How long is Earth’s second moon expected to circle the planet? Everything to know as mini-moon debuts in the night sky

A temporary second moon, known as a mini-moon, started orbiting the Earth on Sunday, September 29. The celestial object is a tiny asteroid named 2024 PT5, part of a small secondary asteroid belt that follows the Earth and orbits the sun called the Arjuna asteroid belt. Due to the small size of the asteroid, it won't be visible to the average skywatcher using amateur telescopes or binoculars.

The object can be observed by a professional telescope with a 30-inch plus diameter and a CCD or CMOS detector. However, unlike Earth's original natural satellite, the mini-moon won't be around for too long. Earth's temporary capture of the asteroid will end on November 25 of this year, and it will go back to being a part of the Arjuna asteroid belt.

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Earth's temporary mini-moon won't be visible to the naked eye

According to NASA's Jet Propulsion Laboratory Horizons system, the Earth's temporary capture of the 2024 PT5 will begin on September 29, 15:54 EDT (1954 UTC) and end on November 25, 11:43 EDT (1543 UTC).

Trapped by the planet's gravity, the 2024 PT5 won't be visible to the naked eye. As per CNBC, Awesome Astronomy podcast host Dr. Jennifer Millard told BBC's Today program that only professional telescopes can pick up the asteroid due to its small size and dull make.

The moon has a diameter of around 2,159 miles but the 2024 PT5 is only 37 feet wide, making the earth's natural satellite 308,108 times the temporary one. Universidad Complutense de Madrid professor and mini-moon event expert Carlos de la Fuente Marcos told Space.com that the object was "well within" the brightness range of professional telescopes used by scientists. He said:

"A telescope with a diameter of at least 30 inches plus a CCD or CMOS detector is needed to observe this object; a 30-inch telescope and a human eye behind it will not be enough."

After the asteroid's two-month orbit around the Earth, it will go back to continue orbiting the sun. Dr. Jennifer Millard said:

"It's not going to complete a full revolution of our planet, it's just going to kind of have its orbit altered, just twisted slightly by our planet and then it'll continue on its merry way,"

However, mini-moons are not a rare phenomenon. According to Cnet, they are seen almost every year. In 2022, the strange flight path of the 2022 YG asteroid meant that Earth received another natural satellite, the same could also be said for the 2020 CD3 asteroid.

Carlos de la Fuente Marcos further told Space.com that space rocks from the Arjuna asteroid belt have similar orbits to Earth and sit at an average distance of 93 million miles from the sun. Some of the objects from this belt can even approach the planet at a distance of around 2.8 million miles and under a velocity of 2,200 miles per hour.

It was first detected by NASA's Asteroid Terrestrial-Impact Last Alert System (ATLAS) on August 7. After two months of orbiting Earth, the asteroid won't exactly be lost forever, as it is expected to make a comeback way into the future, in 2055.