Astronomers Have Discovered Earth’s Latest Quasi-Lunar Moon

The world has Just added its seventh confirmed semi-lunar moon. This is 2025 PN7, a small Apollo-type asteroid that was detected in August only by its brightness, thanks to the Hawaiian Pan-STARS 1 telescope.

After analyzing its trajectory, scientists concluded that the object maintains a 1:1 resonance with Earth. In other words, it orbits the Sun at the same time as our planet. From a distant perspective, this alignment makes it look like Earth is being accompanied by a tiny asteroid—as if it has an extra moon.

Unlike the Moon, semi-lunar moons are non-gravitational bound to the earth. They are transitory companions, in cosmic terms, following their own paths around the Sun. Only at certain times do they come close enough to appear bound. In the case of 2025 PN7, its minimum distance is 299,000 km, while at its furthest it can reach 17 million km. For comparison, the Moon is an average of 384,000 km from Earth.

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

Why is there a half-moon moon on Earth?

So far, seven bodies have been confirmed that appear to accompany the planet in its orbit. Astronomers believe that more may be discovered in the future. Earth is a natural reservoir of semi-moons because Earth’s orbit is similar to that of some nearby objects that inhabit the so-called Arjuna group of asteroids, 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 a legion of near-Earth rocks that orbit the Sun in the same path as our planet. Occasionally, some of these asteroids coincide with our orbit and are classified as semi-moons or small moons, depending on their orbital motion.

Quasiluna’s moon 2025 PN7 sits far from Earth in the Arjuna asteroid group.Illustration: Wired