Search

One of the major goals - and possibly the most challenging one in 21st century exoplanet research - is the investigation of the atmospheric properties for a large number of terrestrial exoplanets. On the one hand, a statistically significant dataset is invaluable for understanding the diversity of planetary bodies, but on the other hand, this is driven the motivation to search for habitable conditions and identify potential biosignatures, i.e., indications of biological activtity, outside our Solar System. First steps in this direction will be taken in the coming 10-15 years with funded or selected ground- and space-based projects and missions. In addition, the US astrophysics decadal recommended a UV-optical-NIR space telescope (the Habitable Worlds Observatory) with an aperture diameter of at least 6 meters as next flagship mission for the 2040s. This telescope shall be sensitive enough to survey dozens of Earth-sized exoplanets. A highly synergistic approach to this mission, which focuses on the reflected light of the exoplanets, is to directly detect the exoplanets’ thermal emission in the mid-infrared by means of a space-based nulling interferometer. In this contribution, we summarize the current status of the European-led LIFE initiative, which has the goal to develop the science, the technology and a roadmap for such an ambitious space mission that will allow humankind to detect and characterize the atmospheres of hundreds of nearby extrasolar planets including dozens that are similar to Earth. Given the outcome of ESA’s "Voyage 2050" process and the corresponding recommendations from the ESA Senior Committee, the direct detection of the thermal emission of temperate terrestrial exoplanets is given very high scientific priority in ESA future science program and is considered as a candidate theme for a future L-class mission. The unique discovery space for a mid-infrared mission, in particular for the detection of atmospheric biosignatures in exoplanets, will be discussed, the international scope of the inititiative (including contributions from the US, Japan and Australia) will be highlighted, and synergies between LIFE and the NASA's future Habitable Worlds Observatory mission will be emphasized.

We briefly outline the basic ideas behind LIFE, the Large Interferometer For Exoplanets, a proposed space mission which topic coincides with one of those recently selected for ESA's Voyage 2050. LIFE is a project initiated in Europe with the goal to consolidate various efforts and define a roadmap that eventually leads to the launch of a large, space based mid-IR nulling interferometer to investigate the atmospheric properties of a large sample of (primarily) terrestrial exoplanets. We summarise the current scientific and engineering efforts related to LIFE.

From the White Paper series within the ESA “Voyage 2050” process [1] and the US Astro 2020 Decadal [2], it is clear that the astronomical community is going to focus on investigating temperate, terrestrial exoplanets to understand their potential habitability and search for atmospheric signatures of biospheres. Various concepts for future space missions have been proposed, from a large IR/O/UV (LUVOIR/HabEx-like) space mission for studies in reflected light [3, 4], to the mid-infrared nulling interferometer LIFE (Large Interferometer for Exoplanets), to characterize the thermal portion of the planetary spectrum [5, 6]. Their goal is to constrain the bulk parameters, atmospheric structure and composition, and the surface conditions of dozens of terrestrial exoplanets. Atmospheric retrieval studies are essential to define the potential of future missions, determine the technical requirements, as well as to validate the analysis pipelines. It is also relevant at this stage to quantify any synergy among the various instruments, in order to identify compelling science cases whose characterization would be enhanced by observation in multiple wavelength ranges. Bayesian retrieval routines are the key to a statistically robust analysis of a measured atmospheric spectrum. The Bayesian retrieval method builds on iteratively fitting a parametric model for the planet spectrum to the observed spectrum to get estimates on the composition of the planet’s atmosphere and its structure. Such a method can be useful to quantify the amount of information that can be extracted from an observed spectrum, depending on its quality (in terms of resolution, signal-to-noise ratio, observing time, and wavelength range). Retrieval studies are currently being performed in order to determine the requirements for the upcoming missions. In this talk, I will summarize the main results of the latest atmospheric retrieval studies that were performed during the studies of some future space mission concepts., EPSC Abstracts, 16

Bulletin of the American Astronomical Society, 54 (4), ISSN:0002-7537, AASTCS 9: Exoplanets IV Abstracts

Bulletin of the American Astronomical Society, 54 (5), ISSN:0002-7537, AASTCS 9: Exoplanets IV Abstracts

LIFE Collaboration: S. P. Quanz et al., [Context] One of the long-term goals of exoplanet science is the atmospheric characterization of dozens of small exoplanets in order to understand their diversity and search for habitable worlds and potential biosignatures. Achieving this goal requires a space mission of sufficient scale that can spatially separate the signals from exoplanets and their host stars and thus directly scrutinize the exoplanets and their atmospheres., [Aims] We seek to quantify the exoplanet detection performance of a space-based mid-infrared (MIR) nulling interferometer that measures the thermal emission of exoplanets. We study the impact of various parameters and compare the performance with that of large single-aperture mission concepts that detect exoplanets in reflected light., [Methods] We have developed an instrument simulator that considers all major astrophysical noise sources and coupled it with Monte Carlo simulations of a synthetic exoplanet population around main-sequence stars within 20 pc of the Sun. This allows us to quantify the number (and types) of exoplanets that our mission concept could detect. Considering single visits only, we discuss two different scenarios for distributing 2.5 yr of an initial search phase among the stellar targets. Different apertures sizes and wavelength ranges are investigated., [Results] An interferometer consisting of four 2 m apertures working in the 4–18.5 μ.m wavelength range with a total instrument throughput of 5% could detect up to ≈550 exoplanets with radii between 0.5 and 6 R⊕ with an integrated S/N ≥ 7. At least ≈160 of the detected exoplanets have radii ≤1.5 R⊕. Depending on the observing scenario, ≈25–45 rocky exoplanets (objects with radii between 0.5 and 1.5 R⊕) orbiting within the empirical habitable zone (eHZ) of their host stars are among the detections. With four 3.5 m apertures, the total number of detections can increase to up to ≈770, including ≈60–80 rocky eHZ planets. With four times 1 m apertures, the maximum detection yield is ≈315 exoplanets, including ≤20 rocky eHZ planets. The vast majority of small, temperate exoplanets are detected around M dwarfs. The impact of changing the wavelength range to 3–20 μm or 6–17 μm on the detection yield is negligible., [Conclusions] A large space-based MIR nulling interferometer will be able to directly detect hundreds of small, nearby exoplanets, tens of which would be habitable world candidates. This shows that such a mission can compete with large single-aperture reflected light missions. Further increasing the number of habitable world candidates, in particular around solar-type stars, appears possible via the implementation of a multi-visit strategy during the search phase. The high median S/N of most of the detected planets will allow for first estimates of their radii and effective temperatures and will help prioritize the targets for a second mission phase to obtain high-S/N thermal emission spectra, leveraging the superior diagnostic power of the MIR regime compared to shorter wavelengths., This work has been carried out within the framework of the National Centre of Competence in Research PlanetS supported by the Swiss National Science Foundation. S.P.Q., E.A. and H.S.W. acknowledge the financial support of the SNSF. S.K. acknowledges funding from an ERC Starting Grant (grant agreement no. 639889). D.E. acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (project FOUR ACES; grant agreement no. 724427). J.L.-B. acknowledges financial support received from “la Caixa” Foundation (ID 100010434) and the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 847648, with fellowship code LCF/BQ/PI20/11760023. R.A. is a Trottier Postdoctoral Fellow and acknowledges support from the Trottier Family Foundation. This work was supported in part through a grant from FRQNT. T.L. acknowledges funding from the Simons Foundation (SCOL award no. 611576). Part of this work was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France, and of the Washington Double Star Catalog maintained at the U.S. Naval Observatory. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. This research has made use of the following Python packages: astropy (Astropy Collaboration 2013, 2018), matplotlib (Hunter 2007), numpy (Van Der Walt et al. 2011), and scipy (Virtanen et al. 2020).

[Context] The Large Interferometer For Exoplanets (LIFE) initiative is developing the science and a technology road map for an ambitious space mission featuring a space-based mid-infrared (MIR) nulling interferometer in order to detect the thermal emission of hundreds of exoplanets and characterize their atmospheres., [Aims] In order to quantify the science potential of such a mission, in particular in the context of technical trade-offs, an instrument simulator is required. In addition, signal extraction algorithms are needed to verify that exoplanet properties (e.g., angular separation and spectral flux) contained in simulated exoplanet data sets can be accurately retrieved., [Methods] We present LIFESIM, a software tool developed for simulating observations of exoplanetary systems with an MIR space-based nulling interferometer. It includes astrophysical noise sources (i.e., stellar leakage and thermal emission from local zodiacal and exozodiacal dust) and offers the flexibility to include instrumental noise terms in the future. Here, we provide some first quantitative limits on instrumental effects that would allow the measurements to remain in the fundamental noise limited regime. We demonstrate updated signal extraction approaches to validating signal-to-noise ratio (S/N) estimates from the simulator. Monte Carlo simulations are used to generate a mock survey of nearby terrestrial exoplanets and determine to which accuracy fundamental planet properties can be retrieved., [Results] LIFESIM provides an accessible way to predict the expected S/N of future observations as a function of various key instrument and target parameters. The S/Ns of the extracted spectra are photon noise dominated, as expected from our current simulations. Signals from multi-planet systems can be reliably extracted. From single-epoch observations in our mock survey of small (R < 1.5 REarth) planets orbiting within the habitable zones of their stars, we find that typical uncertainties in the estimated effective temperature of the exoplanets are ≲10%, for the exoplanet radius ≲20%, and for the separation from the host star ≲2%. Signal-to-noise-ratio values obtained in the signal extraction process deviate by less than 10% from purely photon-counting statistics-based S/Ns., [Conclusions] LIFESIM has been sufficiently well validated so that it can be shared with a broader community interested in quantifying various exoplanet science cases that a future space-based MIR nulling interferometer could address. Reliable signal extraction algorithms exist, and our results underline the power of the MIR wavelength range for deriving fundamental exoplanet properties from single-epoch observations., This work has been carried out within the framework of the National Centre of Competence in Research PlanetS supported by the Swiss National Science Foundation. S.P.Q. acknowledges the financial support of the SNSF. TL was supported by the Simons Foundation (SCOL award No. 611576). This research has made use of the following Python packages: astropy (Astropy Collaboration 2013, 2018), matplotlib (Hunter 2007), numpy (Van Der Walt et al. 2011), scipy (Virtanen et al. 2020). Author contributions: M.O. and F.D. contributed equally to this paper. M.O. wrote the original LIFESIM tool, carried out the main analyses and wrote part of the manuscript. F.D. contributed to the main analyses and the LIFESIM tool, programmed the publicly available github version, led the instrumental noise analyses and wrote part of the manuscript. S.P.Q. initiated and guided this project and wrote part of the manuscript. R.L., E.F. and A.Gh. contributed to the LIFESIM tool. All authors discussed the results and commented on the manuscript. D.D. and R.L. acknowledge the support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement CoG-866070).

Talk at PLATO Mission Conference 2021

EPSC Abstracts, 15

EPSC Abstracts, 15

Context Current knowledge suggests that temperate terrestrial exoplanets commonly occur in our galaxy (Bryson et al., 2021). One long-term goal of exoplanet research is to characterize the atmospheres of a sizable sample of temperate planets. Such measurements will add to our knowledge of the diversity of worlds in our galaxy, which is a driving force behind this effort, and they will enable the discovery of habitable worlds. The sensitivity of currently planned space- and ground-based observatories will unlikely allow for the characterization of a large number of temperate exoplanet atmospheres. Concepts for future missions (e.g. NASA's LUVOIR [a] and HabEx [b]), capable of characterizing exoplanet atmospheres in reflected light (optical and near-infrared (NIR) range), have been proposed. Complementary to these efforts, the LIFE mission introduced in Quanz et al. (2018) (see also Angerhausen et al. (2021, this conference) for a general overview) is a proposed space-based nulling interferometer which measures the mid-infrared (MIR) thermal emission of exoplanets. The MIR regime is particularly powerful, since it provides probes for atmospheric molecules not accessible in the optical or NIR (e.g. the biosignatures CH4 and N2O). Furthermore, MIR emission observations, in contrast to optical and NIR observations, allow us to probe the temperature structure, radius and surface conditions on exoplanets (Quanz et al., 2019; Konrad et al. in prep.). Previous work has focussed on constraining technical requirements for LIFE via retrievals of cloud-free Earth-twin MIR spectra (Konrad et al., 2020; Konrad et al. in prep.). We now generalize these estimates by looking beyond the cloud-free Earth-twin. Specifically we consider Venus (this submission) and Earth’s evolution through time (Alei et al. (2021, this conference)). Methods Our approach is based on the Bayesian retrieval of simulated mock observations with LIFE for a Venus-twin exoplanet around a sun-like star located at 10 pc. We generate Venus’ emission spectrum using the 1D radiative transfer tool petitRADTRANS (Mollière et al. 2019). The model takes the planetary radius and mass, the pressure-temperature (PT) profile, the atmospheric composition and cloud properties as input. We parametrize Venus’ PT profile via a 3rd order polynomial and consider line and collision-induced absorption by H2O, CO2, and CO as well as absorption and emission contributions from Venus’ opaque H2SO4 clouds. With LIFESim(Ottiger et al. in prep.), we simulate the wavelength-dependent SNR expected for observations with LIFE for a Venus-twin. LIFESim considers noise contributions from stellar leakage, local zodiacal dust, and exozodiacal dust. Our retrieval mechanism is built upon the Multinest algorithm (Feroz et al., 2009). Using the LIFESim noise estimate as uncertainty on the Venus spectrum, we retrieve for the mass and radius, the PT profile, the surface pressure, the molecular abundances and the cloud parameters. By covering a range of different wavelength ranges (3-20 μm, 6-17 μm), spectral resolutions (R = 20, 35, 50, 100) and signal to noise ratios (S/N = 5, 10, 15, 20), we obtain estimates for the technical requirements LIFE needs to meet to: Differentiate between a Venus- and an Earth-twin. Find evidence for clouds in Venus’ atmosphere. Accurately characterize structure and composition of Venus’ atmosphere. This approach will show whether the previously determined technical requirements for LIFE (Konrad et al., in prep.) are sufficient. Many similar MIR retrieval studies have been performed for Earth-like exoplanets. However, to the best of our knowledge, no MIR retrieval studies exist for a Venus-like planet. Results In Figures 1 and 2, we provide first preliminary results, as a proof of concept from testing our approach for retrieving cloudy MIR spectra with our retrieval framework. We used a Venus-twin spectrum (range = 3 - 20 μm, R = 50, SNR = 20) assuming a distance of 10 pc from the Sun as input for this retrieval run. Please note, that for these retrieval validation runs, we only consider the planet’s photon noise and not yet additional noise sources. Figure 1 shows the spectrum corresponding to the retrieved parameters in relation to the input spectrum. From this plot we see that our retrieval provides a good fit to the input spectrum. Figure 2 shows that the PT profile parameters are well retrieved for the upper atmosphere of Venus. Due to the opaque cloud layer in Venus’ atmosphere at approx. 0.1 bar, the surface temperature and surface pressure are no longer retrievable (as can be seen from the cut in the green uncertainty at 0.1 bar). Instead we interpret the retrieved “surface” pressure as the pressure at which Venus’ cloudy atmosphere becomes opaque. With these first retrieval runs we demonstrate that our retrieval suite produces reliable results for cloudy atmospheres. Further studies are currently carried out and will be presented at the conference. Furthermore, we will address the points listed above and discuss how results from cloudy retrievals could be safely interpreted. References Quanz, S. P., et al., 2018, Proc. SPIE, 107011I Bryson, S. et al., 2021, AJ, 161, 36. doi:10.3847/1538-3881/abc418 Quanz, S. P. et al., 2019, arXiv e-prints arXiv:1908.01316 Konrad, B. S., et al., 2020, European Planetary Science Congress Mollière, P., et al., 2019, A&A, 627:A67 Feroz, F., et al., 2009, MNRAS, 398(4):1601–1614 Websites [a] https://www.luvoirtelescope.org [b] https://www.jpl.nasa.gov/habex/

Summary The Large Interferometer For Exoplanets (LIFE) mission concept is a project initiated in Europe with the goal to consolidate various efforts and define a road map that eventually leads to the launch of a large, space-based mid-infrared (MIR) nulling interferometer observatory. This mission will be able to investigate the atmospheric properties of a large sample of terrestrial, potentially habitable exoplanets. In this contribution we present a status report and summarize new results from the LIFE Mission initiative. Context One of the major goals of exoplanetary science and possibly the most challenging question in 21st century exoplanet research is the investigation of the atmospheric properties for a large number (~100) of terrestrial exoplanets. This is only partially driven by the idea to search for habitable conditions and identify potential biosignatures, since such a statistically significant data-set is - in a more general sense - invaluable for understanding the diversity of planetary bodies. First steps in this direction will be taken in the coming 10-15 years with funded or selected ground- and space-based projects and missions. And while exoplanet science is omnipresent on the road maps of all major space agencies, none of them will be able to deliver such a comprehensive and consistent, big data set. An alternative to the mainly discussed large space-based coronographic missions or the starshade concept is to separate the light emitted by the planet from that of its host star by means of an interferometer.In this contribution we summarize new results from the LIFE Mission initiative, which addresses this issue by investigating the scientific potential and technological challenges of an ambitious mission employing a formation-flying nulling interferometer in space working at mid-infrared wavelengths [1,2,3]. Centered around clear and ambitious scientific objectives the project will define the relevant science and technical requirements. The status of key technologies will be re-assessed and further technology development will be coordinated. LIFE is based on the heritage of ESA/Darwin and NASA/TPF-I, but significant advances in our understanding of exoplanets and newly available technologies will be taken into account in the LIFE mission concept. Advances in our knowledge of the exoplanet population as well as significant progress in relevant technologies justify the need, but also the feasibility for a future mission like LIFE to investigate one of the most fundamental questions of mankind: How unique is the phenomenon we call life in the universe? Artist's impression of the LIFE concept. New Results and Progress Over the past year the LIFE community grew significantly into an initiative with more than 100 collaborators from all over the world. We will present the current structure of teams and working groups and the lead personnel in these. Furthermore we will summarize a number of new science results (other LIFE contributions to this conference in brackets): an updated yield estimate for the LIFE mission ([4], see also Kammerer et al. 2021, this conference), where we used simulations based on Kepler statistics to demonstrate that a MIR space-based nulling interferometer like LIFE could yield at least as many exoplanet detections as a large, single aperture optical/NIR telescope. the release of our simulator software LIFEsim that incorporates various telescope sizes and a new noise model that takes into account all astrophysical noise sources. This enables us to systematically study our mission requirements in order to optimize our observing strategy ([5], Dannert et al 2021, this conference). in two other submission (Alei et al. 2021, Konrad et al. 2021, this conference) we discuss how our spectral retrieval routine performs when attempting retrievals of terrestrial exoplanets, using case scenarios like the Earth in Time and Venus. a study on the search for phosphine in various exoplanetary contexts [6], that also serves guidance for the community by providing easy-to-scale first estimates for a large part of detection space of such a mission Outlook Besides various activities on the technology side, defining the auxiliary science and in other working groups we are currently focusing on a detailed simulation of the impact on scheduling for the survey and characterisation phases of the LIFE mission. In this context we are also investigating modern machine learning methods that are crucial to scale up front to end simulations of the full LIFE survey. This in turn will not only inform the aforementioned scheduling consideration but also help to define sensitivity, wavelength coverage and spectral resolution requirements on the technology side. References [1] Quanz, S. P., Kammerer, J., Defrère, D., et al. 2018, Optical and Infrared Interferometry and Imaging VI,10701,107011I. [2] Defrère, D., Léger, A., Absil, O., et al. 2018, Experimental Astronomy, 46, 543. [3] Quanz,S.P., et al.2019.,arXive-printsarXiv:1908.01316. [4] Quanz, S.P., Ottiger, M., Fontanet, E., et al. 2021,arXiv:2101.07500 [5] Ottiger, M., et al. : Large Interferometer For Exo-planets (LIFE):II. Signal simulation, signal extraction andfundamental exoplanet parameters from single epoch ob-servations, 2021 (in prep.) [6] Angerhausen, D., et al. : Large Interferometer ForExoplanets (LIFE): IV. Where is the phosphine?Observing exoplanetary PH3 with a space based MIRnulling interferometer, 2021 (in prep.)