May 23, 2024

Discover a new companion to Earth.

It’s called 2023 FW13, it’s about 20 meters high and it “orbits the Earth”. However, it is not a true satellite, even temporarily. This asteroid is actually what is called a quasi-satellite.

Made March 28th Pan Starrs, an asteroid search program in Hawaii, made an unusual discovery. The discovery was made on the first of April Officially announced – This is no joke – after other observatories in Hawaii (Canada-France-Hawaii Telescope) and Arizona (Kate Peak and Mount Lemon) noticed the asteroid.


The visible small object, which has since been officially designated 2023 FW13, has a half-major axis orbit better than one in a thousand identical to Earth’s, which I quickly noticed. So on April 3rd I started one Simulation with Tony Dunn orbit simulator. The simulation quickly confirmed my suspicions: this asteroid is in 1:1 resonance with the Earth, meaning the Earth takes a long time to revolve around the Sun. There are many configurations that correspond to this type of resonance, and in this case this asteroid is in what is known as a “quasi-satellite” configuration.

© Small-Body Database Lookup, Jet Propulsion Laboratory. Orbit of asteroid 2023 FW13 (in white). Mercury’s orbit is pink, purple, and blue, and Mars is red. The position of the objects is the position on April 5, 2023 at 00:00 UTC.

A quasi-satellite is not a real satellite, but this small object still accompanies us on our journey around the sun. More specifically, a quasi-satellite is an asteroid orbiting (1:1 resonance) in its elliptical orbit, but with the same mean longitude (i.e. the same position relative to the sun) as the planet. Viewed from Earth, the asteroid appears to go backwards and orbit Earth for one year without actually being in orbit: the dominant gravity acting in 2023 FW13 is that of the Sun, and Earth overlaps it only slightly, keeping its own orbit. It is close to our planet.

Confirmation with archival materials

This constellation means that 2023 FW13 regularly flies within a few million kilometers of Earth – a convenient location for observing it. This year, for example, the asteroid about 20 meters across came within 9.8 million kilometers of Earth on March 2. That’s not very close – it’s 25 times farther than the Moon – but what’s interesting is the replication of these methods: every year between 2019 and 2027 it flies past our planet at a distance of less than 15 million kilometers, huh, and this asteroid also indicated it can be found Back in the archival notes. So I informed them Society on the Little Planet mailing list Immediately after running the above simulation on April 3rd.

The next day, Sam Dean announced that he had found observations of the asteroid going back to 2016. These additional observations then allowed him to narrowly constrain the asteroid’s orbit. Looking at all observations from 2016 to 2023, Tony Dunn ran a new simulation with 100 clones, confirming that 2023 FW13 has been a quasi-satellite of Earth for centuries and will remain so for many more centuries to come. Since then it has been new Notes It has been announced since 2012.

2023 FW13 isn’t Earth’s first known quasi-satellite—the Chinese Tianwen-2 probe will spot one—but such a discovery is still relatively rare, with only about a dozen asteroids known to be in this configuration or will be.

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Editor: Futura, by Adrian Covennet.

Cover image: © alejomiranda, Adobe Stock – Artist’s rendering of an asteroid approaching Earth

2 Figure: © Small Object Database Search, JPL.