“What, second moon,” you ask? Astronomers call it 2020 SO, a tiny object that dropped into Earth’s orbit about halfway between our planet & the moon in September 2020. Temporary satellites like these are referred to as minimoons, though calling it a moon is a bit deceptive in this case, in December 2020, NASA researchers learned that the object is not a space rock, but rather the remains of a 1960s rocket booster involved in American Surveyor moon missions.
This non-moon minimoon made its closest approach to Earth on December 1 (the day before NASA identified it as the long-lost booster), but it is coming back for one more victory lap, consistent with EarthSky.org. Minimoon 2020 SO will make a final close approach to Earth on Tuesday (February 2) at roughly 140,000 miles (220,000 kilometers) from Earth, or 58 percent of the way between Earth & the moon.
The booster drift away after that, leaving Earth’s orbit entirely by March 2021, consistent with EarthSky. Then, the previous minimoon will be just another object orbiting the sun. The Virtual Telescope Project in Rome will host an online farewell to the object on the night of February 1.
NASA learned that the object has made several close-approaches to Earth over the decades, even coming relatively near in 1966, the year that the agency launched its Surveyor 2 lunar probe on the back of a Centaur rocket booster. That gave scientists a first big clue that 2020 SO was man-made, they confirmed it, after comparing the object’s chemical make-up thereupon of another rocket booster, that has been in orbit since 1971.
Godspeed, minimoon 2020 SO. We built you, we abandoned you & now, you abandon us.