Mini-moon 2020 SO to enter Earth’s orbit - but oh so slowly

It is likely to appear in our skies in October but might only be visible for a few months

The virtual sessions by Expo 2020 will coincide with World Space Week. AFP

A new mini-moon is about to join Earth’s orbit, making it only the third to have been detected by astronomers.

After its global orbit, expected to last a few months or even years, the mini-moon will be cast back out into space.

Only two have previously been spotted circling Earth. The first confirmed sighting was of 2006 RH120, in orbit between 2006 and 2007, followed by 2020 CD3, spotted earlier this year and in orbit between 2018 and 2020.

The 2020 CD3 mini-moon was spotted earlier this year by the Gemini Observatory. Gemini Observatory

The new mini-moon has been named 2020 SO and is heading towards Earth’s orbit on a path far slower and lower than those of its forebears. It was tracked by the Pan-STARRS1 telescope at the Haleakala Observatory in Hawaii on September 17.

San Francisco-based physics teacher Tony Dunn tweeted that 2020 SO was likely to arrive in October and also demonstrated a simulation of where it will begin orbiting.

There is a school of thought, however, that 2020 SO may not be a mini-moon at all.

Its unusually low velocity has led scientists to assert that it could actually be space junk - a man-made substance. Dr Paul Chodas, manager of the Centre for Near-Earth Object Studies (CNEOS), has suggested it may be the remnants of the Surveyor 2 Centaur stage rocket body, launched in 1966.

"I suspect this newly discovered object 2020 SO to be an old rocket booster because it is following an orbit about the Sun that is extremely similar to Earth's, nearly circular, in the same plane, and only slightly farther away the Sun at its farthest point." he told CNN.

A NASA Centaur upper stage similar to the 1966 rocket that is suspected of being 2020 SO. AFP

Rockets are frequently lost in space, another scientist said.

"You have to keep tracking these things, or you can just sort of lose sight of them really easily," space archaeologist Alice Gorman told ScienceAlert. "It's quite astonishing the number of things that have gone missing."

Ms Gorman supported Dr Chodas’ suggestion, flagging up the relatively slow speed of the body. "The velocity seems to be a big one,” she said. “What I'm seeing is that it's just moving too slowly, which reflects its initial velocity. That's essentially a big giveaway."

The link between 2020 SO and Centaur stage has also been made because their respective size is very similar: 2020 SO is thought to measure between 6.5 -14 metres across (21 and 46 ft) while Centaur stage is 12.5m (41.6 ft).

Astronomers will have the opportunity to carry out detailed observation in early December and again in February next year when 2020 SO is due to make pass near to Earth, although neither arc will be low enough for the body to enter Earth’s atmosphere.