The earth had a minimoon for almost three years before drifting away

By Leah Crane

The Minimoon 2020 CD3 is the white point in the middle, while the colored stripes are stars

The international Gemini Observa

Good night moon. Earlier this year, astronomers found a minimoon orbiting the earth. It has now gone away, but we should be able to spot more of these miniature companions soon.

When astronomers at the Catalina Sky Survey in Arizona in February discovered a faint object called 2020 CD3 racing across the sky, they couldn’t be sure whether it was a minimoon or an artificial object like a rocket booster. In the months that followed, Grigori Fedorets of Queen’s University in Belfast, UK, and colleagues used a number of telescopes around the world to take more measurements of the object and find out what it was.

They found that it was about four feet in diameter. Because of its color and brightness, it was likely made of silicate rock, like many rocks in the asteroid belt. Researchers also tracked its orbit to see where it might have come from before it was trapped in Earth orbit about 2.7 years earlier.


“Based on simulations, the average collection time for Minimoons is only nine months, so it was recorded longer than expected,” says Fedorets. “But this object flew very close to them [regular] Moon, and that put it in a more stable orbit. “

2020 CD3 left Earth orbit in March, but researchers predict that once the Vera C. Rubin Observatory – a giant telescope currently being built in Chile – is completed, we will be able to find many more objects like this one.

“In the best case scenario, we could spot a minimoon every two or three months,” says Fedorets. “In the worst case, maybe once a year.” This could be important as we know very little about these types of relatively small asteroids. When we find them in orbit, we can examine them up close in a unique way.

Journal reference: The Astronomical Journal, DOI: 10.3847 / 1538-3881 / abc3bc

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