Detecting molecules in Ariel low resolution transmission spectra

The Ariel Space Mission aims to observe a diverse sample of exoplanet atmospheres across a wide wavelength range of 0.5 to 7.8 microns. The observations are organized into four Tiers, with Tier 1 being a reconnaissance survey. This Tier is designed to achieve a sufficient signal-to-noise ratio (S/N) at low spectral resolution in order to identify featureless spectra or detect key molecular species without necessarily constraining their abundances with high confidence. We introduce a P-statistic that uses the abundance posteriors from a spectral retrieval to infer the probability of a molecule’s presence in a given planet’s atmosphere in Tier 1. We find that this method predicts probabilities that correlate well with the input abundances, indicating considerable predictive power when retrieval models have comparable or higher complexity compared to the data. However, we also demonstrate that the P-statistic loses representativity when the retrieval model has lower complexity, expressed as the inclusion of fewer than the expected molecules. The reliability and predictive power of the P-statistic are assessed on a simulated population of exoplanets with H2-He dominated atmospheres, and forecasting biases are studied and found not to adversely affect the classification of the survey

Predicting the optical performance of the Ariel Telescope using PAOS

The Ariel Space Mission is the M4 mission in ESA's Cosmic Vision program and will observe a large and diverse sample of exoplanetary atmospheres in the visible to the near-infrared range of the electromagnetic spectrum. Assessing the impact of diffraction, aberrations, and related systematics on the Ariel optical performance before having a system-level measurement is paramount to ensuring that the optical quality, complexity, costs, and risks are not too high. Several codes offer Physical Optics Propagation (POP) calculations, although generally, they are not easily customizable, e.g., for Monte Carlo simulations, are not free access and publicly available, or have technical limitations such as not providing support for refractive elements. PAOS, the Physical Ariel Optics Simulator, is an end-to-end Physical Optics Propagation (POP) model of the Ariel telescope and subsystems. PAOS implements Fresnel diffraction in the near and far fields to simulate the propagation of the complex electromagnetic wavefront through the Ariel optical chain and deliver the realistic PSFs vs. lambda at the intermediate and focal planes. PAOS is written with a full Python 3 stack and comes with an installer, documented examples, and an exhaustive guide. PAOS is meant to be easy to use, generic and versatile for POP simulations of optical systems other than Ariel’s, thanks to its generic input system and built-in GUI providing a seamless user interface and simulations

ExoRad 2.0: The generic point source radiometric model

ExoRad 2.0 is a generic radiometric simulator compatible with any instrument for point source photometry or spectroscopy. Given the descriptions of an observational target and the instrumentation, ExoRad 2.0 estimates several performance metrics for each photometric channel and spectral bin. These include the total optical efficiency, the measured signal from the target, the saturation times, the read noise, the photon noise, the dark current noise, the zodiacal emission, the instrument-self emission and the sky foreground emission. ExoRad 2.0 is written in Python and it is compatible with Python 3.8 and higher. The software is released under the BSD 3-Clause license, and it is available on PyPi, so it can be installed as pip install exorad. Alternatively, the software can be installed from the source code available on GitHub. Before each run, ExoRad 2.0 checks for updates and notifies the user if a new version is available. ExoRad 2.0 has an extensive documentation, available on readthedocs, including a quick-start guide, a tutorial, and a detailed description of the software functionalities. The documentation is continuously updated along with the code. The software source code, available on GitHub, also includes a set of examples of the simulation inputs (for instruments and targets) to run the software and reproduce the results reported in the documentation. The software has been extensively validated against the Ariel radiometric model ArielRad (Mugnai et al., 2020), the time domain simulator ExoSim (Sarkar et al., 2021) and custom simulations performed by the Ariel consortium. ExoRad 2.0 is now used not only by the Ariel consortium but also by other missions, such as the balloon-borne NASA EXCITE mission (Nagler et al., 2022), the space telescope Twinkle (Stotesbury et al., 2022), and an adaptation for the James Webb Space Telescope (Gardner et al., 2006) is under preparation. Such JWST adaptation has been tested against the JWST Exposure Time Calculator (Pontoppidan et al., 2016) and returned consistent results, providing a validation of the code against a working system. Although the code has been validated and used mostly for space and airborne-based telescopes, we foresee no practical limitation to adaptation for ground-based system

Detecting molecules in Ariel low resolution transmission spectra

The Ariel Space Mission aims to observe a diverse sample of exoplanet atmospheres across a wide wavelength range of 0.5 to 7.8 microns. The observations are organized into four Tiers, with Tier 1 being a reconnaissance survey. This Tier is designed to achieve a sufficient signal-to-noise ratio (S/N) at low spectral resolution in order to identify featureless spectra or detect key molecular species without necessarily constraining their abundances with high confidence. We introduce a P-statistic that uses the abundance posteriors from a spectral retrieval to infer the probability of a molecule’s presence in a given planet’s atmosphere in Tier 1. We find that this method predicts probabilities that correlate well with the input abundances, indicating considerable predictive power when retrieval models have comparable or higher complexity compared to the data. However, we also demonstrate that the P-statistic loses representativity when the retrieval model has lower complexity, expressed as the inclusion of fewer than the expected molecules. The reliability and predictive power of the P-statistic are assessed on a simulated population of exoplanets with H2 -He dominated atmospheres, and forecasting biases are studied and found not to adversely affect the classification of the survey

Alfnoor: Assessing the information content of Ariel's low-resolution spectra with planetary population studies

The Ariel Space Telescope will provide a large and diverse sample of exoplanet spectra, performing spectroscopic observations of about 1000 exoplanets in the wavelength range 0.5–7.8 μm. In this paper, we investigate the information content of Ariel’s Reconnaissance Survey low-resolution transmission spectra. Among the goals of the Ariel Reconnaissance Survey is also to identify planets without molecular features in their atmosphere. In this work, (1) we present a strategy that will allow us to select candidate planets to be reobserved in Ariel’s higher-resolution tier, (2) we propose a metric to preliminary classify exoplanets by their atmospheric composition without performing an atmospheric retrieval, and (3) we introduce the possibility to find other methods to better exploit the data scientific content

FEA testing the pre-flight Ariel primary mirror

Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) is an ESA M class mission aimed at the study of exoplanets. The satellite will orbit in the lagrangian point L2 and will survey a sample of 1000 exoplanets simultaneously in visible and infrared wavelengths. The challenging scientific goal of Ariel implies unprecedented engineering efforts to satisfy the severe requirements coming from the science in terms of accuracy. The most important specification – an all-Aluminum telescope – requires very accurate design of the primary mirror (M1), a novel, off-set paraboloid honeycomb mirror with ribs, edge, and reflective surface. To validate such a mirror, some tests were carried out on a prototype – namely Pathfinder Telescope Mirror (PTM) – built specifically for this purpose. These tests, carried out at the Centre Spatial de Liège in Belgium – revealed an unexpected deformation of the reflecting surface exceeding a peek-to-valley of 1µm. Consequently, the test had to be re-run, to identify systematic errors and correct the setting for future tests on the final prototype M1. To avoid the very expensive procedure of developing a new prototype and testing it both at room and cryogenic temperatures, it was decided to carry out some numerical simulations. These analyses allowed first to recognize and understand the reasoning behind the faults occurred during the testing phase, and later to apply the obtained knowledge to a new M1 design to set a defined guideline for future testing campaigns

PAOS, the Physical Optics Propagation model of the Ariel optical system

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, is a medium-class space mission part of ESA's Cosmic Vision programme, due for launch in 2029. Ariel will survey a diverse sample of about 1000 extrasolar planets in the visible and infrared spectrum to answer questions about their composition, formation and evolution. Ariel mounts an off-axis Cassegrain telescope with a 1100 mm x 730 mm elliptical mirror and has two separate instruments (FGS and AIRS) that cover the 0.5-7.8 micron spectral range. To study the Ariel optical performance and related systematics, we developed PAOS, the Proper Ariel Optical Simulator, an End-to-End physical optics propagation model of the Ariel Telescope and subsystems based on PROPER, an optical propagation library for IDL, Python and Matlab. PAOS is a Python code that consists of a series of calls to PROPER library functions and procedures that reproduces the Ariel optical design, interleaved with additional code that can be specified according to the simulation. Using PAOS, we can investigate how diffraction affects the electromagnetic wavefront as it travels through the Ariel optical systems and the resulting PSFs in the photometric and spectroscopic channels of the mission. This enables to perform a large number of detailed analyses, both on the instrument side and on the optimisation of the Ariel mission. In particular, PAOS can be used to support the requirement on the maximum amplitude of the aberrations for the manufacturing of the Ariel primary mirror, as well as to develop strategies for in-flight calibration, e.g. focussing procedures for the FGS and AIRS focal planes, and to tackle systematics such as pointing jitter and vignetting. With the Ariel mission now in the process of finalizing the instrument design and the data analysis techniques, PAOS will greatly contribute in evaluating the Ariel payload performance with models to be included in the existing Ariel simulators such as ArielRad, the Ariel Radiometric model, and ExoSim, the Exoplanet Observation simulator, for the purpose of studying and optimising the science return from Ariel

ExoRad 2.0: The generic point source radiometric model

ExoRad 2.0 is a generic radiometric simulator compatible with any instrument for point source photometry or spectroscopy. Given the descriptions of an observational target and the instrumentation, ExoRad 2.0 estimates several performance metrics for each photometric channel and spectral bin. These include the total optical efficiency, the measured signal from the target, the saturation times, the read noise, the photon noise, the dark current noise, the zodiacal emission, the instrument-self emission, and the sky foreground emission

A fine functional homology between chitinases from host and parasite is relevant for malaria transmissibility

High levels of plasma chitotriosidase are a marker of macrophage activation in several pathologies and, in particular, in human malaria. Plasmodium falciparum, during its maturative cycle in the midgut of the Anopheles mosquito, secretes a chitinase to disrupt the peritrophic membrane, a necessary step in the migration of the parasite from the midgut to the salivary glands of malaria's vector. The cooperation between human chitotriosidase (Chit) and the chitinase from P. falciparum in attacking the peritrophic membranes in the Anopheles midgut has been recently demonstrated by in vivo experiments. The present study confirms, by computational methods, this functional homology. A simple sequence analysis method, potentially useful to assess fine textual closeness in families of homologous proteins, is reported here and applied to a set of chitinases from mammals and plasmodia. This analysis confirms the clustering and the phylogenetic relationships obtained with well-known alignment methods, but also shows that the sequences of chitinases from malaria hosts and malaria parasites are correlated. This correlation, a sign of functional homology, is discussed as a condition for the spreading of different forms of malaria. From this perspective, one can get insight into the origins of malaria and its genetic or pharmacological control

A new model for the replacement priority value of medical equipment

A simple model has been defined aimed at computing the so-called Replacement Priority Value (RPV) of medical equipment. With respect to the well-known model by Fennigkoh (1992), RPV is computed in two steps, of which the second one concerns only the instruments selected as critical during the first one. Also the attributes considered by the model and their weighting factors have been modified with respect to Fennigkoh's model, in order to adapt model behaviour to the specific context where it is to be applied. When tested on a sample of 31 medical devices, the model was easy to use and its recommendations showed "good sense". Such a kind of quantitative tools may greatly help the hospital top management in planning equipment replacement policy