TOI-421 b Archives - Astrobiology

Isolines of planet radius versus mass, extracting cross-sections from our grid of models by holding other variables constant (top-right text box). Top (a): sensitivity to instellation (colour) and atmosphere mass fraction 𝑓𝑎 (line width, five values). Bottom (b): sensitivity to atmospheric metallicity log10 𝑍𝑎 (colour) and 𝑓𝑎 (line width, five values). For visualisation, only five sets of secondary variables (line widths) are shown. Dashed blue lines show airless cases with different core sizes (Zeng et al. 2019). -- astro-ph.EP)

Exoplanets, -moons, -comets, Habitable Zones, Press Release, Stellar Cartography

Beyond The Mass-radius Plane: Integrated Radiative-convective And Interior Structure Simulations Of The Exoplanet Continuum

by Keith CowingApril 23, 2026April 23, 2026

Static structure models, which map mass-radius constraints to bulk planet composition, are frequently used to categorise exoplanets due to their computational efficiency and the high-level insight they offer into planetary […]

TOI-421 b -- NASA.gov

Astronomy & Telescopes, Exoplanets, -moons, -comets, Press Release

The ATREIDES Program In Search Of Lost Exo-Neptunes

by Keith CowingSeptember 17, 2025September 17, 2025

An international team led by the University of Geneva (UNIGE), including scientists from the National Centre of Competence in Research PlanetS, the University of Warwick, and the Canary Islands Institute […]

Envelope composition in the H–He–C–N–O–Si chemical system of TOI-421b (𝑅MEB = 1.65𝑅⊕, 𝑅𝑃 = 2.64𝑅⊕, 𝑀𝑃 = 6.7𝑀⊕, 𝑇MEB = 3000 K) as a function of H mass fraction. Elemental budgets, reactions, gas solubility laws, and real gas equations are described in Sect. 2. MEB partial pressures of the considered gases for (a) 1× solar metallicity and 100% mantle melt (IW–6.2 to IW–5.7), (b) 100× solar metallicity and 100% mantle melt (IW–5.5 to IW–5.2), (c) 1× solar metallicity and 1% mantle melt (IW–3.4 to IW–3.1), and (d) 100× solar metallicity and 1% mantle melt (IW–2.3 to IW–1.6). Full range of MEB partial pressures is shown in Fig. A2. The corresponding partitioning of volatile elements in magma and real gas fugacity coefficients are given in Fig. B1 and Fig. B2, respectively. -- astro-ph.EP

Astrogeology, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Imaging & Spectroscopy, Lava / magma ocean / Volcanic Worlds, Press Release

Silane-Methane Competition in Sub-Neptune Atmospheres As A Diagnostic Of Metallicity And Magma Oceans

by Keith CowingSeptember 1, 2025September 1, 2025

The James Webb Space Telescope is characterising the atmospheres of sub-Neptunes. The presence of magma oceans on sub-Neptunes is expected to strongly alter the chemistry of their envelopes (100 bar-100 […]

Time evolution of the gas disk and planetary envelopes after the tidal disruption of a Jupiter-like planet. - Disc surface density evolution for the 10 M⊕ case; circles indicate the closer VEP. -- astro-ph.EP

Astrogeology, Exoplanets, -moons, -comets, Status Report

Volatile Enrichment In Low-mass Planets: Signatures Of Past Planetary Disruption?

by Keith CowingJuly 29, 2025July 29, 2025

Context: Tidal disruption and engulfment events around main-sequence stars, such as the luminous red nova ZTF SLRN-2020 (a candidate planetary-engulfment event), reveal the destruction of close-in giant planets. While current […]

Exoplanet TOI-421 b -- NASA

Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Press Release

Webb Studies Hot Sub-Neptune Exoplanet TOI-421 b

by Keith CowingMay 6, 2025May 12, 2025

Though they don’t orbit around our Sun, sub-Neptunes are the most common type of exoplanet, or planet outside our solar system, that have been observed in our galaxy. These small, […]

Hot sub-Neptune exoplanet TOI-421 b (NIRISS/NIRSpec transmission spectrum) -- ESA - larger image

Astrochemistry, Astrogeology, Astronomy & Telescopes, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

Hot sub-Neptune Exoplanet TOI-421 b NIRISS/NIRSpec Transmission Spectrum

by Keith CowingMay 6, 2025

This is a transmission spectrum captured by the NASA/ESA/CSA James Webb Space Telescope that reveals the presence of water (H2O) and the possible presence of sulfur dioxide (SO2) and carbon […]

Comparison of the combined exoTEDRF + Eureka! transmission spectrum to Aurora retrievals (top) and various PLATON forward models (bottom). The best-fit retrieval model is shown in the top panel with the darkness of the shading indicating the 1- and 2-σ limits, and is re-plotted in the bottom panel for comparison against the other forward models. The middle panel shows the absorption cross-sections for key molecules, which demonstrates how the spectrum is a poor fit both for CH4 and CO2. The plotted forward models include different metallicity and C/O scenarios, as well as a water-rich composition, and the inclusion of disequilibrium SO2. Forward models incorporating equilibrium chemistry are shown with dashed lines. The ‘10× Solar + SO2’ model has 108 times the equilibrium SO2 abundance as its counterpart. Offsets have been applied to the forward models at 2.8 µm to account for the best-fit offset between the NIRISS/SOSS and NIRSpec/G395M data. -- astro-ph.EP

Astronomy & Telescopes, Atmospheres, Climate, Weather, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Icy Worlds, Imaging & Spectroscopy, Status Report, Water/Hycean Worlds & Oceanography

TOI-421 b: A Hot Sub-Neptune with a Haze-Free, Low Mean Molecular Weight Atmosphere

by Keith CowingJanuary 10, 2025January 10, 2025

Common features of sub-Neptunes atmospheres observed to date include signatures of aerosols at moderate equilibrium temperatures (~500-800 K), and a prevalence of high mean molecular weight atmospheres, perhaps indicating novel […]

Stability analysis of the TOI-421 planetary system. For fixed initial conditions (Table 6), the parameter space of the system was explored by varying the orbital period Pb and the eccentricity eb of planet-b (left panel) and the eccentricities of both planets (right panel). The step size was 10−3 day in orbital period and 0.0025 in eccentricity. For each initial condition, the system was integrated over 5000 yr and a stability indicator was calculated, which involved a frequency analysis of the mean longitude of the inner planet. The chaotic diffusion was measured by the variation in the frequency (see text). Red points correspond to highly unstable orbits, while blue points correspond to orbits which are likely to be stable on a billion-years timescale. The black dots show the values of the best fit solution (Table 6). -- astro-ph.EP

Astronomy & Telescopes, Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

Characterisation Of The TOI-421 Planetary System Using CHEOPS, TESS, and Archival Radial Velocity Data

by Keith CowingApril 20, 2024

The TOI-421 planetary system contains two sub-Neptune-type planets and is a prime target to study the formation and evolution of planets and their atmospheres.