“A Mysterious Object Is Hurtling Towards Earth, and Scientists Don’t Know What It Is,” read Newsweek’s headline on Monday, describing an object projected to pass 31,605 miles from earth. (One astronomer told them that was roughly 13% of the average distance between the earth and the moon).
But then a computer model calculated its past trajectories through space, according to the director for NASA’s Center for Near Earth Object Studies (CNEOS). “One of the possible paths for 2020 SO brought the object very close to Earth and the Moon in late September 1966,” he said in a statement. “It was like a eureka moment when a quick check of launch dates for lunar missions showed a match with the Surveyor 2 mission.”
On Wednesday NASA described how a team led by Vishnu Reddy, an associate professor/planetary scientist at the Lunar and Planetary Laboratory at the University of Arizona, tried to prove what they’d seen was a 54-year-old booster rocket:
Through a series of follow up observations, Reddy and his team analyzed 2020 SO’s composition using NASA’s IRTF and compared the spectrum data from 2020 SO with that of 301 stainless steel, the material Centaur rocket boosters were made of in the 1960’s. While not immediately a perfect match, Reddy and his team persisted, realizing the discrepancy in spectrum data could be a result of analyzing fresh steel in a lab against steel that would have been exposed to the harsh conditions of space weather for 54 years. This led Reddy and his team to do some additional investigation.
“We knew that if we wanted to compare apples to apples, we’d need to try to get spectral data from another Centaur rocket booster that had been in Earth orbit for many years to then see if it better matched 2020 SO’s spectrum,” said Reddy. “Because of the extreme speed at which Earth-orbiting Centaur boosters travel across the sky, we knew it would be extremely difficult to lock on with the IRTF long enough to get a solid and reliable data set.”
However, on the morning of Dec. 1, Reddy and his team pulled off what they thought would be impossible. They observed another Centaur D rocket booster from 1971 launch of a communication satellite that was in Geostationary Transfer Orbit, long enough to get a good spectrum. With this new data, Reddy and his team were able to compare it against 2020 SO and found the spectra to be consistent with each another, thus definitively concluding 2020 SO to also be a Centaur rocket booster…
So what happens next?
2020 SO made its closest approach to Earth on Dec. 1, 2020 and will remain within Earth’s sphere of gravitational dominance — a region in space called the “Hill Sphere” that extends roughly 930,000 miles (1.5 million kilometers) from our planet — until it escapes back into a new orbit around the Sun in March 2021.
As NASA-funded telescopes survey the skies for asteroids that could pose an impact threat to Earth, the ability to distinguish between natural and artificial objects is valuable as nations continue to explore and more artificial objects find themselves in orbit about the Sun.
Astronomers will continue to observe this particular relic from the early Space Age until it’s gone.