In a recent study published a team of researchers from the University of Texas at Arlington, Valdosta State University, the Georgia Institute of Technology and the National Radio Astronomy Observatory estimated how many moons could theoretically orbit Earth as it is. conditions such as orbital stability. This study opens up the potential for a better understanding of planet formation processes, which could also be used to identify exomoons that could orbit Earth-like exoplanets.
“In earlier work, I investigated the planetary arrangement for the binary star Alpha Centauri,” said Dr. Billy Quarles, assistant professor of astronomy and astrophysics at Valdosta State University and co-author of the study. “In that case, I made an estimate of the number of planets that could exist in each star’s habitable zone. In this scenario, the habitable zone provided natural boundary conditions where I was able to apply the same dynamical formalism to the problem of moons. (using the Earth-Sun system as binaries ).To define the outer limit, one of my co-authors developed a scheme that we could use. Combining these ideas, we expected that >10 Ceres-, 6 Pluto-, and 4 Luna-sized objects would be possible.
While there are over 200 moons in our solar system, only three orbit terrestrial (rocky) planets: our moon (Luna) around Earth and Phobos and Deimos around Mars. The remaining 200+ moons orbit all the gas giants, including Jupiter, Saturn, Uranus, and Neptune. As the study notes, this large difference is expected because they “experience different formation mechanisms and orbital evolution processes.”
The study discusses how the maximum allowable number of moons that could exist around Earth depends on the assumed sizes of the moons themselves. In this case, scientists used objects the size of Ceres, Pluto, and Luna to determine how many of them could successfully orbit Earth. The results showed that orbital stability can be maintained with satellites of 7 ± 1 Ceres mass, 4 ± 1 Pluto mass, and 3 ± 1 Moon mass.
“The surprise was that the lighter weight prototypes were more constrained, which we attribute to their increased likelihood of scattering (from lower inertia),” Quarles said. “Perturbations from neighboring moons are enough to cause a significant scatter over a few thousand years. We had to reduce the number of moons to account for this.”
As seen on Jupiter’s Galilean moons, small satellites orbiting a much larger planetary body can result in what is known as tidal heating, where the constant stretching and compression of much smaller satellites leads to interesting results, including volcanism on Io and an internal ocean on Io. Europe. But could a multi-moon system with Earth experience the same results as well?
Tidal heating of the moons themselves may be possible, but without detailed simulations it is not clear to what extent this heating is,” said Dr. Quarles. partly due to mean motion resonances with the other Galilean moons. In our systems, mean motion resonances largely destabilize the satellite system as the sun contributes to each moon’s eccentricity growth and eventual dispersion.”
Along with the potential for tidal heating, this study also potentially expands the search for exomoons that orbit exoplanets. Unfortunately, while the number of confirmed exoplanets is in the thousands, the number of confirmed exomoons is currently less than a fraction of that number.
“We currently have 2 exomoon candidates (Kepler-1625b-i and Kepler-1708b-i), but their respective host planets are similar to Jupiter,” said Dr. Quarles. “The candidate moons are also both larger than Earth. These more exotic cases are easier to identify in the same way that Hot Jupiters were easier to spot above smaller planets in the early days of exoplanets. However, several planetary systems were discovered soon after.” the first bony fide exoplanets. We expect something similar for exomoons.
Having several candidate exomoons orbiting the same planet will make our work more useful. The constraints we find are quite optimistic, where more realistic conditions are likely to limit the number of moons further. In photometric measurements, background objects could mimic the transit signal of a candidate exomoon, and our work provides a physical basis for constraining the number of moons expected when testing different hypotheses.”
Dr. Suman Satyal, an assistant professor of physics at the University of Texas at Arlington and lead author of the study, said that because Earth can have more than one moon, it “increases the likelihood” of detecting exomoons. “This should give exomoon observers an idea of ​​an upper limit on the number of moons around an Earth-mass planet orbiting a Sun-like star,” he said. Only time will tell that How many exomoons are there in the universe, and is there an Earth-like exoplanet with several exomoons capable of supporting life.
Source Reference: Moon-packing around an Earth-mass Planet, arXiv:2208.03604v1 [astro-ph.EP]
doi.org/10.48550/arXiv.2208.03604
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