About this Research Topic
Exomoons and exorings are at present one of the next ‘frontiers’ in exoplanetary science. Saturn’s rings are extensive ~80,000 km away from Saturn (more than twice its radius) yet are less than one five thousandth of a lunar mass. Jupiter and Saturn’s total mass in moons amounts to barely a tenth of an Earth-mass. To that end, a terrestrial (~1 M⊕) exoplanet today represent state-of-the-art exoplanet detection. Therefore innovative methods are required to confirm exomoons and exorings. In 2019, 50 years after man landed on the moon, several candidate exomoon/exoring systems were announced by several independent teams using independent methods. Today, we must validate these photometric and spectroscopic searches for exomoons orbiting exoplanets with modeling and new experiments. A popular article in the March 2021 issue of Scientific American “Alien Moons” has recently summarized the race to ‘discover the first moon around a planet beyond our solar system.’
Exomoons and their resultant exorings, should vastly outnumber planets by at least two orders of magnitude based on our knowledge of planet and satellite formation. The sheer diversity of lunar bodies in the solar system (with 20 moons identified in 2019 itself) provides powerful insights for comparative planetology for better understanding planet formation & evolution. We therefore invite papers that span both theoretical (dynamical--how to keep moons stable around stars?) and observational (how can we find them?) based on the astronomical methods below:
Transit timing variations (TTV)-- targeting large exomoons
Visible light variability in photometry-- targeting exorings and/or orphaned exomoons/exocomets
Electron Cyclotron Maser Instability (ECMI)--targeting magnetic exoplanet-exomoon interactions in the radio
Direct Imaging--targeting giant exomoons
Evaporative transmission spectra-- targeting small volcanic exomoons
Stellar metallicity studies of spallation --targeting dead exomoons precipitated onto host star
We also encourage synergies with solar system science, using solar system analogues to support exomoon searches and evaluating exomoon candidates. We may be able to constrain the presence of an exomoon based on their geologic/atmospheric characteristics - Icy satellites (e.g. exo-Europa/Enceladus/Ganymede), rocky/volcanic satellites (e.g. exo-Ios), or Nitrogen & methane-rich exomoons(eg. exo-Titans/Tritons) may provide powerful signatures which can be ascertained through state-of-the-art spectroscopic analyses and theoretical tools that merge astronomy and planetary physics. These bodies are prime targets for the search for geologic activity beyond the solar system. Using available dynamical data, we can now generate geophysical and astrochemical models, reproducing the environments of these different types of exomoons. These conditions, part of a wide parameter space involving intrinsic interactions between the moon, result in evaporating exomoon signatures (and in consequence, exorings) which we can readily be observed by focusing on a specific atomic or molecular line frequency in visible/IR/radio. Therefore, we particularly encourage the use of spectroscopy in addition to photometry to identify moons in this issue.
Image credit: Thibaut Roger, University of Bern.
Keywords: Exomoons, exorings
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