Although you won’t be able to see a man on it or cheese in it — or see it at all with your naked eye, in fact — Earth is getting a “mini” moon this month, and a University of Iowa astronomer said the school bus-sized asteroid orbiting the planet actually is much closer than the moon you can see.

“It’s coming close — but we mean close in a space sense,” UI Associate Professor of Physics and Astronomy Casey DeRoo told The Gazette. “So that's going to be about 150,000 kilometers, plus or minus say 25,000 kilometers.”

The asteroid — named 2024 PT5 — actually came its closest to Earth around the time it was discovered Aug. 7 by an Asteroid Terrestrial-Impact Alert System telescope in South Africa.

“It is easier to find things when they're close, because we get more of their reflective light,” DeRoo said. “And we found it after it had already slingshotted by us. Maybe that doesn't make us feel good. It doesn't help us sleep at night necessarily.”

But, he said, NASA researchers have gotten adept at tracking asteroids capable of causing global or civilization-scale damage.

“In part, that comes out of a mandate that was actually given to NASA by the United States Congress,” he said. “Part of NASA's mission, essentially, since the mid-2000s has been to find and catalog all near-Earth asteroids that could potentially cause civilization-level damage.

“And so we are pretty confident that we have something like 97 or 98 percent completion of any asteroids that would be a kilometer or greater that would be capable of causing that level of impact.”

What makes this PT5 object unique and deserving of a mini-moon label is its “horseshoe orbit” — slingshotting around and then slowing down to orbit the Earth between Sept. 29 and Nov. 25.

Although there is plenty of “orbital debris” — including things like rocket boosters and other man-made articles — DeRoo said researchers believe PT5 is “a natural object,” possibly a remnant of the “collision that we think formed the moon.”

And while researchers feel confident PT5 is going to leave Earth’s orbit later this fall, “We're not entirely sure what's going to end up happening with this over, say, the next 100 years,” he said. “Its orbital parameters are really well determined right now, and it's due for another interaction with Earth in about 30 years from now.

“But the models that we use to predict the dynamics of small bodies in the solar system, they diverge after that point.”

by Vanessa Miller, The Gazette.