For a short time, our planet was orbited by a second, tiny natural satellite. But now one veteran observer says that Asteroid 2020 CD3 has been “tossed back into orbit around the sun” and is tailing us on our annual journey around our star.
The small asteroid is probably only about the size of a large appliance or a compact car and it was first spotted in February, but astronomers think it was probably stuck in orbit around Earth for at least a year, if not longer.
Bill Gray, who created a software package astronomers use to track nearby asteroids and comets, told me that he’s certain our mini-moon has gone back to orbiting the sun rather than our planet. He explained that 2020 CD3 likely came in for a close pass of Earth’s level without sufficient energy to escape our planet’s gravity and wound up held in orbit for a while by the combined gravity of Earth and the moon.
Gray called the orbit of temporarily captured object “a somewhat complicated dance around the earth and moon.”
That dance comes with a chance of colliding with one object or the other, but in the case of 2020 CD, its dance eventually allowed it to “steal” a bit of energy from the Earth and moon, allowing it to escape back out to a longer orbit around the sun.
Now our former moon is behind us on our own orbital path and getting gradually fainter.
“2020 CD3’s new orbit takes a little over a year to get around the sun,” Gray explained. “It’s a bit like two cars sharing a track, with one (the earth, in this case) completing laps just a little faster than the other, gradually pulling ahead.”
At some point, we’ll actually lap 2020 CD3 – Gray says it will happen next in March 2044 – but this pass won’t be close enough for the space rock to be captured again.
“It’s hard to predict past that point, but there will probably be more close approaches every 25 years or so,” Gray said. “Eventually, one of those close approaches will be close enough, and in the right direction, for it to get captured again. And then probably lost again, unless it hits the Earth or moon in the process. At some point in the next hundred thousand years or so, that will probably happen.”
Such an impact probably wouldn’t amount to much more than a few fireballs in the sky as a once proud moon burns up in the atmosphere.
But there are likely to be many other mini-moons between now and then.
We know of a couple other objects besides 2020 CD3 that have been temporarily captured over the past few decades. It’s probably happened many other times over our planet’s long history and certainly will again.