a second moon around the Earth

The Earth is going to have a second moon. It’s scheduled for September 29, according to astronomers’ calculations: an asteroid will orbit the Earth for two months. It won’t be visible – too small. But technically it will be a second moon.

We’re monitoring the orbit: Earth will soon have a second Moon! Mathilde Fontez, editor-in-chief of the magazine Epsiloon Today we are talking about an astonishing astronomical phenomenon.

franceinfo: In a few days, the Earth will have a second moon. Another satellite in orbit?

Mathilde Fontez: Yes, the countdown has begun. It will be September 29, according to astronomers’ calculations. So in a week, next Sunday: Terra will have two moons. So it won’t be spectacular unfortunately, don’t set the alarm to try to observe it. This second moon is much smaller: it measures 10 meters in diameter – compared to 3500 kilometers for our main Moon.

Even with a powerful telescope, it appears only as a small fuzzy dot in the sky. We will have to imagine it: a small celestial body, an asteroid, is going to enter orbit around our planet. It’s called 2024 PT5.

This asteroid has just been discovered?

Yes, it was captured on August 7th, by the land impact warning system: routine observations that monitor asteroids falling on our planet. Everything happened very quickly after that: several telescopes were mobilized to try to follow it. Its orbit was calculated on August 30, using data collected by NASA’s Jet Propulsion Laboratory.

At the moment, it is orbiting the Sun. But its speed is very low, it is very close, which is why it will be captured by the gravity of the Earth. He will stay in orbit with us for a month. Yes, it is a temporary moon: on November 25, the asteroid will detach itself from Earth’s orbit and resume its course around the Sun.

In a way, it makes sense that asteroids sometimes end up in orbit around the Earth…

Yes, we know that there is a zone around us where the gravity of our planet takes over that of the Sun, a large zone 100 times the size of the Earth… Many asteroids can pass through it.

But they need a particular speed and trajectory for them to turn into Earth’s satellite. And it’s only been about twenty years since astronomers began to see these temporary minimoons. 2024 PT5 is not the first.

There was one in orbit from July 2006 to July 2007. Another one was discovered in 2020, when it was about to break away. Scientists estimated that it must have been there for a few years. Another one was also seen in 2022.

A French researcher, Jérémy Vaubaillon, from the institute of celestial mechanics and ephemeris calculation of Paris even calculated, by simulating the trajectory of asteroids, that statisticallythere is always a second moon around the Earth. There is always a minimoon alongside the big one. We don’t see it, it’s never the same, but it’s always there.