Has Earth acquired a second moon? Not exactly.
Astronomers recently discovered a new quasi-moon. This asteroid with a diameter of 50 feet will be accompanying Earth as it orbits the Sun for the next 60 years, astronomers estimated in a study published in September in the journal American Astronomical Society.
Dubbed "2025 PN7," the quasi-moon is actually one of many quasi-moons sharing Earth's orbit.
"This is not the first quasi-moon that we've had," said Scott Fisher, a professor of astronomy at the University of Oregon. "We actually have about a half-dozen of them at this very moment that are hanging around Earth."
What is a mini-moon vs. a quasi-moon?
Quasi-moons and mini-moons are not the same. They are both small objects that approach Earth, but the difference comes down to their orbits.
Quasi-moons orbit the sun and happen to be in line with Earth's orbit. Fisher compared it to two cars driving in adjacent lanes on the highway.
A mini-moon is pulled into Earth's gravity. A mini-moon may partially or full orbit Earth for a time. Some may remember "2024 PT5" discovered last August, which made a horseshoe-like orbit around the Earth before escaping out in space. Fisher said he likes to think of them as "temporary moons."
PN7 is a quasi-moon, as it will not orbit Earth.
Why are there so many moons?
There are several quasi-moons in the sky right now. Fisher said this is not due to some increase in the number of quasi-moons; rather it is a product of improving technology.
"I'm confident we've had quasi-moons for millennia," Fisher said. "It's just that we have the telescopes and the technology to see these guys. These are really hard to detect. ... It's a technological wonder that we can detect these guys."
There are likely more quasi-moons yet to be discovered, Fisher said.
Scientists estimate that PN7 already had been a quasi-moon for decades before being discovered by the Pan-STARRS at the Haleakala Observatory in Hawaii in August.
"We are in an era of a sort of revolution in astronomy," Fisher said. "This next generation of telescopes and the next generation of cameras, it's allowing us to do things we've never done before."
What is PN7 like?
For scale, PN7's diameter is roughly the length of three cars parked end to end.
Although researchers haven't definitively said what PN7 is made of, Fisher said they can make educated guesses based on similar asteroids they already know.
"We presume that it has the same composition as many of the rocky asteroids that we see," Fisher said. "Asteroids are made of the same kind of rocks that we would find even here in Oregon -- carbon-based, silicone-based rocks."
Will the 2025 PN7 quasi-moon be visible in Oregon skies?
Like the mini-moon discovered in 2024, this quasi-moon will not be visible to Oregonians. Spotting it requires an extremely powerful telescope and detection equipment.
Fisher said even UO's Pine Mountain Observatory, which has one of the largest telescopes in the Pacific Northwest, will not be able to see it.
Could the new quasi-moon threaten Earth?
Fisher said there is no cause for concern that PN7 could impact Earth.
At its farthest point from our planet, 2025 PN7 is about 11 million miles away and it only gets as close as 2.5 million miles, roughly 10 times the distance between Earth and the Moon, according to SyFy.com. It is expected to orbit the Sun alongside Earth until 2083.
Fisher said, however, those small, difficult-to-detect asteroids are a concern for astronomers, more so than a large asteroid.
"We're not worried about a big, old asteroid like the movie 'Armageddon,'" Fisher said. "We know where the big ones are, but what we don't know are where these little fellows are, these ones that are 50 feet up to even a couple hundred feet across. An object that size could be devastating if it actually hit Earth.
"That's what we call 'city killers.'"
He said these asteroids are small and move fast, making them extremely difficult to detect. But, Fisher said, the field continues evolving and improving as new technology and telescopes help detect these potential threats, like the new Vera C. Rubin Observatory in Chile.
"Truly, we've once again changed our place in the universe," Fisher said. "When I was a kid, the only planets we knew of were around our star, the Sun. And now, we know that there are planets everywhere up there in the sky. As you might imagine, that changes our ideas about the chances for life and things like that."
Miranda Cyr reports on education for The Register-Guard. You can contact her at [email protected] or find her on Twitter @mirandabcyr.