K2-18 Archives - Astrobiology

Left panel: The rotation period-effective temperature distribution for M dwarfs across open clusters. Each data point is colour-coded according to its corresponding cluster. The spectral type is indicated on a second y-axis. The filled circles are coloured according to their corresponding cluster membership: Pleiades (age:0.12 Gyr) in blue; Praesepe (age: 0.67 Gyr) in green; NGC 6811 (age: 1 Gyr) in purple; NGC 752 (age: 1.4 Gyr) in pink; Ruprecht 147 (age: 2.7 Gyr) in yellow; M67 (age: 4 Gyr) in cyan. K2-18 and TOI 732 are shown as magenta and blue star symbols, respectively. Right panel: Log-log plot of age and rotation period for M dwarfs in the dataset from Engle & Guinan 2023 (shown in black circles). The red colour-coded data points represent cluster members (as reported by Curtis et al. 2020 and Godoy-Rivera et al. 2021) spectral types ranging from M2 to M6, as indicated by the colour bar. A third-degree polynomial best fit (Eqn. 5) to the dataset from Engle & Guinan 2023 is shown as an orange line. The grey shaded area represents the ±1𝜎 confidence interval around the fitted model. The magenta and blue vertical lines show the estimated age ranges as given in Table 4 for K2-18 and TOI-732, respectively. -- astro-ph.EP

Astrochemistry, Astronomy & Telescopes, Atmospheres, Climate, Weather, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Mapping, Geodesy, Cartography, Bathymetry, Status Report, Stellar Cartography, Water/Hycean Worlds & Oceanography

Characterising M Dwarf Host Stars Of Two Candidate Hycean Worlds

by Keith CowingMarch 27, 2025March 27, 2025

Planetary systems orbiting M dwarf host stars are promising targets for atmospheric characterisation of low-mass exoplanets.

Top panels: evolution of CHZ and UVH for Trappist-1, Proxima Centauri, GJ 273, GJ 163, K2-18, GJ 832, GJ 357, GJ 229A, HD 40307 and Kepler-62. In each plot the vertical gray line represents the host star age found in the literature and the relative errors (the gray shaded region around the gray line). Yellow, orange and dark orange lines represent the ages at which fraction of systems with at least one rocky planet without a primordial envelope in the CHZ is equal to 20%, 30%, 40% for each system (according to NGPPS model). The dashed line represents the time where each star settled onto the main sequence. Bottom panels: evolution of the fraction of the radial extension of the CHZ that is overlapping the radial extension of the UVZ for three different values of the NUV atmospheric transmission. -- astro-ph.EP

Biophysics, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Proxima Centauri, Radiation, Space Weather & Heliophysics, Status Report, TRAPPIST-1, Water/Hycean Worlds & Oceanography

The Time Evolution Of The Ultraviolet Habitable Zone

by Keith CowingSeptember 5, 2024September 5, 2024

For stars hosting Circumstellar Habitable Zone (CHZ) exoplanets, we investigate the time-evolution of their ultraviolet habitable zone (UHZ), the annular region around a star where an exoplanet could experience a […]

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 […]

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 […]

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.

Secular evolution of K2-18 planets in a two-planet configuration. Numerical integration of orbital motion was performed for 30 Kyr with the initial conditions: e1(0) = 0.01, e2(0) = 0.05, i1(0) = 0, i2(0) = 5 ◦ , ω1(0) = ω2(0) = 0, and Ω1(0) = Ω2(0) = 0. The black curves show the actual output of the numerical simulations. The red curves show the best fits with the theoretical model (2). Upper left panel: inner planet K2-18 c eccentricity. Upper right panel: inner planet K2-18 c inclination in degrees. Lower left panel: outer planet K2-18 b eccentricity. Lower right panel: outer planet K2-18 b inclination in degrees. -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Status Report

Secular Orbital Dynamics of the Possibly Habitable Planet K2-18 b with and without the Proposed Inner Companion

by Keith CowingNovember 1, 2023November 1, 2023

The transiting planet K2-18 b is one of the best candidates for a relatively nearby world harboring biological life. The long-term orbital evolution of this planet is investigated using theoretical […]

This artist’s concept shows what exoplanet K2-18 b could look like based on science data. K2-18 b, an exoplanet 8.6 times as massive as Earth, orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth. A new investigation with NASA’s James Webb Space Telescope into K2-18 b has revealed the presence of carbon-bearing molecules including methane and carbon dioxide. The abundance of methane and carbon dioxide, and shortage of ammonia, support the hypothesis that there may be a water ocean underneath a hydrogen-rich atmosphere in K2-18 b. Credits: Illustration: NASA, CSA, ESA, J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University)

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

Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18 b

by Keith CowingSeptember 11, 2023September 11, 2023

A new investigation with NASA’s James Webb Space Telescope into K2-18 b, an exoplanet 8.6 times as massive as Earth, has revealed the presence of carbon-bearing molecules including methane and […]