Earth’s new moon, invisible to the naked eye! Credit: KACPER WIERZCHOS / CATALINA SKY SURVEY / THE UNIVERSITY OF ARIZONA

So as it turns out, we have had a secret, tiny moon lurking around our planet for potentially up to 3 years – and we had no idea!

It’s not surprising we missed it – it’s no Europa for sure. It’s so small it is invisible to the naked eye. In fact, it’s only estimated to be the size of a small car. So how has it been discovered?

Source: Vajiram & Ravi

The little moon was first spotted during the nightly sky observations of the Catalina Sky Survey in Arizona. Two astronomers, namely Kacper Wierzchos and Teddy Pruyne, were scanning the sky for potential asteroids headed our way and noticed a few pixels of light moving across the dark sky. It was then deduced that the movement of the tiny object suggested it had been gravitationally bound to our planet for more than a year – perhaps as much time as three years.

So what is it like and what is it doing?

Objects like our new little moon are not uncommon. Essentially this new moon is a small captured asteroid that by chance found its way to our planet. A combination of our gravity and its gravity has resulted in us holding on to it for a few years. Other planets have moons like this: the moons of Mars, Phobos and Deimos, are certainly larger than this mini moon but are basically the same. They too are so called “captured asteroids”, note their irregular shapes.

The moons of Mars. Credit: NASA

So our new moon is an asteroid that by chance wandered into our gravitational pull – what does the mean going forward?

Mini moon’s interesting path around our solar system. Credit: @WierzchosKacper

The first thing to note is that its journey around our little corner of the galaxy is irregular. It traces a loop around our planet every 4 months and as you can see from the graphic above, it dips in and out around our Earth with no real pattern. This irregular path points to an unfortunate truth; just as soon as we have discovered this mini moon it will leave us. It is not in a stable orbit around us and so will eventually leave our gravitational pull; likely within the next month or so! It will most likely return to orbiting the sun instead of us.

As a parting gift, it was named 2020 CD3 – not exactly catchy. The good news is that if you liked having an extra moon for a while you won’t be disappointed for long – it is likely that we will gain another temporary moon again within the next decade as there are plenty of asteroids out there to capture.

In closing, farewell 2020 CD3; we barely knew thee.

2020 CD3. Coloured lines are stars. Credit: Gemini Observatory


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