Earth’s Companion: The Quasi-Moon 2025 PN7 & Mini-Moons Explained

Astronomers have identified a small rocky body, designated 2025 PN7, that is currently accompanying Earth in its orbit around the Sun. While not a second moon in the traditional sense, the object is classified as a ‘quasi-moon’ – a dynamically interesting category that challenges conventional views of our solar system’s orbital landscape.

Unlike true moons, quasi-moons don’t orbit Earth directly. Instead, their orbital path around the Sun closely aligns with our planet’s. This proximity creates a prolonged gravitational interaction, resulting in a complex orbital dance. The discovery highlights the surprisingly active nature of the space surrounding Earth, according to experts in orbital dynamics.

“These objects force us to rethink a static view of the solar system,” explains Ben Sharkey, an astronomer at the University of Maryland. “Analysis shows that small bodies can share Earth’s orbit for decades without becoming natural satellites.”

What is a Quasi-Moon?

Quasi-moons orbit the Sun with a period nearly identical to Earth’s. From our planet’s perspective, their movement appears as a looping pattern against the background stars. However, this apparent looping doesn’t indicate a stable gravitational bond like that between Earth and its Moon. The gravitational connection is far more tenuous.

Data from the Minor Planet Center and the Planetary Science Institute indicates that Earth currently has at least seven known quasi-moons.

The object 2025 PN7 was initially detected by the Pan-STARRS system in Hawaii. Orbital analysis reveals it has been in this configuration since the mid-20th century. Its relatively small size – comparable to a building – explains why it remained unnoticed for so long. These objects are typically observed only with telescopes capable of capturing the faint sunlight reflected off small, rapidly moving bodies.

“The detection depends directly on technological advances,” says Grigori Fedorets, an astronomer at the University of Turku. “Most of these objects are simply too small for traditional instruments.”

Mini-Moons, Origin, and Scientific Value

It’s important to distinguish quasi-moons from ‘mini-moons.’ Mini-moons are temporarily captured by Earth’s gravity, but their stay is typically less than a year, and their orbits are unstable. Studies published in the journal Icarus have confirmed the direct observation of four mini-moons to date.

The origin of these objects remains a topic of ongoing research. Investigations by the Planetary Science Institute and the University of Maryland suggest that some originate from the main asteroid belt. Gravitational interactions with Jupiter may have nudged them inward toward the inner solar system.

Other spectroscopic analyses, such as those conducted on the quasi-moon Kamoʻoalewa, have revealed similarities to lunar composition. This suggests that certain bodies may be fragments ejected from Earth’s Moon following ancient impacts.

“Observing quasi-moons allows us to study celestial mechanics in real-time,” explains planetary scientist Kat Volk of the Planetary Science Institute. “These processes usually unfold over much longer timescales in other regions of the solar system.”

While the term “second moon” is attention-grabbing, astronomers agree that 2025 PN7 doesn’t meet the criteria for a permanent natural satellite. Its presence does, however, confirm that Earth travels accompanied by a dynamic population of small bodies. The ongoing discovery of these quasi-moons and mini-moons is providing valuable data for refining our understanding of the complex gravitational interactions within our solar system and the origins of near-Earth objects.