Potentially dangerous “planet killer” asteroid discovered lurking in the inner solar system

Potentially dangerous “planet killer” asteroid discovered lurking in the inner solar system

Asteroid orbits closer to the sun than Earth's orbit

Twilight observations with the U.S. Department of Energy-manufactured Dark Energy Camera at NOIRLab’s Cerro Tololo Inter-American Observatory in Chile have enabled 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 object potentially dangerous to Earth discovered in the past eight years. Credit: DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA/J. da Silva/Spaceengine

Twilight observations spot three large near-Earth objects lurking in the inner solar system.

Astronomers have spotted three near-Earth asteroids (NEA) hiding in the sun’s glare thanks to twilight observations with the U.S. Department of Energy-manufactured Dark Energy Camera at Cerro Tololo Inter-American Observatory in Chile. These NEAs are part of an elusive population lurking in 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] of every object in our solar system. The surface becomes hot enough to melt lead during its orbit.

“Our twilight survey is scouring the area within the orbits of Earth and Venus for asteroids,” said Scott S. Sheppard, an astronomer with the Earth and Planets Laboratory at the Carnegie Institution for Science and the lead author of the paper published in The Astronomical Magazine describing this work. “So far we have found two large near-Earth asteroids with a diameter of about 1 kilometer, a size we call planet killers.”

“There are probably only a few NEAs of similar size left, and these large undiscovered asteroids probably have orbits that keep them within the orbits of Earth and Venus most of the time,” Sheppard said. “Only about 25 asteroids completely orbiting Earth’s orbit have been discovered so far because of the difficulty of observing the sun’s glare up close.”

Locating asteroids in the inner Solar System is a formidable observational challenge. Each night, astronomers have only two short 10-minute windows to survey this area and face a clear background sky due to the sun’s glare. In addition, such sightings are very close to the horizon. This means astronomers are stuck observing a thick layer of Earth’s atmosphere, which can obscure and distort their observations.[2]

Despite these great difficulties, DECam’s unique observation capabilities made it possible to discover these three new asteroids. As one of the best performing widefield CCD cameras in the world, this state-of-the-art instrument offers astronomers the ability to capture large areas of the sky with great sensitivity. When observations capture faint objects, astronomers call them “deep.” The ability to capture both deep and wide sightings is indispensable when hunting for asteroids in Earth’s orbit. DECam was built and tested at DOE’s Fermilab and was funded by the United States Department of Energy (DOE).

“Large swathes of the sky are needed because the inner asteroids are rare, and deep images are needed because asteroids are faint and you’re fighting the clear twilight sky near the sun and the distorting effect of Earth’s atmosphere,” Sheppard said. . “DECam can cover large areas of the sky to depths not achievable with smaller telescopes, allowing us to go deeper, cover more sky and explore the interior of the Solar System in ways that have never been done before.”

In addition to detecting asteroids that could potentially pose a threat to Earth, this research is an important step towards a better understanding of the distribution of small bodies in our solar system. Asteroids that are farther from the sun than Earth are the easiest to detect. Therefore, these more distant asteroids tend to dominate current theoretical models of the asteroid population.[3]

Detecting these objects will also help astronomers understand how asteroids are transported through the inner solar system and how gravitational interactions and the sun’s heat may contribute to their fragmentation.

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

“After a decade of remarkable service, DECam continues to make important scientific discoveries while 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 between 2013 and 2019 by the DOE and the US National Science Foundation.


  1. Einstein’s general theory of relativity explains how massive objects distort the fabric of spacetime and how this affects the motion of objects in the universe. In our solar system, this influence can be measured directly as, for example, the precession of the orbit of the planet Mercurywhich cannot be accurately explained with Newtonian physics alone.
  2. Observing towards the inner solar system is a challenge for ground-based 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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