Earth has captured a tiny object, probably a 1960s rocket

This animation shows the temporary 2020 SW orbit around the Earth from November to March 2021. The object is thought to be the Centaur upper stage booster rocket from the Surveyor 2 mission launched to the Moon in 1966. While the Surveyor 2 lander is crashed into the lunar surface, the depleted Centaur rocket drifted past the moon and landed in an unknown solar orbit. Over 50 years later, the Centaur rocket has apparently returned, entering Earth’s orbit on November 10 where it will remain until March 2021 before escaping again into a new solar orbit. This animation has been speeded up a million times faster than real time. Credit: NASA / JPL-Caltech

In 1966, NASA launched Surveyor 2 to the moon. Now its rocket thruster has apparently returned to near-Earth space.

Earth has captured a tiny object from its orbit around the Sun and will keep it as a temporary satellite for a few months before it escapes into a solar orbit again. But the object is probably not an asteroid; it is likely the upper-stage Centaur rocket that helped lift NASA’s ill-fated Surveyor 2 spacecraft to the moon in 1966.

This story of celestial capture and release begins with the detection of an unknown object by the NASA-funded Pan-STARRS1 survey telescope in Maui in September. Pan-STARRS astronomers noted that this object followed a light but distinctly curved path in the sky, which is a sign of its proximity to Earth. The apparent curvature is caused by the observer’s rotation around the Earth’s axis as our planet rotates. Presumably an asteroid orbiting the Sun, the object received a standard designation from the Minor Planet Center in Cambridge, Massachusetts: 2020 SO. But scientists at NASA’s Jet Propulsion Laboratory’s Center for Near-Earth Object Studies (CNEOS) in Southern California saw the object’s orbit and suspected it was not an ordinary asteroid.

Most asteroid orbits are more elongated and inclined than Earth’s orbit. But the 2020 SW orbit around the Sun was very similar to that of Earth: it was roughly the same distance, almost circular, and on an orbital plane that almost exactly matched that of our planet – very unusual for a natural asteroid. .

As astronomers from Pan-STARRS and around the world made further observations of SO 2020, the data also began to reveal the degree to which solar radiation was changing the trajectory of SO 2020 – an indication that it may not after all be an asteroid.

This photograph shows a model of the lander Surveyor. Credit: NASA / JPL-Caltech

The pressure exerted by sunlight is small but continuous and has a greater effect on a hollow object than on a solid one. A spent rocket is essentially a hollow tube and therefore is a low-density object with a large surface area. So it will be propelled by the pressure of solar radiation more than by a solid mass of high-density rock – just as an empty soda can will be pushed by the wind more than a small stone.

“The pressure of solar radiation is a non-gravitational force caused by the light photons emitted by the Sun hitting a natural or artificial object,” said Davide Farnocchia, navigation engineer at JPL, which analyzed the trajectory of SO 2020 for CNEOS. “The resulting acceleration on the object depends on the so-called area-to-mass ratio, which is greater for small and light, low-density objects.”

With the analysis of more than 170 detailed measurements of the position of SO 2020 over the past three months, including observations made by the NASA-funded Catalina Sky Survey in Arizona and ESA’s Optical Ground Station in Tenerife, Spain, the impact of The pressure of solar radiation has become evident and confirmed the low-density nature of 2020 SO. The next step was figuring out where the suspected rocket might have come from.

This photograph from 1964 shows a Centaur rocket in the upper stage before being coupled to an Atlas booster. A similar centaur was used during the launch of Surveyor 2 two years later. Credit: NASA

Space age artifact

The Surveyor 2 lunar lander was launched to the moon on September 20, 1966 on an Atlas-Centaur rocket. The mission was designed for reconnaissance of the lunar surface prior to the Apollo missions which resulted in the first manned lunar landing in 1969. Shortly after takeoff, Surveyor 2 separated from the Centaur upper stage booster as intended. But control of the spacecraft was lost the next day when one of its thrusters failed to fire, causing it to spin. The spacecraft crashed into the moon just southeast of the Copernicus crater on September 23, 1966. The Centaur rocket in the upper stage, meanwhile, passed past the moon and disappeared into an unknown orbit around the sun.

Suspicious that the 2020 SO was a remnant of an old lunar mission, CNEOS director Paul Chodas “turned the clock back” and swiped the object’s orbit back to determine where it had been in the past. Chodas found that the 2020 SO had somehow come close to Earth a few times over the decades, but the 2020 SO’s approach in late 1966, according to his analysis, would have been close enough to have. originated from Land.

“One of the possible pathways for 2020 SO brought the object very close to Earth and the Moon in late September 1966,” Chodas said. “It was like a eureka moment when a quick check of the launch dates for the lunar missions showed a match with the Surveyor 2 mission.”

Now, in 2020, the Centaur appears to have returned to Earth for a brief visit. On November 8, 2020, the SO slowly slipped into Earth’s sphere of gravitational dominance, a region called the Hill sphere that extends approximately 930,000 miles (1.5 million kilometers) from our planet. This is where 2020 SO will stay for about four months before it escapes again into a new orbit around the Sun in March 2021.

Before it leaves, 2020 SO will make two grand laps around our planet, with its closest approach on December 1st. During this time, astronomers will take a closer look and study its composition using spectroscopy to confirm whether 2020 SO is indeed an early space age artifact.