A5049162541- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Atmospheric Ozone and Climate
- Space Science and Extraterrestrial Life
- Isotope Analysis in Ecology
- Calibration and Measurement Techniques
- Scientific Research and Discoveries
- Adaptive optics and wavefront sensing
- Gamma-ray bursts and supernovae
- Spectroscopy and Laser Applications
- Solar and Space Plasma Dynamics
- Origins and Evolution of Life
- Space Exploration and Technology
- Planetary Science and Exploration
- Astronomical Observations and Instrumentation
- Photoreceptor and optogenetics research
- Molecular Spectroscopy and Structure
- Atmospheric and Environmental Gas Dynamics
- Spaceflight effects on biology
- Paleontology and Stratigraphy of Fossils
- Superconducting and THz Device Technology
- Spacecraft and Cryogenic Technologies
- Marine and coastal ecosystems
York University
2022-2024
ETH Zurich
2024
University of Oxford
2019-2023
Space Science Institute
2019-2020
University of St Andrews
2016-2019
Cornell University
2015-2019
Max Planck Society
2018
Center for Astrophysics Harvard & Smithsonian
2013-2018
Harvard University Press
2016
CFA Institute
2012
Ground- and space-based planet searches employing radial velocity techniques transit photometry have detected thousands of planet-hosting stars in the Milky Way. The chemistry these atmospheres is controlled by shape absolute flux stellar spectral energy distribution, however, distributions relatively inactive low-mass are poorly known at present. To better understand exoplanets orbiting stars, we executed a panchromatic (X-ray to mid-IR) study 11 nearby hosting {\it Measurements Ultraviolet...
The ultraviolet (UV) spectral energy distributions of low-mass (K- and M-type) stars play a critical role in the heating chemistry exoplanet atmospheres, but are not observationally well-constrained. Direct observations intrinsic flux Lyman alpha line (the dominant source UV photons from stars) challenging, as interstellar HI absorbs entire core for even closest stars. To address existing gap empirical constraints on K M dwarfs, MUSCLES HST Treasury Survey has obtained 11 nearby dwarfs...
We present a catalog of panchromatic spectral energy distributions (SEDs) for 7 M and 4 K dwarf stars that span X-ray to infrared wavelengths (5 {\AA} - 5.5 {\mu}m). These SEDs are composites Chandra or XMM-Newton data from 5 ~50 {\AA}, plasma emission model 100 broadband empirical estimates 1170 HST 5700 including reconstruction stellar Ly{\alpha} at 1215.67 PHOENIX spectrum 55000 {\AA}. Using these SEDs, we computed the photodissociation rates several molecules prevalent in planetary...
Context. One of the long-term goals exoplanet science is atmospheric characterization dozens small exoplanets in order to understand their diversity and search for habitable worlds potential biosignatures. Achieving this goal requires a space mission sufficient scale that can spatially separate signals from host stars thus directly scrutinize atmospheres. Aims. We seek quantify detection performance space-based mid-infrared (MIR) nulling interferometer measures thermal emission exoplanets....
We model the atmospheres and spectra of Earth-like planets orbiting entire grid M dwarfs for active inactive stellar models with Teff = 2300 K to 3800 six observed MUSCLES UV radiation data. set at 1 AU equivalent distance show from visible IR (0.4–20 μm) compare detectability features in different wavelength ranges James Webb Space Telescope other future ground- spaced-based missions characterize exo-Earths. focus on effect activity levels detectable atmospheric that indicate habitability...
Hydrogen cyanide (HCN) is a key feedstock molecule for the production of life's building blocks. The formation HCN in an N2-rich atmospheres requires first that triple bond between N≡N be severed, and then atomic nitrogen find carbon atom. These two tasks can accomplished via photochemistry, lightning, impacts, or volcanism. requirements producing appreciable amounts are free availability N2 local to oxygen ratio C/O ≥ 1. We discuss chemical mechanisms by which formed destroyed on rocky...
Temperate terrestrial exoplanets are likely common objects, but their discovery and characterization is very challenging. Concepts for optimized space missions to overcome these challenges being studied. The LIFE initiative focuses on the development of a space-based mid-infrared (MIR) nulling interferometer probing thermal emission large sample exoplanets. We derive first estimates signal-to-noise (S/N), spectral resolution (R), wavelength requirements LIFE. Using an Earth-twin exoplanet as...
An important future goal in exoplanetology is to detect and characterize potentially habitable planets. Using nulling interferometry, LIFE will allow us constrain the radius effective temperature of (terrestrial) exoplanets, as well provide unique information about their atmospheric structure composition. We explore potential characterizing emission spectra Earth at various stages its evolution. perform Bayesian retrievals on simulated 8 different scenarios, which correspond cloud-free...
Mini-Neptunes orbiting M stars are a growing population of known exoplanets. Some them located very close to their host star, receiving large amounts UV radiation. Many emit strong chromospheric emission in the H i Lyman α line (Lyα) at 1215.67 Å, brightest far-UV line. We show that effect incoming Lyα flux can significantly change photochemistry mini-Neptunes' atmospheres. use GJ 436b as an example, considering different metallicities for its atmospheric composition. For solar composition,...
Future observations of terrestrial exoplanet atmospheres will occur for planets at different stages geological evolution. We expect to observe a wide variety and with alternative evolutionary paths, some resembling Earth epochs. For an Earth-like atmospheric time trajectory, we simulate from prebiotic current atmosphere based on data. use stellar grid F0V M8V ($T_\mathrm{eff}$ = 7000$\mskip3mu$K 2400$\mskip3mu$K) model four epochs Earth's history corresponding world (3.9$\mskip3mu$Ga), the...
We present model atmospheres for an Earth-like planet orbiting the entire grid of main sequence FGK stars with effective temperatures ranging from Teff = 4250K to 7000K in 250K intervals. remotely detectable spectra planets clear and cloudy at 1AU equivalent distance VIS IR (0.4 {\mu}m - 20 {\mu}m) compare detectability features different wavelength ranges accordance JWST future design concepts characterize exo-Earths. also explore effect stellar UV levels as well spectral energy...
Abstract Recent work has demonstrated that high levels of X-ray and UV activity on young M dwarfs may drive rapid atmospheric escape temperate, terrestrial planets orbiting within the habitable zone. However, secondary atmospheres older, less active be stable present more promising candidates for biomarker searches. In order to evaluate potential habitability Earth-like around old, inactive dwarfs, we new Hubble Space Telescope Chandra Observatory observations Barnard’s Star (GJ 699), a 10...
Abstract As part of the Mega-Measurements Ultraviolet Spectral Characteristics Low-Mass Exoplanetary Systems Hubble Space Telescope ( HST ) Treasury program, we obtained time-series ultraviolet spectroscopy M2.5V star, GJ 674. During far-ultraviolet (FUV) monitoring observations, target exhibited several small flares and one large flare E FUV = 10 30.75 erg) that persisted over entirety an orbit had equivalent duration >30,000 s, comparable to highest relative amplitude event previously...
Abstract Exoplanet science is one of the most thriving fields modern astrophysics. A major goal atmospheric characterization dozens small, terrestrial exoplanets in order to search for signatures their atmospheres that indicate biological activity, assess ability provide conditions life as we know it, and investigate expected diversity. None currently adopted projects or missions, from ground space, can address these goals. In this White Paper, submitted ESA response Voyage 2050 Call, argue...
Various proxies and numerical models have been used to constrain O2 levels over geological time, but considerable uncertainty remains. Previous investigations using 1-D photochemical predicted how O3 concentrations vary with assumed ground-level concentrations, indicate the ozone layer might developed Earth history. These classic utilised simplification of fixed mixing ratio boundary conditions. Critically, this modelling assumption requires verification that fluxes biogenic volcanic gases...
The UV environment of a host star affects the photochemistry in atmosphere, and ultimately surface for terrestrial planets therefore conditions origin evolution life. We model radiation Earth-sized orbiting FGKM stars at 1AU equivalent distance Earth through its geological evolution. explore four different types atmospheres corresponding to an early atmosphere 3.9 Gyr ago three covering rise oxygen present day levels 2.0 ago, 0.8 modern (Following Kaltenegger et al. 2007). In addition...
The current progress in the detection of terrestrial type exoplanets has opened a new avenue characterization exoplanetary atmospheres and search for biosignatures life with upcoming ground-based space missions. To specify conditions favorable origin, development sustainment as we know it other worlds, need to understand nature astrospheric, atmospheric surface environments habitable zones around G-K-M dwarfs including our young Sun. Global environment is formed by propagated disturbances...
M dwarf stars are known for their vigorous flaring. This flaring could impact the climate of orbiting planets, making it important to characterize flares at short wavelengths that drive atmospheric chemistry and escape. We conducted a far-ultraviolet flare survey 6 dwarfs from recent MUSCLES (Measurements Ultraviolet Spectral Characteristics Low-mass Exoplanetary Systems) observations, as well 4 highly-active with archival data. When comparing absolute energies, we found active-M-star be...
Abstract A number of transiting, potentially habitable Earth-sized exoplanets have recently been detected around several nearby M dwarf stars. These worlds represent important targets for atmospheric characterization the upcoming NASA James Webb Space Telescope (JWST). Given that available time exoplanet will be limited, it is critically to first understand capabilities and limitations JWST when attempting detect constituents Earth-like orbiting cool Here, we explore coupled...
The Large Interferometer For Exoplanets (LIFE) initiative aims to develop a space based mid-infrared (MIR) nulling interferometer measure the thermal emission spectra of temperate terrestrial exoplanets. We investigate how well LIFE could characterize cloudy Venus-twin exoplanet to: (1) test our retrieval routine on realistic non-Earth-like MIR spectrum known planet, (2) clouds impact retrievals, (3) refine requirements derived in previous Earth-centered studies. run retrievals for simulated...
Context. Following the recommendations to NASA (in Astro2020 Decadal survey) and ESA (through Voyage2050 process), search for life on exoplanets will be a priority in next decades. Two concepts direct imaging space missions are being developed this purpose: Habitable Worlds Observatory (HWO) Large Interferometer Exoplanets (LIFE). These two operate different spectral regimes: HWO is focused reflected light spectra ultraviolet, visible, near-infrared (UV/VIS/NIR), while LIFE mid-infrared...
Planets composed of large quantities water that reside in the habitable zone are expected to have distinct geophysics and geochemistry their surfaces atmospheres. We explore these properties motivated by two key questions: whether such planets could provide conditions they exhibit discernable spectral features distinguish a water-planet from rocky Earth-like planet. show recently discovered Kepler-62e -62f first viable candidates for water-planet. use as test cases discussing those...
Abstract Characterizing the UV spectral energy distribution (SED) of an exoplanet host star is critically important for assessing its planet’s potential habitability, particularly M dwarfs, as they are prime targets current and near-term characterization efforts atmospheric models predict that their radiation can produce photochemistry on habitable zone planets different from Earth. To derive ground-based proxies emission use when Hubble Space Telescope ( HST ) observations unavailable, we...