Astronomers Discover Three Large Near-Earth Asteroids

Astronomers Discover Three Large Near-Earth Asteroids

Astronomers using the Dark Energy Camera (DECam) on the Víctor M. Blanco 4-m telescope at Cerro Tololo Inter-American Observatory have discovered two rare Atira/Apohele asteroids, which have orbits completely interior to Earth’s orbit, and one Apollo-type asteroid that crosses Earth’s orbit. The latter is likely the largest Potentially Hazardous Asteroid (PHA) discovered in about eight years.

An artist’s impression of an asteroid that orbits closer to the Sun than Earth’s orbit. Image credit: DOE / FNAL / DECam / CTIO / NOIRLab / NSF / AURA / J. da Silva / Spaceengine.

The population of small body in the Solar System interior to Earth’s and Venus’ orbits has not been extensively explored to date because of the difficulty in observing near the glare of the Sun.

Astronomers have only two brief 10-min windows each night to survey this area. Additionally, such observations are very near to the horizon, meaning that they have to observe through a thick layer of Earth’s atmosphere, which can blur and distort their observations.

Discovering the new asteroids despite these challenges was possible thanks to the unique observing capabilities of DECam.

“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,” said Dr. Scott Sheppard, an astronomer with the Carnegie Institution for Science.

“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.”

One of the newly-discovered asteroids, 2022 AP7, is an Apollo-type object with a diameter of 1.5 km and an orbit that may someday place it in Earth’s path.

The other asteroids, 2021 LJ4 and 2021 PH27, have orbits that safely remain completely interior to Earth’s orbit.

2021 PH27 is about 1 km in size and is 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.

2021 PH27 has strong interactions with Venus and will soon become a PHA to this planet.

“Our twilight survey is scouring the area within the orbits of Earth and Venus for asteroids,” Dr. Sheppard said.

“So far we have found two large near-Earth asteroids that are about 1 km across, a size that we call planet killers.”

“There are likely only a few near-Earth asteroids 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.”

The discovery is described in a paper in the Astronomical Journal.

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Scott S. Sheppard et al. 2022. A Deep and Wide Twilight Survey for Asteroids Interior to Earth and Venus. AJ 164, 168; doi: 10.3847/1538-3881/ac8cff

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