Earth To Acquire A Second Moon This Month — But It’s Only Temporary

In September 2024, Earth will briefly gain a second, temporary moon in the form of asteroid 2024 PT5. Unlike our regular moon, which has accompanied Earth for billions of years, this new mini-moon will remain for about two months before it returns to orbit around the sun.

This temporary phenomenon provides an exciting glimpse into the dynamic nature of objects in space that interact with Earth’s gravity. Asteroids like 2024 PT5, which belong to the Arjuna asteroid group, follow orbits similar to Earth's.

These asteroids orbit the sun at roughly the same distance from Earth as Earth itself, around 93 million miles (150 million kilometers). As part of the near-Earth object population, some asteroids can approach Earth closely, within 2.8 million miles (4.5 million kilometers). When this happens, under specific conditions, Earth's gravity can capture them temporarily, turning them into mini-moons for a brief time.

2024 PT5's upcoming capture is a short-term event, lasting just weeks before the asteroid resumes its journey around the sun. Mini-moon events like this are categorized into two types.

The first type involves asteroids that orbit Earth fully for an extended period, even completing one or more revolutions. The second type, like 2024 PT5, only involves a brief stay.

These short mini-moon episodes are much more frequent than long-term ones, occurring every few years, while long captures happen only once every decade or two.

This month, Earth will welcome a second moon in the shape of a small asteroid known as 2024 PT5.

Carlos de la Fuente Marcos, a researcher at Universidad Complutense de Madrid, and his team are among the scientists who have identified this mini-moon event. Marcos explains that for an object like 2024 PT5 to become temporarily bound to Earth, it needs to approach at a slow velocity of around 2,200 miles per hour (3,540 kilometers per hour) and a specific distance.

Under these conditions, the object’s energy relative to Earth can become negative, temporarily causing it to enter Earth’s gravitational pull.

"Under these conditions, the geocentric energy of the object may become negative, and the object may become a temporary moon of Earth. This particular object will undergo this process starting next week and will remain for about two months. It will not follow a full orbit around Earth," said Carlos de la Fuente Marcos.Robert Lea (created with Canva)

So far, only two long-term mini-moons have been identified: 2006 RH120 and 2020 CD3. In contrast, several short-term mini-moons have been recorded, including 1991 VG, 2022 NX1, and 2024 PT5. Despite the excitement, most of these events are invisible to the naked eye.

Unfortunately, 2024 PT5 is too small and dim for casual stargazers to observe, even with typical amateur telescopes. Only large, professional-grade telescopes equipped with advanced detectors can capture a view of this temporary visitor.

"The object is too small and dim for typical amateur telescopes and binoculars. However, it is well within the brightness range of typical telescopes used by professional astronomers. A telescope with a diameter of at least 30 inches, along with a CCD or CMOS detector, is needed to observe this object; a 30-inch telescope and a human eye behind it will not be sufficient," Marcos explained.

Astrophysicist Dr. Neil deGrasse Tyson emphasizes that temporary moons like asteroid 2024 PT5 offer a unique opportunity for scientific observation and education. He explains that these mini-moons can help astronomers understand how celestial bodies interact with Earth's gravitational pull, which is crucial for predicting the paths of future asteroids.

Public engagement in astronomy can also be fostered through these events. Tyson suggests that schools and community centers should organize viewing parties, encouraging families to learn about space science together. This can ignite interest in STEM fields while also making abstract concepts more relatable.

Concentric rings are set against a black background, with a bright dot at the center representing Earth.

Once its brief stay near Earth is over, 2024 PT5 will continue its journey around the sun, again becoming part of the Arjuna asteroid group. While it won’t stay long, such mini-moon events remind scientists of the ever-changing nature of space and Earth’s gravitational interactions with nearby objects.

Gravitational disturbances, primarily from the sun, will eventually cause the mini-moon’s ejection from Earth’s vicinity, sending it back into space.

Though 2024 PT5 will not be visible to most, astronomers like Marcos and his colleagues plan to study it closely using telescopic observations.

By examining its light patterns and spectra, they aim to learn more about its composition and properties, contributing valuable knowledge to our understanding of minor asteroids that periodically visit Earth’s neighborhood.

Navigating the Science of Mini-Moons

Dr. Lindley Johnson, planetary defense officer at NASA, notes that monitoring near-Earth objects like 2024 PT5 is essential for planetary safety. He stresses the importance of public awareness regarding celestial events, as understanding these phenomena helps demystify space science and fosters a culture of curiosity.

Johnson also recommends that educational institutions incorporate mini-moon events into their curricula, emphasizing hands-on activities such as simulations or model-building. By doing so, educators can create a more engaging learning environment that encourages critical thinking about space and its impact on Earth.

The temporary presence of asteroid 2024 PT5 around Earth highlights the dynamic nature of our cosmic neighborhood. Experts like Dr. Tyson and Dr. Johnson advocate for community engagement and educational initiatives to harness public interest in these phenomena. By promoting active learning experiences, we can inspire the next generation of scientists and explorers.

Incorporating these events into school programs not only enriches students' understanding of astronomy but also empowers them to appreciate the broader implications of space science on our planet’s safety and future. This interconnectedness between education and exploration is vital for fostering a scientifically literate society.