Elena Mamonova

• Mamonova, E.; Herbst, K.; Kofman, V.; Ozgurel, Ozge; Kowalski, A. F. & Wedemeyer, S. [Vis alle 7 forfattere av denne artikkelen] (2026). Stellar-flare-driven evolution of primordial early exo-Earth atmospheres: Insights from the young M dwarf flare model. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 710. doi: 10.1051/0004-6361/202558763. Fulltekst i vitenarkiv Vis sammendrag

  Context . M dwarfs are key targets for terrestrial exoplanet studies, with prospects for atmospheric spectroscopy. However, strong stellar magnetic activity and frequent flaring require modelling efforts to assess their impact on planetary atmospheres. Aims . We investigated one year of atmospheric chemical evolution of a young exo-Earth orbiting an active M dwarf by coupling our young M dwarf flare (YMDF) model of stellar activity with the photochemical kinetic code VULCAN. Methods . The YMDF model provides time-resolved spectral energy distributions for high- and low-energy electron beam–driven flares, which are used as external radiative inputs to VULCAN to compute the time-dependent photochemistry and kinetics for different primordial atmospheric scenarios. Results . We present the impact of stellar flares on atmospheres with a varying water vapour content, ranging from a plausible primordial atmosphere with solar abundances (representative of a planet-forming region in a dissipating protoplanetary disk) to an extreme water-steam atmosphere with other species reduced to trace abundances. This was explored across several configurations: variable flux in the YMDF model, the previous model representing an active but older M dwarf with 10 or 400K additional bottom boundary heat flux, and a constant stellar flux model. Conclusions . Our study suggests that compared to the previous model, the YMDF model produces synthetic flares that exert significantly greater stress on primordial atmospheres, regardless of the water-vapour content. Increased activity and prevalence of mid-size flares has the potential to induce permanent changes in atmospheric mixing ratios, especially in species with low abundances.

• Mamonova, Elena; Kowalski, A.F.; Herbst, Konstantin; Wedemeyer, Sven & Werner, Stephanie C. (2026). Young M-dwarfs flare activity model: Towards better exoplanetary atmospheric characterisation. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 705. doi: 10.1051/0004-6361/202556844. Fulltekst i vitenarkiv Vis sammendrag

  Context. Stellar flares can significantly influence the atmospheres and habitability of orbiting exoplanets, especially around young and active M dwarfs. Understanding the temporally and spectrally resolved activity of such stars is essential for assessing their impact on planetary environments. Aims. We aim to examine in detail state-of-the-art concepts of flare models to identify what is missing in our understanding of energy deposition during the flare event. By comparing synthetic and observed flare spectra, we seek to determine the modelling frameworks best suited for representing flare energetics and spectral far-ultraviolet features while providing a foundation for investigating flare impacts on exoplanet atmospheres. Methods. In this work, we built the Young M dwarf flare (YMDF) model utilising the combination of radiative-hydrodynamic (RHD) stellar atmosphere models with a high- and low-energy electron beam and corresponding synthetic observables. These models are based on physical principles and were validated with solar and stellar observations. Results. The newly developed YMDF model reproduces the observed continuum rise in both the TESS photometric band and the FUV-A spectral range. Furthermore, the flare distributions generated within this framework show consistency with those observed in our sample of stars. Conclusions. We have developed the YMDF model as a tool to reproduce the time-dependent spectra of flaring young M dwarfs, providing a physically motivated description of their spectral and temporal evolution during flare events.

• Mamonova, Elena; Shan, Yutong; Kowalski, Adam F.; Wedemeyer, Sven & Werner, Stephanie (2025). Flare frequency in M dwarfs belonging to young moving groups. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 700. doi: 10.1051/0004-6361/202554614. Fulltekst i vitenarkiv Vis sammendrag

  Context. M stars are preferred targets for upcoming studies of terrestrial exoplanets aimed at obtaining their atmosphere spectra over the next decade. However, M dwarfs have long been known for their strong magnetic activity and the ability to frequently produce optical and broadband emission flares. Aims. We aim to characterise the flaring behaviour of young M dwarfs in the temporal, spectral, and energy dimensions, as well as examine the stellar parameters governing this behaviour. In this way, we aim to improve our understanding of the energy and frequency of the flare events capable of shaping the exoplanet atmosphere. Methods. Members of young moving groups (YMGs) provide a unique age-based perspective on stellar activity. By examining their flare behaviour in conjunction with rotation, mass, and Hα data, we can obtain a comprehensive understanding of flare-activity drivers in young stars. Results. We demonstrate that young stars sharing similar stellar parameters could also exhibit a broad range of flare frequency distributions. We also find that the flare behaviour shows indications of difference between optical and far ultraviolet (FUV). We propose that the period of rotation (and not the age of the star) can serve as a good proxy for assessing flaring activity. Furthermore, we recommend that instead of a simple power law for describing the flare frequency distribution, a piecewise power law can be used to describe mid-size and large flare distributions in young and active M dwarfs. Conclusions. Using known periods of rotation and fine-tuned power laws governing the flare frequency, we can produce a realistic sequence of flare events to study whether the atmosphere of small exoplanets orbiting M dwarf could withstand such activity until the emergence of life.

• Rauer, Heike; Aerts, Conny; Cabrera, Juan; Deleuil, Magali; et, al., including: & Erikson, Anders [Vis alle 847 forfattere av denne artikkelen] (2025). The PLATO mission. Experimental astronomy (Print). ISSN 0922-6435. 59. doi: 10.1007/s10686-025-09985-9. Fulltekst i vitenarkiv Vis sammendrag

  PLATO (PLAnetary Transits and Oscillations of stars) is ESA’s M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2R) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5%, 10%, 10% for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO‘s target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile towards the end of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases.

• Mamonova, Elena; Shan, Yutong; Hatalova, Petra & Werner, Stephanie C. (2024). Planets similar in size are often dissimilar in interior. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 685. doi: 10.1051/0004-6361/202347049. Fulltekst i vitenarkiv Vis sammendrag

  The number of discovered exoplanets now exceeds 5500 allowing statistical analyses of planetary systems. Multi-planet systems are mini-laboratories of planet formation and evolution, and analysing their system architectures can help us to constrain the physics of these processes. Recent works have found evidence of significant intrasystem uniformity in planet properties such as radius, mass, and orbital spacing, collectively termed ‘peas in a pod’ trends. In particular, correlations in radius and mass have been interpreted as implying uniformity in planet bulk density and composition within a system. However, the samples used to assess trends in mass tend to be small and biased. In this paper, we re-evaluate correlations in planet properties in a large sample of systems with at least two planets for which mass and radius have been directly measured, and therefore bulk density can be calculated. Our sample was assembled using the most up-to-date exoplanet catalogue data, and we compute the relevant statistics while using a procedure to ‘weight’ the data points according to measurement precision. We find a moderate correlation in radius and a weak correlation in the densities of adjacent planets. However, masses of neighbouring planets show no overall correlation in our main sample and a weak correlation among pairs of planets similar in size or pairs restricted to Mp<100 M⊕, Rp<10 R⊕. Similarly, we show that the intrasystem dispersion in radius is typically less than that in mass and density. We identify ranges in stellar host properties that correlate with stronger uniformity in pairs of adjacent planets: low Teff for planet masses, and low metallicity and old age for planet densities. Furthermore, we explore whether peas in a pod trends extend into planet compositions or interior structures. For small neighbouring planets with similar radii, we show that their masses and interior structures are often disparate, indicating that even within the same system, similarity in radii is not necessarily a good proxy for similarity in composition or the physical nature of the planets.

• Hatalova, Petra; Brasser, R.; Mamonova, Elena & Werner, Stephanie C. (2023). Forming rocky exoplanets around K-dwarf stars. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 676. doi: 10.1051/0004-6361/202346332. Fulltekst i vitenarkiv Vis sammendrag

  Context. New space telescopes, such as the upcoming PLATO mission, aim to detect and study thousands of exoplanets, especially terrestrial planets around main-sequence stars. This motivates us to study how these planets formed. How multiple close-in super-Earths form around stars with masses lower than that of the Sun is still an open issue. Several recent modeling studies have focused on planet formation around M-dwarf stars, but so far no studies have focused specifically on K dwarfs, which are of particular interest in the search for extraterrestrial life. Aims. We aim to reproduce the currently known population of close-in super-Earths observed around K-dwarf stars and their system characteristics. Additionally, we investigate whether the planetary systems that we form allow us to decide which initial conditions are the most favorable. Methods. We performed 48 high-resolution N -body simulations of planet formation via planetesimal accretion using the existing GENGA software running on GPUs. In the simulations we varied the initial protoplanetary disk mass and the solid and gas surface density profiles. Each simulation began with 12 000 bodies with radii of between 200 and 2000 km around two different stars, with masses of 0.6 and 0.8 M ⊙ . Most simulations ran for 20 Myr, with several simulations extended to 40 or 100 Myr. Results. The mass distributions for the planets with masses between 2 and 12 M ⊕ show a strong preference for planets with masses M p &lt; 6 M ⊕ and a lesser preference for planets with larger masses, whereas the mass distribution for the observed sample increases almost linearly. However, we managed to reproduce the main characteristics and architectures of the known planetary systems and produce mostly long-term angular-momentum-deficit-stable, nonresonant systems, but we require an initial disk mass of 15 M ⊕ or higher and a gas surface density value at 1 AU of 1500 g cm −2 or higher. Our simulations also produce many low-mass planets with M &lt; 2 M ⊕ , which are not yet found in the observed population, probably due to the observational biases. Earth-mass planets form quickly (usually within a few million years), mostly before the gas disk dispersal. The final systems contain only a small number of planets with masses M p &gt; 10 M ⊕ , which could possibly accrete substantial amounts of gas, and these formed after the gas had mostly dissipated. Conclusions. We mostly manage to reproduce observed K-dwarf exoplanetary systems from our GPU simulations.

Se alle arbeider i NVA

• Shan, Yutong; Hatalova, Petra; Tabernero, Hugo; Timmermann, Anina; Mamonova, Elena & Werner, Stephanie C. (2024). Current limitations in chemical abundance measurements for M dwarfs and implications for exoplanet characterisation. Fulltekst i vitenarkiv
• Shan, Yutong; Wedemeyer, Sven; Werner, Stephanie C. & Mamonova, Elena (2024). En leteaksjon av en annen verden: Kavliprisen i astrofysikk for 2024 hedrer forskerne som har pionert studien av eksoplaneter. Bladet Astronomi. Fulltekst i vitenarkiv
• Mamonova, Elena (2026). A thorny path to a habitable world. Studying primordial exoplanet atmospheres with the Young M Dwarf Flare model. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Exoplanets exhibit a remarkable diversity in sizes, compositions, and orbital configurations that exceed those within our Solar system. Characterising their atmospheres is essential for understanding planetary formation, evolution, and potential habitability. Previous, ongoing, and future missions employ techniques such as high-resolution transmission spectroscopy to detect key atmospheric molecules, thermal structures, and cloud properties, unveiling complex atmospheric processes including photochemistry and energy transport. These efforts integrate data across ultraviolet to infrared wavelengths, enabling comprehensive modelling of atmospheric compositions and dynamics. M dwarfs are preferential targets for exoplanet studies due to their unique characteristics: their smaller radii and lower luminosities enhance the detectability of Earth-sized planets via transit and radial velocity methods. Their habitable zones lie closer to the star, and thus, due to increased transit probability, enabling more frequent and precise atmospheric characterisation. Additionally, the long lifetimes of M dwarfs provide extended windows for planetary and potentially biological evolution. However, their high stellar activity, especially during early evolutionary stages, significantly influences planetary atmospheres through intense flare and ultraviolet radiation, impacting habitability and atmospheric retention. This work investigates the stellar activity in young M dwarf planetary systems, combining observational data analysis, theoretical modelling, and numerical simulations. Using spectral observations and photometry, the stellar activity of a sample of young M dwarfs is characterised, revealing flare energies significantly higher than in solar flares, and flare frequency distributions departing from the power law that governs older or brighter stars’ activity. I developed the Young M Dwarfs Flare (YMDF) model that uses radiative-hydrodynamic simulations in stellar atmospheres with electron beam energy inputs to simulate temporal and spectral evolution of flares. I validated this model, based on solar observations and numerical simulations of stellar atmospheres, by comparing the results to optical and far-ultraviolet observations of M dwarfs. I integrated this model with chemical kinetics to study the effects of flare activity on the atmospheric chemistry in young exo-Earths. My simulations spanned a grid of atmospheres with water vapour fractions ranging from 0.1 to 100% by weight, culminating in a hypothesised steam atmosphere dominated by water vapour and minimal other species. The representative YMDF model reveals that radiative flare stress penetrates up to 50% of the atmospheric depth for minor species, in stark contrast to earlier models of older (≥800 Myr) but still active M dwarfs, which predict efficient depletion of most species only in the uppermost atmospheric layers, leaving these regions being dominated by hydrogen, while the composition of lower atmospheric layers remains comparatively stable. Nevertheless, my chemical kinetics simulations in young evolving planetary systems exemplify flare-induced planet atmospheric evolution, favouring the emergence of potentially habitable or even hospitable surface water reservoirs within tens of millions of years. The simulations further predict prominent abiotic oxygen production occurring consistently not only in exo-Earth atmospheres but also in super-Earths and mini-Neptunes with extreme water-vapour content (Ø40% H2O). The water absorption features, falling within the sensitivity range of the James Webb Space Telescope’s visible-wavelength instruments, offer observational prospects for identifying such water worlds. The similarity of these photochemical processes across planet sizes, as demonstrated by my models, implies that the detection of large water worlds would suggest the existence of smaller water-rich exo-Earths that currently lie beyond the observational capabilities. Furthermore, the simulated atmospheres, regardless of their water vapour content, maintain stable H2O concentrations over the simulation timescales, and therefore, challenge the conventional paradigm of rapid photoevaporation-driven atmospheric loss in young planetary systems. While the observed similarity in planetary radii within exoplanetary systems may partly arise from observational biases such as those inherent to the Kepler mission, the prevalence of mini-Neptunes exhibiting lower densities compared to terrestrial planets, coupled with my findings on the stability of dominant atmospheric species, calls into question simple atmospheric stripping scenarios. Instead, these results suggest alternative planet formation and atmospheric evolution mechanisms may be at play beyond those traditionally assumed.

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