The Moon dominates our nighttime view of the celestial vault as the only satellite orbiting Earth, but that does not imply that there are no other smaller objects surrounding us. Our planet has at least one mini-moon orbiting around it, and now astronomers are theorizing that such a rock was once part of the Moon.
Earth’s Companion Mini-Moon
When we think of the Earth‘s surrounding space, we may imagine a big, dark, icy void, but the truth is that there are more objects there than we can imagine. There are at least 21 orbiting objects circling us that come and go, but of all of them, there is one that has been following our footsteps for millions of years, the so-called Kamo’oalewa asteroid.
Kamo’oalewa was discovered in 2016 with Pan-STARRS at NASA’s Haleakala Observatory. Since then, it was known to be an unusual object, as its orbit changes over time, but no matter how many modifications it undergoes it always remains close to Earth.
Not all small bodies and minor rocks that roam the Solar System have heliocentric orbits, some of them also orbit around massive planets. These types of objects are called coorbital, and there are three types: Trojans (T), Horseshoes (HS), and Retrograde Satellite/Quasi-Satellite (QS). In this case, the ones that matter to us are the last two.
The Earth has 21 coorbital objects, of which two are Trojans, six are in retrograde satellite state, and 13 show horseshoe motions. But of all of them, Kamo’oalewa, which is a type of retrograde Quasi-Satellite (QS) object, is very different from all of them.
It is called this way because although it is surrounding the Earth, the Sun exerts a greater influence on it than our planet. After all, it is located beyond the Hill Sphere. The latter is the region of space around a planet that dominates the attraction of the satellites. The Moon, therefore, is inside the Hill Sphere of the Earth, and although it presents small perturbations in its orbit, it remains stable surrounding the planet.
“Considering its Earth-like orbit and its physical resemblance to lunar surface materials, we explored the hypothesis that it may have originated as a fragment of debris from a meteorite impact with the lunar surface,” states new research.
A Fragment of the Moon
To learn more about the mini-moon, numerical simulations of the dynamical evolution of particles launched from different locations on the lunar surface with a range of ejection velocities were carried out, the authors say. Most of the particles leave the Earth-Moon system and go on to orbit the Sun, which is not surprising since the Sun has a much more influential gravitational field. But they also found simulations of asteroids that remained orbiting around the Earth, as is the case with Kamo’oalewa.
“We find that a small fraction of the launch conditions produces results that are compatible with the dynamical behavior of Kamo’oalewa.” The retrograde quasi-satellites that remained in Earth orbit have one thing in common: launch velocity. “The most favored conditions are launch velocities slightly higher than the escape velocity of the lunar back hemisphere,” the research says.
This is why they believe that at some point the object ejected from the Moon at the necessary velocity and with adequate launch thrust to remain spinning around the Earth. The discovery could bring a breakthrough in the understanding of the Moon, since if samples of the asteroid are collected, we would be facing a time machine of samples of a fully newly formed Moon, which would explain its origin and dynamics with the Earth.
Story written in Spanish by Alejandra Martínez in Ecoosfera
