An object, discovered in September by astronomers looking for asteroids near Earth, sparked interest in the planetary scientific community due to its size and unusual orbit.
Using data collected at NASA’s Infrared Telescope Facility (IRTF) and orbit analysis by the Center for Near-Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory, the scientists confirmed that Near-Earth Object (NEO) 2020 SO is, in fact, a Centaur rocket from the 1960s.
The object, discovered in September by astronomers searching for near-Earth asteroids by the NASA-funded Pan-STARRS1 survey telescope in Maui, has sparked interest in the planetary scientific community due to its unusual size and orbit, and has been studied by observers from all over the world.
Further analysis of the 2020 SO orbit revealed that the object had approached Earth a few times over the decades, with an approach in 1966 that brought it close enough to suggest it may have originated from Earth. Comparing this data to the history of previous NASA missions, Paul Chodas, director of CNEOS, concluded that 2020 SO could be the Centaur rocket for the upper stage of NASA’s ill-fated 1966 Surveyor 2 mission to the moon.
Equipped with this knowledge, a team led by Vishnu Reddy, associate professor and planetary scientist at the Lunar and Planetary Laboratory at the University of Arizona, performed follow-up 2020 SO spectroscopic observations using NASA’s IRTF on Maunakea. , Hawai’i.
“Due to the extreme weakness of this object following the CNEOS prediction, it was a difficult object to characterize,” Reddy said. “We got color observations with the Large Binocular Telescope, or LBT, which suggested that 2020 SO was not an asteroid.”
Through a series of follow-up observations, Reddy and his team analyzed the composition of 2020 SO using NASA’s IRTF and compared the 2020 SO spectrum data with that of 301 stainless steel, the material of which they are Centaur boosters were made in the 1960s. While not immediately a perfect match, Reddy and his team insisted, realizing that the discrepancy in the spectrum data could be the result of analyzing fresh steel in a lab against steel that would have been exposed to the harsh conditions. space weather for 54 years. This led Reddy and his team to do some additional investigations.
“We knew that if we wanted to compare apples to apples, we would have to try to get spectral data from another Centaur rocket that had been in Earth orbit for many years and then see if it better matched the 2020 SO spectrum,” Reddy said. “Because of the extreme speed at which Centaur repeaters in Earth orbit travel across the sky, we knew it would be extremely difficult to lock into IRTF long enough to get a solid and reliable data set.”
However, on the morning of December 1st, Reddy and his team realized what they thought was impossible. They observed another Centaur D rocket from the 1971 launch of a communications 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 to the 2020 SO and found that the spectra were consistent with each other, thus definitively concluding the 2020 SO as well as a Centaur rocket.
“This conclusion was the result of a huge team effort,” Reddy said. “We have finally been able to solve this mystery thanks to the great work of Pan-STARRS, Paul Chodas and the team from CNEOS, LBT, IRTF and observations around the world.”
2020 SO made its closest approach to Earth on December 1, 2020 and will remain within the sphere of Earth’s gravitational domination – a region in space called the “Hill sphere” that spans approximately 930,000 miles (1.5 million of kilometers) from our planet – until it escapes again into a new orbit around the Sun in March 2021. As NASA-funded telescopes scan the skies for asteroids that could pose a threat to the impact on Earth, the ability to distinguish between natural and man-made objects is invaluable as nations continue to explore man-made objects found in orbit around the sun. Astronomers will continue to observe this particular relic from the first space age until it is gone.
For more information on NASA’s Planetary Defense Coordination Office, please visit: https://www.nasa.gov/planetarydefense
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