(CNN) – Earth is about to get a new “minimoon,” but it won’t stay around long.
The newly discovered asteroid, called 2024 PT5, will be temporarily captured by Earth’s gravity and will orbit our planet from September 29 to November 25, according to astronomers. The space rock will then return to a heliocentric orbit, which is an orbit around the sun.
Details about the ephemeral minimoon and the horseshoe-shaped path it travels were published this month in the journal Research Notes of the American Astronomical Society.
Astronomers first spotted the asteroid on August 7 using the South Africa-based NASA-funded Asteroid Impact Late Alert System, or ATLAS, observatory.
The asteroid is likely about 11 meters in diameter, but more observations and data are needed to confirm its size, said the study’s lead author, Carlos de la Fuente Marcos, a researcher at the Faculty of Mathematical Sciences at the Complutense University of Madrid. .
The space rock could be between 5 and 42 meters in diameter, potentially larger than the asteroid that entered the Earth’s atmosphere over Chelyabinsk, Russia, in 2013. Said asteroid, among 17 and 20 meters in sizeexploded in the air, releasing 20 to 30 times more energy than the atomic bomb launched over Hiroshima (Japan) and generating a brightness greater than that of the sun. Debris from the space rock damaged more than 7,000 buildings and injured more than 1,000 people.
But as a minimoon that it is, asteroid 2024 PT5 does not present any danger of colliding with Earth either now or in the coming decades, de la Fuente Marcos said. The space rock will orbit about 4.2 million kilometers away, or about 10 times the distance between the Earth and the Moon.
An animation shows what it could look like when the minimoon passes around the Earth. Credit: CNN/Adobe Stock
Minimoons can be of two types, according to Fuente Marcos.
Long episodes involve asteroids called temporary capture orbiters, which complete one or several revolutions around our planet that can last one or several years. During the short episodes, however, the asteroid does not even complete a full revolution around the Earth.
These short-lived episodes, also known as temporal capture flybys, are, like 2024 PT5, mini-moons lasting a few days, weeks or a few months, he said.
Earth has previously captured other temporary mini-moons, such as asteroid 2020 CD3. Although that asteroid was first seen orbiting Earth in February 2020 and moved away a couple of months later, research showed that it had orbited our planet for a few years before being detected.
Asteroid 2020 CD3 is considered a long-capture minimoon, while the newly detected asteroid 2024 PT5 is a short-capture one.
Short minimoons can occur several times a decade, but long minimoons are rare and only occur every 10 to 20 years, de la Fuente Marcos said.
It is not easy for asteroids to become mini-moons because they have to travel at the right speed and direction to be captured by Earth’s gravity.
“To become a minimoon, an incoming body has to slowly approach Earth at a short distance,” de la Fuente Marcos said. Asteroids that become minimoons approach within 4.5 million kilometers of Earth at speeds less than 3,600 kilometers per hour, he added.
“Whether an asteroid is captured by Earth is independent of its size or mass, it only depends on its speed and trajectory as it approaches the Earth-Moon system,” said Robert Jedicke, a specialist emeritus in solar system bodies at the Institute for Astronomy of the University of Hawaii, in an email. “Almost all asteroids that approach Earth do so too fast and at the wrong angle to be captured, but sometimes the combined pulls of all the objects in the solar system manage to allow a particular (slow) object to the correct angle is briefly captured.”
Jedicke was not involved in the new study.
Asteroid 2024 PT5 comes from the Arjuna asteroid belt, made up of small asteroids that have orbits around the Sun similar to the Earth’s orbit.
“We think there is about one dishwasher-sized minimoon in the Earth-Moon system at any time, but they are so difficult to detect that most of them go undetected during the time they remain Earth-bound,” Jedicke said. “2024 PT5 could be about 10 meters in diameter, making it the largest captured object discovered to date.”
Minimoons may also be asteroids from the main asteroid belt, located between Mars and Jupiter, or they may be fragments of the lunar surface thrown up by asteroid impacts millions of years ago, Jedicke said.
“Determining where they came from could help us understand the cratering process and how material is ejected from the surface of the Moon,” he said.
De la Fuente Marcos and his colleagues plan to observe 2024 PT5 to collect more data and details using the Gran Telescopio Canarias and the Twin Two Meter Telescope, both in the Spanish Canary Islands. But the asteroid will be too small and faint for amateur telescopes or binoculars to observe, he said. It will not create any observable effects on Earth.
After 56.6 days, the Sun’s gravitational pull will return asteroid 2024 PT5 to its normal orbit.
But the space rock is expected to fly close by Earth, 1.7 million kilometers away, on January 9, 2025, before “leaving Earth’s vicinity shortly thereafter, until its next return in 2055,” according to the study.
And when asteroid 2024 PT5 returns again, astronomers expect it to become Earth’s minimoon for a few days in November 2055 and again for a few weeks in early 2084.
