Harrison Nicholls (he/him): Publications

Atmospheric evolution through outgassing and escape on young molten rocky exoplanets

Astronomy & Astrophysics EDP Sciences 714 (2026) A434-A434

Authors:

Emma Postolec, Tim Lichtenberg, Harrison Nicholls, Laurent Soucasse, Floris van der Tak

Abstract:

Context. The earliest rocky planet atmospheres were shaped by the competition between initial volatile inventories and atmospheric escape driven by stellar irradiation. On young magma ocean planets, volatile exchange between the atmosphere and the interior through in- and outgassing competes with atmospheric escape, controlling volatile retention and atmospheric evolution. Aims. We investigate how atmospheric escape and replenishment via outgassing during magma ocean crystallization shape rocky exoplanet atmospheres. Methods. We extended a coupled interior-atmosphere model to simulate rocky planet evolution during the magma ocean era by incorporating an energy-limited atmospheric escape module. Comparing self-consistent radiative-convective and prescribed-convective atmospheres, we quantified how atmospheric energy transport affects escape. We explored a wide range of orbital separations, escape efficiencies, oxidation states, and initial volatile inventories to identify regimes where sustained magma-ocean outgassing or escape dominates. We estimated atmospheric mass loss and compositions for young rocky planets around Sun-like and M dwarf stars over geologic timescales. Results. Atmospheric escape shortens magma ocean lifetimes by weakening greenhouse insulation and accelerating cooling, with radiative-convective atmospheres reducing solidification timescales compared to purely convective cases. Volatile dissolution into the magma ocean interacts with the escape of atmospheric species to chemically fractionate the planetary volatile budget over time by retaining more soluble species. For Earth-mass planets, atmospheres survive if mass-loss rates remain moderate ( Ṁ EL ≈ 10 10 g s −1 ). When atmospheric escape is included, the mantle redox state remains a key control on atmospheric composition: high oxygen fugacity ( f O 2 ) yields heavier H 2 O- and CO 2 -rich atmospheres, while low f O 2 produces light H 2 - or CO-dominated atmospheres, consistent with previous studies. Orbital separation, initial volatile inventory, and stellar type produce diverse evolutionary pathways, from bare rocky planets to magma oceans with thick atmospheres, spanning compositions from H 2 - to SO 2 -dominated atmospheres.

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Probing Exoplanetary Chemistry with Ariel: Scientific Priorities and Observational Strategies

ArXiv 2609.27622 (2026)

Authors:

Olivia Venot, Yamila Miguel, Robin Baeyens, Stefano Bellotti, Giuseppe Cassone, Quentin Changeat, Ryan Cloutier, Athena Coustenis, Dwaipayan Dubey, Billy Edwards, Kaustubh Hakim, Eric Hébrard, Christiane Helling, Helgi Rafn Hrodmarsson, Leoni Janssen, Adam Yassin Jaziri, Gaia Lacedelli, Panayotis Lavvas, Jorge Lillo-Box, Amy Louca, Adrien Masson, Zita Martins, Karan Molaverdikhani, Benjamín Montesinos, Harrison Nicholls, Enric Palle, Paul Rimmer, Donna Rodgers-Lee, Jonathan Tennyson, Shang-Min Tsai, Roméo Veillet, Sergey N Yurchenko, Maria Zamyatina

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Super-Earth Interiors Shrink by About 10% as They Crystallise

ArXiv 2609.23091 (2026)

Authors:

Tim Lichtenberg, Mara Attia, Harrison Nicholls, Mariana Sastre, Dan J Bower, Karen Stuitje, Flavia C Pascal, Laurent Soucasse, Daniel Apai, Patrick Bos, Robb Calder, Lorenzo Cesario, Lisa Dang, Emeline Decocq, Marijn van Dijk, Mohammad Farhat, Kaustubh Hakim, Tadahiro Kimura, Imre Kisvárdai, Sebastiaan Krijt, Yamila Miguel, Ioannis Panagiotou, Emma Postolec, Martin Schlecker, Sara Seager, Anat Shahar, Oliver Shorttle, Paolo A Sossi, Wim van Westrenen

Details from ArXiV

Evolutionary pathways toward survival of a thick CO2- or SO2-rich atmosphere on the lava world TOI-561 b

ArXiv 2609.03144 (2026)

Authors:

Emma Postolec, Tim Lichtenberg, Johanna K Teske, Harrison Nicholls, Mara Attia, Anjali Piette, Lisa Dang, Nicole L Wallack, Mykhaylo Plotnykov, Alex McGinty, Samuel Boucher, Bo Peng, Diana Valencia

Details from ArXiV

Geophysical and atmospheric implications of f O ₂ -dependent melting on rocky exoplanets

Astronomy & Astrophysics EDP Sciences 713 (2026) A159-A159

Authors:

Mariana Sastre, Tim Lichtenberg, Laurent Soucasse, Dan J Bower, Harrison Nicholls, Inga Kamp

Abstract:

The geochemical evolution of long-lived magma oceans is strongly regulated by the volatile exchange between the molten mantle and the atmosphere. For planets inside the runaway-greenhouse limit, this coupled evolution can persist for billions of years, governing bulk density, surface conditions, and long-term geodynamics. However, most existing studies assume Earth-like (oxidized) conditions and neglect the influence of the redox state on melt thermodynamics and volatile release. We quantified how experimentally derived, oxygen-fugacity-dependent melting curves implemented within the coupled interior-atmosphere framework PROTEUS propagate into the thermal structure, melt fraction, and rheological evolution of rocky exoplanet interiors, and applied this to the short-period super-Earth GJ 1132 b. We found strongly non-linear thermal responses to variations in melting curves. In volatile-poor systems, reduced melting curves ( f O 2 ≤ IW, where IW denotes the iron–wüstite buffer) promote earlier deep-mantle crystallization relative to oxidized (IW+2.0) and Earth-like (IW + 4.0) cases (range IW–4.0 to IW + 4.0), favouring late-stage surface magma oceans sustained by greenhouse warming, while oxidized melting curves maintain higher melt fractions and a vertically extended magma ocean. Reduced mantles produce massive H 2 –CO-rich atmospheres; oxidized mantles favour thinner H 2 O–CO 2 envelopes. In volatile-rich systems, the interior reaches radiative equilibrium at high melt fractions, sustaining a steady-state global magma ocean in which melting curve variations do not significantly influence solidification timing. This indicates a hierarchical control: volatile inventory and surface oxygen fugacity act as the primary regulators of thermal state, while oxygen-fugacity-dependent melting relations provide a secondary modulation. These contrasting regimes produce distinct atmospheric compositions and formation timescales, offering testable spectral predictions for close-in rocky exoplanets evaluable with forthcoming JWST observations.

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Harrison Nicholls (he/him)

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Atmospheric evolution through outgassing and escape on young molten rocky exoplanets

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Probing Exoplanetary Chemistry with Ariel: Scientific Priorities and Observational Strategies

Authors:

Super-Earth Interiors Shrink by About 10% as They Crystallise

Authors:

Evolutionary pathways toward survival of a thick CO2- or SO2-rich atmosphere on the lava world TOI-561 b

Authors:

Geophysical and atmospheric implications of f O ₂ -dependent melting on rocky exoplanets

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Harrison Nicholls (he/him)

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Atmospheric evolution through outgassing and escape on young molten rocky exoplanets

Authors:

Abstract:

Probing Exoplanetary Chemistry with Ariel: Scientific Priorities and Observational Strategies

Authors:

Super-Earth Interiors Shrink by About 10% as They Crystallise

Authors:

Evolutionary pathways toward survival of a thick CO2- or SO2-rich atmosphere on the lava world TOI-561 b

Authors:

Geophysical and atmospheric implications of f O 2 -dependent melting on rocky exoplanets

Authors:

Abstract:

Geophysical and atmospheric implications of f O ₂ -dependent melting on rocky exoplanets