For more than 60 years, Earth has been stalked by a space rock without any of us realising. And we have no idea where it even came from.
Well, kind of. Astronomers have discovered that a tiny asteroid, named 2025 PN7, is accompanying our planet in a rare orbital ballet.
The asteroid is estimated to be as small as 62 feet, about as long as a bowling lane.
Most asteroids are ancient rocks made from the leftovers of our solar system’s formation, while others are chunks of the Moon flung into space by an impact on the lunar surface tens of thousands of years ago.
But because there are so few sightings of 2025 PN7, researchers wrote in a recently published article in the journal Research Notes of the American Astronomical Society that there are ‘no real hints about its origins’.
Does the Earth now have two moons?
No, the Earth does not have two moons, stressed Dr Alfredo Carpineti, a science writer for IFLScience.
Dr Carpineti, the author of the upcoming astronomy book, Invisible Rainbows, told Metro that this is because 2025 PN7 doesn’t orbit Earth like the Moon does.
Instead, it orbits the Sun at roughly the same distance as we do, a bit like a car driving in the lane next to you on the motorway.
Because the asteroid’s orbit is in lock step with Earth’s, this means 2025 PN7 is a ‘quasi moon’, rather than a moon, he said.
Wait, what is a quasi-moon?
A quasi-moon is an object ‘that appears to go around the Earth but is not gravitationally bound by it’, said Dr Carpineti.
These are different from ‘mini-moons’, which are objects that orbit our planet. But mini-moons tend to only be fleeting visitors, like 2024 PT5, which circled the blue marble for just two months before packing its bags.
By contrast, quasi-moons can be our cosmic companions for tens or even hundreds of years.
While scientists at the University of Hawaii spotted 2025 PN7 in August, they later realised by combing archival photos that the rock shuffled into its quasi-moon orbit in 1957.
According to observations, 2025 PN7 orbits the sun in an elliptical path that is inside Earth’s orbit part of the time and outside part of the time.
So far, 2025 PN7 has drifted as close to us as 2.5million miles, about 10 times the distance of us to the Moon, and will stray as far away as 11million miles.
But because 2025 PN7 is so small, astronomers have struggled to figure out what the sojourning object is made from, which can be done by looking at how much sunlight its surface reflects.
How long will 2025 PN7 be in orbit?
‘It will leave us in a few decades,’ added Dr Carpineti, referring to Nasa simulations that predict the 2025 PN7 will leave Earth’s orbit in 2083.
Give or take, 2025 PN7 will have been Earth’s neighbour for 126 years before packing its bags and heading off into the void of space.
Will it affect the Earth at all?
After fears that a ‘city-killer’ asteroid would smash into the Earth in a few years, it’s natural to feel a bit nervous about our rocky visitor.
But as Dr Carpineti says, 2025 PN7 ‘won’t affect Earth at all’.
‘It’s a tiny space rock we have sort of picked up on our cosmic journey,’ he added.
The Earth, after all, already had eight quasi-moons flinging around it, and we’ve all lived to tell the tale.
Every time we’ve had a tag-along in space, scientists have raced for their telescopes as each one offers a clue to how our star system came to be.
‘It’s always fun finding a new quasi moon,’ Dr Carpineti says. ‘It shows just how busy the bulk of space is.
‘Hope you enjoy the ride, little quasi-moon.’
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