Can we really call 2024 PT5 a “second moon”?
Tidal currents allow organisms to reproduce and played a key role in the evolution of life as we know it. Moonlight is a crucial resource for many animals in navigation and migration. The climate of Earth is kept much more constant than those of similar-sized planets as they tend to wobble on their axes, causing more extreme seasonal weather patterns. These factors have shaped life on Earth to a profound degree. Crucially, they are all caused by our beloved Moon.
Since the 29th of September, the wandering asteroid known as 2024 PT5 has been pulled into Earth’s orbit to become a “mini-moon”. The asteroid originates from the Arjuna asteroid belt orbiting the sun. Disappointingly, due to its small size (reportedly similar to that of a school bus) and large distance from Earth (ten times further away than our Moon), the asteroid is not visible without the aid of a professional telescope. This elusive ‘moon’ will leave us on November the 25th after completing a horseshoe orbit; departing before even completing a full revolution of the Earth.
Image Credit: Tony Dunn/USA Today
How do we classify a moon and a “mini-moon”? Our moon, conveniently named “The Moon”, has been a subject of fascination for humankind as long as we have existed, inspiring art, music, and its own branch of astronomy: selenology. Theories regarding the formation of the moon are still debated. However, the most widely accepted theory, the giant-impact theory, states that before the Earth as we know it was formed, a smaller, unsolidified “proto-earth” and neighbouring planet Theia (similar to the size of Mars) collided. Energy released in this collision caused the two planets to melt further and merge, forming the Earth as a finished product. The leftover debris orbiting this new planet eventually converged to form a single spherical satellite, the Moon.
In order to officially be classified as a moon, a natural satellite must be in an established orbit around a planet, whereas a “mini-moon” may not complete a full orbit but must be in close range and moving slowly. Ironically, for 2024 PT5, this close range is 2.8 million miles from Earth and its slow speed is a leisurely 2,200mph. Though this may be the first time a “mini-moon” has been a highly popularised spectacle, this is not the first time an event like this has taken place.
2022 NX1 was discovered to be in a 21-day, horseshoe orbit around the Earth two years ago and, though the object’s origin is unknown, it met all the requirements to be classified as a “mini-moon”. Furthermore, this is not the first time 2022 NX1 has visited us; it has been thought to have orbited for 98 days from the end of 1980 to January 1981 and is expected to return around 2051.
Although many small orbital objects have been hailed as “mini-moons”, scientists have pointed out the absurdity of comparing these relatively small asteroids to regular moons. Their tiny mass and incomplete orbits make them seem much more anti-climactic than misleading headlines will have you believe. Considering the substantial impact of the Moon on our life on Earth, this makes the fact that 2024 PT5 passes by not even visible to the naked eye all the more disappointing.
Despite this misconception, the ability to accurately predict the arrival of a “mini-moon” shows an encouraging advancement in our understanding and technology. Andrew Rivkin of Johns Hopkins University’s Applied Physics Laboratory reportedly stated to National Geographic about 2024 PT5 that “it’s a great demonstration of our capabilities to find things, to be able to predict where they go”.
With 2024 PT5 estimated to return to an Earth-centred orbit in 2055, we will once again have the opportunity to prove our own equipment, measurement, and calculations. Therefore, whilst this “Second moon” may not be as exciting as it initially appeared, it does show that we are becoming better at predicting some extra-terrestrial events and understanding our solar system.
