Notes and Background
This project explores the consequences of swapping the Jovian moon Ganymede and the dwarf planet Pluto(plus its moon, Charon) early in the formation of the solar system. Although this is based on my rudimentary knowledge of parts of planetary geology, it may be imperfect and lacking in some aspects—for example, the orbit of Charon around Pluto is tighter to prevent it as being captured as a separate moon, but I’m unsure if it would crash into Pluto as a result, get ejected, or fall victim to some other unforeseen fate. Because of this, if anybody wants to expand or rework this concept, feel free to do so!
The concept of swapping Ganymede with Pluto is also inspired by the usage of images derived from maps of Ganymede to represent Pluto prior to New Horizons imaging the dwarf planet in greater detail. To the best of my knowledge, most of these images come from the render of Pluto on JHT’s Planetary Pixel Emporium (link here: https://planetpixelemporium.com/pluto.html), which is where the image for this project comes from.
This project will also be, for the most part, written from an in-universe viewpoint(that is, the universe where Jupiter has a binary moon and a Mercury-sized dwarf planet has an orbit intersecting with Neptune’s). The only changes made to the timeline of Earth in this project are ones directly related to the study and exploration of the altered bodies(probes and such).
Though my project may include a name for a Jovian moon also used in my Alternate Solar System, the projects aren’t meant to be set in the same universe.
So, without further ado, let’s get into…
The binary moon of Alcmene-Hercules
Credits: Made using PlanetMaker(planetmaker.apoapsys.com)
Alcmene uses File:Pluto-map-sept-16-2015.jpg on Wikimedia as its map, while Hercules uses the texture for Dione
Swapping Pluto and Ganymede
The dwarf planet Pluto
Credits: JHT’s Planetary Pixel Emporium (https://planetpixelemporium.com/index.php), using a map made by Björn Jónsson
Alcmene/Hercules
Jupiter’s binary lunar pair of Alcmene-Hercules is perhaps one of the most interesting orbital arrangements to be found in the solar system. These worlds are the only known pair of binary moons, and the only known instance where a moon has had a natural satellite of its own.
To review, binary pairs like Alcmene-Hercules are common, but more often with asteroids and a few dwarf planets. Such a term derives from how celestial bodies orbit one another; a system of orbiting bodies doesn’t solely revolve around the parent body, but instead around a “barycenter’—a mathematical point at the system’s center of mass. The parent body also “orbits” around this point, though its mass is usually great enough proportionally that the barycenter is close to the center of the parent body. However, what distinguishes binary systems is that this isn’t the case; the ratio between the masses of the parent and orbiting body are more equal. In the case of Alcmene and Hercules, the former is around 10 times more massive than the latter. For perspective, the Earth is around 100 times the mass of its sole Moon.
Still, the orbital circumstances of Alcmene and Hercules are interesting for another reason; the orbit they take in concert around Jupiter is nearly exactly twice the duration of Europa’s orbital period(the next moon in, whose orbital period is twice that of even closer Io). This configuration makes the Alcmene-Hercules binary part of a Laplace resonance—the term used to describe orbital ratios in such a pattern.
All these unusual orbital patterns have created immense tidal stresses for both worlds, and thus have became an integral part of their geologies. Alcmene’s surface has several bright patches formed by newly frozen ice, thrust up by convective currents in a probable mantle of liquid water. Hercules also has signs of activity as well, though more minor; a few major geysers and tectonic rifts from more active eons mark the cratered landscape.