A 50-year-old piece of space history has come home for the holidays, and on December 1, astronomers will get a closer look.
Surveyor 2 blasted off for the Moon on September 20, 1966. The lander was supposed to scout possible landing sites for the Apollo missions, but shortly after Surveyor 2 separated from its Centaur upper stage rocket, the mission spun out of control – literally. A maneuvering thruster didn’t fire when it was supposed to, and Surveyor 2 started spinning. Three days after launch, the lander crashed into the lunar surface just south of Copernicus crater.
The upper stage rocket – empty of fuel and having done its part for the mission –drifted past the Moon to settle into an orbit around the Sun. Nobody bothered plotting its orbit, and nobody really expected to see it again. However, the abandoned rocket booster came drifting back out of the darkness this past fall, like a Space Age ghost ship.
Apparently, the Surveyor 2 rocket’s unmapped orbit happened to intersect Earth’s orbit again, decades after parting ways. It passed close enough to get snagged by Earth’s gravity, but the empty rocket stage is moving too quickly for our planet’s gravity to hold onto it for long. Over the next few months, the 55-year-old rocket will make two wide orbits around its former home – and December 1 is its closest approach. Sometime in March, its velocity will carry it beyond our gravity’s influence again, into a new orbit around the Sun.
We may see the abandoned rocket stage again, however. Astronomer Paul Chodas, director of the Center for Near Earth Object Studies, retracted the rocket’s orbit based on how astronomers have watched it moved since September. And it turns out that Surveyor 2’s spent upper stage has passed close to Earth in the past, apparently unseen.
This encounter was different. Astronomers at the Pan-STARRS1 survey telescope in Maui, which scans the skies for nearby asteroids and other objects, spotted something unusual in September. The object’s path across the night sky seemed to curve, which meant that whatever it was, it was very close to Earth. As the planet rotates, an observer standing on the surface will move relative to things in space, making their paths seem to curve across the sky. But unless the object is very close, within a few hundred thousand miles or so, that relative motion won’t make a noticeable difference.
Most asteroids that orbit our planet have long, very elliptical orbits, and they’re usually tilted in relation to the plane on which we orbit the Sun. But the object Pan-STARRS1 had spotted, dubbed 2020 SO, seemed to be in a much flatter, nearly circular orbit. It also seemed to be getting blown around by the pressure of the Sun’s radiation, which suggested it was hollow rather than a solid chunk of rock. 2020 SO just got weirder and weirder – until Chodas checked its orbit against NASA’s launch records.
“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 to the press. “It was like a Eureka moment when a quick check of launch dates for lunar missions showed a match with the Surveyor 2 mission.”
As 2020 SO makes its closest pass by Earth on December 1, astronomers will use spectrometers to study its composition and try to confirm that it is, in fact, the spent rocket from Surveyor 2. Astronomers aren’t sure exactly what the rocket’s new path around the Sun will look like, but it could cross our paths again in the future, like a spacefaring Flying Dutchman.