Harrison Nicholls

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TLDR; The PSF has made the decision to put our community and our shared diversity, equity, and inclusion values ahead of seeking $1.5M in new revenue. Please read and share. pyfound.blogspot.com/2025/10/NSF-...
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True-color image of the Earth’s Western Hemisphere collected at about 2:00 PM Pacific Daylight Saving Time. There’s no atmospheric correction, so the atmosphere gets more opaque at the edges, and there’s a smooth fade from day to night.

True-color image of the Earth’s Western Hemisphere collected at about 2:00 PM Pacific Daylight Savings Time, corrected for Rayleigh scattering. The atmospheric correction enhances the appearance of the land and ocean, but flattens out the atmosphere and introduces a sharp transition between day and night.

Success! @noaa.gov GOES-West full disk, without (left) the Rayleigh correction that 99% of the published imagery uses. I still need to tweak the settings, but I always thought the removal of atmospheric scattering makes Earth look too flat.

Thanks to @stim3on.bsky.social & @simonsat.bsky.social

With @xoplanets.bsky.social, @timlichtenberg.bsky.social, @climatebook.bsky.social, Richard Chatterjee, and Hamish Hay.

In our now-published paper we model the early history of three exoplanets to specifically study the role of tidal heating on their capacity to solidify. A physically robust feedback mechanism can keep them molten, even with relatively thin atmospheres, which may extend to lots of rocky exoplanets.

See also my explainer thread below!
bsky.app/profile/nich...

Finally and importantly, in this paper, we explain the atmospheric abundances inferred from JWST by invoking the photochemical production of SO2 from H2S.

Our models, which include realistic atmosphere structure calculations, show that the radius of this planet has shrunk over its ~5 Gyr lifetime from that of a sub-Neptune to that of a super-Earth at the present day. This also corresponds with age-radius trends in the Kepler Survey.

Instead, this planet has a mostly H2+H2S+SO2 atmosphere and an internal magma ocean which has been sustained across its multi-billion-year lifetime, making it an interesting window into interactions between atmospheres and magma oceans. It is molten by a greenhouse atmosphere and tidal heating.

In this new paper, we show that this planet must have formed rich in HCNS volatiles, particularly sulfur; incompatible with the typical "gas-dwarf" birth interpretation. Our analysis also finds that this planet’s interior must be geochemically reduced, which also opposes the "water-world" scenario.

L 98-59 d is known to have a low density but a high MMW. We calculate its complete evolutionary history using our fully-coupled open source planetary modelling framework (PROTEUS; Nicholls+24).

In our new paper we model the complete evolution of L 98-59 d from 'birth' up to the present day. We show that it cannot be a gas dwarf or a water world; it's a 'hybrid' planet with an H2-rich atmosphere containing H2S and SO2 (photochemistry!), and a deep magma ocean.

@timlichtenberg.bsky.social

Water world
Gas dwarf
Sub-Venus
Bare rocks
Earth-like (define as you will)
Free floating planets

Absence of a Runaway Greenhouse Limit on Lava Planets Climate transitions on exoplanets offer valuable insights into the atmospheric processes governing planetary habitability. Previous pure-steam atmospheric models show a thermal limit in outgoing long-...

New paper on arXiv today: "Absence of a Runaway Greenhouse Limit on Lava Planets" by Iris Boer,
@nichollsh.bsky.social, and me (arxiv.org/abs/2505.11149). The runaway greenhouse limit is non-existent on molten planets (which is how planets form), questioning the general "habitable zone" concept.

A time-lapse of some images of asteroid (52246) Donaldjohanson during the encounter by Lucy!

Images taken on April 20, 2025, from a distance of 1,600 to 1,100 km.

Credit: NASA/Goddard/SwRI/Johns Hopkins APL

science.nasa.gov/image-articl...

#PlanetSci #SciComm 🧪

Planet Definitions xkcd.com/3063

Enceladus, by Cassini.

Credit: NASA/JPL-Caltech/SSI/CICLOPS/Kevin M. Gill (@kevinmgill.bsky.social)

Skew-T Log-P xkcd.com/3032

This is the second paper derived from my PhD, and a direct follow-up from arxiv.org/abs/2411.19137

@climatebook.bsky.social @timlichtenberg.bsky.social

Synthetic planet-average emission spectra (1 to ~20 microns) for HD 63433 d and TRAPPIST-1 c at the point of model termination. For HD 63433 d. Instrument bandpasses are marked on the plots.

Additionally, synthetic planet-averaged emission spectra show absorption features associated with mantle redox (fO2). Deep near-isothermal stratospheres also indicate that cool brightness temperatures could be inferred if observed photometrically.

To do this, we develop a new radiative-convective atmosphere model which is integrated into the PROTEUS magma ocean framework.

These models find that TRAPPIST-1 c solidifies within 100 Myr. HD 63433 d maintains a permanent magma ocean.

Our new paper on atmospheric convection on lava worlds is now on arXiv (accepted in MNRAS).

We model the early time-evolution of two terrestrial-mass planets, and find that their atmospheres are not always convective. However, they can still have permanent magma oceans!

arxiv.org/abs/2412.11987

Follow up paper coming soon :)

We used a coupled interior-atmosphere model to simulate how these planets evolve over time. Sometimes they solidify and sometimes they don't - but this strongly depends on the redox state of the mantle.

Excited to share that our paper on atmospheres on lava planets has been accepted in JGR: Planets!

You can find it on arXiv here:
arxiv.org/abs/2411.19137

Looks great! Maybe you could add clouds?