Earth Is About to Capture an ‘Asteroid’ That Might Be a Discarded Rocket

Earth has one single, solitary moon. Well, most of the time. Our little blue marble occasionally picks up a temporary asteroidal visitor, sometimes called a minimoon. The planet is set to pick up one of these transient moons in the coming weeks, but there’s something a bit different about this one. The orbit and speed of “2020 SO” suggest it might be of human origin

Earth doesn’t usually have a minimoon — most objects that get close enough to be influenced by Earth’s gravity either fall into the atmosphere or are flung off into space. Our ability to track these small objects is still evolving, but scientists have identified two temporary moons in the 21st century. 2006 RH120 hung around from 2006 to 2007, and 2020 CD3 orbited Earth from 2018 until earlier this year. 

2020 SO is currently on a trajectory that should allow it to enter an unstable orbit around the planet. Current projections suggest it will arrive next month and escape from Earth orbit in May 2021. The way it’s approaching is a bit unusual, though. 2020 SO is moving much more slowly than other near-Earth asteroids, and its orbital inclination is very similar to Earth’s. 

Currently, 2020 SO is classified as an Apollo asteroid, a class of objects with Earth-like orbits. Sometimes space rocks coming toward Earth from the moon will be noticeably slow, but 2020 SO is even slower than that. Many astronomers are expecting 2020 SO will turn out to be a large piece of space junk. We might even know what this object is — the leading suspect is a Centaur rocket booster from the 1966 launch of Surveyor 2. The estimated size of 2020 SO is a match for the Centaur booster at 21 to 46 feet long (6.4 and 14 meters). The Centaur was 41.6 feet long (12.68 meters). 

Despite all the interest in reusable rocket technology from SpaceX or Blue Origin, most vehicles in use are still expendable. First stage boosters are usually discarded in the ocean, and other parts are jettisoned in space to float forever in the void. Well, unless they come back for a visit 60 years later. 

Sky-watchers expect 2020 SO to make two close passes of Earth before flying off into space again. The first pass will be on December 1, 2020, and the second will be on February 2, 2021. The first pass will be just 50,000 kilometers distant, and 2020 SO is moving slowly enough that astronomers may be able to get a good look at it. Observing the state of a rocket that’s been hanging around in interplanetary space for decades could be interesting, but the predicted orbit could still change considerably in the lead-up to rendezvous.

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