Earth is bidding adieu to its 'mini moon': What secrets did 2024 PT5 leave behind?

Earth is bidding farewell to its “mini moon,” asteroid 2024 PT5, a fascinating celestial visitor that captured the attention of astronomers worldwide during its brief stay in our cosmic neighbourhood.

First spotted in August 2024, the asteroid has been orbiting near Earth since September, following a horseshoe-shaped trajectory. Its departure on November 25, 2024, marks the end of a rare event, with the asteroid not expected to return until 2055.

How was 2024 PT5, Earth’s ‘mini moon’ discovered?

Asteroid 2024 PT5, measuring about 33 feet (10 metres) in diameter, was discovered in August 2024 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) operated by the University of Hawaii. The asteroid’s size — comparable to a school bus — and its faint visibility made it a challenge to observe without the aid of powerful telescopes.

Initially detected by an ATLAS telescope in South Africa, the asteroid was later confirmed as a natural object and not a man-made artifact.

Mini moon? Not quite! 🪨

This school bus-sized near-Earth asteroid might have a similar orbit to our Moon right now, but it’s 9x further away and not trapped by Earth’s gravity.

Even though it poses no risk to Earth, @NASASCAN will track this distant companion in Jan. 2025. pic.twitter.com/Sas7W9GliA

— NASA Goddard (@NASAGoddard) October 4, 2024

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Nasa’s planetary defence coordination office stated: “Given the similarity between asteroid 2024 PT5’s motion and that of our planet’s, scientists at Nasa’s Center for Near Earth Object Studies suspect that the object could be a large chunk of rock ejected from the moon’s surface after an asteroid impact long ago.”

This unique asteroid has been classified as part of the Arjuna asteroid group, which consists of celestial bodies with orbits that closely mimic Earth’s. Its proximity to Earth and the sun’s gravitational influences made it an ideal candidate for temporary capture.

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Is it really a mini moon for us on Earth?

Despite being popularly referred to as a “mini moon,” asteroid 2024 PT5 was never truly captured by Earth’s gravity. Instead, it followed a sun-centric orbit, with its path temporarily influenced by Earth’s gravitational field. This led to its horseshoe-shaped trajectory around the planet during its two-month stay.

The asteroid’s closest approach to Earth occurred at a distance of approximately 2 million miles (3.2 million kilometres) — roughly nine times the distance to the Moon. During its upcoming flyby in January 2025, it will pass even closer, at just 1.1 million miles (1.8 million kilometers), before speeding away into the solar system.

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Astrophysicists Raul and Carlos de la Fuente Marcos, who extensively studied the asteroid, told AP: “By the time it returns next year, it will be moving too fast — more than double its speed from September — to hang around,” said Raul de la Fuente Marcos.

Where did 2024 PT5 come from?

The origins of 2024 PT5 have been a topic of intense speculation and study. Multiple lines of evidence suggest that the asteroid may be a fragment of Earth’s Moon, ejected during a massive impact event billions of years ago.

Spectral analysis of the asteroid revealed a chemical composition strikingly similar to lunar material returned by the Apollo and Luna missions. Its rapid rotation period of less than an hour and its motion pattern further support the theory of a lunar origin.

This asteroid’s characteristics strongly point to it being a piece of our Moon. Its composition closely matches lunar samples, and its motion aligns with what we would expect from a fragment ejected during an ancient lunar impact.

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Josh Handal of Nasa’s planetary defence coordination office stated: “Rocket bodies from historical launches can also be found in such Earth-like orbits, but after analysis of this object’s motion, it has been determined that 2024 PT5 is more likely of natural origin.”

Nasa analysts also ruled out the possibility of it being a discarded rocket body or debris from past space missions, further strengthening its natural and lunar origin.

Why is the ‘mini moon’ leaving?

2024 PT5’s departure is a natural consequence of celestial mechanics. While Earth’s gravity temporarily influenced its motion, the sun’s stronger gravitational pull will eventually dominate, pulling the asteroid away.

This marks the end of its temporary association with Earth, a phenomenon that astronomers have closely monitored since September.

Earth has a temporary, tiny companion.

While not quite a "mini moon," since it will never be captured by Earth's gravity, Asteroid 2024 PT5 does have a similar orbit as our planet and will linger in our vicinity for a few months. https://t.co/5fB0Mvf6nq pic.twitter.com/k6HW3GuZZn

— NASA JPL (@NASAJPL) October 2, 2024

The asteroid’s exit trajectory will send it back into the vast expanse of the solar system. Although it will return briefly in January 2025, its next significant approach to Earth won’t occur until 2055.

Its increasing speed — projected to be more than double its September velocity by the time of its January flyby — will prevent it from being temporarily captured again.

Is the ‘mini moon’ rare?

Temporary mini moons like 2024 PT5 are rare. These events typically occur when small asteroids enter Earth’s gravitational field, either completing partial or full revolutions around the planet before breaking free.

There are two known scenarios for mini moons:

2. Long-term captures: Lasting years, where the asteroid completes multiple orbits.

3. Short-term captures: Temporary stays lasting days or months, like 2024 PT5’s two-month visit.

Nasa’s increasing ability to detect such objects through advanced asteroid surveys means that these events, while rare, could become more commonly observed in the future.

Nasa is preparing to maximise the scientific opportunities during 2024 PT5’s January 2025 flyby. The asteroid will come within 1.1 million miles of Earth, allowing scientists to conduct detailed observations using advanced radar systems.

The Goldstone Solar System Radar in California’s Mojave Desert, part of Nasa’s Deep Space Network, will be deployed to study the asteroid over a week-long observation period. This effort aims to gather detailed data on the asteroid’s size, shape, spin rate, and surface composition.

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With inputs from agencies