Video description: The quasi-satellite 2016 HO3 moves around the Earth on a stable orbit while also orbiting around the Sun. It is not a satellite in the strict sense as it is not gravitationally captured by the Earth, but it remains in resonance with it in its orbit around the Sun. Video credit: NASA.
In April 2016, astronomers discovered a small celestial object orbiting the Sun, named 2016 HO3. This asteroid, just a few tens of meters in diameter, has a fascinating characteristic: it is in resonance with the Earth and behaves like a quasi-satellite. Although it is not directly captured by Earth's gravity like the Moon, it follows an orbit that keeps it close to our planet on a regular basis.
2016 HO3 follows a complex and stable orbit around Earth while remaining in orbit around the Sun. Sometimes it is closer to Earth than Earth is to the Sun, and sometimes it is farther. Its trajectory is such that it oscillates around Earth over a period of several hundred years.
Simulations have shown that 2016 HO3 is in resonance with Earth, meaning its orbital period around the Sun is close to that of our planet. This particular relationship allows it to remain in a stable region of space near Earth without being gravitationally captured. This quasi-satellite has been in Earth's vicinity for almost a century and will continue to accompany it for several centuries more.
A quasi-satellite is a particular type of co-orbital object, meaning it shares a planet's orbit around the Sun without being captured by it. Unlike true natural satellites, like the Moon, which orbit directly around the planet, quasi-satellites follow an orbit around the Sun but remain close to the planet in question for extended periods.
Other similar objects, called trojans, also share a planet's orbit but are found in stable regions known as Lagrange points. Quasi-satellites, however, are not located at the Lagrange points but instead oscillate around the planet with which they are in resonance.
The study of 2016 HO3 and other quasi-satellites is important for understanding the complex orbital dynamics in the solar system. These objects may also offer unique opportunities for future space missions. A quasi-satellite like 2016 HO3 is relatively easy to access for space probes, as it stays close to Earth while being gravitationally independent. This makes it a potential target for asteroid studies and exploration missions.
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