New “Mini-Moon” Is Approaching Earth

How many moons does Earth have? You were probably taught that the answer is one, but the number turns out to change from time to time.

Projection/simulation of the trajectory of the object 2020 SO. The white circle is the orbit of Earth’s longtime natural satellite, Luna. Photo: Orbit Simulator

In recent years, two “mini-moons” have been spotted orbiting Earth for a year or two before moving back on to the solar system at large.

One circled Earth between 2006 and 2007, and another from 2018 to 2020. Both were small space rocks, only a few feet in size, captured by Earth’s gravity into loopy, impermanent orbits–so can officially qualify as natural satellites.

It’s almost certain that this kind of thing has happened many times in the past, but these tiny temporary moons are so small that we are only beginning to develop the technologies and observation programs to spot them.

But now a “new mini-moon” seems to be approaching us and is expected to hang out with Earth starting in October.

Testing a Centaur upper-stage rocket in 1964. Photo: NASA

But wait, there’s more! The size, orbit, and speed of this newly detected object, called “2020 SO,” hints that it might not be a natural asteroid, but a derelict space artifact, possibly the Centaur-D booster rocket stage from the Surveyor 2 moon mission in 1966! The Surveyor 2 robotic lander crashed into the Moon after communication was lost, the Centaur rocket that carried it there flew on by the Moon and into a solar orbit.

Has the long-lost rocket stage, unseen for 54 years, come home? If so, it is only the second time this kind of thing has happened. The first was the return of the upper stage of the Saturn 5 rocket from the Apollo 12 mission, which re-entered Earth orbit in 2002.

The object, whatever it is, will come closest to Earth on December 1. Then, maybe we’ll get a closer look at it–and be reminded that we humans are notorious litterbugs, even in space. Stay tuned.