What you need to know about ‘mini-moon’ visiting Earth for the second time
A visitor from space is about to join our planet for a brief visit - and become a ‘second moon’.
An asteroid, known as 2024 PT5, will become a ‘mini-moon’ of Earth for a few weeks, orbiting our planet before escaping Earth’s gravity and resuming its orbit of the Sun.
The 33-foot asteroid will arrive on 29 September, and will orbit for a couple of months before the Sun’s stronger gravitational pull pulls it back into its normal orbit. The asteroid will depart Earth on 25 November, according to a scientific paper explaining its discovery.
Why has it appeared?
‘Mini-moons’ are captured when the pull of Earth’s gravity is strong enough to briefly ‘catch’ an asteroid orbiting the Sun - usually ones orbiting relatively near Earth and at low speeds.
The 2024 PT5 asteroid is a type of mini-moon which is only briefly captured, and will not complete a full orbit of Earth.
In a paper announcing the discovery, Universidad Complutense de Madrid researchers wrote: "Earth can regularly capture asteroids from the Near-Earth Object (NEO) population and pull them into orbit, making them mini-moons. Sometimes, these temporary captures do not complete one revolution before dropping out of orbit.
"NEOs that follow horseshoe paths, and approach our planet at close range and low relative velocity, may undergo mini-moon events.’
How can you see it?
The asteroid is believed to be 33 feet in diameter (and poses no threat to Earth) - but will not be visible to the naked eye, or with normal telescopes.
It’s also made of relatively dim rock, making it even harder to spot.
Carlos de la Fuente Marcos, one of the researchers at Complutense University of Madrid who spotted the object, told Space.com that a telescope of at least 30 inches will be needed to see 2024 PT5.
The Sky Live has a regularly updated map showing the position of 2024 PT5.
How rare is it?
In the paper describing PT5, the researchers describe four other mini-moons known to have been captured by Earth - 1991 VG, 2022 NX1, 2006 RH120 and 2020 CD3.
The first two are like 2024 PT5, and only remained briefly (the researchers describe these as ‘flybys’, while the other two are captured for longer than one orbit and are described as ‘orbiters’.
What is its trajectory?
Scientists believe this is not the first time 2024 PT5 has paid a visit to Earth, with calculations of its orbit suggesting it was briefly a mini-moon in 1960.
At the time, telescopes on Earth did not spot it.
Researchers believe it will return again in 2055.
The asteroid belongs to the Arjuna asteroid belt, a secondary asteroid belt of rocks which follows an orbit not dissimilar to Earth’s
Orbiting the sun at around 93 million miles, objects in the Arjuna asteroid belts are considered ‘near Earth objects’.
