The asteroid orbits close to the sun from Earth's orbit

Observations of the aurora using the US Department of Energy’s Dark Energy Camera at NOIRLab’s Cerro Tololo Inter-American Observatory in Chile enabled astronomers to spot three Near-Earth Asteroids (NEAs) hiding in the glare of the Sun. These near-Earths are part of an elusive population that lurks within the orbits of Earth and Venus. An asteroid is the largest potentially dangerous object on Earth discovered in the past eight years. Credit: DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA/J. da Silva/Spaceengine

Auroras observations have spotted three large near-Earth objects lurking in the inner solar system.

Astronomers have discovered three near-Earth (NEA) asteroids hiding in the sun’s glare thanks to aurora observations with the US Department of Energy’s Dark Energy Camera at the Cerro Tololo Inter-American Observatory in Chile.. These NEAs are part of an elusive group that lurks within Earth’s orbits and[{” attribute=””>Venus. One of the asteroids is the largest object that is potentially hazardous to Earth to be discovered in the last eight years.

An international team of astronomers has discovered three new near-Earth asteroids (NEAs) hiding in the inner Solar System, the region interior to the orbits of Earth and Venus. Due to the intense glare of the sun, this is a notoriously challenging region for asteroid hunters to make observations. The detections were possible due to observations using the Dark Energy Camera (DECam) mounted on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF’s NOIRLab.

However, the astronomers uncovered an elusive trio of NEAs by taking advantage of the brief yet favorable observing conditions during twilight. One of the NEAs is a 1.5-kilometer-wide (0.9-mile-wide) asteroid called 2022 AP7. It has an orbit that may place it in Earth’s path at some point in the future. Fortunately, the other asteroids, designated 2021 LJ4 and 2021 PH27, have orbits that safely remain completely interior to Earth’s orbit. Also of special interest to astronomers and astrophysicists, 2021 PH27 is the closest known asteroid to the Sun. Subsequently, it has the largest general-relativity effects[1] From any object in our solar system. Its surface becomes hot enough to melt lead as it orbits.

Scott Sheppard, an astronomer in the Earth and Planetary Laboratory at the Carnegie Institution for Science and lead author of the paper published in Astronomical Journal describing this work. “So far we have found two large asteroids near Earth that are about one kilometer in diameter, a size we call planetary killers.”

“It’s possible that there are only a few new planets left of similar sizes, and it’s possible that these large, undiscovered asteroids have orbits that keep them within the orbits of Earth and Venus most of the time,” Sheppard said. “Only about 25 asteroids with orbits completely within Earth’s orbit have been discovered so far due to the difficulty of observing near the glare of the sun.”

Locating asteroids in the inner solar system presents a formidable observational challenge. Every night astronomers have two short 10-minute windows to survey this area and have to deal with the bright sky background caused by the glare of the sun. In addition, such observations are very close to the horizon. This means astronomers are stuck observing through a thick layer of Earth’s atmosphere, which can distort and distort their observations.[2]

Despite these great difficulties, the unique observational capabilities of DECam made it possible to discover these three new asteroids. As one of the world’s best and highest performing wide-field CCD imagers, this state-of-the-art instrument offers astronomers the ability to capture large areas of the sky with great sensitivity. If observations pick up faint objects, astronomers refer to them as “deep.” The ability to capture both deep and wide field observations is indispensable when searching for asteroids within Earth’s orbit. DECam was built and tested at the Department of Energy’s Fermilab and was funded by the US Department of Energy (DOE).

“Large swaths of sky are required because inner asteroids are rare, and deep images are needed because asteroids are faint and you counteract bright twilight skies near the sun as well as the distorting influence of Earth’s atmosphere,” Sheppard said. “DECam can cover large areas of the sky to depths unattainable on smaller telescopes, allowing us to go deeper, cover more of the sky, and explore the inner solar system in ways never done before.”

In addition to discovering asteroids that potentially pose a threat to Earth, this research is an important step toward understanding the distribution of small objects in our solar system. Asteroids farther from the Sun than Earth are the easiest to detect. Because these distant asteroids tend to dominate current theoretical models of asteroid populations.[3]

Discovering these objects also allows astronomers to understand how asteroids traveled throughout the inner solar system and how gravitational interactions and the heat of the sun can contribute to its fragmentation.

“Our DECam survey is one of the largest and most sensitive ever searches for objects within Earth’s orbit and near the orbit of Venus,” Sheppard said. “This is a unique opportunity to understand the kinds of things lurking in the inner solar system.”

“After ten years of remarkable service, DECam continues to make important scientific discoveries while at the same time contributing to planetary defense, a critical service that benefits all of humanity,” said Chris Davis, NSF Program Director for NOIRLab.

DECam was originally built to conduct the Dark Energy Survey, which was conducted by the Department of Energy and the US National Science Foundation between 2013 and 2019.


  1. Einstein’s general theory of relativity explains how massive objects distort the fabric of spacetime and how this affects the motion of things in the universe. In our solar system, this effect can be measured directly, for example, by the orbital cycle of Mercury, which cannot be accurately explained using only Newtonian physics.
  2. Observing towards the inner solar system is challenging for terrestrial telescopes and impossible for optical/infrared telescopes in space such as[{” attribute=””>NASA’s Hubble and JWST telescopes. The intense light and heat of the Sun would fry the sensitive electronics. For this reason, both Hubble and JSWT are always pointed away from the Sun.
  3. Atria asteroids — also known by the Hawaiian term Apohele asteroids — are the smallest group of near-Earth asteroids. Their orbits have an aphelion (farthest point from the Sun) smaller than Earth’s perihelion (nearest point to the Sun).

Reference: “A deep and wide twilight survey for asteroids interior to Earth and Venus” by Scott S. Sheppard, David J. Tholen, Petr Pokorný, Marco Micheli, Ian Dell’Antonio, Shenming Fu, Chadwick A. Trujillo, Rachael Beaton, Scott Carlsten, Alex Drlica-Wagner, Clara Martínez-Vázquez, Sidney Mau, Toni Santana-Ros, Luidhy Santana-Silva, Cristóbal Sifón, Sunil Simha, Audrey Thirouin, David Trilling, A. Katherina Vivas and Alfredo Zenteno, 29 September 2022, The Astronomical Journal.
DOI: 10.3847/1538-3881/ac8cff

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