Minimoon Orbits Earth for 3 Years, But No One Knew?

The Catalina Sky Survey, which NASA calls the CSS, is an Arizona-based project that aims to track near-Earth objects, or NEOs, especially the ones that potentially have a negative impact on Earth.

In order for the astronomers at the CSS to do this, they look at the size of the object. Typically, those that are larger than 140 meters--that's about 460 feet--are considered hazardous. Smaller ones, however, are identified and studied as well.

Earth's new but not-so new minimoon

Just recently, scientists at the CSS have identified what may be one of Earth's minimoons, which are asteroids that orbit a specific planet, but only temporarily. This is due to the pull of the planet's gravity.

This new minimoon, is named 2020 CD3 and is around 6.2 to 11.5 feet in diameter. However, as the CSS reports, this minimoon is not so new after all. Apparently, 2020 CD3 has been orbiting the Earth for three years now.

Kacper Wierzchos of the Catalina Sky Survey tweeted, saying that he and his partner Teddy Pruyne have found a "20th magnitude object".

How did they not catch it?

So three years and we're finding out just now--why? Well, what's considered as "near-Earth" is pretty vast. We are considering countless extremely small asteroids going about their own ways. And because they speed around aimlessly, astronomers do not know where to look. Aside from this, the asteroids don't really reflect a sufficient amount of sunlight, making them difficult to see. So among about millions, only 22,211 has been by far discovered. Some short-lived asteroids--the ones that do not classify as minimoons--either proceed to the atmosphere and turn into fireballs, or hang around a bit before they speed up and leave their orbits.

These asteroids usually get captured by the Earth's gravity easily since they are so small and many. But most of them do not really orbit the Earth long enough to be called minimoons. In a simulation done in 2012, only 18,000 out of 10 million virtual asteroids were captured in the Earth's orbit--that's less than two percent.

This shows that in addition to being almost invisible, they are very rare and this does not really make them known to astronomers.

What does this mean?

All these being said, 2020 CD3 is a big deal in astronomy. Not only is it super rare, but it also opens possibilities for exploration of bodies like asteroids. For one thing, sending spacecrafts to asteroids for observation implies expensive and time-consuming projects, mostly because it involves covering a great distance. So if and when astronomers find a minimoon, its proximity to the Earth offers convenience.

Unfortunately, it may be too late to study 2020 CD3 since it's been hanging around for three years now, and it may be on its way out this April. Scientists are, of course, still observing its behavior since their simulation may not give accurate results. Astronomer Tony Dunn, posted on Twitter, an animation of the orbit followed by 2020 CD3.