Asteroid discovered by Carnegie’s Scott Sheppard right before it zooms past Earth

Diagram showing the 2020 YE5 asteroid's Near Earth Trajectory
The asteroid 2020 YE5 will be as close to Earth as the Moon around 9 AM EST on Friday, January 22. The blue line represents Earth’s orbit, the white circle represents the moon’s orbit, and the white line crossing through both represents the trajectory of 2020 YE5. Image: JPL/NASA
Thursday, January 21, 2021 

In December 2020, Carnegie astronomer Scott Sheppard was working on his continuing project to search for distant objects near the fringe of our Solar System, beyond Pluto, when something odd caught his eye. A faint and slow-moving point of light was showing up on his survey—and it was moving backward.

“When I saw the weird movement of the object, I was immediately intrigued because the more distant main-belt asteroids and even more distant objects beyond Neptune move in the opposite direction as this object was moving,” explained Sheppard.

Sheppard was observing on the Magellan Telescope in Chile. As soon as he observed the strange object, he sent his data to a colleague for confirmation. Said Sheppard, “I immediately reported this object to David Tholen at the University of Hawaii, who got additional observations of the object and quickly determined the object was very near the Earth and likely to get even closer in the coming days.”

Upon inspection, the object turned out to be a small “near-Earth asteroid,” which has since been named 2020 YE5. At only a few tens of meters in length, the newly discovered asteroid could fit inside a baseball field’s inner diamond.

Scientists have found and are tracking most of the "planet killer" asteroids near the Earth (asteroids larger than 1 km), but smaller “city-killer” asteroids can still surprise us. These smaller asteroids, only a few hundred meters across, may not pose an existential threat to our planet, but they could undoubtedly devastate a city or region if they were to collide with Earth. 

Said Sheppard, “These ‘city killer’ asteroids are hard to find because they are small and faint and thus only visible to our telescopes when they are near Earth, but they spend the vast majority of their time well away from the Earth.” He continued, “This is true for 2020 YE5. I found this asteroid very near Earth, but for most of 2020 YE5’s orbit, we would not be able to observe it. It would be too faint.”

For now, 2020 YE5 poses no immediate risk to Earth, but it will come very close. The asteroid will zoom past only 437,691 km away from Earth, almost as close as our own Moon. It will be at its nearest on Friday, January 22 at around 9:08 AM EST (14:08 UTC). According to Sheppard, someone with a good backyard telescope could catch a glimpse.

The white ellipse shows YE5 2020’s orbit that crosses paths with Earth and Mars every couple of years. Credit: NASA/JPL

It will then zoom off again on its elongated orbit, crossing the orbits of Earth and Mars every few years. 2020 YE5 will not pass this close to the Earth again for another 75 years. Says Sheppard, “It will likely pass very near the Earth in 2095 with a very small impact probability at that time.”

Right now, the few observations we do have can’t tell us the impact hazard of this particular asteroid past 75 years in the future. Between now and 2095, we will need to observe 2020 YE5 to more precisely determine its orbit and better understand its potential hazard to Earth.