L 98-59 d Archives - Astrobiology

The Cosmic Shoreline. Light-green dots are all known exoplanets with reported atmospheric detections from the ExoAtmospheres database, noting that some of these detections are tentative or remain contested in the literature (e.g., GJ 1132 b). Solar System objects are marked as black crosses or green triangles if they host an atmosphere. The red dashed line is the cosmic shoreline as defined by Zahnle & Catling (2017). The black dotted is the same classical line, preserving the slope, but taking as zero point the exoplanet 55 Cnc e. The black dashed-dotted line is our newly proposed Empirical Exoplanet Cosmic Shoreline (EECS), which makes use of both Mars and several exoplanet atmospheric detections to define the slope and zero-point value. The numbers highlighted in the inset show the names of the seven planets discussed in the definition of the EECS. -- astro-ph.EP

An Empirical Determination Of The Cosmic Shoreline

by Keith CowingJune 23, 2026June 23, 2026

The cosmic shoreline concept was introduced to separate planets with atmospheres from those without, by relating the cumulative X-ray and extreme-ultraviolet (XUV) instellation (integrated over the planet’s lifetime) to the […]

Additional analysis for the tentative cross-correlation signal observed for H2S. We show the cross-correlation S/N as a function of the orbital parameters of the planet. In each case, the expected parameters are marked with crosshairs. Left: The S/N is shown as a function of planetary velocity space, parameterised by 𝐾p and 𝑉sys, reproduced from the top panel of Figure 3 but with a more zoomed in colorscale. A tentative peak with a S/N of 1.7 is observed at the expected systemic velocity. Right: the time duration of the observed H2S cross-correlation signal is constrained with a value that is consistent with the literature value for the transit duration of the planet. This is measured by varying the number of spectra considered to be in-transit (𝑁in) when calculating the cross-correlation S/N, with 𝐾p fixed to that expected for this planet. -- astro-ph.EP

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

Ground-based Atmospheric Characterization of Super-Earth L 98-59 d at High Spectral Resolution

by Keith CowingMarch 8, 2026March 8, 2026

Atmospheric characterization of exoplanets using ground-based high-resolution transmission spectroscopy has traditionally focussed on large and close-in planets, such as hot Jupiters.

Family portrait of the five planets in the L 98-59 system showing their transit (or absence of transit) observed by TESS in the top panels and their Doppler signature from HARPS (red circles) and ESPRESSO (white/black circles for pre/post data) in the bottom panels. Only the error bars for ESPRESSO are shown to improve visibility. Black curves represent best-fit models from the transit analysis (top) and joint RV–TTV fit (bottom, using fixed orbital inclinations, see Sect. 4.5). For L 98- 59 e and f, 1000 predicted transit curves are shown in red using posterior samples from the RV–TTV fit and radii estimated from their minimum masses using spright (Parviainen et al. 2024). Planets e and f do not transit L 98-59. -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Status Report

Detailed Architecture Of The L 98-59 System And Confirmation Of A Fifth Planet In The Habitable Zone

by Keith CowingJuly 16, 2025July 16, 2025

The L 98-59 system, identified by TESS in 2019, features three transiting exoplanets in compact orbits of 2.253, 3.691, and 7.451 days around an M3V star, with an outer 12.83-day […]

Modelled planetary bulk-density over time. The initial hydrogen inventory of each bulk-density evolution track is shown by the line colour. Blue/green shaded regions are reference densities for a planet of this mass (Zeng et al., 2019). Black dashed/dotted lines demarcate edges of the radius valley (at this planet mass) for low mass stars (Ho et al., 2024). The region ±1σ compatible with the estimated bulk-density of this planet is indicated by the blue errorbar (Rajpaul et al., 2024; Demangeon et al., 2021). Top panel: evolution of surface temperature (coloured) and stellar XUV energy flux (black). For visual clarity, this figure only shows cases with S/H=8. -- astro-ph.EP

Exoplanets, -moons, -comets, Status Report

Volatile-rich Evolution Of Molten Super-Earth L 98-59 d

by Keith CowingJuly 7, 2025September 18, 2025

Small low-density exoplanets are sculpted by strong stellar irradiation but their origin is unknown.

Simulated behaviour of L 98-59 b calculated with a semi-analytic toy model for its thermal evolution. Temperature is plotted over time for different initial temperatures 𝑇0 (line style) and tidal heating amplitudes 𝐹𝑐 (line colour). The shaded region shows the temperature regime in which tidal heating is significant, via Equation A5. The black line shows the temperature at which tidal heating is maximised. The dotted blue line shows the pureradiative equilibrium temperature. astro-ph.EP

Astrogeology, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Lava / magma ocean / Volcanic Worlds, Status Report

Self-limited Tidal Heating And Prolonged Magma Oceans In The L 98-59 System

by Keith CowingMay 14, 2025May 14, 2025

Rocky exoplanets accessible to characterisation often lie on close-in orbits where tidal heating within their interiors is significant, with the L 98-59 planetary system being a prime example.

This plot shows the retrieved spectra from the main retrieval scenarios of stellar inhomogeneities with planetary atmospheres and stellar inhomogeneities only extended to the 0.6 - 12 µm JWST wavelength range. The gas contributions for H2S and SO2 are highlighted. The available wavelength ranges for different JWST instruments are marked on the top of the plot. Several H2S features in the NIRISS SOSS range, combined H2S and SO2 features in NIRSpec G395H range, and SO2 features in the MIRI LRS range may be detectable in future observations. -- astro-ph.EP

Astrochemistry, Astronomy & Telescopes, Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Lava / magma ocean / Volcanic Worlds, Status Report

Atmospheric Retrievals Suggest The Presence of a Secondary Atmosphere and Possible Sulfur Species on L 98-59 d from JWST NIRSpec G395H Transmission Spectroscopy

by Keith CowingNovember 4, 2024November 4, 2024

L 98-59 d is a Super-Earth planet orbiting an M-type star. We performed retrievals on the transmission spectrum of L 98-59 d obtained using NIRSpec G395H during a single transit, […]

100 TO These plots show the range of outcomes for oxygen accumulation (top row, green) and water retention (bottom row, blue) for the set of simulations with 100 TO initial water content on each of the planets. The distributions for the water behavior can be found in Figure 6, bottom row. Given 100 TO, all three planets are likely to retain water past 1 Gyr, making observations of water relatively likely. In addition, thousands of bars of oxygen may be produced for each planet in this scenario. Details on planet b’s behavior, similar to Figure 3, are given in Section 4. -- astro-ph.EP

Astronomy & Telescopes, Atmospheres, Climate, Weather, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Status Report

Atmospheric Escape From Three Terrestrial Planets In The L 98-59 System

by Keith CowingDecember 4, 2023December 3, 2023

A critically important process affecting the climate evolution and potential habitability of an exoplanet is atmospheric escape, in which high-energy radiation from a star drives the escape of hydrogen atoms […]