New Quasi-Moon Discovered Orbiting Earth, but It's Been Around for Decades
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A new quasi-moon, 2025 PN7, has been discovered orbiting Earth, but it's been around for decades, sparking discussion about its origin, orbit, and implications for our understanding of Earth's orbital neighborhood.
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Looking up 2025 PN7 [1], it says:
> Over time, it may transition between quasi-satellite and horseshoe orbits due to gravitational perturbations.
[0] https://en.wikipedia.org/wiki/Horseshoe_orbit
[1] https://en.wikipedia.org/wiki/2025_PN7
The locals refer to "East" as in the direction of orbit (prograde), "In" as towards the central star, and teach their children: "East takes you Out, Out takes you West, West takes you In, In takes you East, North and South take you back."
[0] https://kaiserscience.wordpress.com/physics/gravity/physics-...
"This so-called “quasi-moon” isn’t a true moon or a mini-moon, because it orbits the Sun rather than our planet."
Our Moon also orbits the Sun rather than the Earth, in the sense that its orbit is always concave towards the Sun--in other words, the pull of the Sun's gravity on the Moon is always stronger than the pull of the Earth's gravity, so the Moon's net acceleration due to gravity is always towards the Sun.
Our Moon's orbit is of course much more closely tied to the Earth's than 2005 PN7, but one still has to be careful about exactly how that works.
Yes, that's true. Indeed, when we take into account other planets (and the Moon, and the asteroids, etc., etc.), all of these objects orbit a common barycenter.
However, that doesn't change the fact that the Moon does not orbit the Earth in this sense; its net acceleration (in a barycentric inertial frame) is never towards the Earth, or towards a common barycenter of the Earth-Moon system. Only if we ignore the motion around the solar system barycenter do we get the approximation in which the Moon and Earth orbit a common center of mass.
All that said, it is kind of fun to consider.
In what sense? You state this like it's an obvious fact. It isn't. It contains a number of hidden assumptions, not all of which stand up to close scrutiny.
> Given there's no absolute spatial frame of reference, I'd argue that piling such caveats atop each other doesn't "move" us closer to a truer understanding.
I disagree, because "there's no absolute frame of reference" is not the same as "all frames of reference are equally useful". The former is true. The latter is not.
Once you face up to the fact that different frames are useful for different purposes, you should realize why you can't just state things like "the moon circles the earth" as obvious facts. At the very least, you have to explain why you've picked the frame of reference (centered on the Earth) in which that's (approximately) true. Basically, that would be because you're ignoring the rest of the universe and you only care about the Earth and the Moon. Which is fine for many purposes (it worked for sending humans to the Moon and back), but not for others (like saying "the moon orbits the earth" as opposed to "the moon orbits the sun"--which is simply not true, once we bring the Sun into the picture, you can no longer ignore the Sun's effect on the moon).
And does it end there? I guess that galaxies are far enough apart from one another to escape this logic with their relative escape velocity.
Not according to the definition I gave. Calculate the acceleration of the Earth and Sun towards the center of the Milky Way and compare it with the Earth's acceleration towards the Sun.
If it's an asteroid it could be a good opportunity pick up some samples, given its proximity.
You would wonder if it could even be coaxed into a Lagrange point for longer term study.
/Justice for Pluto/
It's been at least 3 days since first news articles about it appeared, and there's not a single image of its orbit relative to Earth
best I can find it https://earthsky.org/upl/2025/09/2025-PN7-NASA-Sep-7-2025-e1... showing orbit relative to Sun
Is there really no consumer program to show orbit relative to Earth? Can't you just shove orbital parameters into Universe Sandbox and press "center camera on" Earth?
https://dahlend.github.io/2025_PN7_Orbit_1900-2100.png
Its hanging out for a while near us.
Shameless plug for my software I used compute it:
https://github.com/dahlend/kete
My new grandma is also orbiting Earth, but it's been around for decades /s