sub-Neptune Archives - Page 18 of 19 - Astrobiology

Our super-Earth models are shown in dark-blue circles, compared with a sample of observed exoplanets from the NASA Exoplanet archive with masses and radii constrained to 20% and 5% respectively. In the left-hand panel, we show the mass-radius diagram, whereas, in the right-hand panel, we show normalised density as a function of planet mass, which is the density of each planet when scaled to be 1M⊕. Grey lines represent an Earth-like density of ∼ 5.5 g cm−1 . The blue-shaded region is the inferred 1σ range in interior density from the population-level evolution analysis from Rogers & Owen (2021). The orange-shaded region is the range of plausible sizes (or densities) of sub-Neptunes hosting significant hydrogen-dominated atmospheres from Rogers et al. (2023c), which accounts for thermal evolution, including cooling and mass loss. -- astro-ph.EP

Astrogeology, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Habitable Zones, Status Report

The Imprint of Escaping Hydrogen Atmospheres on Super-Earth Interiors

by Keith CowingFebruary 23, 2024February 23, 2024

Small, close-in exoplanets are divided into two sub-populations: super-Earths and sub-Neptunes. Most super-Earths are thought to have lost their primordially accreted hydrogen-dominated atmospheres via thermally driven winds.

Artistic representation of an exoplanet whose water ice on the surface is increasingly vaporizing and forming an atmosphere during its approach to the central star of the planetary system. This process increases the measured planetary radius compared to the value the planet would have at its place of origin. CREDIT Thomas Müller (MPIA)

Astronomy & Telescopes, Exoplanets, -moons, -comets, Gas Giants, Press Release, Water/Hycean Worlds & Oceanography

Migration Solves An Exoplanet Puzzle

by Keith CowingFebruary 9, 2024February 9, 2024

Ordinarily, planets in evolved planetary systems, such as the Solar System, follow stable orbits around their central star. However, many indications suggest that some planets might depart from their birthplaces […]

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.

Radius histograms of synthetic planets with orbital periods shorter than 100 days for different model assumptions without any bias applied. For each panel, the full distribution is shown in gray and colored histograms are showing different compositional subsets (pure rocky in green, water-rich without any H/He in blue, with some H/He in red). The left panel shows the nominal model, in the middle panel water was assumed to be condensed out in a solid ice layer resistant to evaporation below H/He, and the right panel uses the nominal treatment of water but excludes evaporation. The dotted histogram shows the full distribution from the nominal simulations. As in Fig. 1, bin counts are normalized by the total number of planets in the different samples. -- astro-ph.EP

Astrogeology, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Status Report

A Radius Valley Between Migrated Steam Worlds And Evaporated Rocky Cores

by Keith CowingJanuary 11, 2024January 10, 2024

The radius valley (or gap) in the observed distribution of exoplanet radii, which separates smaller super-Earths from larger sub-Neptunes, is a key feature that theoretical models must explain. Conventionally, it […]

An exoplanet size demographics histogram up to R/R(E) = 6 (R: radius, R(E): Earth’s radius; bottom) shown together with the implications of our experiments on the radius cliff (top). Schematic diagrams for the structures of sub-Neptunes with P (AMB) < 15 GPa and P (AMB) > 25 GPa are shown (AMB: atmosphere-magma boundary). In the histogram, three horizontal bars show the estimated radii of sub-Neptunes (2 wt% H2 atmosphere with an Earth-like interior composition) for different pressures (in GPa) at the atmosphere-magma boundary (see Text 5 for method). -- astro-ph.EP

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

Stability Of Hydrides In Sub-Neptune Exoplanets With Thick Hydrogen-Rich Atmospheres

by Keith CowingJanuary 8, 2024January 8, 2024

Many sub-Neptune exoplanets have been believed to be composed of a thick hydrogen-dominated atmosphere and a high-temperature heavier-element-dominant core.

Future radii of planets b, c, d at an age of 5 Gyr. The current radii of planets c, d and b are shown as dashed lines, together with the current and final radii for a range of planetary masses for the outer two planets d and b; the core is represented by a black circle, while the envelope is shown as a colored circle around the core. The core size increases with increasing mass. Note that the size scaling of the envelope compared to the core is arbitrary. It is chosen such that one can easily compare present and final planetary radii and immediately see, which configuration can hold on to some fraction of the envelope and remain above the gap. While the outermost planet b will retain enough envelope to remain well above the radius gap around 1.8 R⊕ for all masses considered, we find that for planet d there is an intermediate mass range between ∼7 to 18 M⊕, for which planets can retain an envelope and survive above the gap. Lower mass planets will experience enough mass loss to completely lose their envelope, while higher mass planets only have very thin envelopes at present age to match the observed radius due to their larger core size, that their thin envelope is easily lost, in spite of their large mass. Planet c is assumed to be rocky at present and will not change its size significantly. The current radius of planet c matches well with the radii predicted for Earth-like rocky cores in the mass regime of 3-5 M⊕. -- astro-ph.HE

Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Habitable Zones, Status Report

Three Young Planets Around The K-dwarf K2-198: High-energy Environment, Evaporation History And Expected Future

by Keith CowingNovember 15, 2023November 15, 2023

Planets orbiting young stars are thought to experience atmospheric evaporation as a result of the host stars’ high magnetic activity. We study the evaporation history and expected future of the […]

The pebble surface density for scenario 1 (top) and scenario 2 (bottom) is depicted for different α-viscosities, dependent on disk radius and time. In each case, the red vertical line denotes the water-ice line, and the green line marks the position of the gas giant, if present. In the scenario with a gas giant, the accumulation of blocked pebbles exterior to the gas giant’s position is visible. Further accumulations within the water-ice line result from the recondensation of outwardly diffusing gas at different evaporation lines. -- astro-ph.EP

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

Constraining The Formation History Of The HAT-P-11 System By Atmospheric Abundances

by Keith CowingOctober 23, 2023October 20, 2023

The chemical fingerprint of a planet reveals information about its formation history regarding when and where it formed. The water content of a planet can help to constrain its formation […]

AI - Data - Apps - Cybernetics, Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Status Report

Modelling Non-Condensing Compositional Convection for Applications to Super-Earth and Sub-Neptune Atmospheres

by Keith CowingOctober 13, 2023October 13, 2023

Compositional convection is atmospheric mixing driven by density variations caused by compositional gradients. Previous studies have suggested that compositional gradients of atmospheric trace species within planetary atmospheres can impact convection […]

Water detection in the transmission spectrum of GJ 9827 d. Transmission spectrum of GJ 9827 d (black points) shown with our model transmission spectra constraints from the nested sampling atmosphere retrieval (blue) and from the photometry-informed “transit light-source effect” retrieval (orange). The dark blue and light blue shaded regions show the 1σ and 2σ Bayesian credible intervals from the atmosphere retrieval respectively. The atmospheric median transmission model is shown in blue and the best-fitting model is shown in red. The best-fitting TLS model is shown in orange along with the 1σ and 2σ Bayesian credible intervals in light orange. -- astro-ph.EP

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

Water Absorption In The Transmission Spectrum Of The Water-world Candidate GJ9827d

by Keith CowingSeptember 21, 2023September 21, 2023

Recent work on the characterization of small exoplanets has allowed us to accumulate growing evidence that the sub-Neptunes with radii greater than ∼2.5R⊕ often host H2/He-dominated atmospheres both from measurements […]

Evolution of the s-BGLS periodogram of the CARMENES, HIRES, and HARPS RV data around 36 d (left) and in the region between 90 d and 130 d (right). The periodograms were generated using the residuals after subtracting the respective other periodicity, namely, the 113-d period in the left panel and the 36-d signal in the right panel. Both s-BGLS periodograms include the stellar rotation period. The colorbar on the top shows the Bayesian probability, where higher values are more likely. The right side of each plot indicates the instrument from which the individual added data points originate. -- astro-ph.EP

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

The CARMENES Search For Exoplanets Around M Dwarfs. A Sub-Neptunian Mass Planet In The Habitable Zone Of HN Lib

by Keith CowingMay 31, 2023May 31, 2023

We report the discovery of HN Lib b, a sub-Neptunian mass planet orbiting the nearby (d≈ = 6.25 pc) M4.0 V star HN Lib detected by our CARMENES radial-velocity (RV) […]