[Paper Review] A comprehensive understanding of planet formation is required for assessing planetary habitability and for the search for life

Dániel Apai, F. J. Ciesla+15 more|arXiv (Cornell University)|Mar 23, 2018

Stellar, planetary, and galactic studies1 references3 citations

TL;DR

This paper argues that a comprehensive understanding of planet formation and evolution is essential for assessing planetary habitability and interpreting biosignatures in exoplanets, as many key habitability parameters—such as bulk composition, volatile inventory, and geological activity—are not directly observable. The authors advocate for integrated, multi-disciplinary research through large-scale grants, improved communication channels, and faster funding cycles to accelerate progress in identifying truly habitable, Earth-like exoplanets.

ABSTRACT

Dozens of habitable zone, approximately earth-sized exoplanets are known today. An emerging frontier of exoplanet studies is identifying which of these habitable zone, small planets are actually habitable (have all necessary conditions for life) and, of those, which are earth-like. Many parameters and processes influence habitability, ranging from the orbit through detailed composition including volatiles and organics, to the presence of geological activity and plate tectonics. While some properties will soon be directly observable, others cannot be probed by remote sensing for the foreseeable future. Thus, statistical understanding of planetary systems' formation and evolution is a key supplement to the direct measurements of planet properties. Probabilistically assessing parameters we cannot directly measure is essential to reliably assess habitability, to prioritizing habitable-zone planets for follow-up, and for interpreting possible biosignatures.

Motivation & Objective

• To address the critical gap in directly observing key habitability parameters such as bulk composition, volatile inventory, and geological activity in exoplanets.
• To emphasize that remote sensing alone cannot determine whether a planet is truly habitable or Earth-like, necessitating a systems-level understanding of planetary formation and evolution.
• To identify systemic challenges in current research funding and communication that hinder progress in multi-disciplinary planet formation science.
• To propose structural reforms in research funding and collaboration to accelerate the integration of knowledge across disciplines.
• To guide future observational campaigns by prioritizing exoplanets with favorable formation histories for biosignature detection.

Proposed method

• Integrating data from multi-mission surveys (e.g., GAIA, TESS, WFIRST) to infer indirect constraints on planet formation and evolution.
• Using statistical and probabilistic modeling to infer unobservable planetary properties—such as volatile delivery and past atmospheric loss—based on formation pathways.
• Applying comparative planetology by studying the solar system as a reference point within the broader context of exoplanetary systems.
• Proposing a two-step grant model to support high-risk, high-reward projects, with initial seed funding followed by larger grants upon feasibility demonstration.
• Establishing modern, interdisciplinary communication platforms to accelerate knowledge transfer between fields such as cosmochemistry, exoplanet population statistics, and atmospheric science.
• Advocating for large-scale, multi-investigator grants to synthesize findings from narrowly focused single-investigator studies into a unified understanding of planet formation.

Experimental results

Research questions

• RQ1 Which planetary system properties—beyond direct observables—determine habitability and are essential for interpreting biosignatures?
• RQ2 How can formation and evolutionary histories be used to probabilistically infer the presence of geological activity and volatile inventories in Earth-sized exoplanets?
• RQ3 What structural changes in research funding and collaboration are needed to accelerate progress in multi-disciplinary planet formation science?
• RQ4 How can indirect constraints on unobservable parameters like atmospheric loss history or bulk composition be reliably derived from formation models?
• RQ5 What role does system-level context—such as orbital evolution and disk dispersal—play in determining long-term planetary habitability?

Key findings

• Many key habitability parameters, including detailed bulk composition and volatile/organic inventory, are not directly measurable via remote sensing and require formation and evolution models.
• Geological activity and atmospheric stability—critical for habitability—are difficult to assess remotely but can be inferred probabilistically from formation history.
• Current funding models favor low-risk, incremental research, limiting progress on high-impact, integrative, or paradigm-shifting questions in planet formation.
• The typical idea-to-publication timeline of 4–5 years is too slow to align with the operational lifetimes of major telescopes like JWST and ELTs.
• Faster, two-step grant mechanisms (e.g., one-year seed grants followed by larger awards) could significantly accelerate innovation and risk reduction in planet formation research.
• Improved interdisciplinary communication—using modern tools and platforms—is essential to close knowledge gaps between fields such as cosmochemistry and exoplanet population studies.