In a few days the Earth will gain about two months of second celestial companion in addition to the Moon. Two Spanish astronomers, Carlos of the Fountain Marcos And Raul of the Marcos Fountainthey have in fact discovered, thanks to the telescopes of theAsteroid Terrestrial impact Last Alert system in South Africa, a small asteroid of about 10 meterscalled 2024 PT5That from September 29th to November 25th 2024 will remain trapped in the Earth’s gravitational field becoming a sort of second moon for our planet. More than the moon, in reality, we are talking about mini-moon given the small size of 2024 PT5. For this reason and for its great distance from Earth (we are talking about a few million kilometers) it will be extremely weak and therefore impossible to see with the naked eye. It is difficult to observe even for professional telescopes, so much so that it was discovered only thanks to a network of telescopes dedicated to the discovery of objects that pass a few million kilometers from Earth, the so-called Near Earth Objects (NEOs). 2024 PT5 will perform a horseshoe orbit around the Earth gaining enough speed to escape the Earth’s gravitational pull and continue its course in the Solar System, but not before having spent 56 days in the company of our planet with which however – it is good to reiterate – there is no risk of collision.
What are the features of 2024 PT5
2024 PT5 has an average diameter of just over 10 meters and will be extremely faint with an apparent magnitude of 27.6 (the higher the magnitude, the less bright the object), that is, about 250 million times weaker of the faintest star visible to the human eye (magnitude 6). It has been discovered August 7, 2024the day before its closest approach to 560,000 km from Earth, 2024 PT5 will be captured by the Earth’s gravitational field from September 29th to November 25thThe asteroid will pass close to the Earth at a very low speed in astronomical terms, equal to approximately 1600 km/h about 3.5 million kilometers from our planet (for comparison, the Moon is about 380,000 km from us). A speed so low that the asteroid he won’t be able to escape to the Earth’s gravitational field: in technical jargon it is said that the asteroid will have negative geocentric energy during the 56 days it will travel on its horseshoe-shaped path around the Earth.
The orbit a horseshoe is a common trait of mini-moons like 2024 PT5. This allows them to acquire enough escape velocity to escape the Earth’s gravitational field and continue their race towards deep space. The next perigee (point of maximum approach) to Earth will instead occur later, January 9, 2025when the asteroid will pass at a distance of about 1.8 million kmbut at a speed of about 3700 km/henough to keep it from orbiting Earth.
What is a mini-moon?
The Earth gravitationally capture frequently small asteroids from the population of near-Earth objects, the so-called Near Earth Objects (NEOs)dragging them into orbit and thus transforming them into mini-moons. Sometimes, these captures are so fleeting that the mini-moons have no not even time to complete a single revolution around the Earth before leaving Earth’s orbit and returning to their regular heliocentric trajectories, that is, around the Sun. It is therefore not the first time that this type of event happens, for example we had other mini-moons in the period 2006-2007 with the asteroid 2006 RH120 or in 1981 and 2022 with the mini-moon 2022 NX1. 2024PT5 therefore represents only the most recent example of this class of objects. Minimoons are of great interest because they may contain precious metals, which could one day be mined by space missions.
When and how it was discovered
There mini moon 2024 PT5 it was discovered on August 7, 2024 from the telescopes stationed in South Africa that are part of the project Asteroid Terrestrial-impact Last Alert Systema joint NASA and University of Hawaii project for the robotic surveillance of the celestial vault in order to identify objects close to the Earth potentially dangerousThis type of object is identified by taking a photo successive images at short intervals of time of the same portion of the sky. Objects near the Earth will be in different positions in consecutive images than those further away, which appear to remain fixed.
From the analysis of many consecutive images (122 in the case of 2024 PT5) it is possible to try to reconstruct the object’s orbitwith some uncertainty given the small size of these objects. The positions are then fed into sophisticated computer simulations that can predict the objects’ future positions and velocities by solving Newton’s equations of universal gravitation.
