Resumen:

M-dwarfs comprise 75\% of the stars in the Milky Way and also host a large fraction of the potentially habitable exoplanets. However, the high levels of stellar activity are a challenge in a biological conext. They exhibit frequent and intense flares, exposing their planets to high levels of ultraviolet (UV) radiation. This radiation is crucial for biological systems, but excessive exposure can cause damage to important cell structures. Thus, the aim of this work is to investigate whether life could withstand the environmental conditions of planets orbiting M-dwarfs. For our analysis, we choose, Proxima Centauri b, an exoplanet discovered in 2016 and recently confirmed. It has 1.17 times the mass of Earth and is located in the habitable zone of the system, which is a favorable characteristic for life as we know it. To obtain the results, we performed irradiation experiments with the yeast Rhodotorula collected in Diamantina, MG. The first experiment was performed with a tubular lamp that covers only the UVC region. The second experiment was conducted with a continuous spectrum lamp that covers the entire UV range. The last experiment was carried out in the Space and Planetary Simulation Chamber (AstroCam) to simulate hypothetical conditions on the surface of Proxima b. We simulated atmospheres of 100\% CO$_2$ and primitive Earth (80\% CO$_2$ and 20\% N$_2$), with a pressure of 1000 mbar, and the continuous spectrum lamp coupled to AstroCam. The results showed that irradiations using the continuous spectrum lamp are more lethal than the tubular lamp. Additionally, we observed that cells resisted to a dose of 60000 J/m$^2$ for the UVC lamp. Assuming an average flux value for the flares on Proxima b (7 W/m$^2$), this dose would be reached in about 2.38 hours. Our results provide important data to guide studies searching for biosignatures on exoplanets.

Resumen:

Clouds influence most aspects of extrasolar atmospheres and, therefore, shape their emergent spectra. Studying these clouds is essential to learn about the thermal structure, composition, detectability, and habitability of planetary atmospheres. In anticipation of JWST observations of cloudy exoplanet atmospheres, we analyze all Spitzer mid-infrared spectra of ultracool dwarfs and find the following results, which constitute a paper series: 1) silicate clouds are near ubiquitous in (L-type) extrasolar atmospheres, 2) these clouds form, then thicken, and sediment in the 2000-1300 K effective temperature range, 3) young atmospheres are cloudier due to a slower settling of dust clouds, 4) variable objects are more likely to have higher dust cloud opacity, and 5) equatorial latitudes are cloudier compared to the poles. These results significantly grow our knowledge of the formation, composition, and evolution of dust clouds in extrasolar atmospheres and partially explain the spectral diversity observed in directly-imaged exoplanets and brown dwarfs by invoking their viewing geometry. Our ongoing JWST higher resolution and SNR observations of extrasolar atmospheres will further inform about the physical properties and chemistry of dust clouds.

Resumen:

Protoplanetary disk and giant planet formation models have been interpreted to suggest that a giant planet's atmospheric abundances can be used to infer its formation location in its parent protoplanetary disk. It has been reported that the hot Jupiter $\beta$ Pictoris $b$ has subsolar carbon and oxygen abundances ratios. Assuming solar carbon and oxygen abundances for its host star $\beta$ Pictoris, $\beta$ Pictoris $b$'s atmospheric carbon and oxygen abundances possibly indicate that it slowly formed via core-acretion somewhere between the disk's H$_{2}$O and CO$_{2}$ ice lines. However, due to $\beta$ Pic's photospheric parameters, it is notoriously difficult to directly infer carbon and oxygen abundances from $\beta$ Pictoris. We characterize star HD 181327, part of $\beta$ Pictoris's moving group, and argue that its stellar abundances are the best way to infer the elemental composition of the protoplanetary disk from which $\beta$ Pictoris $b$ was formed. We also perform our own retrieval of $\beta$ Pic $b$. Our inferred C/O abundances for HD 181327 and $\beta$ Pic $b$ corroborates the scenario outlined by previous studies, showing $\beta$ Pic $b$ formed via core-accretion beyond the water ice line. We reinforce that giant planet atmospheric abundance ratios can only be meaningfully interpreted relative to the possibly non-solar mean compositions of their parent protoplanetary disks.

Resumen:

We are at a unique time to study giant exoplanets. With more than 5000 exoplanets found and facilities like JWST that provide unprecedented data on their atmospheres, we moved from an era of discovery to an era of exoplanet characterisation. On the other hand, extremely accurate measurements by Juno and Cassini missions, make this an exceptional time to combine the detailed information on the solar system's giant planets and the large amount of data from exoplanets to get a better understanding of planetary physics and a better comprehension on planet formation and evolution. Because the giant planets in our solar system are and will remain to be the touchstone to understanding the detailed processes that happen in these worlds, in this talk I will present my recent study on the amount and distribution of heavy elements in Jupiter’s interior and I will also discuss the implication of this study on giant exoplanets, presenting some unpublished work towards a better characterisation of giant exoplanet interiors using JWST data.

Resumen:

Although the analysis of exoplanet atmospheres has become one of the most pertinent topics within planetary sciences, characterising these objects directly from their spectra is still a challenge. To interpret the observed spectrum of an exo-atmosphere, one can apply a technique known as atmospheric retrieval, i.e. fitting a model to this data in order to infer the properties of the atmosphere, such as temperature, chemical composition, and presence of clouds. This work considers a retrieval framework which includes H2O as the main molecular opacity source, and optional opacity features such as additional molecules (e.g. CH4, CO2, CO), collision-induced absorption (CIA), Rayleigh scattering, and clouds. Furthermore, our retrieval code accounts for a non-isobaric transit chord, setting atmospheric opacity sources to a full pressure dependency. We perform non-isobaric retrievals in 38 Hubble Space Telescope Wide Field Camera 3 (WFC3) near-infrared transmission spectra to establish how the variation of pressure affects the estimation of atmospheric parameters. Our results show that, for WFC3 wavelength range and resolution, mainly H2O-only cloud-free and constant/grey cloud atmospheres are retrieved. We compare our findings with previous analyses in the literature, concluding that Rayleigh scattering is negligible in most of our retrievals, except in the ones where shorter-wavelength WFC3 data is available. On the other hand, CIA is strongly dependent on pressure, therefore helping set the H2O abundance, which is unclear in the former isobaric studies. Additionally, we acknowledge the degeneracy between molecular abundances and the reference parameter (i.e. where the atmosphere is optically thick), as pointed out by previous studies, may be broken for cloud-free fits, but is still indirectly present in cloudy results. Finally, we suggest new approaches that could help identify additional atmospheric features imprinted in the spectra, considering data in complementary wavelengths, as well as retrieval analyses using higher-quality James Webb Space Telescope spectra.

Resumen:

Exoplanets with ultra-short periods (P < 1 day) might experience orbital decay due to the tidal dissipation effect with the host star. My current work allows verification of the orbital ephemeris of the WASP-19b with the availability of long-term high-precision photometric and spectroscopic data including 20 unpublished transits from the Danish telescope. This place limits on the modified tidal quality factor Q’*. The same data allows for a detailed study of the atmospheric properties of WASP-19b, via transmission photometry and spectroscopy. WASP-19A is an active host star with its surface littered with starspots, which if not correctly modeled, systematics are introduced into the transit timing measurements and transit depth, which latter affects the exoplanetary transmission spectrum. Additionally the signal from stellar inhomogeneities can outweigh the signal from planetary spectral characteristics (Rackham, B., V., et al. 2022, arXiv, 220109905, submitted to RAS Techniques and Instruments as invited review.). Therefore, to perform a full and complete orbital ephemeris study of WASP-19b requires the modeling of detected starspots. Incidentally, failing to model both occulted and unocculted starspots can skew measurements in the planetary radius affecting the broadband transmission spectrum. Using the transit-starspot model, PRISM we perform the most complete, detailed, homogeneous analysis of all available data to estimate Q’* and study the atmospheric properties of WASP-19b with the help of ground- and space-based archival data.