Exocomets from a Solar System Perspective

Abstract

Exocomets are small bodies releasing gas and dust which orbit stars other than the Sun. Their existence was first inferred from the detection of variable absorption features in stellar spectra in the late 1980s using spectroscopy. More recently, they have been detected through photometric transits from space, and through far-IR/mm gas emission within debris disks. As (exo)comets are considered to contain the most pristine material accessible in stellar systems, they hold the potential to give us information about early stage formation and evolution conditions of extra solar systems. In the solar system, comets carry the physical and chemical memory of the protoplanetary disk environment where they formed, providing relevant information on processes in the primordial solar nebula. The aim of this paper is to compare essential compositional properties between solar system comets and exocomets to allow for the development of new observational methods and techniques. The paper aims to highlight commonalities and to discuss differences which may aid the communication between the involved research communities and perhaps also avoid misconceptions. The compositional properties of solar system comets and exocomets are summarized before providing an observational comparison between them. Exocomets likely vary in their composition depending on their formation environment like solar system comets do, and since exocomets are not resolved spatially, they pose a challenge when comparing them to high fidelity observations of solar system comets. Observations of gas around main sequence stars, spectroscopic observations of “polluted” white dwarf atmospheres and spectroscopic observations of transiting exocomets suggest that exocomets may show compositional similarities with solar system comets. The recent interstellar visitor 2I/Borisov showed gas, dust and nuclear properties similar to that of solar system comets. This raises the tantalising prospect that observations of interstellar comets may help bridge the fields of exocomet and solar system comets.

Planetesimal/Debris discs

“…Welsh et al, 1998;Eiroa et al, 2016;Hales et al, 2017;Iglesias et al, 2018;Rebollido et al, 2020). For a more in depth description of the gas seen in absorption and its comparison with Solar System comets see the recent review by Strøm et al (2020).…”

A Bayesian Analysis of Technological Intelligence in Land and Oceans

“…Looking beyond the solar system, the discovery of debris disks (comprising analogs of the Kuiper Belt) and exocomets (Matthews et al 2014;Hughes et al 2018;Rappaport et al 2018;Rebollido et al 2020;Strøm et al 2020), in a sizeable fraction of planetary systems (Montesinos et al 2016;Sibthorpe et al 2018), supports the surmise that small icy bodies-which could host subsurface oceans of liquid water in principle-are prevalent in the Milky Way. Changing tack, a combination of exoplanet observations and modeling has demonstrated that many of them are likely to be ocean worlds-building on early proposals by Kuchner (2003) and Léger et al (2004)-with only oceans and no landmasses on the surface (Zeng et al 2019;Mousis et al 2020;Venturini et al 2020;Zeng et al 2021;Luque & Pallé 2022;Neil et al 2022).…”

Simulating Observations of Ices in Protoplanetary Disks

“…H 2 O ice also exhibits emission features at 44 and 62 µm. Ices have been studied across all star and planet forming environments, including molecular clouds (e.g., Whittet et al 1983;Bergin et al 2005), dense cores (e.g., Boogert et al 2011), protostellar envelopes (e.g., Boogert et al 2008;Öberg et al 2011), and in comets/icy planetesimals both in our solar system (Mumma & Charnley 2011;Altwegg et al 2019) and around other stars (Matrà et al 2017(Matrà et al , 2018Strøm et al 2020).…”