Discovery of a potentially dangerous “planet-killer” asteroid hidden in the inner solar system

Twilight observations with the Dark Energy Camera made by the US Department of Energy at NOIRLab’s Cerro Tololo Inter-American Observatory in Chile have allowed astronomers to spot three near-Earth asteroids (NEAs) hidden in the glow of the Sun. These NEAs are part of an elusive population lurking inside the orbits of Earth and Venus. One of the asteroids is the largest potentially Earth-hazardous object discovered in the past eight years. Credit: DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA/J. da Silva/space engine

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

Astronomers have spotted three near-Earth asteroids (NEAs) lurking in the Sun’s glow through twilight observations with the Dark Energy Camera made by the US Department of Energy at the Cerro Tololo Inter-American Observatory in Chile. These NEAs are part of an elusive population lurking inside 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 any object in our solar system. Its surface becomes hot enough to melt lead during its orbit.

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

“There are probably only a few NEAs of similar sizes left to be found, and these large undiscovered asteroids likely have orbits that keep them inside the orbits of Earth and Venus most of the time,” Sheppard said. “Only about 25 asteroids with orbits completely inside Earth’s orbit have been discovered so far due to the difficulty of observing near the Sun’s glare.”

Locating asteroids in the inner solar system is a formidable observational challenge. Each night, astronomers have only two brief 10-minute windows to survey this area and must contend with bright background skies resulting from glare from the Sun. Moreover, these observations are very close to the horizon. This means that astronomers are forced to observe through a thick layer of Earth’s atmosphere, which can blur and distort their observations.[2]

Despite these major difficulties, DECam’s unique observation capabilities made it possible to discover these three new asteroids. As one of the world’s most capable wide-field CCD imagers, this state-of-the-art instrument offers astronomers the ability to capture large areas of sky with high sensitivity. If observations capture faint objects, astronomers call them “deep.” The ability to capture both deep-field and wide-field observations is essential when hunting asteroids inside Earth’s orbit. DECam was built and tested at DOE’s Fermilab and was funded by the US Department of Energy (DOE).

“Large areas of sky are needed because interior asteroids are rare, and deep images are needed because asteroids are faint and you’re fighting the bright twilight sky near the Sun as well as the distorting effect of Earth’s atmosphere,” Sheppard said. “DECam can cover large areas of the sky at depths impossible to reach with smaller telescopes, allowing us to reach further, cover more sky, and probe the inner solar system in ways never before possible. .”

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

Detecting these objects also allows astronomers to understand how asteroids are transported through the inner solar system and how gravitational interactions and heat from the Sun can contribute to their fragmentation.

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

“After ten years of outstanding service, DECam continues to produce important scientific discoveries while contributing to planetary defense, a crucial service that benefits all of humanity,” said Chris Davis, NSF Program Director for NOIRLab.

DECam was originally designed to carry out the Dark Energy Survey, which was conducted by DOE and the US National Science Foundation between 2013 and 2019.


  1. Einstein’s general theory of relativity explains how massive objects warp the fabric of spacetime and how this influences the motion of objects in the Universe. In our solar system, this influence can be directly measured as, for example, the precession of the orbit of the planet Mercurywhich cannot be accurately explained using Newtonian physics alone.
  2. Inward observation of the solar system is difficult for ground-based telescopes and impossible for space-based optical/infrared telescopes like " data-gt-translate-attributes="[{" attribute="">NasaThe Hubble and JWST telescopes. The intense light and heat from the Sun would fry sensitive electronics. For this reason, both Hubble and JSWT are always directed away from the Sun.
  3. The 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 (closest point to the Sun).

Reference: “A deep and large 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, September 29, 2022, The Astronomical Journal.
DOI: 10.3847/1538-3881/ac8cff

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