Tracing the horizons of habitability with Venus and warm rocky exoplanets

One of the primary objectives of astronomy and planetary science is the search for life beyond Earth. This search is conducted on two frontiers: one via exploration of extreme environments within the Solar System; the other via remote sensing of exoplanets that orbit distant stars. Venus, our nearest planetary neighbour in the Solar System, holds unique significance for the limits of habitability on both of these frontiers: first, Venus represents the paradigm of an Earth-like planet that either did not form or did not hold onto surface conditions habitable to known terrestrial life; second, the extreme environment of Venus's cloud layer may potentially be inhabited today by more exotic forms of life. For both of these reasons, Venus holds profound consequences for the horizons of habitability on exoplanets. In this thesis, I examine the horizon of extreme habitability in Venus’s clouds, and the horizon of surface hostility and the death of habitability that Venus epitomises for the wider population of rocky exoplanets. I begin by reviewing the history of Venus exploration, the current status of the Venus life hypothesis, and our present knowledge of Venus’s atmospheric chemistry and climate history. I explore how we can trace the possibility of extreme habitability in Venus’s cloud layer by modelling the metabolic signatures of an aerial biosphere that, if present, would be imprinted in the atmospheric chemistry. I then explore how we can trace the limit of surface habitability, using Venus as the paradigm of a warm rocky exoplanet. I investigate how the atmospheres of Venus-like exoplanets respond to irradiation by cool host stars and identify unique observational indicators that can break the degeneracy between Venus-like and Earth-like paradigms. Finally, placing these results into their astronomical context, I develop a self-consistent atmospheric model to determine how we can trace the inner edge of the liquid-water habitable zone across the known population of warm rocky exoplanets with current and future telescopes.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Jordan, Sean

Advisors dc:contributor.advisor

• Shorttle, Oliver
• Rimmer, Paul

• Astrobiology
• Atmospheric chemistry
• Exoplanet Science
• Planetary Science
• Venus

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/0bff7831-47e4-4469-8bc6-7d31a2da81de/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.111823

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/373333