameters ≳1 km. 2022 AP7 is likely the largest Potentially Hazardous Asteroid (PHA) discovered in about eight years. To date we have covered 624 square degrees of sky near to and interior to the orbit of Venus. The average images go to 21.3 mag in the r band, with the best images near 22nd mag. Our new discovery 2021 PH27 has the smallest semimajor axis known for an asteroid, 0.4617 au, and the largest general relativistic effects (53 arcsec/century) known for any body in the solar system. The survey has detected ∼15% of all known Atira NEOs. We put strong constraints on any stable population of Venus co-orbital resonance objects existing, as well as the Atira and Vatira asteroid classes. These interior asteroid populations are important to complete the census of asteroids near Earth, including some of the most likely Earth impactors that cannot easily be discovered in other surveys. Comparing the actual population of asteroids found interior to Earth and Venus with those predicted to exist by extrapolating from the known population exterior to Earth is important to better understand the origin, composition, and structure of the NEO population.

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