The 'second moon' left the Earth, and astronomers captured its farewell

This image of the temporary "mini-moon" as it left the sky on November 25 was taken with the Two-Meter Binocular Telescope in Spain.

In late September, an asteroid became Earth's second "moon." But before it passed us, astronomers captured a photo of it that gave us a glimpse of what it looks like.

This asteroid is numbered 2024PT5. It is a near-Earth asteroid (NEO). It was temporarily captured by the Earth’s gravity on September 29, 2024 and became a temporary "mini-moon".

However, from the moment it was discovered, scientists knew it was just a "temporary visit" that would not last more than a few weeks. Carlos de la Fuente Marcos of the Complutense University of Madrid, Spain, is one of the scientists studying 2024 PT5 and participated in the observation of 2024 PT5.

As previously predicted, 2024PT5 left Earth on Monday, November 25, and returned to its usual location in the Atina asteroid belt, which orbits the Sun in an orbit similar to that of the Earth, with an average distance of about 150 million kilometers from the Sun.

Asteroids are like wanderers in the solar system, occasionally coming into close contact with the Earth. 2024PT5 is one of these wanderers, and under certain conditions and times, it will be temporarily captured by the Earth's gravity, presenting a brief astronomical spectacle.

2024PT5 is only about 11 meters in size, close to the height of a 4-story building, so it is very dim and not easy to observe for most astronomy enthusiasts. However, with the help of the Two-Meter Twin Telescope (TTT) of the Canary Astrophysics Institute (IAC) in Spain, Marcos and his colleagues conducted an in-depth study of the asteroid and found some interesting information. For example, its composition suggests that it may be a fragment of the moon that was splashed out after being hit by an asteroid.

Although they are somewhat reluctant to see 2024PT5 leave, astronomers still seize this precious opportunity to record its departure.

This artist's concept depicts the scene of 2024PT5 "leaving" the Earth.

It is worth noting that 2024PT5 will not be away from the Earth for too long. According to the Small Body Query Database of NASA's Jet Propulsion Laboratory (JPL), 2024PT5 will approach the Earth again on January 9, 2025, and the distance will be even closer than this time, only 1.1 million kilometers.

However, because it moves at a speed of about 3,700 kilometers per hour, it will not be captured by the Earth's gravity and become the second "moon". The next time 2024PT5 comes close to the Earth will not be until 2055.

Marcos explained: "According to the latest data, it is almost certain that 2024PT5 will return in 2055. According to the previously determined orbit, it will be captured by the Earth by then; however, the latest observations show that this capture event will not happen."

After that, there is a great deal of uncertainty about the next few encounters between the Earth and 2024PT5 , mainly because of the long time span of orbital predictions. At present, it seems that the closest encounter with this asteroid after 2055 will occur on January 7, 2084, when 2024PT5 is expected to fly within about 1.6 million kilometers of the Earth at a speed of about 3,700 kilometers per hour.

Then, on May 8, 2084, the asteroid 2024PT5 will return to Earth again, when it is estimated to come within about 3.2 million kilometers of Earth at a speed of 3,240 kilometers per hour, and may once again briefly become a mini-satellite of Earth.

References

https://www.space.com/mini-moon-2024pt5-asteroid-depart-image

https://www.space.com/goodnight-second-moon-asteroid-2024PT5

Compiled by: Liu Yun

Reviewed by: Li Xin, Research Librarian of Beijing Planetarium