Hycean worlds Archives

Hycean and mini-Neptune scenarios with two photochemical models. Top row: Original simulations from Wogan et al. (2024), showing the mixing ratio of molecules against atmospheric pressure in bar. Bottom row: VULCAN simulations of the same scenarios with equivalent assumptions (see main text). The scenarios are: an uninhabited Hycean (left column), an inhabited Hycean (middle column), and a mini-Neptune case (right column). The given molecular constraints are from the “One offset” case (Madhusudhan et al. 2023b) as this case gives the best fit to the observed data. 1-σ error bars are given for detected molecules (CH4 - orange; CO2 - green), and 2-σ upper limits are given for CO (purple), H2O (blue), and NH3 (grey), which were not detected by Madhusudhan et al. (2023b). The photosphere, the region in the atmosphere which impacts the transmission spectrum observed, is given in a light grey shade between 10−2 – 10−4 bar. A variety of simulations were run with both the W24 setup (see Table A1) and VULCAN (see Table A2). All of the simulations shown in this figure use the GJ 176 spectrum. Only the inhabited Hycean scenarios in both models are consistent with the retrieved abundances. -- astro-ph.EP

Considerations for Photochemical Modeling of Possible Hycean Worlds

by Keith CowingOctober 11, 2024September 18, 2025

JWST is revolutionising the study of temperate sub-Neptunes, starting with the first detection of carbon-bearing molecules in the habitable-zone sub-Neptune K2-18 b. The retrieved abundances of CH4 and CO2 and […]

Number densities of condensate droplets and gas molecules, and their respective molecular weights, as a function of height R/Rp for the atmosphere shown in Figure 8 with Kzz = 1×104 . Left: Numbers of dots at each height in the atmosphere represent the relative number densities of droplets, and the symbol sizes are proportional to droplet sizes. Right: Numbers of dots represent the relative number densities of molecules. In both plots, colors indicate molecular weights at each height (note different color scales in the two panels). Curves for absolute number densities of droplets (left) and gas molecules (right) are overlain for comparison. -- astro-ph.EP

Astrogeology, Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Status Report, Water/Hycean Worlds & Oceanography

Phase Equilibria of Sub-Neptunes and Super-Earths

by Keith CowingAugust 22, 2024

We investigate the consequences of non-ideal chemical interaction between silicate and overlying hydrogen-rich envelopes for rocky planets using basic tenets of phase equilibria. Based on our current understanding of the […]

The transmission spectrum of the sub-Neptune K2-18 b, a candidate Hycean world (from Madhusudhan et al. 2023). The observed JWST spectrum is shown in the orange and red data obtained with the NIRISS and NIRSpec instruments on JWST as noted in the legend. The dark blue line denotes the median-fit model spectrum while medium and lighter blue regions denote the 1σ and 2σ contours, respectively. CH4 and CO2 are detected robustly at 5σ and 3σ confidence, respectively, as evident from their strong spectral features labelled in the figure. Only marginal evidence for DMS is found in regions of the spectrum overlapping with the strong CH4 and CO2 features as shown. The yellow circles show the median-fit model binned to the same resolution as the data. -- astro-ph.EP

Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Gaia - Planetary Perspectives, Habitable Zones, Origin & Evolution of Life, Status Report, Water/Hycean Worlds & Oceanography

The Hycean Paradigm in the Search for Life Elsewhere

by Keith CowingJune 19, 2024June 19, 2024

The search for habitable conditions and signs of life on exoplanets is a major frontier in modern astronomy. Detecting atmospheric signatures of Earth-like exoplanets is challenging due to their small […]

This infographic compares the characteristics of three classes of stars in our galaxy: Sunlike stars are classified as G stars; stars less massive and cooler than our Sun are K dwarfs; and even fainter and cooler stars are the reddish M dwarfs. The size of the habitable zone is different for each class of star. In our solar system, the habitable zone begins just beyond the orbit of Venus and almost encompasses Mars. Credits: NASA, ESA and Z. Levy (STScI)

Astronomy & Telescopes, Atmospheres, Climate, Weather, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Press Release

Reconnaissance Of Potentially Habitable Worlds With Webb Space Telescope

by Keith CowingJune 5, 2024June 5, 2024

Exoplanets are common in our galaxy, and some even orbit in the so-called habitable zone of their star. NASA’s James Webb Space Telescope has been busy observing a few of […]

Rendering of the likely view on a Hycean world. (AI generated by Shang-Min Tsai/UCR)

Astrochemistry, Atmospheres, Climate, Weather, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Press Release, Water/Hycean Worlds & Oceanography

Webb Telescope Probably Didn’t Find Life On An Exoplanet – Yet

by Keith CowingMay 3, 2024

Recent reports of NASA’s James Webb Space Telescope finding signs of life on a distant planet understandably sparked excitement. A new study challenges this finding, but also outlines how the […]

Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Status Report, Water/Hycean Worlds & Oceanography

Biogenic Sulfur Gases As Biosignatures On Temperate Sub-Neptune Waterworlds

by Keith CowingMarch 24, 2024March 24, 2024

Theoretical predictions and observational data indicate a class of sub-Neptune exoplanets may have water-rich interiors covered by hydrogen-dominated atmospheres. Provided suitable climate conditions, such planets could host surface liquid oceans.

Amount of Gibbs energy that could be harnessed by synthesizing CH4 from CO2 and H2 at the surface of an ocean on exoplanet K2-18b. The unknown atmospheric pressure is a key driver on hycean worlds. Solid vs. dashed curves show how changing the temperature from 25 to 120°C also affects energy availability. Dashed curves start at 3 bar to make sure the system is on the liquid side of the saturation curve of water. A nominal case with 1% mixing ratios of CO2 and CH4 is indicated by the black curve. Colored curves represent cases where the abundances of CO2 and CH4 are at their 1σ limits in ways that maximize (high CO2-low CH4) or minimize (low CO2-high CH4) the affinity. Equilibrium corresponds to zero affinity. The estimated affinity range for Enceladus’s subsurface ocean (Waite et al. 2017) and a canonical value for the minimum affinity needed to support methanogenic life on Earth (Hoehler 2004) are shown for comparison. -- astro-ph.EP

Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Habitable Zones, Icy Worlds, Imaging & Spectroscopy, Origin & Evolution of Life, Status Report, Water/Hycean Worlds & Oceanography

The Geochemical Potential for Metabolic Processes on the Sub-Neptune Exoplanet K2-18b

by Keith CowingMarch 7, 2024March 7, 2024

Quantifying disequilibria is important to understand whether an environment could be habitable. It has been proposed that the exoplanet K2-18b has a hydrogen-rich atmosphere and a water ocean, making it […]

1-dimensional cross-section of a possible ocean of TOI-270 d. This corresponds to a case with ocean depth 443 km. The maximum ocean depth on Earth is shown as a dashed line, at 11 km. -- astro-ph.EP

Astrogeology, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Habitable Zones, Status Report, Water/Hycean Worlds & Oceanography

On The Ocean Conditions Of Hycean Worlds

by Keith CowingFebruary 21, 2024February 20, 2024

Recent studies have suggested the possibility of Hycean worlds, characterised by deep liquid water oceans beneath H2-rich atmospheres.

Total atmospheric surface pressure (bar) and volume mixing ratio of NH3, and CO2 output from the atmospheremagma ocean system over the parameter space which we have sampled, outlined in table 1. This corresponds to the output of step 2 in the schematic presented in figure 1. Points are colour-coded by the log of the planetary hydrogen budget, in units part-per-million of the planetary mass. Histograms of the distribution of NH3 mixing ratios (top left), CO2 mixing ratios (top right) and total surface pressures (lower right) from across the model runs are shown alongside. -- astro-ph.EP

Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Lava / magma ocean / Volcanic Worlds, Status Report, Water/Hycean Worlds & Oceanography

Distinguishing Oceans Of Water From Magma On Mini-Neptune K2-18b

by Keith CowingJanuary 12, 2024May 11, 2024

Mildly rradiated mini-Neptunes have densities potentially consistent with them hosting substantial liquid water oceans (`Hycean’ planets).

Astrochemistry, Atmospheres, Climate, Weather, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Status Report

Carbon-bearing Molecules In A Possible Hycean Atmosphere

by Keith CowingSeptember 17, 2023September 17, 2023

The search for habitable environments and biomarkers in exoplanetary atmospheres is the holy grail of exoplanet science. The detection of atmospheric signatures of habitable Earth-like exoplanets is challenging due to […]