Where do mini-moons come from on Earth and what do we know about them?

Discovered earlier this year, asteroid 2020 CD3 is only Earth’s second natural satellite (or mini-moon) known to science. His journey side by side with our planet did not last long, but we learned something interesting about this unusual “companion” and why a mission to intercept similar objects is a good idea.

Sometimes the Earth has unexpected satellites, the nature of which is far from always amenable to deciphering. Scientists have figured out what one such “space wanderer” is

Asteroid 2020 CD3 was first discovered by astronomers from the Catalina Sky Survey at the University of Arizona on February 15, 2020. Some preliminary calculations have been made regarding its size and orbit, but a new study published in the Astronomical Journal provides the most accurate analysis of this rare celestial body.

In fact, “rare” may not be the correct expression for such an object. Rather, “rarely found”. Such temporary natural satellites, according to scientists, are quite common – they are simply difficult to see due to their small size and unstable nature. But as the University of Hawaii Institute of Astronomy (IfA) points out in a statement, roughly 1 in every 1,000 meteors that burn in Earth’s atmosphere was once a mini-moon. These objects are not large enough to cause serious problems on the surface of the Earth, and tend to make several bizarre loops around the planet before resuming their journey in orbit of the larger object, the Sun.

First of all, the new article ruled out the possibility that the 2020 CD3 was just a piece of space junk. The object’s area-to-mass ratio and low luminosity suggest that it is a silicate asteroid, and not, for example, an ejected rocket booster or a wayward Tesla roadster. The same cannot be said about the “promising” mini-moon discovered in September this year – in all likelihood, it is the second stage of the Centaur rocket launched by NASA in 1966.

Asteroid 2020 CD3 is not very large. Its width is about 1.2 meters, so it is only slightly larger than a dishwasher. The study’s authors say it is likely a fragment that broke away from a larger asteroid somewhere between Mars and Jupiter.

“It seems incredible, but modern astronomical telescopes can indeed detect objects the size of large boulders at the same distance that the Earth is from the Moon,” explained astronomer and IfA study co-author Robert Jedike.

Scientists were also able to more accurately describe the object’s orbit. As it turns out, the 2020 CD3 has been in mini-moon mode for the last 2.5 years – we just didn’t know about it. The object has been circling the Earth since 2018, but got close to it and was eventually discovered by scientists using the Catalina Sky Survey.

In total, 2020 CD3 spent 2.7 years as a temporary natural satellite of the Earth before resuming its journey around the Sun. Such a long stay in orbit caught the authors of the study by surprise, since the timing did not coincide with the timing of the theoretical model. In addition, in reality, the object rotates faster than on paper, and therefore scientists decided to reconsider their vision of how such small astroids behave.

Why are mini moons so important? Well, researchers agree that such objects can be excellent candidates for the development of the first space deposits of useful resources. Asteroids are rich in metals, and mini-moons, moreover, fly very close to the Earth – thereby reducing the cost of mining and increasing its speed.

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