For nearly two months, two moons have orbited Earth. By Monday, there will be only one moon again.
2024 PT5, an asteroid that’s been lurking around Earth’s neighborhood for a few billion years, was temporarily captured by the planet’s gravitational pull at the end of September. With a bit of help from the sun, the “mini-moon” will hurtle back into space at about 9:43 a.m. Nov. 25.
“Were it not for the gravity of the sun, it would remain in orbit around the Earth,” said Max Gilbraith, planetarium coordinator for the University of Wyoming. “But as it kind of gets towards apogee, it'll feel an extra pull from the sun, and that will pull it back out of Earth orbit.”
Gilbraith is usually a strong proponent for Wyomingites to go outside and take in all the splendor of the night skies, whether it be this month’s Beaver supermoon, a bombardment of multiple meteor showers or a once-in-humanity comet. You’d think a temporary second mini-moon would be on that list, but there’s nothing to see here — at least with the naked eye.
“I’d imagine trying to see a 36-foot-wide lump from 2 million miles away would be difficult,” he said. “Research telescopes can detect objects like this, but average backyard observers will find themselves frustrated.”
Mini Moon
2024 PT5 is an asteroid discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in South Africa on Aug. 7 and was captured by Earth’s gravity as a temporary satellite Sept. 29.
A temporary satellite is any natural object captured by a planet’s gravitational field that eventually drifts out of orbit. Unlike the moon, which is permanently in sync with the planet, 2024 PT5 is just making a temporary visit.
“It will be around 2,221,000 miles away from us on Nov. 25,” Gilbraith said. “That'll be the day it gets pulled out of orbit when the sun gets its pull on it. Without outside influences, it would have an orbital period of 1.35 years.”
This happens more often than many realize. Another asteroid, 2022 NX1, spent 22 days as a mini-moobbetween June 11 and July 3, 2022, before drifting away. It’s expected to be temporarily captured again in December 2051.
These asteroids are among a growing number of near-Earth objects discovered by astronomers worldwide, Gilbraith said. There’s an ongoing collaborative effort by international astronomers to keep Earth safe from potential extraterrestrial impacts close to home by identifying and tracking as many near-Earth objects as possible.
“We've been developing the catalog of near-Earth objects for the last couple of decades,” he said. “There are plans to accelerate that to participate in a planetary defensive action. The earlier we can detect a near-Earth Object, the more feasible it is to redirect it and put it on a safe trajectory for us. It’s probably one of the more important defense projects because you can't negotiate with an asteroid.”
Grandkids In Tow
The mini-moon Earth gained, and will soon lose, came from one of the many fields of planetary debris following our planet through space. Much of this debris came from the cataclysmic event that formed the moon, the collision of Earth and another planet-sized body called Theia around 4.5 billion years ago.
Asteroid 2024 PT5 came from the Apollo asteroids, the largest of four well-established groups of asteroids with similar orbital periods to Earth — the asteroids inside the cluster range in diameter from a few feet to over five miles.
“This asteroid looks like it's a moon fragment, so it's kind of our grandchild,” Gilbraith said. “There's a whole fleet of them out there, and they come in and out of our orbit relatively frequently, at least in the astronomical sense.”
Nothing To See Here
Gilbratih said that astronomers rarely try to observe these objects directly. They use a network of telescopes aimed at specific spots in the night sky, following the asteroid’s trajectory as it passes in front of and blocks the light of stars.
Still, a 36-foot-wide asteroid could cause tremendous devastation if it hurtled toward Earth. The 0.737-mile Meteor Crater in Arizona was caused by a meteorite that was 160 feet across.
Fortunately, nobody’s concerned about the future trajectory of 2024 PT5. Once the sun tugs it out of its earthly orbit, it will rejoin the Apollo asteroid group.
This isn’t the first mini-moon to visit Earth and is unlikely to be the last. But even if it isn’t a permanent partner, 2024 PT5 isn't going far.
“This one's just going to cruise around and check us out,” Gilbraith said. “This might be our only encounter with it. It will turn back on itself, get tucked back into the Apollo asteroids, and drift in tow with the Earth for what will most likely be the remainder of the time.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
