K2-18b Archives

K2-18 b vertical velocity 𝜔 at the 0.01 bar level. Negative (positive) 𝜔 indicates upwards (downwards) motion. The global overturning circulation is clearly visible. Irradiation concentrated on the dayside heats and expands these atmospheric regions, driving upwards motion. There is corresponding subsidence on the nightside. -- astro-ph.EP

Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Habitable Zones, Status Report, TRAPPIST-1, Water/Hycean Worlds & Oceanography

A New Convection Scheme For GCMs Of Temperate Sub-Neptunes

by Keith CowingFebruary 19, 2025February 19, 2025

Atmospheric characterisation of temperate sub-Neptunes is the new frontier of exoplanetary science with recent JWST observations of possible Hycean world K2-18b.

Magma ocean planets that contain water - like the Earth-like exoplanet GJ 1214 b in this artist's impression - have only a tiny fraction of water on their surface. Most of it is stored deep inside. (Image: NASA/JPL-Caltech/R. Hurt)

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

Planets Contain More Water Than Previously Thought

by Keith CowingAugust 21, 2024April 14, 2026

Most of a planet’s water is generally not found on the surface, but is hidden deep inside. This affects the potential habitability of distant worlds, as model calculations by researchers […]

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 […]

Combined transmission spectrum LHS1140b obtained with NIRISS SOSS on December 1st and 26th 2023 overlaid with HST observations (solid grey points; Edwards et al. 2021). The orange 2-envelope is the best TLS model dominated by facula. The dashed line is the predicted GCM model of the mini-Neptune scenario of Cadieux et al. (2024); this model is excluded at more than 5  (Cadieux et al., in prep). -- astro-ph.EP

Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Status Report, TRAPPIST-1

Do Temperate Rocky Planets Around M Dwarfs have an Atmosphere?

by Keith CowingMarch 20, 2024

Detecting an atmosphere on nearby temperate planets is one of the most important scientific objectives of the Webb mission, an endeavour in practice limited to a handful of well-characterized planets: […]

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 […]

Habitable Zones, Status Report

JWST Observations Of K2-18b Can Be Explained By A Gas-rich Mini-Neptune With No Habitable Surface

by Keith CowingJanuary 24, 2024January 23, 2024

JWST recently measured the transmission spectrum of K2-18b, a habitable-zone sub-Neptune exoplanet, detecting CH4 and CO2 in its atmosphere.

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).

Boundaries of the Habitable Zone under various climate and atmospheric models as a function of radiative flux received from the host star, relative to Earth. Dashed lines represent the extended boundaries due to subglacial liquid water suggested in this work: blue for the inner HZ boundary (nightside ice evaporates due to heat transport, the percentage marks the global transport parameter f) and violet for the outer one (Martian polar lakes). Solid green lines and green shading denote the conservative HZ boundaries: inner one (moist greenhouse) and outer one (maximum CO2 greenhouse), calculated using the 1-D climate model. Also marked is the recent Venus boundary (dashed green line). The orange curve marks the tidal locking radius. Circles denote the terrestrial planets in the solar system and a few Earth-sized exoplanets orbiting M-dwarf stars. -- Hebrew University of Jerusalem

Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Habitable Zones, Icy Worlds, Press Release, Water/Hycean Worlds & Oceanography

Extended Habitability Of Exoplanets Due To Subglacial Water

by Keith CowingNovember 10, 2023November 10, 2023

Professor Amri Wandel, from Hebrew University of Jerusalem, has unveiled research that promises to redefine our comprehension of habitable exoplanets. In a recent study published in the Astronomical Journal, Professor […]

Habitable Zones, Press Release

Large Exoplanet Could Have The Right Conditions For Life

by Keith CowingFebruary 26, 2020

Astronomers have found an exoplanet more than twice the size of Earth to be potentially habitable, opening the search for life to planets significantly larger than Earth but smaller than […]

Habitable Zones, Press Release

Water Vapor On The Habitable-Zone Exoplanet K2-18b

by Keith CowingSeptember 10, 2019

Ever since the discovery of the first exoplanet, astronomers have made steady progress towards finding and probing planets in the habitable zone of their host stars, where the conditions could […]