Astronomers have discovered Earth’s newest quasi-lunar moon

Earth has just added its seventh confirmed quasi-lunar moon. It is 2025 PN7, a miniature Apollo-type asteroid discovered in August based solely on its brightness with Hawaii’s Pan-STARRS 1 telescope.

After analyzing its trajectory, scientists concluded that the object maintains a 1:1 resonance with the Earth. In other words, it orbits the Sun at the same time as our planet. From a distant perspective, this synchronicity gives the impression that Earth is accompanied by a diminutive asteroid – as if it had an extra moon.

Unlike the Moon, quasi-lunar moons do not operate under gravity related to the Earth. In cosmological terms, they are ephemeral companions following their own path around the Sun. Only at certain moments do they get close enough to appear connected. In the case of 2025 PN7, its minimum distance is 299,000 kilometers, while at its furthest point it may reach 17 million km. For comparison, the Moon remains at an average distance of 384,000 km from Earth.

According to the article published in AAS Research Notes, the asteroid has been in the quasi-satellite phase since 1965 and is expected to remain so for 128 years. Some researchers estimate that 2025 PN7 will finally move away in 2083.

Why does Earth have quasi-lunar moons?

So far, seven bodies have been confirmed that appear to accompany the planet in its orbit. Astronomers believe that even more may be discovered in the future. Earth is a natural reservoir of quasi-moons because Earth’s orbit is similar to that of some nearby objects that inhabit the so-called Arjuna asteroid group, a population that has only recently begun to be studied in more detail.

The Arjuna group does not form a ring like the asteroid belt between Mars and Jupiter, but consists of a legion of near-Earth rocks that orbit the sun in a similar path to our planet. Occasionally, some of these asteroids align with our trajectory and, depending on their orbital dynamics, are classified as quasi-lunar or mini-moons.