Why doesn't the earth have two moons?

Smaller than the little prince's asteroid : The earth just has a second moon

On February 15, astronomers at the Catalina Sky Survey Telescope, located in Tucson, Arizona, searching for asteroids, discovered a celestial body that orbits the earth like the moon. This is reported by the astro portal "EarthSky.org".

“Shortly after my teammate Teddy Pryne and I discovered the object, we determined the orbit and found that it was captured by gravity,” Kacper Wierzchos reports to Tagesspiegel. It was still unclear whether it was a natural or artificial object, such as space junk. He then called it "possible mini-moon".

Maximum 3.5 meters tall

As the Minor Planet Center of the International Astronomical Union has now announced, more than 50 observations have now confirmed the existence of the body called 2020 CD3. According to Wierzchos, the companion is an asteroid between 1.9 and 3.5 meters in size.

It is currently orbiting the earth at a distance of 2.6 times the moon. The analysis of the orbit suggests that the chunk entered an earth orbit three years ago. The modeled orbit has little in common with the usual ellipse of the big moon, it is more of a wild back and forth that at best gives an idea of ​​the relationship to the earth.

Only a small chunk - but it is "a big deal", writes Wierzchos on Twitter, that out of around one million known asteroids, only the second that orbits the earth has been identified.

The other, "2006 RH120", was also discovered by the Catalina Sky Survey and orbited the earth four times in 2006/2007 before moving away again. The object, which is just a few meters in size, is currently on a circuit around the sun.

2020 CD3 is also referred to by the Minor Planet Center as "an object that is temporarily bound to the earth". This happens when the orbit of asteroids near the earth is so disturbed that they remain near the earth for a few months or years as they orbit the sun, orbiting it several times when viewed from the earth.

However, this orbit is not stable in the long term, which is why astronomers do not speak of a “second moon”. This also applies to 2020 CD3, which, according to Wierzchos, will leave Earth orbit in around a month and return to a sun-bound orbit.

Not every short-term moon can escape the earth again

Not every “temporary mini moon” succeeds in escaping forward, it can also end on earth. This likely happened in August 2016. At that time a meteor fell over South Australia.

Researchers led by Patrick Shober from Curtin University in Perth reconstructed what had happened and found that the object was rather slow at only eleven kilometers per second before it burned up.

They suspect that it was an asteroid that had also previously been captured by Earth's gravity and thus slowed down. You reported on it in 2019 in the "Astronomical Journal".

In the future, thanks to survey telescopes, such events could perhaps also be predicted, write Shober and his team.

Now new: We give you 4 weeks of Tagesspiegel Plus! To home page