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Earth's new "quasi-moon" will stick around for hundreds of years

Astronomers have recently discovered an asteroid that tags along with our planet during its annual journey around the sun. Dubbed 2023 FW13, this asteroid is considered by experts to be a “quasi-moon” or “quasi-satellite.”

The asteroid was given this classification because it orbits the sun in a similar time frame as the Earth does. However, it is only slightly influenced by our planet’s gravitational pull.

The asteroid measures only 50 feet (15 meters) in diameter. It is located at a distance of about nine million miles (14 million kilometers) from the Earth.

2023 FW13 was first spotted on March 28, 2023 by the Pan-STARRS survey telescope. This telescope is located on the top of Haleakalā, a dormant volcano on the Hawaiian Island of Maui. 

Soon after, its presence in the Earth’s vicinity was confirmed by the Canada-France-Hawaii telescope and two observatories in Arizona (the Kitt Peak National Observatory and Mt. Lemmon SkyCenter).

On April 1, it was officially listed by the Minor Planet Center at the International Astronomical Union. This is an organization responsible for designating new planets, moons, and other astronomical objects in our solar system.

Classifying 2023 FW13 as a quasi-moon

This news caught the attention of journalist and astronomer Adrien Coffinet, who used an orbit simulator developed by amateur astronomer Tony Dunn to map the asteroid’s path.

The model showed that 2023 FW13 travels around the sun in the same amount of time the Earth does. However, it also circles around our planet. This led Coffinet to classify it as a “quasi-moon.” 

However, as Alan Harris – a senior research scientist at the Space Science Institute in Boulder, Colorado – stresses, since the Earth plays essentially no role in the asteroid’s motion, its classification as a “quasi-satellite” may be a bit far-fetched.

Our cosmic companion 

Regardless of its classification, 2023 FW13 seems to have been our planet’s cosmic companion since at least 100 BCE. It will most likely continue to follow the Earth in its orbit around the sun until around 3,700 CE. “It seems to be the longest quasi-satellite of Earth known to date,” Coffinet said.

Fortunately, despite hovering relatively close to our planet, this asteroid is unlikely to be on a collision course with the Earth. “The good news is, such an orbit doesn’t result in an impacting trajectory ‘out of the blue,’” Harris said.

According to Richard Binzel, an astronomer at the Massachusetts Institute of Technology (MIT), astronomical objects such as this one could act as “stepping stones” to Mars.

This means that spacecraft could soon access them due to their relatively low velocity. Their near-match to the Earth’s orbit causes their speed.

A space mission trying to reach such asteroids “makes sense as a way to practice deep-space missions. Committing a crew and hardware to a longer mission to Mars needs practice. It’s a shakedown cruise,” Binzel concluded.

What is a quasi-moon?

A quasi-moon refers to a celestial object that, while not directly orbiting a planet, nonetheless shares a similar orbital path and maintains a steady, if not strict, relative position to that planet.

Unlike true moons, which maintain a relatively consistent distance from their planet, quasi-moons may travel in complex paths relative to the planet. This is due to the combined gravitational influences of the planet and the Sun.

Orbital characteristics

Quasi-moons undertake a horseshoe or tadpole-like orbit. This means they are observed to move ahead of or behind a planet in its orbit around the Sun. This unusual orbit occurs because the gravitational pull between the quasi-moon, the planet, and the Sun creates a complex dynamic. This leads to a delicate balance in the trajectory of the quasi-moon.

When quasi-moons move ahead of the planet in its orbit, they gradually slow down and eventually fall behind, due to the planet’s gravitational influence. Similarly, when they fall behind, they eventually speed up and move ahead. This constant shifting creates a horseshoe shape when viewed from a fixed point in space, while the orbits appear as tadpole shapes when viewed from the perspective of the planet.

Known quasi-moons

Earth has two recognized quasi-moon. The first one discovered is named 3753 Cruithne.

First-observed in 1986, Cruithne is about 5 kilometers in diameter and takes approximately 770 years to complete one horseshoe-shaped orbit around the Earth. Although it shares an orbital period with Earth, it is not considered a true moon due to its complex, non-elliptical orbit.

Observation and research

Quasi-moons present unique research opportunities for scientists. Their distinctive orbits make them ideal for studying the intricacies of celestial mechanics and gravitational influences. Additionally, their proximity to their parent planets may also offer insights into the formation and evolution of planetary systems.

In the future, quasi-moons may also serve as stepping stones for space exploration. Missions to quasi-moons could provide valuable information about these celestial bodies and pave the way for further exploration of the solar system.

In summary, quasi-moons, though not true moons, play an important role in our understanding of the solar system. Their distinctive orbits and interactions with their parent planets provide a wealth of information about gravitational dynamics and planetary system formation. As we continue to explore the cosmos, these celestial bodies will undoubtedly remain objects of great interest.

What is an asteroid?

Asteroids, often described as minor planets or planetoids, are rocky, airless remnants left over from the early formation of our solar system about 4.6 billion years ago. These celestial bodies mainly populate the Asteroid Belt, a region of space situated between the orbits of Mars and Jupiter.


Asteroids vary greatly in size, from tiny specks of dust to large bodies nearly 1000 kilometers in diameter. These celestial objects often have irregular shapes, particularly the smaller ones, while some larger asteroids may have a more spherical shape.

Unlike planets, asteroids do not have a structured layered system. They consist of different kinds of rocks and metals with no atmospheric covering. Some asteroids have moons, and there are even binary (double) systems where two asteroids of similar size orbit each other.


Asteroids divide into three primary classes based on their composition: C-type (carbonaceous) asteroids, S-type (silicate) asteroids, and M-type (metallic) asteroids. C-type asteroids, the most common kind, have a dark, carbon-rich surface.

S-type asteroids, mainly composed of stony materials and nickel-iron, are slightly brighter. M-type asteroids are metallic (nickel-iron). The diverse composition of asteroids offers valuable insights into the early solar system’s makeup and history.

The Asteroid Belt

The Asteroid Belt, located between Mars and Jupiter, hosts most of the asteroids in our solar system. The belt likely contains millions of asteroids, ranging widely in size.

Despite the large number of these objects, their wide spread across the vastness of space makes a spacecraft’s chance of a collision relatively low.

Asteroids and Earth

While most asteroids remain in the Asteroid Belt, some do make their way closer to Earth. These are known as Near-Earth Asteroids (NEAs).

Scientists monitor these NEAs closely due to the potential risk they pose. Historical evidence suggests that asteroid impacts have significantly affected Earth’s ecosystem, including a leading theory that an asteroid impact led to the extinction of the dinosaurs.

Research and exploration

Studying asteroids has become a major focus of modern space exploration. These old celestial bodies provide information about the solar system’s history, potentially contributing to our understanding of the origin of life.

NASA and other international space agencies have sent several missions to investigate asteroids, including the notable OSIRIS-REx and Hayabusa2 missions, which aimed to retrieve samples from asteroids and return them to Earth for study.

In summary, asteroids, the rocky remnants from the solar system’s formation, offer a window into the past. Their diverse compositions and locations provide vital clues about the early solar system and the materials that contributed to planet formation. As our exploration capabilities continue to grow, our understanding of these intriguing celestial objects will undoubtedly expand.

By Andrei Ionescu, Staff Writer

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