Earth now has another moon, in a manner of speaking -- a car-sized chunk of space rock has been captured by Earth's gravitational pull and is now regularly orbiting the planet, just like the moon we're all familiar with has been doing for billions of years. This one, however, has only been with us for about three years.
As New Scientist reports, on February 19, astronomers at the Catalina Sky Survey in Arizona noticed a dim object moving swiftly across the sky. Several other observatories were notified and told when and where to look, and sure enough, astronomers at other telescopes noticed and tracked the object, too.
As is standard procedure for these things, the first thing astronomers had to do was rule out the usual suspects -- a satellite that had been lost, for example, or a random piece of space junk, or perhaps an asteroid just passing by. Once that had been done, and once the numbers had been crunched, the Minor Planet Center deemed that a piece of space rock -- likely a bit of an asteroid -- had been captured by Earth's gravity and is now in orbit around our planet.
That means that, unlike what you were taught in elementary school, Earth does not have exactly one natural satellite in its orbit -- it has two, if not more.The new moon, named 2020 CD3, is believed to have been hanging around our corner of the solar system for about three years. It's believed to measure about 6.2 to 11.4 feet across, making it roughly equivalent in size to a car or van. For now, scientists believe that it orbits Earth once every 47 days, in an oval-shaped orbit that takes it way beyond our actual moon at the outer reaches of its path around our planet.
2020 CD3 won't be joining our moon permanently, however. Grigori Fedorets at Queen's University Belfast says that the rock is in an unstable path that will eventually -- possibly as soon as April -- fling it out of Earth's orbit and back into space.
This is not the first time a second "moon" has joined the one we already have. Back in 2006, scientists identified and tracked 2006 RH120, another space rock that briefly got caught up in Earth's orbit and served -- albeit temporarily -- as a second moon before flinging itself away.
Of the eight planets in our solar system, two (Mercury and Venus) have no moons; Earth officially has one; Mars has two; Jupiter has 79 (56 named, 23 awaiting names); Saturn has 82 (53 named, 29 awaiting names); Uranus has 27; Neptune has 14. This list excludes the possibility of moons that haven't yet been discovered.