Asteroid or space junk?

Astronomers are always on the lookout for objects that might be heading our way. And when a new blip appeared on the radar recently, scientists assumed it was an asteroid and tracked it. But, now they’ve had a rethink. Could it, they’re wondering, instead be a legacy of our past forays into space from decades gone by? Ben McAllister has the details...

Ben - In September a telescope in Hawaii was diligently scanning the skies, looking for large space rocks on a collision course with Earth, which could pose a threat to human life. What it found, among other things, was a tiny asteroid on a course to make a close approach. The object, labelled Asteroid 2020SO, is expected to enter our orbit in October and stay for about 7 months, orbiting much like our own Moon.

The capture of a small new moon, what we call a “mini moon”, is pretty fascinating in and of itself - but 2020SO has some strange characteristics which have caused astronomers to come to unexpected conclusions. Experts now believe that 2020SO might not be a space rock after all, but rather a long lost piece of man-made junk, returning to Earth after nearly 60 years in the void.

Specifically, researchers at NASA think that the object could be a part of a rocket used to propel the Surveyor 2 lander to the Moon back in 1966. After helping the lander get to its destination the rockets were shot off into space, never to be seen again - perhaps until now!

There are a few aspects of 2020SO’s trajectory which make it look a little bit artificial.

Firstly, the object is travelling pretty slowly for an asteroid - plodding along at a poky 2400 km/h - making it look much more like something we primitive humans would have been capable of flinging into space 60 years ago.

Secondly, our new solar neighbour is on a nearly circular orbit around the Sun, which is pretty similar to the Earth, and pretty atypical for an asteroid.

Finally, the plane in which the mysterious mini moon orbits the Sun is aligned with the Earth’s. That is to say, if you picture the orbits of the Earth and 2020SO around the Sun as two rings floating in space, the rings aren’t tilted at any angle to each other - they are aligned.

This is very odd for a space rock, which we are used to seeing travelling at all kinds of angles - but it would be totally consistent with something we shot out towards the Moon ourselves.

Whatever our strange new friend is, we’ll be able to get clearer answers as it gets closer to Earth. We might be able to discern a rough shape, figure out whether or not it is painted, and observe the way it interacts with the heat and light from the sun to see if it looks more like something light and hollow, like an old piece of space junk, or something dense like a rock.

If it does turn out to be a long-forgotten rocket part we could potentially learn quite a lot from it about the way man-made objects hold up in the harsh conditions of space over decades long timescales. And if it turns out to be a real asteroid, it would be fascinating as well, due to the peculiarities of its orbital trajectory when compared with things we’ve seen before.

Either way - it’ll only be with us for the next 7 months, so make sure to wave as it passes by.