Astronomy Physics


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Earth and Moon/NASA Could a tiny moon orbiting a moon survive the gravitational pull?

You read the title right. Recently, some astronomers thought they had spotted an “exomoon,” a moon orbiting an exoplanet. There are, of course, bound to be some.

But now Gizmodo introduces us to the concept of the moonmoon, a submoon orbiting a moon. One research team is taking on the possibility:

The team’s short analysis found that small submoons, perhaps 10 kilometers in radius, could only survive around large moons (such as the ones we see in our Solar System) far away from the host planet, according to the paper published on the arXiv preprint server. Moons that are too close to their host planets or too small might lose their submoons to tidal forces from the planet—shredding the submoon up, sending it crashing into the moon or planet, or shooting it out into space.

But even though the Solar System doesn’t have known submoons, there are some moons that could once have had submoons, based on their size, according to the analysis. That includes Earth’s own Moon. Ryan F. Mandelbaum, “Astronomers Wonder: Can Moons Have Moons?” at Gizmodo

Here’s the paper by Kollmeier and Raymond. (open access)

It’s more likely we will find one orbiting a moon in the vicinity of an exoplanet than that the term “moonmoons,” which has a pop culture history, will win out over “submoon,” mainly for linguistic reasons.

See also: Nerdist: “As for the actual science of moonmoons, Kollmeier and Raymond write, “While many planet-moon systems are not dynamically able to host long-lived sub-moons [a very large moon with a very small moon that can avoid being pulled away by a star’s gravity], a handful of known moons are, however, capable of hosting long-lived submoons: Saturn’s moons Titan and Iapetus, Jupiter’s moon Callisto, and Earth’s Moon.””

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See also: Astronomers: First possible exomoon is the size of Neptune, and orbiting a “Jupiter.” Nature News: Teachey’s proposed exomoon is already throwing up some surprises. Evidence suggests the moon is about the size of Neptune, orbiting a planet roughly the size of Jupiter. That would make it unlike anything in the Solar System, where most moons are much smaller than the planets they orbit.

One Reply to “Moonmoons

  1. 1

    Moon moons are unstable. It’s the classic three-body problem. We should know, we orbited s/c Clementine around the Moon until the orbit went unstable.

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