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Possible first discovered exomoon

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Toliman:
Orbital Stability of Exomoons and Submoons with Applications to Kepler 1625b-I
https://arxiv.org/pdf/2005.06521.pdf

An intriguing question in the context of dynamics arises: Could a moon possess a moon itself? Such a configuration does not exist in the Solar System, although this may be possible in theory. Kollmeier & Raymond (2019) determined the critical size of a satellite necessary to host a long-lived sub-satellite, or submoon. However, the orbital constraints for these submoons to exist are still undetermined. Domingos et al. (2006) indicated that moons are stable out to a fraction of the host planets Hill radius RH,p, which in turn depend on the eccentricity of its host’s orbit. Motivated by this, we simulate systems of exomoons and submoons for 105 planetary orbits, while considering many initial orbital phases to obtain the critical semimajor axis in terms of RH,p or the host satellite’s Hill radius RH,sat, respectively. We find that, assuming circular coplanar orbits, the stability limit for an exomoon is 0.40 RH,p and for a submoon is 0.33 RH,sat. Additionally, we discuss the observational feasibility of detecting these sub-satellites through photometric, radial velocity, or direct imaging observations using the Neptune-sized exomoon candidate Kepler 1625b-I (Teachey & Kipping 2018) and identify how stability can shape the identification of future candidates.


--- Quote ---An intriguing question in the context of dynamics arises: Could a moon possess a moon itself? Such a configuration does not exist in the Solar System, although this may be possible in theory. ...
--- End quote ---
Well, it start be too crazy even for me... ;D But interesting idea, eltur tìtxen si nìngay :)


Toliman:
Exploring formation scenarios for the exomoon candidate Kepler 1625b I
https://arxiv.org/pdf/2005.10138.pdf

If confirmed, the Neptune-size exomoon candidate in the Kepler 1625 system will be the first natural satellite outside our Solar System. Its characteristics are nothing alike we know for a satellite. Kepler 1625b I is expected to be as massive as Neptune and to orbit at 40 planetary radii around a ten Jupiter mass planet. Because of its mass and wide orbit, this satellite was firstly thought to be captured instead of formed in-situ. In this work, we investigated the possibility of an in-situ formation of this exomoon candidate. To do so, we performed N-body simulations to reproduce the late phases of satellite formation and use a massive circum-planetary disc to explain the mass of this satellite. Our setups started soon after the gaseous nebula dissipation, when the satellite embryos are already formed. Also for selected exomoon systems we take into account a post-formation tidal evolution. We found that in-situ formation is viable to explain the origin of Kepler 1625b I, even when different values for the starplanet separation are considered. We show that for different star-planet separations the minimum amount of solids needed in the circum-planetary disc to form such a satellite varies, the wider is this separation more material is needed. In our simulations of satellite formation many satellites were formed close to the planet, this scenario changed after the tidal evolution of the systems. We concluded that if the Kepler1625 b satellite system was formed in-situ, tidal evolution was an important mechanism to sculpt its final architecture.

Toliman:
Impact of Tides on the Potential for Exoplanets to Host Exomoons
https://arxiv.org/pdf/2007.01487.pdf

Exomoons may play an important role in determining the habitability of worlds outside of our solar system. They can stabilize conditions, alter the climate by breaking tidal locking with the parent star, drive tidal heating, and perhaps even host life themselves. However, the ability of an exoplanet to sustain an exomoon depends on complex tidal interactions. Motivated by this, we make use of simplified tidal lag models to follow the evolution of the separations and orbital and rotational periods in planet, star, and moon systems. We apply these models to known exoplanet systems to assess the potential for these exoplanets to host exomoons. We find that there are at least 36 systems in which an exoplanet in the habitable zone may host an exomoon for longer than one gigayear. This includes Kepler-1625b, an exoplanet with an exomoon candidate, which we determine would be able to retain a Neptune-sized moon for longer than a Hubble time. These results may help provide potential targets for future observation. In many cases, there remains considerable uncertainty in the composition of specific exoplanets. We show the detection (or not) of an exomoon would provide an important constraint on the planet structure due to differences in their tidal response.

Toliman:
Astronomers discover 6 possible new exomoons
https://earthsky.org/space/astronomers-discover-6-possible-new-exomoons

Astronomers from Western University in Canada have discovered six more possible exomoons orbiting distant exoplanets, in data from the Kepler Space Telescope.

Toliman:
Exomoon candidates from transit timing variations: eight Kepler systems with TTVs explainable by photometrically unseen exomoons
http://www.astro.uwo.ca/~wiegert/papers/2021_MNRAS_Fox.pdf

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