Near-Earth 'planet killer' asteroid is looming large

Astronomers have discovered a so-called 'planet killer' asteroid, which has an orbit that may someday place it in the Earth's path.

An international team of asteroid hunters based in Chile chanced upon the space rock when making observations of the inner solar system, between the orbits of Earth and Venus, which is a notoriously tricky region to study because of the glare from the sun.

The asteroid, which is called 2022 AP7, is 1.5 kilometers wide, making it the largest potentially hazardous asteroid detected in the past eight years. For an object to be deemed potentially hazardous it must orbit within 7.5 million kilometers of Earth, and be large enough to cause significant damage in the event of an impact.

The consequences of a large asteroid colliding with Earth depend on a number of factors, including its density, velocity, the angle of approach, and the location of the impact. It is thought that the asteroid that wiped out the dinosaurs 66 million years ago was around 10 kilometers wide.

An asteroid the size of 2022 AP7 has the potential to cause climate effects on a global scale, hugely disrupting civilization and leading to the extinction of many species, perhaps even the human race.

The team of astronomers from Spain, Italy, Chile, and the United States discovered two other asteroids, called 2021 LJ4 and 2021 PH27, which have orbits that are unlikely to intersect with the Earth.

"So far, we have found two large near-Earth asteroids that are about 1 kilometer across, a size that we call 'planet killers," said Scott Sheppard, an astronomer at the Earth and Planets Laboratory of the Carnegie Institution for Science in the US, and the lead author of the study, published in the Astronomical Journal this week.

"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," he added.

The team managed to make out 2022 AP7 by using the Dark Energy Camera, or DECam. The camera was mounted on the Victor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in northern Chile, a region favored by astronomers due to its high altitude and clear skies.

The DECam is highly sensitive, particularly in the red and near-infrared parts of the spectrum, and was originally constructed for a 2013-2019 survey that explored the nature of dark energy. Due to the sun's glare, the astronomers only had a brief 10-minute period during twilight hours to collect their data.

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