Earth and Planetary Astrophysics (astro-ph.EP)

Abstract: Fundamental to our understanding of planetary bulk compositions is the relationship between their masses and radii, two properties that are often not simultaneously known for most exoplanets. However, while many previous studies have modeled the two-dimensional relationship between planetary mass and radii, this approach largely ignores the dependencies on other properties that may have influenced the formation and evolution of the planets. In this work, we extend the existing nonparametric and probabilistic framework of \texttt{MRExo} to jointly model distributions beyond two dimensions. Our updated framework can now simultaneously model up to four observables, while also incorporating asymmetric measurement uncertainties and upper limits in the data. We showcase the potential of this multi-dimensional approach to three science cases: (i) a 4-dimensional joint fit to planetary mass, radius, insolation, and stellar mass, hinting of changes in planetary bulk density across insolation and stellar mass; (ii) a 3-dimensional fit to the California Kepler Survey sample showing how the planet radius valley evolves across different stellar masses; and (iii) a 2-dimensional fit to a sample of Class-II protoplanetary disks in Lupus while incorporating the upper-limits in dust mass measurements. In addition, we employ bootstrap and Monte-Carlo sampling to quantify the impact of the finite sample size as well as measurement uncertainties on the predicted quantities. We update our existing open-source user-friendly \texttt{MRExo} \texttt{Python} package with these changes, which allows users to apply this highly flexible framework to a variety of datasets beyond what we have shown here.

Abstract: Cloud computing offers an opportunity to run compute-resource intensive climate models at scale by parallelising model runs such that datasets useful to the exoplanet community can be produced efficiently. To better understand the statistical distributions and properties of potentially habitable planetary atmospheres we implemented a parallelised climate modelling tool to scan a range of hypothetical atmospheres.Starting with a modern day Earth atmosphere, we iteratively and incrementally simulated a range of atmospheres to infer the landscape of the multi-parameter space, such as the abundances of biological mediated gases (\ce{O2}, \ce{CO2}, \ce{H2O}, \ce{CH4}, \ce{H2}, and \ce{N2}) that would yield `steady state' planetary atmospheres on Earth-like planets around solar-type stars. Our current datasets comprises of \numatmospheres simulated models of exoplanet atmospheres and is available publicly on the NASA Exoplanet Archive. Our scalable approach of analysing atmospheres could also help interpret future observations of planetary atmospheres by providing estimates of atmospheric gas fluxes and temperatures as a function of altitude. Such data could enable high-throughput first-order assessment of the potential habitability of exoplanetary surfaces and sepcan be a learning dataset for machine learning applications in the atmospheric and exoplanet science domain.

Abstract: India's third Moon mission Chandrayaan 3 will deploy a lander and a rover at a high latitude location of the Moon enabling us to carry out first ever in-situ science investigations of such a pristine location that will potentially improve our understanding on primary crust formation and subsequent modification processes. The primary landing site (PLS), is situated at 69.367621 degS, 32.348126 degE. As a contingency, an alternate landing site (ALS) was also selected at nearly the same latitude but nearly 450 km west to PLS. In this work, a detailed study of the geomorphology, composition, and temperature characteristics of ALS has been carried out using the best-ever high resolution Chandrayaan 2 OHRC DEMs and Ortho images, datasets obtained from Chandrayaan 1 and on-going Lunar Reconnaissance Orbiter. For understanding the thermophysical behaviour, we used a well-established thermophysical model. We found that the Chandrayaan 3 ALS is characterised by a smooth topography with an elevated central part. The ALS is a scientifically interesting site with a high possibility of sampling ejecta materials from Tycho and Moretus. Based on the spectral and elemental analysis of the site, Fe is found to be near approx. 4.8 wt.%, with Mg approx. 5 wt.%, and Ca approx. 11 wt.%. Compositionally, ALS is similar to PLS with a highland soil composition. Spatial and diurnal variability of around 40 K and 175 K has been observed in the surface temperatures at ALS. Although belonging to similar location like PLS, ALS showed reduced daytime temperatures and enhanced night-time temperatures compared to PLS, indicating a terrain of distinctive thermophysical characteristics. Like PLS, ALS is also seems to be an interesting site for science investigations and Chandrayaan 3 is expected to provide new insights into the understanding of lunar science even if it happens to land in the alternate landing site.

Abstract: We present ground and space-based photometric observations of TOI-270 (L231-32), a system of three transiting planets consisting of one super-Earth and two sub-Neptunes discovered by TESS around a bright (K-mag=8.25) M3V dwarf. The planets orbit near low-order mean-motion resonances (5:3 and 2:1), and are thus expected to exhibit large transit timing variations (TTVs). Following an extensive observing campaign using 8 different observatories between 2018 and 2020, we now report a clear detection of TTVs for planets c and d, with amplitudes of $\sim$10 minutes and a super-period of $\sim$3 years, as well as significantly refined estimates of the radii and mean orbital periods of all three planets. Dynamical modeling of the TTVs alone puts strong constraints on the mass ratio of planets c and d and on their eccentricities. When incorporating recently published constraints from radial velocity observations, we obtain masses of $M_{\mathrm{b}}=1.48\pm0.18\,M_\oplus$, $M_{c}=6.20\pm0.31\,M_\oplus$ and $M_{\mathrm{d}}=4.20\pm0.16\,M_\oplus$ for planets b, c and d, respectively. We also detect small, but significant eccentricities for all three planets : $e_\mathrm{b} =0.0167\pm0.0084$, $e_{c} =0.0044\pm0.0006$ and $e_{d} = 0.0066\pm0.0020$. Our findings imply an Earth-like rocky composition for the inner planet, and Earth-like cores with an additional He/H$_2$O atmosphere for the outer two. TOI-270 is now one of the best-constrained systems of small transiting planets, and it remains an excellent target for atmospheric characterization.