Astronomers have discovered a peculiar ‘moon’ shadowing Earth as it moves through space. Known as a quasi-moon, it doesn’t orbit our planet directly but stays nearby as both travel around the Sun.
According to new research published in Research Notes of the American Astronomical Society, the space rock may have been accompanying Earth for as long as 60 years.
Known as 2025 PN7, it may have evaded previous observation because it’s so small. While its exact size isn’t yet known, researchers think it’s about 30m (98ft) across. That’s roughly the wingspan of a typical short-haul passenger plane – making it the smallest known quasi-moon to have orbited Earth.
“We are discovering Near Earth Objects faster than ever before, thanks to rapid advancements in technology,” Dr Darren Baskill, astronomy lecturer at the University of Sussex, told BBC Science Focus. “Digital cameras are more sensitive than ever before, allowing us to see such faint objects, and computers are now able to rapidly sift through vast amounts of data.”
The celestial object, at its closest, comes 300,000km (186,400 miles) away from Earth. Typically, it sits about 384,000km (238,600 miles) away – but during its horseshoe-shaped orbit, it can drift as far as 297 million km (185 million miles).
That means it can only be noticed when it’s near – as it was in August 2025, when researchers from the Complutense University of Madrid in Spain spotted it from Hawaii’s Pan-STARRS observatory.
Looking back through old records, the scientists realised it matched an object that’s likely been accompanying Earth for decades.
“The main question is: where could 2025 PN7 have originated?” said Baskill. “When at its closest, 2025 PN7 is at a similar distance from the Earth as the Moon, giving a hint as to a potential lunar origin.
“Another clue you can spot yourself simply by looking at the Moon on a clear night – it is full of craters. Each impact would have thrown debris skywards, and some material could have escaped the gravitational hold of the Moon into space.”
A different theory is that the space rock came from an asteroid belt – but, according to Baskill, “collecting enough light from such a moving object to observe its chemical composition – and so identify its origin – is challenging.”
He added: “Astronomers have to be patient and wait to take observations only when PN7 is at its brightest, which is when the object is closest to the Earth.”
2015 PN7 is just one of seven quasi-satellites near Earth right now. Another is space rock Kamo‘oalewa, the target of China’s Tianwen-2 mission. In May 2025, Tianwen-2 launched with the aim of collecting samples from the asteroid to learn more about Earth’s origin and how asteroids form.
“Thanks to their occasional proximity, some of these Near Earth Objects could potentially be targets for the first-ever mining operations beyond Earth, or even enter the Earth’s atmosphere,” said Baskill.
2025 PN7 will be around until 2085, at which point gravitational pull will yank it out of its orbit.
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