For a little over a month now, the Earth has been joined by a new ‘mini-moon.’ The object is an asteroid that has been temporarily accompanying Earth on its journey around the Sun. By 25th November it will have departed but before then, astronomers across the world have been turning their telescopes to study it. A new paper of 2024 PT5 reveals its basaltic nature – similar to volcanic rocks on Earth – with a composition that makes it similar to lunar material. There have been many close encounters to Earth allowing many of its secrets to be unveiled.
The Moon is perhaps one of the most well known astronomical objects. It’s Earth’s only permanent natural satellite and has been in orbit since early in the planet’s history. It lies approximately 384,400 kilometres away and has played a crucial part in stabilising are axial tilt and regulating the climate and seasons. In addition to the Moon we are occasionally joined by asteroids that briefly orbit around the Earth before continuing their journey through the Solar System.
The partial lunar eclipse from October 2023 as seen from Oxfordshire UK. Credit: Mary McIntyre FRAS. 2024 PT5 is a small asteroid that has served as a temporary “mini-moon” for Earth, orbiting near the planet for about six weeks. Analysis has revealed that the asteroid spins rapidly, completing one full rotation in under an hour and measures no more than 15 metres across. While it will leave Earth’s vicinity in just a few days, its brief presence has offered valuable insight and data on the properties of near-Earth objects.
Space agencies like NASA and ESA are both exploring commercial space operations to support the growing global space economy. Exploring and mining asteroids is an activity that is well suited to this endeavour. Asteroids like 2024 PT5 which is in close proximity to Earth is well suited to this. The paper that has been published in Astronomy & Astrophysics and was authored by R. de la Fuente Marcos and a team of Spanish astronomers.
The asteroid Dimorphos was captured by NASA’s DART mission just two seconds before the spacecraft struck its surface on Sept. 26, 2022. Observations of the asteroid before and after impact suggest it is a loosely packed “rubble pile” object.
Credit: NASA/JHUAPLThe study focussed attention on changes to the short-term orbital properties and used N-body simulations (a technique to simulate a dynamic system under other physical forces such as the force of gravity.) They also explored the spectral class of the asteroid from reflectance spectra analysis obtained with the OSIRIS spectrograph and assessed its rotational properties.
The team confirmed that 2024 PT5 is a natural object (thankfully) that has a spectra which is consisted with the so called Sv-type asteroid, similar to breccia found in the Lunar mare. Assessment of its rotational properties revealed it is completing one rotation in less than an hour. They could not rule out whether the asteroid was tumbling in an erratic fashion, further analysis is needed. Finally through astrometric observations the team concluded that the orbits of 2024 PT5 and 2022 NX1 (another near Earth asteroid which is just 10 metres across) are very similar.
Both ESA and NASA now consider a cost-effective strategy for NEO missions essential with a focus on small body science and planetary defence. The approach includes reusing and active missions and identifying accessible objects like 2022 NX1 and 2024 PT5 using ground-based observatories.
