We all know and love our moon. It has been Earth’s faithful companion for billions of years. But it’s not our only friend. From time to time, smaller objects are captured in the orbit of our planet.
Despite several detections of temporarily captured tiny-moons, only two cases were confirmed: 2006 RH120 travelled in 2006, 2007 and 2020 CD3 in Earth orbit, from 2018 to 2020. Right now, astronomers have seen a new object, called 2020 SO. It has probably been temporarily captured by earth’s gravity. The images show an object that will arrive in October 2020 and circulate until May 2021, and then it will depart elsewhere.
As you can see in the simulation below, the trajectory of the object suggests that it will enter and exit through two gravitationally stable points created by Earth’s gravitational interaction with the Sun, called Earth’s Lagrange points.
Asteroid 2020 SO may get captured by Earth from Oct 2020 – May 2021. Current nominal trajectory shows shows capture through L2, and escape through L1. Highly-chaotic path, so be prepared for lots of revisions as new observations come in. @renerpho @nrco0e https://t.co/h4JaG2rHEd pic.twitter.com/RfUaeLtEWq
— Tony Dunn (@tony873004) September 20, 2020
2020 SO was classified as an Apollo asteroid in the Jet Propulsion Laboratory database, that is, a class of asteroids whose paths cross Earth’s orbit. These kinds of asteroids often have close contacts with Earth. But there is some evidence that 2020 SO is not like the others. Earth-like orbit and the low speed of 2020 SO suggest that it is not actually an asteroid. Its characteristics, according to the experts, have more to do with something man-made.
What’s interesting is that objects that have come from the Moon also have a slower speed than asteroids. As Alice Gorman, a space archaeologist from Flinders University in Australia pointed out that 2020 SO is even slower than the moon rocks.
All of this points to the object being either space junk or, according to Paul Chodas of the Jet Propulsion Laboratory, a stage of a rocket that launched an experimental payload called Surveyor 2 to the Moon in September 1966.
Asteroid #2020SO is suspected of being the Surveyor 2 centaur rocket booster, launched on 20 September 1966. The Earth-like orbit and low relative velocity suggest a possible man-made object.
— Kevin Heider (@kpheider) September 21, 2020
Reusable rockets are just a recent invention because recovery is incredibly difficult technically. The solution widely used for decades was to launch multi-stage rockets designed to fall apart. The booster stage returns to Earth for reuse, while the rest of the rocket, carrying the payload, falls apart into space once it does its job. These discarded stages constitute a large amount of space junk. And, according to Gorman, they are surprisingly easy to lose.
“There are so many factors in the space environment, like gravitational factors and other things that affect movement, that it can sometimes be quite unpredictable,” said the scientist, cited by ScienceAlert.
The calculated size of 2020 SO matches the properties of the 1960s Centaur stage. According to NASA’s database, the object is between 6.4 and 14 meters long, and the Centaur stage measures 12.68 meters.
Asteroids are detected in the sky as bright moving objects, like a dot in the dark. From that, we can establish the velocity and orbit and make an estimate of the size, but it is impossible to determine the shape or composition without more detailed observations.
2020 SO must perform two near-Earth flights. On December 1, 2020, it will pass a distance of about 50,000 kilometres. Around February 2, 2021, it will fly at 220,000 kilometres. It is also not close enough to enter Earth’s atmosphere – the object does not pose any danger. But these distances, particularly at slow speeds, maybe enough to study it more closely and determine what 2020 SO is.
We might be able to distinguish a rough shape. Spectroscopy could help determine if the object is painted. And the amount of light it reflects could even provide information to help plan long-term space missions. If 2020 SO is a 1966 Centaur stage, it has been in space for 54 years.
Of course, whether or not it’s a rocket stage, the properties of 2020 SO can help scientists identify other objects approaching Earth in the future.