1184379230

Photo by: Bernt Ove Moss / EyeEm

Bernt Ove Moss / EyeEm

Farewell, Earth’s Mini-moon

It's time to say goodbye to the mini-moon that's no bigger than your car.

March 11, 2020

Right now the Earth has a second, miniature moon. In a few months, it won’t. Oh well, it was nice while it lasted.

Its official name is 2020 CD3, but everyone is calling it the “mini-moon”, so that’s what we’ll go with. Its “mini” designation is rightly deserved. We can’t measure its size directly, because its too far away, but we can measure its brightness. Based on that, if we assume that it has the typical color of a random piece of space rock (if you’re curious, a dark, drab grey), then we can calculate an estimated size of no more than a dozen feet across.

In other words, no bigger than your car.

And yet, the mini-moon is in orbit around the Earth, which is what it takes to transform an object from “random space junk” to “moon”.

But it won’t be here for long.

The mini-moon was discovered in February of 2020 (hence the “2020” in its official designation), and based on its current orbit astronomers suspect it has been hanging out near the Earth, shyly trying to be friends, for the past few years. And by April of 2020, it will simply wander away.

The reason for this temporary friendship is that the mini-moon isn’t really in orbit around the Earth; it’s really in orbit around the sun, and happens by sheer coincidence to share the same orbit as our planet.

Earth and Sun, computer artwork.

460712879

Earth and Sun, computer artwork.

Photo by: SCIEPRO

SCIEPRO

So for ages upon ages, the mini-moon isn’t a moon at all, just a wandering piece of asteroidal debris leftover from the formation of the solar system. Then every once in a rare while, the rock comes close to the Earth with a slow enough speed that it can be captured by us, spending a few years making lazy circles around us, before chaotic motions send it wandering away to spend another few ages in isolation again.

Despite the brief celestial dance, we can learn a lot from objects like 2020 CD3. For one, we’re generally worried about rocks from space crashing into the Earth and causing general mayhem - and these rocks that share our orbit and occasionally come close are the hardest to spot, as evidenced by the fact that we had a mini-moon for years without anybody noticing, not even professional astronomers.

Secondly, we’re also interested in setting up some homes outside the Earth (partly for the reason outlined above). Lots of folks are debating the relative merits of a (regular) Moon base vs a colony on Mars, but what about rocks?

Asteroids offer a few advantages: they can be spun up to provide artificial gravity, they can be hollowed out for resources, and...they’re close.

Illustration of an asteroid approaching the Cretaceous Earth, poised to exterminate the dinosaurs. Near-Earth asteroids are a constant threat to our planet.

1055491912

Illustration of an asteroid approaching the Cretaceous Earth, poised to exterminate the dinosaurs. Near-Earth asteroids are a constant threat to our planet.

Photo by: MARK GARLICK/SCIENCE PHOTO LIBRARY

MARK GARLICK/SCIENCE PHOTO LIBRARY

The mini-moon spent years not much further away than the Moon, making it much more accessible than Mars. And while this particular mini-moon wouldn’t make much of a colony (because, remember, it’s no bigger than your car), its other friends in Earth-like orbits could be much more attractive.

So thanks, mini-moon, catch you in a few orbits.

Paul M. Sutter

Paul M. Sutter is an astrophysicist at Stony Brook University and the Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of How to Die in Space.

Next Up

The Perseid Meteor Shower Reaches its Peak

Stargazers rejoice! The annual Perseid meteor shower is upon us. Here's what you need to know...(updated August 11, 2022)

Scientists Have Discovered Enormous Balloon-Like Structures in the Center of Our Galaxy

There's something really, really big in the middle of our Milky Way galaxy — one of the largest structures ever observed in the region, in fact.

How to Watch the Orionids Meteor Shower in 2021

If you've seen a shooting star on a recent stargazing jaunt, you've spotted the very beginning of the Orionids meteor shower. It happens every fall in October or early November, and peak viewing hours are coming soon to skies near you.

Astronomers May Have Found a Rare “Free-Floating” Black Hole

How do you see a perfectly black object in the middle of a pitch-dark night? It sounds like the start of an annoying riddle, but it’s really the question faced by astronomers when they want to search for black holes.

Saving Earth from Killer Asteroids

Only about 40% of an estimated 25,000 near-Earth asteroids with the potential to destroy the planet have been detected. Scientist Dr. Ed Lu, along with his nonprofit B612 are working to create a way to detect the other 60%.

How Do We Know How Old the Sun Is?

Scientists estimate that our Sun is about 4.57 billion years old. They’re surprisingly confident about that number, too, which opens up an immediate question: how do we know that? The short answer is “a lot of science and math”, but I have a feeling you’re not here for the short answer.

Scientists in China Discover Rare Moon Crystal that Could Power Earth

A rare lunar crystal found on the near side of the moon is giving scientists hope of providing limitless power for the world – forever.

NASA's Biggest 2021 Milestones

From making history on Mars to supersonic aircraft, NASA continues to astound us with science from this past year.

William Shatner is going where no 90-year-old has gone before

The Star Trek star will become the oldest person to go to space when he launches aboard a Blue Origin rocket on Wednesday, October 13. Watch live coverage on Space Launch LIVE: Shatner in Space on Discovery and Science Channel starting at 8:30A ET with liftoff scheduled for 10A ET.

Space Launch LIVE Discussion Guide

Tune into Discovery Channel and use this companion discussion guide to spark meaningful conversation about the next era of space flight. Stream SPACE LAUNCH LIVE on discovery+.

Related To: