Earth is about to get a 2nd moon, for 57 days only. Here's what you need to know.

• Earth is getting a second moon, a mini-moon asteroid called 2024 PT5, on September 29.
• This asteroid from the Arjuna asteroid belt will follow a horseshoe path around Earth for 57 days.

Earth is about to pluck a second moon from an asteroid belt — but we only get this mini-moon for 57 days.

It's an asteroid about the size of a school bus, at 35 feet long, and it has a typical, un-snazzy asteroid name: 2024 PT5.

Earth is poised to pick up this hitchhiker from the nearby Arjuna asteroid belt on September 29.

According to a paper published in the Research Notes of the American Astronomical Society this month, the 2024 PT5 asteroid will then be in the grasp of Earth's gravity, following a horseshoe-like path around our planet until November 25, when it will return to an orbit around the sun.

"You may say that if a true satellite is like a customer buying goods inside a store, objects like 2024 PT5 are window shoppers," Carlos de la Fuente Marcos, the paper's lead author, told Space.com.

The asteroid poses no threat to Earth.

You'll probably only see the mini-moon in photos

This mini-moon is nothing like our real moon. It's super mini. Forget about spotting it with your naked eye or even a pair of binoculars.

In fact, according to Dan Bartlett, an astrophotographer in California, asteroid 2024 PT5 is so faint that it's "well beyond the limits of most of the best amateur telescopes."

That won't stop him from trying to photograph it, though.

From his dark-skies vantage point in the middle of the Sierra Nevada mountains, Bartlett thinks he might be able to catch the asteroid by imaging all night long with his sophisticated telescope equipment on an extra-dark night when the main moon is not in the sky.

"The image probably won't look like much but you never know until you try," Bartlett told BI in an email.

However, telescopes used by professional astronomers should be able to image 2024 PT5 easily, according to Marcos.

So stay tuned for pictures.

When the mini-moon returns

The asteroid won't make its closest approach to Earth until after it loses mini-moon status, though.

On January 8, 2025, according to NASA, it will skim past Earth at a distance of about 1.1 million miles (1.8 million kilometers).

For reference, the main moon (the big one you see in the sky at night) is, on average, about 238,855 miles (384,400 kilometers) away from us. It will probably still be impossible to see with binoculars or the naked eye.

After that, our temporary moonlet won't fly by again until 2055.

It's not our first mini-moon and it won't be the last. Another asteroid, called 2022 NX1, briefly fell into Earth's orbit in 2022. Astronomers declared it to be a mini-moon, or a "short-term natural satellite," and determined that it would return again in 2051.

The situation brings Bartlett to a simple conclusion, which you may have reached too: "Space is neat," he said.