Collisional formation of massive exomoons of superterrestrial exoplanets

Abstract

Exomoons orbiting terrestrial or super-terrestrial exoplanets have not yet been discovered; their possible existence and properties are therefore still an unresolved question. Here we explore the collisional formation of exomoons through giant planetary impacts. We make use of smooth particle hydrodynamical (SPH) collision simulations and survey a large phase-space of terrestrial/superterrestrial planetary collisions. We characterize the properties of such collisions, finding one rare case in which an exomoon forms through a graze & capture scenario, in addition to a few graze & merge or hit & run scenarios. Typically however, our collisions form massive circumplanetary discs, for which we use followup N-body simulations in order to derive lower-limit mass estimates for the ensuing exomoons. We investigate the mass, long-term tidal-stability, composition and origin of material in both the discs and the exomoons. Our giant-impact models often generate relatively iron-rich moons, that form beyond the synchronous radius of the planet, and would thus tidally evolve outward with stable orbits, rather than be destroyed. Our results suggest that it is extremely difficult to collisionally form currently-detectable exomoons orbiting super-terrestrial planets, through single giant impacts. It might be possible to form massive, detectable exomoons through several mergers of smaller exomoons, formed by multiple impacts, however more studies are required in order to reach a conclusion. Given the current observational initiatives, the search should focus primarily on more massive planet categories. However, about a quarter of the exomoons predicted by our models are approximately Mercury-mass or more, and are much more likely to be detectable given a factor 2 improvement in the detection capability of future instruments, providing further motivation for their development.

The wide-binary origin of (2014) MU69-like Kuiper belt contact binaries

“…The miluphCUDA code is implemented with CUDA, and runs on graphics processing units (GPU), with a substantial ∼ 10 1 − 10 2 improvement for single GPU compared to a single CPU. The code has already been successfully applied to several studies involving impact processes 36,37,[39][40][41][42][43][44][45][46][47] .…”

The lifetimes of planetary debris discs around white dwarfs

“…For tidal and perhaps spin discs, this structure may also be referred to as a "ring" because the spatial extent of the detected dust is usually comparable in range to that of some of Saturn's rings. However, the simulations of Malamud & Perets (2020b) show that in fact tidal disruption can spread planetesimals over a much wider range, whereas the transiting signatures around ZTF J0139+5245 (Vanderbosch et al 2020) suggest the presence of a much narrower ring of material. Although this particular ring is likely to be extremely eccentric (with e ≈ 0.97), most dusty disc/ring structures are observed to be near circular (Rocchetto et al 2015;Farihi 2016).…”

Linking the formation and fate of exo-Kuiper belts within Solar system analogues

“…Consequently, we conclude that for the 40 − 1000 au range, ejection predominantly occurs during the early cluster phase. Although post-main-sequence origins of interlopers like 1I/Oumuamua and 2I/Borisov are possible, in this context tidal disruption events around white dwarfs (Rafikov 2018;Malamud & Perets 2020) may be more likely to occur than ejection during the giant branch phases.…”