snowline Archives - Astrobiology

Model prediction for the water budget of the 4 terrestrial planets

Astrochemistry, Astrogeology, Biogeochemical Cycles & Geobiology, Habitable Zones, Mars, Mercury, Status Report, Venus

Astrochemical Inheritance of Terrestrial Planets Water from Local Wet Silicates

by Keith CowingMay 1, 2026May 5, 2026

The delivery of water to the inner Solar System rocky planets, including Earth, remains debated, as standard models assume that they formed from dry grains, inside the snowline of the […]

[LEFT] Final planet mass vs pebble flux across the snowline at time of insertion. Plots A and B are coloured by the planet’s initial and final semi-major axes respectively. Plot C is coloured by the planet’s insertion time 𝑡0, and plot D is coloured by the characteristic disk radius 𝑅0. Plot E is coloured by the disk’s 𝛼 parameter, and plot F is coloured by the fragmentation velocity 𝑣frag. All plots contain outlined numbered points, which correspond to the points numbered in Fig. 2. [RIGHT Final planet mass vs pebble flux across the snowline at 1 Myr. Plots A and B are coloured by the planet’s final and initial semi-major axes respectively. Plot C is coloured by the planet’s insertion time 𝑡0, and plot D is coloured by the characteristic disk radius 𝑅0. Plot E is coloured by the disk’s 𝛼 parameter, and plot F is coloured by the fragmentation velocity 𝑣frag. All plots contain outlined numbered points, which correspond to the points numbered in Fig. 2. -- astro-ph.EP

Astrochemistry, Astrogeology, Comets and Asteroids, Exoplanets, -moons, -comets, Status Report

Simulating The Interplay Between The Snowline Pebble Flux And Ongoing Planet Formation And Migration

by Keith CowingApril 18, 2026April 18, 2026

Pebble drift plays a central role in modern planet formation models. In this work we carry out planet formation simulations (including pebble accretion and migration) for a range of disc […]

Sum of water mass accreted by planets in the habitable zone of their respective stars (color lines) and disk mass fraction along the x-axis. Circle size represents average protoplanet mass among each habitable zone containing 6 to 8 protoplanets. The highest mass protoplanets are also the most water-rich and occur in the middle-mass architecture, while the high-mass architecture is unable to deliver water to protoplanets in the habitable zone (truncated from the plot are models where total water mass < 10−8M⊕). The low-mass architecture features a mix of water and protoplanet mass

Astrochemistry, Astrogeology, Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Habitable Zones, Icy Worlds, Imaging & Spectroscopy, Status Report

Diversity In Planetary Architectures From Pebble Accretion: Water Delivery To The Habitable Zone With Pebble Snow

by Keith CowingSeptember 18, 2025September 18, 2025

“Pebble snow” describes a planet formation mechanism where icy pebbles in the outer disk reach inner planet embryos as the water ice line evolves inward.

Envelope H2O mass fraction as a function of semi-major axis. The same dataset as in Figure 1 is shown. The left panel shows planets that predominantly formed inside the water ice line; the right panel shows those that formed outside. Classification is based on the accreted H2O mass fraction, with a threshold set at 5% of the total planetary mass. The colorbar indicates the molar bulk C/O ratio. Planets formed inside the ice line are systematically depleted in carbon due to the lack of volatile ice accretion and exhibit higher envelope H2O mass fractions. In contrast, planets formed beyond the ice line retain lower H2O content despite higher bulk volatile abundances. Each pie chart shows the mean mass fraction of hydrogen in H2 (gas), H (metal), H2 (silicate), H2O (gas), and H2O (silicate), normalized to the total mean hydrogen inventory for each population. Only components contributing more than 5% are labeled. Planets that formed beyond the ice line store most hydrogen as H2 (gas) and H (metal), while those that formed inside the ice line retain a larger share of hydrogen in H (metal) H2 (silicate) and H2O (gas + silicate). -- astro-ph.EP

Astrochemistry, Astrogeology, Atmospheres, Climate, Weather, Biochemistry & Organic Chemistry, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Ice Giant, Icy Worlds, Status Report, Water/Hycean Worlds & Oceanography

Sub-Neptunes Are Drier Than They Seem: Rethinking the Origins of Water-Rich Worlds

by Keith CowingJuly 3, 2025July 3, 2025

Recent claims of biosignature gases in sub-Neptune atmospheres have renewed interest in water-rich sub-Neptunes with surface oceans, often referred to as Hycean planets.

Schematic illustrating transport mechanisms of volatiles that produce the C/H enhancement seen within the CO snowline in HD 163296 as observed by Zhang et al. (2020). The process begins in the outer disc with dust growing to pebbles as the CO and water vapour freeze out onto the pebbles. As the grains grow, they decouple from the gas and drift inwards towards the CO snowline; within the snowline, the CO sublimates and enhances the C/H ratio of the gas and vapour present; the CO vapour is transported to the upper layers of the disc via diffusion. It also advects inwards, indicated by the grey arrows. Water ice remains on the pebbles and is transported further inward as the pebbles continue to drift toward the water snowline, which is around 1 AU in our model in this paper. Here, water sublimates and becomes readily available for planet formation in the region where terrestrial planets may be forming. Note that the illustrated emission line probe region is specific to CO rotational lines in this context. This schematic was inspired by Fig. 2 of Cuzzi & Zahnle (2004). -- astro-ph.EP

Astrochemistry, Astrogeology, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Interstellar, Status Report

The CO-Fuelled Time Machine: Tracing Birth Conditions and Terrestrial Planet Formation Outcomes in HD 163296 through Pebble Drift-induced CO Enhancements

by Keith CowingJanuary 11, 2025January 11, 2025

The architecture and composition of planetary systems are thought to be strongly influenced by the transport and delivery of dust and volatiles via ices on pebbles during the planet formation […]

WASP-77 A b is a gas giant exoplanet that orbits a G-type star. Its mass is 1.667 Jupiters, it takes 1.4 days to complete one orbit of its star, and is 0.02335 AU from its star. -- NASA

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

The Wanderer: Charting WASP-77A b’s Formation and Migration Using a System-Wide Inventory of Carbon and Oxygen Abundances

by Keith CowingSeptember 6, 2024September 6, 2024

The elemental and isotopic abundances of volatiles like carbon, oxygen, and nitrogen may trace a planet’s formation location relative to H2O, CO2, CO, NH3, and N2 “snowlines”, or the distance […]

Thermal desorption of a mixed H2O:CO2:CO ice film at 100:15:5 ratio recorded during a Temperature Programmed Desorption (TPD) experiment, where the release of each molecule is measured with a mass spectrometer. Carbon monoxide was traced with the 13CO isotope. Four distinct release events are visible: pure-phase CO (1), pure-phase CO2 with CO co-desorbing (2), volcano desorption of CO and CO2 (3), and water desorption with co-desorption of CO and CO2 (4). Desorption and trapping fractions of volatiles can be determined by integrating the TPD trace over discrete temperature ranges. The data are adapted from Kipfer et al. (2024a). -- astro-ph.EP

Astrochemistry, Astrogeology, Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Icy Worlds, Imaging & Spectroscopy, Status Report

Mind the Trap: Non-negligible Effect of Volatile Trapping in Ice on C/O Ratios in Protoplanetary Disks and Exoplanetary Atmospheres

by Keith CowingJune 27, 2024June 27, 2024

The ability of bulk ices (H2O, CO2) to trap volatiles has been well studied in any experimental sense, but largely ignored in protoplanetary disk and planet formation models as well […]

Left: C/O as a function of projected separation or semi-major axis for the eight companions in this study. The points are sized by companion mass, using the mass legend in the right panel. The blue line and region show the solar C/O value from Asplund et al. (2021). Right: In color: 1σ contours of C/O and [C/H] for the eight companions, which are all consistent with solar composition (intersection of dashed gray lines) to the 2σ level. In § 6.4.1, we justify that their host stars likely have solar composition as well. We overplot hot Jupiters which have abundance measurements for at least one oxygen-bearing and one carbon-bearing species from JWST or high-resolution spectroscopy as black points (Alderson et al. 2023; August et al. 2023; Bean et al. 2023; Bell et al. 2023; Brogi et al. 2023; Finnerty et al. 2024; Xue et al. 2024), which are also sized by mass. The hot Jupiters show considerable scatter and super-solar (and super-stellar) metallicities except for one planet, unlike our companions which cluster around solar (and stellar) composition. -- astro-ph.EP

Astronomy & Telescopes, Atmospheres, Climate, Weather, Biochemistry & Organic Chemistry, Brown Dwarfs, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report, Stellar Cartography

Are These Planets Or Brown Dwarfs?

by Keith CowingJune 3, 2024June 3, 2024

Using Keck Planet Imager and Characterizer (KPIC) high-resolution (R~35000) spectroscopy from 2.29-2.49 μm, we present uniform atmospheric retrievals for eight young substellar companions with masses of ~10-30 MJup, orbital separations […]

Dust temperature in our models turning on and off the viscous heating. The blue line is an isothermal contour at T = 115 K in the model with viscous heating added and the cyan the same isothermal contour in the model without viscous heating. We use 115 K as the temperature at which Cieza et al. (2016) locate the spectral index shift in V883 Ori. Left: Image with viscous heating. Right: Image without viscous heating. We observe in the images that when we add viscous heating the snowlines get shifted by almost 20 au. -- astro-ph.SR

Astrochemistry, Astronomy & Telescopes, Comets and Asteroids, Exoplanets, -moons, -comets, Status Report

Viscous Heating As The Dominant Heat Source Inside The Water Snowline Of V883 Ori

by Keith CowingDecember 27, 2023December 27, 2023

FU Orionis-type objects(FUors) are embedded protostars that undergo episodes of high accretion, potentially indicating a widespread but poorly understood phase in the formation of low-mass stars.

NH3-H2O co-deposition experiments. All experiments have been performed on a gold substrate. The TPDs have a ramp of 0.2K/s. The solid lines represent the desorption of NH3 while the dashed-dotted lines represent the desorption of water. Lines of the same colour belong to the same set of experiments. Inset: TPD of NH3 from a gold surface used to calibrate all the consequent experiments. -- astro-ph.SR

Astrochemistry, Astrogeology, Biochemistry & Organic Chemistry, Comets and Asteroids, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Interstellar, Status Report

Experimental Study Of The Binding Energy Of NH3 On Different Types Of Ice And Its Impact On The Snow Line Of NH3 And H2O

by Keith CowingDecember 3, 2023December 2, 2023

N-bearing molecules (like N2H+ or NH3) are excellent tracers of high-density, low-temperature regions like dense cloud cores and could shed light into snowlines in protoplanetary disks and the chemical evolution […]