Blast from the past? Earth to gain new MINIMOON and it could be the remains of an old rocket

Every once in a blue moon, pardon the pun, a small object becomes trapped in Earth's gravity for an extended stay in the planet's orbit before eventually jetting back off into the solar system. 

More often than not, we earthlings are blissfully unaware that we have gained a new natural satellite, often for years at a time. We are aware of only two confirmed so-called 'minimoons' in our history – 2006 RH120, which visited in 2006 and 2007, and 2020 CD3, which orbited the Earth from 2018 to 2020. 

In more recent years, courtesy of advances in technology and planetary defences, we are getting better at spotting these smaller objects, even before they take up a position, revolving around our world. 

Brace yourself for another curveball in 2020, as scientists have spotted 2020 SO, a tiny space rock with a trajectory that's likely to bring it within Earth's gravitational grasp for a short stay between October 2020 and May 2021. 

However, there is a twist in the tale; the object's orbit and low velocity suggest it may not be an asteroid, meteorite or space rock of any description at all. 

In fact, its currently observed behaviour has more in common with man-made objects than it does with naturally occurring spaceborne missiles. 

For the time being, ahead of more close-up observations, NASA has designated 2020 SO as an Apollo asteroid, meaning it will cross Earth’s orbit as it flies through space.

Its orbital path, low inclination relative to the Earth's orbit and a number of other astronomical anomalies all suggest that it is indeed space junk, with the frontrunner theory positing that it is the discarded Centaur stage from an experimental mission called Surveyor 2, which launched in September 1966. 

Indeed, 2020 SO's size, between 6.4 and 14 metres (21 and 46 feet), matches roughly with that of a 1960s-era Centaur stage rocket, 12.68 metres (41.6 feet).

2020 SO is due to make two particularly close flybys of the Earth: On December 1, 2020 at a distance of 50,000 kilometres (31,000 miles) and again on February 2, 2021 at a distance of 220,000 kilometres (136,700 miles).

It is extremely unlikely to re-enter Earth's atmosphere but scientists are hoping to study it and determine how much damage a few decades floating around in space can inflict on our older spacecraft.

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