Last September, astronomers discovered 2020 SO, a small object on Earth approaching our planet. In November, it was temporarily captured by the earth’s gravity and spent a short time in a short orbit, which became known as a ‘mini-moon’. But now the time is over with us and on February 2nd it will break loose and return to its orbit around the sun.
But first, mini-moon 2020 SO will make one last close approach to us, about 220,000 kilometers from Earth, just over halfway between Earth and Moon.
Temporary satellites are fairly common. Small asteroids are captured for a short time before leaving Earth. But since the first detection of 2020 SO, researchers have suspected that the new mini-moon was not actually a natural object, but artificial.
It has a low relative velocity compared to the earth and sunlight has significantly affected its orbit, a clear way to distinguish between natural and artificial small bodies in the vicinity of the earth.
Light can be interpreted as a wave and as a particle. When we consider these particles, the photons, we are looking at massless particles that carry momentum, which means they can repel things. This is how solar sails work. In the case of 2020, SO, with a large surface area and a relatively light mass, resulted in the body exhibiting an acceleration that could not be explained by gravity.
“Solar radiation pressure is a non-gravitational force caused by light photons emitted by the sun, which strikes a natural or artificial object,” said Davide Farnocchia, a navigation engineer at JPL, who created 2020’s SO orbit for the sun. center for object studies near the earth analyzed. (CNEOS), explained in November. “The resulting acceleration on the object depends on the so-called area-to-mass ratio, which is greater for small and light objects with low density.”
This was important evidence to suggest that 2020 SO was man-made, but another came from a detailed projection of its orbital parameters in the distant past. The object has come close to our planet several times, but in 1966 it was so close that it could come from Earth. In fact, it is in line with the launch of NASA’s lunar lander.
“One of the possible paths for 2020 SO brought the object very close to Earth and the Moon at the end of September 1966,” said CNEOS director Paul Chodas. “It was like a eureka moment when a quick look at the launch dates for lunar missions showed a resemblance to the Surveyor 2 mission.”
Observations in December, after the first narrow passage, revealed that it was made of stainless steel, confirming that it was indeed an old piece of the Surveyor 2 Centaur rocket’s top stage, launched on September 20, 1966 is.
After tomorrow’s narrow passage, the piece of rocket will re-enter deep space, but it will visit us for the next few decades, despite the fact that it remains millions of miles away from us.