An upper limit on late accretion and water delivery in the TRAPPIST-1 exoplanet system

Habitable planet formation around low-mass stars: Rapid accretion, rapid debris removal and the essential contribution of external giants

“…Perhaps the investigations most similar to our own in terms of focusing on late volatile delivery from small body reservoirs are Dencs & Regály (2019) and Raymond et al (2021). While both sets of authors' primary focuses were the TRAPPIST-1 planets, their main conclusions were largely similar to our own.…”

“…(1) un-accreted objects that survive the giant impact phase on cold orbits in between planets at small semimajor axes and (2) implanted asteroids on relatively stable orbits with large semi-major axes outside of the planetary regime. While the first population is accreted rather easily in the first few tens of kyr of our bombardment simulations, the second population is dynamically detached from the orbits of TOI-700d, TRAPPIST-1h and Proxima Centauri b Thus, in absence of perturbations from distant giant planets and non-Keplerian accelerations (such as Yarkovsky drift, see discussion in section 4 and: Vokrouhlicky 1998;Bottke et al 2001;Dencs & Regály 2019;Raymond et al 2021), the HZ planets in our planetesimal bombardment simulations are unable to access the majority of the asteroid belt material. While the Proxima Centauri system does possess a Super-Earth at 1.5 au (outside of this hypothetical asteroidal reservoir), we find it to be too distant and too small to perturb asteroids onto orbits that intersect the Exponential decay fits of the bombardment chronologies (probability distribution function) plotted in figure 6.…”

“…As a result of perturbations from the additional planet, the flux of water-rich asteroids striking the HZ worlds was necessarily higher than observed in our simulations (upwards of a few percent of the total belt is accreted by TRAPPIST-1g and h over ∼kyr timescales in their models). Conversely, Raymond et al (2021) utilized the constraint of resonant chain survival to place upper limits on late volatile delivery to the TRAPPIST-1 HZ planets, and considered cases where a rouge planetary embryo perturbs debris disk material, in addition to asteroid belt-analog setups similar to those in Dencs & Regály (2019) and our current work. The authors concluded that interactions with 0.05-0.10 M ⊕ worth of remnant planetesimals typically disrupt the resonant chain, and drive the system towards dynamical instability.…”

“…If this is the case, the potential habitability of these planets hinges on their ability to develop secondary atmospheres; either through the delivery of icy small bodies (e.g. : Kral et al 2018;Dencs & Regály 2019;Raymond et al 2021) or by the outgassing of initially enhanced internal volatile contents (Bolmont et al 2017;Bourrier et al 2017) In spite of considerable effort, the TRAPPIST-1 planets continue to befuddle atmospheric detection campaigns utilizing transmission spectroscopy (de Wit et al 2016(de Wit et al , 2018Gillon et al 2017;Luger et al 2017a;Wakeford et al 2019). Given the degeneracies between plausible planetary compositions in mass-radius space (Zeng & Sasselov 2013; Baraffe et al 2014), computational models of planet formation in these systems remain an essential tool for probing their potential internal and atmospheric structures (e.g.…”

“…: exo-asteroid belts) to deliver volatile-rich material capable of reconstituting the atmospheres of desiccated planets long after their formation (e.g. : Kral et al 2018;Dencs & Regály 2019;Djošović et al 2020;Raymond et al 2021). While the smallest objects typically considered in planet formation simulations have D 1,000 km, cratering records on solar system bodies (e.g.…”