Satellites and small bodies with ALMA: Insights into Solar System formation & evolution

TL;DR

The paper investigates how Solar System formation and volatile evolution are imprinted across disks, planets, moons, and comets, using ALMA to connect debris-disk structure with surface and atmospheric compositions. It highlights thermal emission studies of debris disks and Solar System bodies to infer sizes, masses, emissivity, and formation histories, and it discusses gas-phase chemistry across disks and Solar System objects to probe chemical inheritance. Key results include the ability to measure mass ratios in KBO satellites (e.g., Vanth–Orcus), nitrogen-15 enrichment in nitriles on Titan and in comets, and elevated 34S/32S in Io, all supporting long-standing formation and evolution scenarios. The work emphasizes the need for larger, multi-species isotopic samples and for matching disk observations at analogous radii to Solar System scales, while acknowledging limitations due to observing gas-phase rather than ices.

Abstract

Our understanding of the formation and evolution of planetary systems has made major advances in the past decade. This progress has been driven in large part by the Atacama Large Millimeter/submillimeter Array (ALMA), which has given us an unprecedented view of Solar System bodies themselves, and of the structure and chemistry of forming exoplanetary systems. Within our own Solar System, ALMA has enabled the detection of new molecules and isotopologues across moons and comets, as well as placing new constraints on the compositions and histories of small bodies through thermal emission observations. In this article, we highlight some key areas where ALMA has contributed to a deeper understanding of our Solar System's formation and evolution, and place these discoveries in the context of our evolving understanding of protoplanetary disks.

Figures (2)

• Figure 1: (Left panel) ALMA continuum thermal observations of the debris disk surrounding HD 170773, a nearby $\sim$1.3 solar mass star, from Sepulveda_2019. The emission is from dust created from collisions within a large population of small bodies residing in the debris disk. (Right panel) A solar system example of the types of bodies within the debris is the dwarf planet system Orcus and Vanth, from bb_size. ALMA has detected the tiny barycentric wobble induced on Orcus by Vanth, with a size approximately equal to the circle above the "1 arcsecond" scale bar, showing that the mass ratio of this system is the highest of any measured primary-satellite in the solar system.
• Figure 2: (a) $^{15}$N/$^{14}$N ratios among various astronomical objects (from lellouch2017_plutoglavin2025nosowitz25cordiner24nomura23, and references therein). ALMA is responsible for the observations of HCN, HC$_3$N and CH$_3$CN on Titan, HCN in comet 46P/Wirtanen, the HCN upper limit at Pluto, and nitriles in protoplanetary disks. The average comets value is the error weighted mean of 31 measurements from hily17. Horizontal dashed lines indicate the terrestrial values. (b) $^{34}$S/$^{32}$S ratios in the Solar System (fig adapted from deKleer2024). Abbreviations are used for the designations of comets 67P/Churyumov–Gerasimenko, C/2014 Q2 (Lovejoy), C/2012 F6 (Lemmon), and C/1995 O1 (Hale-Bopp). (c) Map and spectrum of CH$_3$C$^{15}$N from ALMA used to derive the $^{15}$N/$^{14}$N ratio nosowitz25, and (d) Map and spectrum of $^{34}$SO$_2$ from ALMA used to derive the $^{34}$S/$^{32}$S ratio deKleer2024. Vertical ticks indicate the respective molecular line frequencies.