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Exoplanet demographic surveys provide a unique window into planet formation and evolution. In this talk, I will showcase three distinct features in the exoplanet population and offer theoretical interpretation of the physical mechanisms that sculpt them. I will first highlight what recent measurements extending the exoplanetary census beyond the solar neighborhood can tell us about how planet formation has evolved over cosmic time. Second, I will explore the origins of “desert dweller” planets that reside deep in the “sub-Jovian desert” (2 < Rp < 10 R_Earth, periods < 3 days), a region sparsely populated but no longer empty thanks to recent surveys. I will show that “desert dwellers” may serve as laboratories to study the fate of hot Jupiters and the interiors of giant planets in exquisite detail. Lastly, I will discuss the role atmospheric photoevaporation plays in carving the orbital period distribution of puffy, gas-rich sub-Saturns; in this picture, the sub-Saturn orbital period distribution can be leveraged to estimate a fundamental property of the planet population – the core mass function of gas-rich planets. I will outline the observational implications of our theoretical work throughout the talk.

• Speaker: Timothy Hallatt (MIT)
• Tuesday 17 June 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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Observations of debris disks provide unique insight into the environments in which planetary systems form and evolve. Debris disks are planetary systems containing planets, planetesimals, and dust. Collisions among these bodies produce observable secondary gas and dust which act as tracers for a host of processes with in the disk. JWST is revolutionizing our understanding of debris disks through exquisitely sensitive, high angular resolution near- to mid-infrared observations. I will present highlights from Cycle 1 programs including the discovery of (1) large, recent collisions in the archetypal beta Pic debris disk, (2) water ice in exo-Kuiper Belts, and (3) hot, florescent CO gas in young (

• Speaker: Christine Chen, STScI
• Wednesday 11 June 2025, 10:00-11:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Max Sommer.

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Impacts by icy bodies likely played a key role in shaping the composition, and habitability, of Solar-System planets. We determine the role they may play in exoplanetary systems by coupling a cometary impact model with a 3D, Earth-analogue, climate model. I will discuss how both the impact-delivered water and thermal energy affects the global climate and composition, including: i) a modified cloud greenhouse effect and planetary albedo, ii) an enhancement in the abundance of most oxygen-bearing molecules (bar ozone), and iii) an enhancement in the escape rate of hydrogen from the exosphere. I will describe how these responses are shaped by atmospheric circulations driven by the planetary orbital configuration, including the role that impact location plays in setting the vertical transport and hence hydrogen escape rate. Finally, I will quantify the potential observability of individual massive impacts in future observations of exo-Earths.

• Speaker: Felix Sainsbury-Martinez (Leeds)
• Tuesday 10 June 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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Detecting signatures of planet formation in protoplanetary disks is essential for understanding how and where planets form. In this talk, I will summarise the various fingerprints of planets on the distribution of gas and dust solids in protoplanetary disk, and present Dust and gas observations of the disk around 2MASS J16120668 -301027, studied as part of the ALMA Large Program ‘AGE-PRO: ALMA Survey Of Gas Evolution in Protoplanetary Disks’, where several indicator of planet formation were recently identified in dust dust continuum emission and for molecular lines

• Speaker: Anibal Sierra (UCL)
• Tuesday 03 June 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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Gaps and rings are ubiquitous in observations of protoplanetary discs, and their existence may be attributed to (proto-)planets interacting with their natal environments. However, constraining protoplanet masses or ages – or even just confirming that protoplanets are the cause of these substructures – in any given observation requires a clear theoretical understanding of large numbers of different gap processes.

While theoretical and semi-analytical works exist for the viscously dominated end stages of gap evolution, due to the near inviscid nature of protoplanetary discs, time-dependent theories that can account for the nature of the mutual evolution between planet and disc are required to correctly interpret observations. I will first present on how planets form gaps in the simplest possible case: that of a low mass planet in an two-dimensional inviscid isothermal disc and show new analytical theory that is able to predict the initial stages of gap evolution in this case. Using both Athena++ numerical simulations and analytical arguments, I will then discuss how this picture is modified in the cases of viscous, thermodynamically active, or three-dimensional discs. I will show that the treatment of disc thermodynamics has significant effects on the planet disc interaction whereas viscosity – at the levels expected in protoplanetary discs – does not have a significant impact at the early stages of gap formation.

• Speaker: Amelia J. Cordwell (DAMTP)
• Tuesday 27 May 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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It has been almost ten years since CARMENES opened its two spectroscopic eyes at the Calar-Alto observatory. Here’s an up-to-date account of the findings: more than 40 new planets in a sample of 354 M dwarfs; mass estimates of 32 transiting planets; and more than 120 papers, also covering topics such as stellar magnetic activity, binaries, and atmospheric characterization of exoplanets. So, what’s next? Stellar activity is still the main factor limiting the detection of many more planets or estimating the mass of transiting planets around low-mass stars. But for CARMENES , stellar activity is a signal, not just correlated noise. In its spectroscopic time series, it is manifested as a quasiperiodic wavelength-dependent variability, which induces activity-related radial velocity (ARV) variations of at least 2 m/s. For many stars, ARV variability is >10 m/s. Fortunately, ARV variability differs from Doppler shifts: it is usually incoherent, wavelength-dependent, and accompanied by spectral shape variations. These differences can help us distinguish between activity-related and planetary signals and model both phenomena simultaneously.

• Speaker: Lev Tal-Or (Ariel)
• Tuesday 20 May 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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The multitude of detected exoplanets and their diversity never cease to fascinate us, while the statistical trends emerging from these detections present promising opportunities to delve into the past of planetary systems, all the way back to their formation. In this talk, I will give an overview of my group’s recent observational and theoretical results on the formation of gas giants. Owing to their large gravitational influence these planets cannot be overlooked in the evolution of planetary systems towards a life-harbouring system such as our own. Results of RV and direct imaging surveys in recent years revealed that gas giants are not a common outcome of planet formation, and that their most frequent hosts – the intermediate-mass stars (IMSs) seem to hold the answers to their formation.

We investigate the formation of giant planets using the pebble-accretion driven planet formation simulations, exploring a range of different formation conditions. In this work, and in contrast to common approaches in the literature, we implement stellar-mass dependent time evolution of luminosity on the pre-main sequence, and find that this makes a significant difference to giant planet formation outcomes. We successfully reproduce the giant planet occurrence rates as a function of stellar mass, found by RV surveys. This work revealed that mass accretion rate is the key parameter in determining whether a star will likely host a giant planet in its future planetary system.

Our large surveys of pre-main sequence star candidates led to the first unbiased sample of such IMSs, and the result that their protoplanetary discs are dispersed faster than discs around low mass stars, a devastating prospect for giant planet formation unless it happens very fast (e.g., via GI). This is in stark contrast with the observational examples of massive discs actively forming planets at 5-6Myr of age. Our work shows that late gas accretion, as seen in some of those sources, must be the dominant mechanism that sustains the mass reservoir of these older protoplanetary discs. Our surveys, and follow-up with ALMA also allowed a unique insight in the elusive transition state from protoplanetary to debris discs and origin of gas in debris discs.

• Speaker: Olja Panic (Leeds)
• Tuesday 13 May 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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The chemical composition of a planet’s atmosphere is intimately tied to the volatile inventory of the protoplanetary disk in which it forms. Establishing this connection requires detailed measurements of elemental abundances in disks at small spatial scales relevant to planet formation. In this talk, I will present two targeted studies of well-known Herbig Ae/Be systems, combining ALMA observations with chemical modelling to probe disk chemistry. In HD 100546 , we detect complex molecular asymmetries, interpreted as the result of shadowing from planet-induced structures within the inner cavity, generating azimuthal temperature variations that drive chemical diversity. In HD 169142 , we investigate the first detection of SiS emission from a protoplanetary disk—nearly a billion times brighter than predicted under typical conditions—indicative of planet-induced shocks that release silicon from dust grains into the gas phase. These findings reveal that planet formation can significantly reshape the chemical environment of disks, with direct implications for how emerging planets accrete their atmospheres. Together, these studies emphasise the dynamic and heterogeneous nature of disk chemistry and provide new insights into the origins of the wide diversity observed in exoplanetary atmospheres.

• Speaker: Luke Keyte (UCL)
• Tuesday 06 May 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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An outstanding gap in the current planet formation theory is about the first steps of the planet formation process; namely how, when and where the initially ISM like solid dust particles grow into pebbles and planetesimals, the building blocks of planetary cores. Protoplanetary disks provide the initial conditions for the planet formation process. They are weakly magnetized accretion disks that are subject to the magnetorotational instability (MRI), one of the main magnetized processes responsible for their angular momentum transport and gas turbulence. The nonideal magnetohydrodynamic (MHD) effects prevent the MRI from operating everywhere in PPDs, leading to a complex dichotomy between MRI active regions with higher gas turbulence and non-MRI regions with lower gas turbulence. In this talk,  I will present the first numerical framework that describes the evolution of PPDs over millions of years powered by the MRI . It captures the MRI driven gas evolution via nonideal MHD calculations, which accounts for the dynamics and growth of the solid dust particles. An MRI powered mechanism that can spontaneously generate short- and long-lived pressure maxima in the PPD is unveiled. Within the long-lived pressure maxima, solid dust particles can be efficiently trapped, grow into pebbles, and reach high enough dust-to-gas mass ratios to potentially trigger the formation of planetesimals via the streaming instability. These planetesimals and pebbles can further rapidly interact to form planetary cores.

• Speaker: Timmy Delage (Imperial)
• Tuesday 29 April 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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The orbital architecture of planets in the Solar System is thought to have been set shortly after its birth. However, ancient asteroid families are highly dispersed, suggesting that perhaps the Solar System remained chaotic until later in its history. Testing this possibility requires precise dating of the collisions that should have generated such families, but planetary surfaces record little to no information from this time. The meteorite record of asteroid collisions represents a separate and more complete archive of Solar System evolution. In this project, we leveraged recent methodological advances to build an extensive record of in-situ meteorite apatite U-Pb ages, sensitive to collisions that induce parent body break-up events. Most asteroid collisions in our record occurred 4480 +/- 20 million years ago. Only highly dispersed asteroid families are potentially co-eval with our U-Pb ages, demonstrating that strong perturbations modifying the orbital eccentricities and inclinations of asteroids were still operating at 4480 Ma. This is unexpected in scenarios where the planets completed their growth and acquired their current orbits in a few Myr within the dispersal of the protoplanetary disk. Our work provides unique evidence that the asteroid belt was still in a state of dynamical chaos 80 Myr after its formation.

• Speaker: Craig Walton (ETH)
• Tuesday 18 March 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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Observations of gas in exo-Kuiper belts (mostly CO) suggest it may be common in young planetary systems, potentially reshaping our understanding of the Solar System’s youth. Uranus and Neptune’s high atmospheric C/H ratios (60–80× protosolar) could trace late accretion of carbon-rich gas from a primordial Kuiper belt. We model gas release and viscous evolution in a Solar System-analog belt, quantifying gas capture by the ice giants. Using a disk model with varied initial masses (up to 50 M⊕), viscosities, and accretion efficiencies, we simulate CO release and planetary enrichment. Results show a massive belt (∼50 M⊕, similar to that considered in e.g. the Nice model) can supply sufficient CO via late accretion to explain observed C/H values. While solid accretion during formation contributes to carbon enrichment, we find that an additional late accretion may be needed to explain the very high super solar values, which aligns with gas capture from a young, gaseous Kuiper belt. This mechanism may be universal, influencing metallicity in exoplanetary giants, with observational implications for sub-Jupiter exoplanets. Our findings support a once-gas-rich Kuiper belt as a key driver of ice giant atmospheric evolution.

• Speaker: Paul Huet (Paris Observatory)
• Tuesday 11 March 2025, 13:00-14:00
• Venue: Hoyle Committee Room - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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Devolatilization — depletion of volatile elements (e.g., C, O, S, Na and K) in rocky planets relative to their host stars — is a common feature that has been observed in both the Solar System and exoplanet systems. Various mechanisms have been proposed to explain this common feature, ranging from incomplete condensation of dust materials from an ultra-hot nebula with a host stellar composition, partial evaporation of planetesimals by collisional kinetic energy and/or short-lived radiogenic heating, and vaporization of rock-forming volatiles by giant impacts. While summarizing historical data and understandings of this potentially universal phenomenon of devolatilization in rocky planet formation, I will also present in this talk a novel model based on state-of-the-art pebble accretion theory, constrained by volatile depletion of Earth and Mars, that lend support to a hybrid formation scenario where the inner solar system rocky planets grow by a combination of rapid pebble accretion and a prolonged period of planetesimal accretion and giant impacts.

Extending this model to exoplanet systems, aided by disc observations with JWST and ALMA and high-precision bulk-density observations with current and near-future facilities (e.g., CARMENES , SPECULOOS, HARPS3 , and PLATO ), will help make quantitative predictions of volatile budget and bulk composition of rocky exoplanets. The outcome will provide an important testbed for evaluating rocky exoplanetary habitability, together with unprecedented atmospheric observations with JWST and upcoming ELT . It will further provide guidance on target selections for next-generation space missions dedicated to searching for habitable worlds and exo-life signals (e.g., HWO and LIFE ).

• Speaker: Haiyang Wang (Copenhagen)
• Tuesday 04 March 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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