While Earth doesn’t have the twin suns of a “Galaxy Far, Far Away” it is soon expected to pick up another moon – at least for a little while.
Research published this month by the American Astronomical Society indicates that “recently discovered small body 2024 PT5,” is on a path to become a “mini-moon” of Earth from Sept. 29 through Nov. 25. According to the research, this asteroid is following a “horseshoe path” that brings it within Earth’s orbit.
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Moons are natural satellites, which means that they orbit planets or other celestial bodies. While Earth usually has one moon, other planets have more. Mars, for example, has two and Saturn has 146.
This isn’t the first time Earth has taken on an accessory moon. In the recent research, study authors said that 2022 NX1 also became a temporary mini-moon in 1981 and 2022 – it’s expected to return in 2051. They also said 2006 RH120 became a mini-moon for around a year between July 2006 and July 2007 and that 1991VG was “temporarily captured” around February 1992.
“Earth can regularly capture asteroids from the Near-Earth object (NEO) population and pull them into orbit, making them mini-moons,” said study authors Carlos de la Fuente Marcos and Raúl de la Fuente Marcos. “Sometimes, these temporary captures do not complete one revolution before dropping out of orbit and returning to their regular heliocentric trajectories.”
It looks like 2024 PT5 is on a similar path as 2022 NX1. This asteroid was discovered just last month by the Asteroid Terrestrial-impact Last Alert System, observing with an instrument located in Sutherland, South Africa.
CBS News noted that 2024 PT5 is larger than some of Earth’s other past mini-moons, but our main moon is still expected to be brightest and largest object in our night sky as the mini-moon falls into orbit. Space.com described the moon as our planet’s “primary companion” over the past 4 billion years. Researchers expect it to return for another trip orbiting Earth in 2055.
According to NASA, it was likely created when a Mars-sized body collided with our planet. Since then, it has made Earth a more livable planet by moderating the wobble on its axis, thus allowing for a relatively stable climate.
“It also causes tides, creating a rhythm that has guided humans for thousands of years,” NASA added.
As for our mini-moon visitor, Marcos told Space.com that it belongs to Arjuna asteroid belt. This belt is made of space rocks that follow orbits similar to Earth
“Objects in the Arjuna asteroid belt are part of the near-Earth object population of asteroids and comets,” Marcos explained. If these objects get in close range of Earth at low velocities, their geocentric energy can become negative, thus allowing them to become moons. That’s the process 2024 PT5 is expected to go through next week.
Marcos likened it to a “window shopper” rather than a regular customer. Visits from these window shopper mini-moons are relatively frequent, occurring multiple times per decade. Longer visits lasting a year or more are not as frequent – they happen every 10 to 20 years, per Space.com.
“The cause of the ejection of these objects from around Earth are gravitational disturbances caused by the sun,” said Space.com. “Once 2024 PT5 has fulfilled its role as a mini-moon, it will return to a sun-centered orbit, remaining part of the Arjuna asteroid belt.”
Now, for the question most readers are probably asking: will we be able to see it? Unfortunately, the answer is… probably not. Unless you can get access to telescopes used by professional astronomers.
Marcos said 2024 PT5 is too small and dim to be seen by most telescopes and binoculars fused by amateur sky gazers. NASA’s Eyes on Asteroids database lists “2024 PT5” as an object with an average estimated diameter for about 12 yards currently 0.02 astronomical units from Earth.
“However, the object is well within the brightness range of typical telescopes used by professional astronomers,” he said. “A telescope with a diameter of at least 30 inches plus a CCD or CMOS detector are needed to observe this object, a 30 inches telescope and a human eye behind it will not be enough.”
After it leaves our orbit in November, its closest approach to us is expected in January of next year.
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