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Forming Worlds Lab @formingworlds.space · 15/09/2026

🌍✨ Last week, the FormingWorlds group attended the Europlanet Science Congress (#EPSC2026) in The Hague. We had a great time with Karen Stuitje, Saphira Brandenberger, @marianasastre.bsky.social, Emeline Decocq, @marattia.bsky.social, Lorenzo Cesario, Ema Jungová & @timlichtenberg.bsky.social!

The FormingWorlds research group smiling together at the Europlanet Science Congress 2026 in The Hague. Eight members are standing in a conference venue hall.

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Forming Worlds Lab @formingworlds.space · 08/09/2026

So the same mass and radius can be two different planets. WASP-47 e and TOI-1807 b each admit two purely rocky solutions, identical in mass and radius: one fully solid, one with a deep magma ocean on a liquid iron core.

$Two panels, one for the super-Earth WASP-47 e and one for TOI-1807 b. Each plots iron core mass fraction against mantle potential temperature, with colour showing the resulting planet radius from blue at small radii to red at large ones. A black contour of constant radius, the measured value, curves across each panel, and two starred points sit on it: solution A at low temperature and a small core, solution B at high temperature and a much larger core. Both give the same radius.$ Mass-radius curves from a tenth of an Earth mass to a hundred Earth masses, drawn for four mantle temperatures from 300 to 4000 K and three compositions: Earth-like, ten per cent water and fifty per cent water. Curves for hotter interiors sit above cooler ones at the same mass, and the gap between temperatures is comparable to the gap between compositions.

Mass-radius curves from a tenth of an Earth mass to a hundred Earth masses, drawn for four mantle temperatures from 300 to 4000 K and three compositions: Earth-like, ten per cent water and fifty per cent water. Curves for hotter interiors sit above cooler ones at the same mass, and the gap between temperatures is comparable to the gap between compositions.

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Forming Worlds Lab @formingworlds.space · 08/09/2026

Accepted earlier this year in A&A, work led by Mara Attia (@marattia.bsky.social) tackles a core problem in exoplanet interiors: "PALEOS: Multiphase equations of state and mass-radius relations for exoplanet interiors" 🌍 Read: arxiv.org/abs/2605.03741 #Exoplanets

Portrait of Mara Attia with an overlaid white card displaying the title 'PALEOS: Multiphase equations of state and mass-radius relations for exoplanet interiors' and author names.

Screenshot of the paper abstract detailing how internal temperature shifts the mass-radius relationship of rocky exoplanets.

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Forming Worlds Lab @formingworlds.space · 28/08/2026

The phase curve shows a high Bond albedo and moderate global heat transport. When you feed that into general circulation models, the best fit is a highly reflective atmosphere loaded with silicate clouds (like SiO2 and MgSiO3) near the dayside terminator.

Cloud mass mixing ratio and precipitation of silicate clouds on the dayside terminator

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Forming Worlds Lab @formingworlds.space · 28/08/2026

The JWST campaign on TOI-561 b, led by @johannateske.bsky.social, continues to deliver surprises! Samuel Boucher (supervised by @astrolisadang.bsky.social) just posted a new phase curve study on this lava world.

JWST phase curve from the general circulation model that best matches TOI-561 b

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Forming Worlds Lab @formingworlds.space · 24/08/2026

What the planet breathes out is a different matter. Reduced surfaces give hydrogen and carbon monoxide, oxidised ones water and carbon dioxide. Plot: outgassed composition against mantle oxidation state, for three starting water inventories. 🌍

Stacked bar chart of outgassed atmospheric composition against deep-mantle oxidation state, from four log units below the iron-wüstite buffer to four above, with three bars per state for starting water inventories of three, ten and one hundred Earth oceans. Carbon monoxide in pink and hydrogen in orange dominate the reduced and water-poor cases, while water in blue and carbon dioxide in purple take a growing share towards the oxidised end.

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Forming Worlds Lab @formingworlds.space · 24/08/2026

Earlier this summer, Mariana Sastre (@marianasastre.bsky.social) posted her first paper as lead author 🌋 "Geophysical and atmospheric implications of fO2-dependent melting on rocky exoplanets" Read the paper: arxiv.org/abs/2606.20249 #Exoplanets #PlanetaryScience

Line plot of pressure against temperature showing where mantle rock begins and finishes melting, for five oxidation states from four log units below the iron-wüstite buffer to four above. Solid lines mark the solidus and dashed lines the liquidus. The curves fan out across the plot: the most reduced case, in dark blue, melts several hundred kelvin hotter at any given pressure than the most oxidised case, in dark pink.

Portrait of Mariana Sastre, smiling, against a plain background.

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Forming Worlds Lab @formingworlds.space · 31/07/2026

The six states can be told apart. Carbon dioxide dominates the oxidised cases, ammonia the reduced ones, and methane peaks in the middle, which is what separates the two most oxidised cases. Plot: retrieved abundance of each gas, black bars for the true values.

Six-panel plot of retrieved gas abundances against mantle oxidation state, from six log units below the iron-wustite buffer to six above. Coloured points with error bars show what the retrieval recovers, short black bars the true values. Carbon dioxide is high only in the oxidised states, ammonia only in the reduced ones, methane peaks in the middle of the range, and hydrogen and nitrogen have error bars spanning many orders of magnitude.

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Forming Worlds Lab @formingworlds.space · 31/07/2026

New paper from Lorenzo Cesario 🔭 His third first-author paper, and he only finished his MSc this year. "Characterizing the oxidation state of rocky exoplanets with the Large Interferometer for Exoplanets (LIFE)" Read the paper: arxiv.org/abs/2607.28121 #Exoplanets #PlanetaryScience

Six panels of mid-infrared emission spectra from 6 to 16 microns, one per mantle oxidation state. A red line marks the true model spectrum, blue bands the one, two and three sigma retrieved ranges, grey the simulated instrument noise. The three reduced cases on the top row are smooth, sloping curves with few features; the three oxidised cases below carve deep, sharp absorption bands.

Portrait of Lorenzo Cesario, smiling, wearing a light blue shirt against a plain wall.

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Forming Worlds Lab @formingworlds.space · 29/07/2026

Pink is everything a static fit allows for surface pressure and temperature, black the evolving best fit, the ring the truth. Sub-Neptunes stay hard: core fraction and volatile budget still trade off. ⏳ Proof of concept on synthetic planets, built into PROTEUS. @kapteynastro.bsky.social

Three stacked panels, one each for the sub-Neptune, super-Earth and terrestrial test planets, plotting surface pressure in bar on an inverted logarithmic vertical axis against surface temperature from 1000 to 2500 kelvin, labelled along the bottom. Pink contours show the posterior of a static-structure retrieval; grey lines show individual evolution simulations dispatched during the evolutionary retrieval, with the best fit in black; coloured crosshairs and a ringed marker give the true answer. In every panel the pink static posterior is a long diagonal ridge that misses the true point, while the black evolutionary best fit runs close to it. Dashed lines mark the mantle solidus and the hydrogen-water demixing curve.

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Forming Worlds Lab @formingworlds.space · 29/07/2026

Retrievals fit a planet as it is now, because the model has to run thousands of times and so has to be cheap. That leaves ambiguity: a sub-Neptune's density suits a steam atmosphere over a small core about as well as a hydrogen envelope over a dense one. Figure: the three test planets.

Scatter plot of planet radius in Earth radii against orbital period in days, on a logarithmic period axis. Grey contours show the density of 2536 surveyed small exoplanets, peaking around 2 to 5 day periods and 1 to 1.5 Earth radii. Two pink lines mark empirical fits to the small-planet radius valley, one for a Sun-mass host and one for a 0.29 solar-mass host. Three ringed markers show the paper's test planets: a sub-Neptune at about 10 days and 1.9 Earth radii, above the valley, with a blue line tracking its shrinking radius from 2.4; a super-Earth at about 5 days and 1.46 Earth radii, between the two valley lines; and a terrestrial at about 2 days and 1.08 Earth radii, below them. Planets of TRAPPIST-1, L 98-59 and LP 791-18 are plotted as labelled coloured circles for context, with Earth, Venus and Mercury as black symbols at long periods.

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Forming Worlds Lab @formingworlds.space · 29/07/2026

"Constraining the lives and times of exoplanets through evolutionary Bayesian retrievals", by @nichollsh.bsky.social (@cambridgeastro.bsky.social), @timlichtenberg.bsky.social, Ben Riegler, Robb Calder and @vincefort.eurosky.social. Submitted to The Astrophysical Journal.

Portrait of Harrison Nicholls outdoors in front of a college building, wearing a grey knitted jumper and glasses.

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Forming Worlds Lab @formingworlds.space · 23/07/2026

New paper led by Joe Williams (@exeter.ac.uk), with our group among the co-authors ❄️ "Planetesimal Formation Across the Stellar Mass Spectrum and its Influence on Exoplanet-Inherited Volatile Budgets" Read the paper: arxiv.org/abs/2607.20271 #Exoplanets #PlanetaryScience

Two-panel schematic comparing how a protoplanetary disc evolves around a very low mass star and around a heavier one. The top panel, labelled 0.1 solar masses, follows a disc fed briefly by material falling in from the collapsing cloud: the disc expands, dust coagulates into icy pebbles, the pebbles drift inward and deliver their ice to the water snowline where a single generation of planetesimals forms, and the dust is then depleted, leaving grey dehydrated planetesimals. The bottom panel, labelled 0.3 solar masses and above, shows the same sequence but with a first generation of planetesimals already forming during the infall phase and a second generation later at the snowline, leaving a mix of blue water-rich and grey dehydrated bodies. A colour key marks rocky pebbles, the water sublimation front, water ice, dehydrated planetesimals and water-rich planetesimals, and an arrow along the bottom marks time running left to right.

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Forming Worlds Lab @formingworlds.space · 21/07/2026

Last week was our annual Exoplanet Summer BBQ, in Quentin Changeat's garden in Groningen: our group and his exoplanet group together for the afternoon. Lots to catch up on, the latest from Exoplanets 6 in Porto, holiday plans, and celebrating our recent BSc and MSc graduates. 🌞

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Forming Worlds Lab @formingworlds.space · 17/07/2026

Photochemistry only reshapes the thin upper layers; the bulk of the atmosphere stays where outgassing put it. Each bar is one simulated atmosphere, running from reduced mantles on the left to oxidised on the right, green hydrogen giving way to red CO2. Same story around the Sun and around GJ 1132.

Two stacked bar charts of column-averaged atmospheric mixing ratio against mantle oxygen fugacity, from reduced on the left to oxidised on the right, for a Sun-like host above and an M dwarf below. Each redox state has five bars for increasing stellar irradiation. Reduced cases are almost entirely dark green hydrogen with magenta methane on top; oxidised cases are dominated by blue water and red carbon dioxide, with orange sulfur dioxide and olive nitrogen appearing at the most oxidised end.

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Forming Worlds Lab @formingworlds.space · 17/07/2026

New paper led by Ioannis Panagiotou, his first as lead author, on arXiv ten days after he defended his MSc with us 🌋 "Sulfur photochemistry observationally traces mantle redox states of rocky planets" Read the paper: arxiv.org/abs/2607.15204 #Exoplanets #PlanetaryScience

Three stacked panels of synthetic emission spectra for a rocky planet around an M dwarf, plotting planet-to-star flux ratio in parts per million against wavelength from 1 to 15 microns. Coloured dashed vertical lines mark absorption features of water, methane, hydrogen sulfide, carbon dioxide, carbon monoxide and sulfur dioxide. In the top panel, for an intermediate mantle redox state, the black curve including photochemistry drops far below the grey mixing-only curve around 7 and 9 microns, deepening the sulfur dioxide features. The effect weakens in the middle panel and disappears in the bottom panel for the most oxidised mantle. Arrows below the x-axis mark the JWST NIRSpec and MIRI wavelength ranges.

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Forming Worlds Lab @formingworlds.space · 17/07/2026

The atmosphere is also what keeps the mantle molten, so stripping it makes the magma ocean freeze sooner instead of later. The bars show which gas dominates at the end across all 1674 simulations, sorted by orbit, mantle chemistry and host star. Mostly water and hydrogen, sometimes sulfur.

Four stacked bar panels showing which gas ends up dominating the atmosphere across a grid of simulations, as a percentage, broken down by atmosphere model, orbital separation, mantle oxygen fugacity and carbon-to-hydrogen ratio. Hatched bars are M-dwarf hosts, solid bars Sun-like. Water (light blue), hydrogen (grey) and carbon monoxide (red) are the most common outcomes, with carbon dioxide, hydrogen sulfide, sulfur dioxide and elemental sulfur also appearing. Reduced mantles at the bottom of the third panel give mostly hydrogen and carbon monoxide; oxidised mantles at the top give water and carbon dioxide.

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Forming Worlds Lab @formingworlds.space · 17/07/2026

New paper led by Emma Postolec, her first as lead author, PhD student at @kapteynastro.bsky.social 🌋 "Atmospheric evolution through outgassing and escape on young molten rocky exoplanets" Read the paper: arxiv.org/abs/2607.15011 #Exoplanets #PlanetaryScience

$Six panels tracking an Earth-size planet at 0.1 astronomical units from a Sun-like star over ten thousand to ten million years, comparing a model with hydrodynamic atmospheric escape (solid lines) against one without (dashed). In the escape case the atmospheric mass falls to zero and is labelled 'Atmosphere is lost', the mantle melt fraction collapses to 'Mantle solidified', and surface temperature drops sharply. Without escape the atmospheric mass instead grows, labelled 'Atmosphere is retained', and the mantle stays molten in a 'Permanent magma ocean'. Further panels show surface volatile partial pressures, a carbon-dioxide-dominated atmosphere, and the interior volatile partitioning.$ Portrait of Emma Postolec.

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Forming Worlds Lab @formingworlds.space · 16/07/2026

An oxidised, Earth-like interior just deflates steadily instead. Across the population, whether a super-Earth reflates traces its deep chemistry and how it formed. 🔭 Plot: each line a simulated planet's density; red reflate, blue don't, a dot marks a stripped world.

Line plot of normalised bulk density against time since planet formation for many simulated close-in super-Earths. Blue tracks (deflation) dip early then stay flat; red tracks (reflation) rise into a shaded band marking lower bulk density and larger transit radius, several spiking sharply hundreds of millions to billions of years after formation before ending at complete atmospheric erosion. A bold red curve labelled R shows a reflation phase then a final erosion phase; a bold blue curve labelled D stays low.

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Forming Worlds Lab @formingworlds.space · 16/07/2026

New paper led by Lorenzo Cesario, his second first-author paper from his MSc 🌍 Some close-in super-Earths puff their atmospheres back up late in life instead of only shrinking. We call it reflation. Read the paper: arxiv.org/abs/2607.13793 #Exoplanets #PlanetaryScience

Schematic comparing oxidised (blue, top) and reduced (red, bottom) super-Earth atmospheres evolving over time. Three planets shrink from left to right under XUV irradiation arrows driving escape to space. Reduced atmospheres are rich in CO and hydrogen with water; oxidised atmospheres in CO2, CO and water, with SO2 appearing later. The reduced planet swells before shrinking, illustrating the reflation mechanism.

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Forming Worlds Lab @formingworlds.space · 13/07/2026

Ioana built a thermal-escape (Jeans) module and let starlight break molecules apart. Composition decides the outcome: hydrogen-rich air is the most vulnerable, CO₂ and nitrogen the most robust, and photodissociation leaves atomic hydrogen as the main gas slipping away.

Portrait of Ioana Balint, a Forming Worlds Lab BSc graduate, smiling on a stone seawall with the sea and a cloudy sky behind her. She has long dark auburn hair and round glasses, and wears a black jacket.

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Forming Worlds Lab @formingworlds.space · 13/07/2026

Malina traced when atmospheric escape hits a natural brake, the radiation-recombination limit. Light hydrogen and water envelopes pour away freely; heavier CO₂ and nitrogen air runs into the brake, which then governs loss from every sub-Neptune and the larger super-Earths.

Portrait of Malina Ovesen, a Forming Worlds Lab BSc graduate, smiling in front of a green hedge. She has long strawberry-blonde hair and wears a dark blazer over a cream turtleneck.

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Forming Worlds Lab @formingworlds.space · 13/07/2026

🎓 Congratulations to three bachelor's graduates in the Forming Worlds Lab: Malina Ovesen, Ioana Balint and Viesturs Streľčs, who defended their BSc theses last week at @kapteynastro.bsky.social. All from one group project on how planets lose their air to space. 🔭 #Exoplanets #PlanetaryScience

Four members of the Forming Worlds Lab stand smiling under a yellow parasol on a sunny terrace at the Kapteyn Institute in Groningen, with university buildings and green trees behind them. Two of them hold small wrapped gifts. Left to right: co-supervisor Mara Attia, BSc graduate Viesturs Streľčs, project member Renske Beuker, and group leader Tim Lichtenberg.

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Forming Worlds Lab @formingworlds.space · 10/07/2026

Big congratulations to Harrison Nicholls (@nichollsh.bsky.social) 🎓 Two prizes for his PhD on the climates of rocky worlds: the Second Thesis Prize 2026 from the @iop.org Computational Physics Group, and Highly Commended for the UK Planetary Forum Early Career Medal.

Harrison Nicholls smiling on a college rooftop, holding a bottle of prosecco. He is wearing formal academic dress: a dark suit, white shirt and black bow tie, with a dark gown over his shoulders. Behind him are slate college roofs, a spire and a partly cloudy sky.

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Forming Worlds Lab @formingworlds.space · 09/07/2026

Two Forming Worlds researchers are at Origins 2026 in Paris this week, the ISSOL astrobiology conference. Emeline Decocq and Anna Grace Ulses brought posters: one on the earliest Earth, one on false alarms for life on other worlds. With @kapteynastro.bsky.social 🔭 #PlanetaryScience #Astrobiology

Emeline Decocq (left) and Anna Grace Ulses (right) of the Forming Worlds Lab stand smiling beside their scientific posters at the Origins 2026 astrobiology conference in Paris. Decocq's poster is titled "Redox sensitivity of the surface conditions and climate state of the Hadean Earth." Ulses's poster is on the plausibility of abiotic oxygen accumulation in low non-condensable terrestrial atmospheres.

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Forming Worlds Lab @formingworlds.space · 06/07/2026

4/ Both mid-flow during their defence talks. 🔭🌋 Lorenzo on observing ultra-short-period super-Earths with ESA's Ariel mission; 🌋⚛️ Ioannis on sulfur photochemistry in hot rocky worlds.

Lorenzo Cesario giving his MSc defence talk, standing beside a projector screen showing his 'Conclusions' slide on ultra-short-period super-Earths and the Ariel mission.

Ioannis Panagiotou giving his MSc defence talk, standing beside a projector screen showing a slide titled 'Magma Oceans and Outgassed Atmospheres'.

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Forming Worlds Lab @formingworlds.space · 06/07/2026

3/ 🌋⚛️ Ioannis Panagiotou: sulfur photochemistry linking hot rocky planets' interiors and atmospheres, with SO₂ a JWST-detectable tracer of mantle redox (PROTEUS + VULCAN). Co-supervised by @nichollsh.bsky.social and @exoshami.bsky.social. In prep for A&A.

Ioannis Panagiotou in a black shirt holds his printed MSc thesis and stands next to Tim Lichtenberg, both smiling, in front of a framed deep-field astronomy image.

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Forming Worlds Lab @formingworlds.space · 06/07/2026

2/ 🔭🌋 Lorenzo Cesario: an optimal strategy for observing ultra-short-period super-Earths with ESA's Ariel mission (PROTEUS + TauREx), co-supervised by Quentin Changeat. Now being written up for publication.

Three people in front of a framed deep-field astronomy image. Left: Quentin Changeat. Centre: Lorenzo Cesario holding his printed MSc thesis. Right: Tim Lichtenberg.

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Forming Worlds Lab @formingworlds.space · 06/07/2026

1/ Two new master's graduates in the Forming Worlds Lab! 🎓 Congratulations to Lorenzo Cesario and Ioannis Panagiotou, who both defended their MSc theses today at @kapteynastro.bsky.social with excellent work. What they did 👇 🔭 #Exoplanets #PlanetaryScience

Three people smiling in front of a framed deep-field astronomy image. Left: Ioannis Panagiotou in a black shirt holding his printed thesis. Centre: Tim Lichtenberg holding a bouquet of flowers. Right: Lorenzo Cesario in a light blue shirt holding his printed thesis.

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Forming Worlds Lab @formingworlds.space · 03/07/2026

🪐 Emma Postolec: how escape to space vs volatiles locked in a cooling magma ocean set a young planet's air. 🪐 Imre Kisvárdai: is GJ 9827 d really a 'steam world'? Its low density points to a hydrogen-rich, reduced world.

Imre Kisvárdai stands smiling beside his poster (no. 3) on the sub-Neptune GJ 9827 d at the Exoplanets 6 conference in Porto.

Emma Postolec gives a thumbs-up beside her poster (no. 105) on atmospheric outgassing and escape on molten rocky exoplanets at the Exoplanets 6 conference in Porto.

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Forming Worlds Lab @formingworlds.space · 03/07/2026

That's a wrap on #Exoplanets6 in Porto 🇵🇹 The Forming Worlds Lab brought four posters, all using our open PROTEUS model to link a rocky world's interior (magma ocean, redox, outgassing, escape) to what JWST can observe. Featuring @marianasastre.bsky.social, @nichollsh.bsky.social & team 👇

Emma Postolec, Imre Kisvárdai, Mariana Sastre and Harrison Nicholls of the Forming Worlds Lab stand smiling in front of a large orange exo6 sculpture outside the Alfândega do Porto, venue of the Exoplanets 6 conference.

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Forming Worlds Lab @formingworlds.space · 03/07/2026

Hello, and welcome! 👋 We're the Forming Worlds Lab at @kapteynastro.bsky.social, @rug.nl. We study how rocky planets form and evolve, and what makes a world habitable, from magma oceans 🌋 to the skies of distant exoplanets 🪐, and we build the open-source PROTEUS framework our science runs on. 🔭

Around eighteen members of the Forming Worlds Lab together outdoors on a paved terrace, with trees and a university building behind them, at the University of Groningen.

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