The definition of a moon is simple. A moon is a naturally-formed celestial body that orbits a planet or other larger celestial body that is not a star. Moons are solid bodies, and are essentially natural satellites of their host planets. So technically, yes! Earth is getting its second, temporary moon for the next two months, as 2024 PT5, an asteroid will be orbiting our planet as its new ‘Mini-Moon’. So, what exactly is a mini-moon? A mini-moon is an asteroid or comet that is moving at a slow pace, which gets caught in the gravitational pull of a planet, and ends up orbiting it for a certain period, before breaking free from its threshold, and going into a completely different trajectory.
The Earth’s gravity is slated to capture Asteroid 2024 PT5, which will start revolving around the planet in an elliptical horseshoe-like orbit, from September 29, for the next 52.6 days, before going on its own trajectory in heliocentric orbit, by November 25, 2024.
Astronomers first spotted the asteroid on August 7, through the South Africa-based observatory of the NASA’s Asteroid Terrestrial-impact Last Alert System (ATLAS). They speculate that it may be a fragment of our Moon, which split away millions of years ago. The diameter of 2024 PT5 is believed to be around 37-feet-wide and is approximated to be the size of a standard city bus, while its length is estimated to be between 16 feet and 138 feet. However, more data is required to confirm its actual size.
Not the first
Mini-moons are not restricted to Earth, and have been studied across other planets in the Solar System as well. Astronomers have classified mini-moon events into two types. Long-episode events involve asteroids referred to as temporarily-captured orbiters, which complete one or more revolutions around a planet, lasting for one or more years. During short-episode events, however, an asteroid does not even complete one full pass around the planet. These short-timers, also known as temporarily-captured flybys, are — like 2024 PT5 — mini-moons for a matter of days, weeks or months. Also, short mini-moon events occur several times in a decade, but long mini-moon events are rare, occurring every 10 or 20 years. However, it is not easy for asteroids to become mini-moons, since they have to be traveling at just the right speed and direction to be captured by a planet’s gravity.
Hence, its speed and trajectory matter. Researchers suggest that in order to become a mini-moon, an incoming celestial object has to approach the Earth slowly at close range. Asteroids that become mini-moons generally come within 4.5 million km of a planet, at speeds under 3,600 kmph, which is less than a snail’s pace on a universal scale. 2024 PT5 has been clocked travelling at a maximum speed of 4,988.96 kmph.
While the Earth has had only one consistent Moon orbiting it for billions of years, Asteroid 2024 PT5 is not our planet’s first or only mini-moon. The Earth has already captured several mini-moons in its gravitational pull, some of which had been orbiting the planet for years. The first-ever known mini-moon was captured by Earth’s gravity way back in the second half of 1991, and was called 1991 VG. This mini-moon orbited the planet for a few months, before going on its own trajectory in early 1992. In 2002, amateur astronomer Bill Yeung also spotted a celestial object that he thought was a mini-moon, J002E3. However, now, it is believed to be a part from the third stage of the Apollo Saturn V rocket (S-IVB), instead of a natural mini-moon. The next natural mini-moon was spotted in July 2006, the 2006 RH120, which orbited the Earth for a year, before ejecting. The next mini-moon, 2020 CD3, was captured by Earth’s orbit for over two years, and escaped in May 2020. Asteroid 2020 CD3 is considered a long-capture mini-moon, while the newly detected Asteroid 2024 PT5 is a short-capture one. The 2022 NX1 was another asteroid that came into our planet’s gravitational influence, and was assumed to be an artificial mini-moon until further studies revealed that it came from a cluster called Arjuna that revolves around the Sun. Amateur astronomers Grzegorz Duszanowicz and Jordi Camarasa were able to spot the 2022 NX1 mini-moon using the Moonbase South Observatory in Namibia. Further studies showed that while it might have been discovered in 2022, and named 2022 NX1, the very same asteroid had already orbited the planet once before, in 1981, and is likely to return in 2051.
Nothing to fear
The periodic occurrence of this fascinating phenomenon helps astronomers and scientists study, understand and demystify the vastness of the cosmos. While 2024 PT5 may be revolving around our planet for the next couple of months at least, it will not be visible to the naked eye, or an amateur telescope either, because it is too small and will be revolving from a much farther distance, compared to the actual Moon. Accordingly, there is no risk of the asteroid colliding with the Earth, as it will orbit the planet from at least 4.2 million km away, which is about 10 times the distance between the Earth and the Moon. After escaping the planet’s gravity in November, 2024 PT5 is expected to come close to our planet once again in 2025 as well, before returning in 2055. So, are you excited to be able to partake of this cosmic phenomenon?!
Larger than the Chelyabinsk meteor
Asteroid 2024 PT5 is theorised to be anywhere between 16 and 138 feet in diameter, potentially larger than the meteor that entered Earth’s atmosphere over Chelyabinsk, Russia, in 2013. About 55-65 feet in size, the Chelyabinsk meteor exploded in the air, releasing 20-30 times more energy than that of the atomic bomb dropped on Hiroshima, Japan, in 1945, and generating brightness greater than the Sun. Debris from the space rock damaged more than 7,000 buildings and injured more than 1,000 people.