Discovery Files

Largest potentially hazardous asteroid detected in 8 years

Twilight observations spot 3 large near-Earth objects lurking in the inner solar system

Twilight observations with the Dark Energy Camera at the Cerro Tololo Inter-American Observatory in Chile, a program of the U.S. National Science Foundation-supported NOIRLab, have enabled astronomers to spot three near-Earth asteroids, or NEAs, hiding in the glare of the sun. One is the largest object potentially hazardous to Earth to be discovered in the last eight years. The NEAs are part of an elusive population that lurks inside the orbits of Earth and Venus.

This is a notoriously challenging region for observations because asteroid hunters must contend with the glare of the sun. By taking advantage of the brief yet favorable observing conditions during twilight, however, the astronomers found an elusive trio of NEAs. The results are reported in The Astronomical Journal.

One is a 1.5-kilometer-wide asteroid called 2022 AP7, which has an orbit that may someday place it in Earth's path. The other asteroids, called 2021 LJ4 and 2021 PH27, have orbits that safely remain interior to Earth's orbit. 2021 PH27 is the closest known asteroid to the sun. As such, during its orbit, its surface gets hot enough to melt lead.

"Our twilight survey is scouring the area within the orbits of Earth and Venus for asteroids," said Scott Sheppard, an astronomer at the Carnegie Institution for Science and the lead author of the paper describing this work. "So far we have found two large near-Earth asteroids that are about 1 kilometer across, a size we call planet-killers."

There are likely only a few NEAs with similar sizes left to find, he said. "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."

Added Martin Still, a program director in NSF's Division of Astronomical Sciences, "Evidence of NEO impacts is all over our planet, and major collisions in the past have substantially altered the course of life on Earth. Discoveries like this help raise awareness and understanding of planetary threats and build a 'census' of NEOs."

Funding for the Dark Energy Survey and construction and integration of the Dark Energy Camera was provided by the U.S. Department of Energy, U.S. National Science Foundation, Ministry of Education and Science (Spain), Science and Technology Facilities Council (UK), Higher Education Funding Council (England), National Center for Supercomputing Applications, Kavli Institute for Cosmological Physics, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo a Pesquisa, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência e Tecnologia (Brazil), the German Research Foundation-sponsored cluster of excellence "Origin and Structure of the Universe" and the Dark Energy Survey collaborating institutions.