Astronomers have discovered a new quasi-moon following Earth

Astronomers have discovered an asteroid in space that’s been following Earth around the sun for the last two millennia and they say the celestial rock is one of our planet’s oldest quasi-moons. But what does that mean and should we be worried?

A quasi-moon or quasi-satellite is a type of object in space that orbits the sun within a similar timeframe to Earth while being slightly influenced by the planet's gravitational pull according to a description of the phenomena from the Scientific American. 

The quasi-moon we're talking about was first discovered in March by astronomers at the Pan-STARRS observatory in Hawaii and was later labeled with the designation FW13 by astronomers. But researchers needed a little more proof of the asteroid's existence. 

FW13’s existence was confirmed by the Canada-France-Hawaii Telescope as well as two other observatories in Arizona according to Scientific American before being officially listed on April 1st by the Minor Planet Center at the International Astronomical Union.

Earth’s new quasi-moon is estimated to be about 50 feet in diameter and the Scientific America said that’s equivalent to three large SUV’s parked bumper to bumper. At its closest, the space rock comes within nine million miles of Earth during its orbit of the sun. 

To put that distance into comparison, the Earth’s moon has a diameter of 2159 miles and at its closest point comes to within 226,000 miles of our planet according to data that was published by NASA and reported on by the Scientific American for this story. 

Sky & Telescope said that Earth’s newest companion has caused quite a bit of a stir with asteroid watchers since it has such an interesting orbital path compared to other similar space rocks that have been found to align our planet. 

“It turns out to be on an orbit that is not only in a 1:1 resonance with the Earth,” wrote Sky & Telescope’s David Chandler, “but follows a path that actually circles Earth.” 

Quasi-moons tend to follow the Earth only for a few decades according to Chandler, and that makes FW13 very unique since researchers believe the rock has been entangled with our planet for several thousand years, and won't stop for at least another thousand. 

Chandler noted that some estimates say FW13 has circled the Earth since 100 BC and predict that it won’t stop until 3700 AD. “If that’s correct, 2023 FW13 would be the most stable quasi-satellite of Earth ever found,” the Sky & Telescope reporter wrote. 

“When I saw the announcement, the very Earth-like semimajor axis looked suspicious to me,” French astronomer and journalist Adrien Coffinet told Sky & Telescope. 

Coffient was the first person to figure out the orbital trajectory of FW13 after running data from the quasi-moon through a simulator that deciphered its possible past and future orbits. 

“It seems to be the longest quasi-satellite of Earth known to date,” Coffient said. But you should remember that FW13 isn’t actually orbiting the Earth. It’s orbiting the sun, which means there's always the potential for a collision. But would that even be possible?

Alan Harris of the Space Science Institute told Sky & Telescope that at any given time there are at least three objects like FW13 in orbital resonance with Earth but also noted that they aren’t really something we have to worry about. 

“The good news is, such an orbit doesn't result in an impacting trajectory ‘out of the blue,’” Harris explained, adding that “such an orbit has greater long-term stability than other non-resonant orbits,” meaning if FW13 was about to hit Earth then we’d know it. 

FW13 isn’t the first quasi-moon to be discovered recently. In 2021, researchers found a small asteroid about the size of a Ferris wheel they dubbed Kamo`aolewa—which they believed to be a piece of the lunar surface that broke off according to Live Science.