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

Will this second moon be visible during its temporary orbit around Earth?

Damjan

• Published in News
• September 20, 2024

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 stay 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 roughly the same distance from Earth as Earth, 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 the Earth fully for a more extended period, even completing one or more revolutions. The second type, like 2024 PT5, only affects 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 grow negative, and the object may become a temporary moon of Earth. This particular object will undergo this process starting next week and for about two months. It will not follow a full orbit around Earth." said Carlos de la Fuente Marcos.

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, the 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, the object is well within the brightness range of typical telescopes used by professional astronomers. A telescope with a diameter of at least 30 inches plus a CCD or CMOS detector are needed to observe this object, a 30 inches telescope and a human eye behind it will not be enough." Marcos explained.

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.

Damjan