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The launch of JWST has opened the era of atmospheric characterization of potentially habitable exoplanets. Observations of the nearby temperate terrestrial exoplanets around TRAPPIST-1 have already begun. Here, we report on forward modeling work conducted in preparation for JWST GTO Exoplanet Transit Spectroscopy team observations of TRAPPIST-1 e (PI: N. Lewis). We have performed a model comparison exercise between petitRADTRANS (Mollière et al. 2019), PICASO (Batalha et al. 2019), and POSEIDON (MacDonald 2023), identifying and harmonizing causes for disagreement. We have combined our simulated spectra with JWST noise simulations (PANDEXO; Batalha et al. 2017) and compared our noise model with the observed uncertainty from JWST observations of TRAPPIST-1g. The four transits in our GTO Program will permit initial reconnaissance of TRAPPIST-1e's atmosphere, though a close consideration is required for which atmospheric scenarios we will be able to support or reject with our expected data. We will be able to evaluate specific atmospheric compositions such as a low mean molecular weight, primordial H2/He-dominated atmosphere, and the presence of strong absorbers, such as CO2 and CH4. We further consider a suite of atmospheric scenarios for TRAPPIST-1e, including "abiotic Earth-like”, massive atmospheres (H2, O2, N2-N2 CIA, N2-CO2 CIA, etc.), large O2 (from escape, buildup), and photochemical runaway (e.g, Zahnle 1986; Kasting 2014, Lustig-Yaeger et al. 2019; Ranjan et al. 2022)., On behalf of the JWST Telescope Scientist GTO Exoplanet Transit Spectroscopy Team

Ammonia (NH3) in a terrestrial planet atmosphere is generally a good biosignature gas, primarily because terrestrial planets have no significant known abiotic NH3 source. The conditions required for NH3 to accumulate in the atmosphere are, however, stringent. NH3's high water solubility and high bio-useability likely prevent NH3 from accumulating in the atmosphere to detectable levels unless life is a net source of NH3 and produces enough NH3 to saturate the surface sinks. Only then can NH3 accumulate in the atmosphere with a reasonable surface production flux. For the highly favorable planetary scenario of terrestrial planets with H2-dominated atmospheres orbiting M dwarf stars (M5V), we find a minimum of about 5 ppm column-averaged mixing ratio is needed for NH3 to be detectable with JWST, considering a 10 ppm JWST systematic noise floor. When the surface is saturated with NH3 (i.e., there are no NH3-removal reactions on the surface), the required biological surface flux to reach 5 ppm is on the order of 10^10 molecules cm-2 s-1, comparable to the terrestrial biological production of CH4. However, when the surface is unsaturated with NH3, due to additional sinks present on the surface, life would have to produce NH3 at surface flux levels on the order of 10^15 molecules cm-2 s-1 (approx. 4.5x10^6 Tg year-1). This value is roughly 20,000 times greater than the biological production of NH3 on Earth and about 10,000 times greater than Earth's CH4 biological production. Volatile amines have similar solubilities and reactivities to NH3 and hence share NH3's weaknesses and strengths as a biosignature. Finally, to establish NH3 as a biosignature gas, we must rule out mini-Neptunes with deep atmospheres, where temperatures and pressures are high enough for NH3's atmospheric production., under revision, submitted to Astrobiology on 18-Aug-2020

We recover PH3 in the atmosphere of Venus in data taken with ALMA, using three different calibration methods. The whole-planet signal is recovered with 5.4{\sigma} confidence using Venus bandpass self-calibration, and two simpler approaches are shown to yield example 4.5-4.8{\sigma} detections of the equatorial belt. Non-recovery by Villanueva et al. is attributable to (a) including areas of the planet with high spectral-artefacts and (b) retaining all antenna baselines which raises the noise by a factor ~2.5. We release a data-processing script that enables our whole-planet result to be reproduced. The JCMT detection of PH3 remains robust, with the alternative SO2 attribution proposed by Villanueva et al. appearing inconsistent both in line-velocity and with millimetre-wavelength SO2 monitoring. SO2 contamination of the ALMA PH3-line is minimal. Net abundances for PH3, in the gas column above ~55 km, are up to ~20 ppb planet-wide with JCMT, and ~7 ppb with ALMA (but with signal-loss possible on scales approaching planetary size). Derived abundances will differ if PH3 occupies restricted altitudes - molecules in the clouds will contribute significantly less absorption at line-centre than equivalent numbers of mesospheric molecules - but in the latter zone, PH3 lifetime is expected to be short. Given we recover phosphine, we suggest possible solutions (requiring substantial further testing): a small collisional broadening coefficient could give narrow lines from lower altitude, or a high eddy diffusion coefficient could allow molecules to survive longer at higher altitudes. Alternatively, PH3 could be actively produced by an unknown mechanism in the mesosphere, but this would need to be in addition to cloud-level PH3 detected retrospectively by Pioneer-Venus., Comment: Revised and updated re-analysis of the phosphine spectra in Venus' clouds; Submitted to Nature Astronomy "Matters Arising" on Apr/19/2021

We first respond to two points raised by Villanueva et al. We show the JCMT discovery spectrum of PH3 can not be re-attributed to SO2, as the line width is larger than observed for SO2 features, and the required abundance would be an extreme outlier. The JCMT spectrum is also consistent with our simple model, constant PH3-abundance with altitude, with no discrepancy in line profile (within data limits); reconciliation with a full photochemical model is the subject of future work. Section 2 presents initial results from re-processed ALMA data. Villanueva et al. noted an issue with bandpass calibration. They have worked on a partially re-processed subset of the ALMA data, so we note where their conclusions, and those of Greaves et al., are now superseded. To summarise: we recover PH3 in Venus' atmosphere with ALMA (~5{\sigma} confidence). Localised abundance appears to peak at ~5-10 parts-per-billion (ppb), with suggestions of spatial variation. Advanced data-products suggest a planet-averaged PH3 abundance ~1-4 ppb, lower than from the earlier ALMA processing (which indicated 7+ ppb). The ALMA data are reconcilable with the JCMT detection (~20 ppb) if there is order-of-magnitude temporal variation; more advanced processing of the JCMT data is underway to check methods. Independent PH3 measurements suggest possible altitude dependence (under ~5 ppb at 60+ km, up to ~100 ppb at 50+ km; see Section 2: Conclusions.). Given that both ALMA and JCMT were working at the limit of observatory capabilities, new spectra should be obtained. The ALMA data in-hand are no longer limited by calibration, but spectral ripples still exist, probably due to size and brightness of Venus in relation to the primary beam. Further, spatial ripples are present, potentially reducing significance of real narrow spectral features., Comment: Response to the Matters Arising: "No phosphine in the atmosphere of Venus" by G. Villanueva et al., preprint at arXiv:2010.14305; v2 contains updated values and additional technical details

Potentially-habitable planets orbiting M-dwarfs are of intense astrobiological interest because they are the only rocky worlds accessible to biosignature search over the next 10+ years due to a confluence of observational effects. Simultaneously, recent experimental and theoretical work suggests that UV light may have played a key role in the origin of life on Earth, and especially the origin of RNA. Characterizing the UV environment on M-dwarfs planets is important to understanding whether life as we know it could emerge on such worlds. In this work, we couple radiative transfer models to observed M-dwarf spectra to determine the UV environment on prebiotic Earth-analog planets orbiting M-dwarfs. We calculate dose rates to quantify the impact of different host stars on prebiotically-important photoprocesses. We find that M-dwarf planets have access to 100-1000 times less bioactive UV fluence than the young Earth. It is unclear whether UV-sensitive prebiotic chemistry that may have been important to abiogenesis, such as the only known prebiotically plausible pathways for pyrimidine ribonucleotide synthesis, could function on M-dwarf planets. This uncertainty affects objects like the recently-discovered habitable-zone planets orbiting Proxima Centauri, TRAPPIST-1, and LHS 1140. Laboratory studies of the sensitivity of putative prebiotic pathways to irradiation level are required to resolve this uncertainty. If steady-state M-dwarf UV output is insufficient to power these pathways, transient elevated UV irradiation due to flares may suffice; laboratory studies can constrain this possibility as well., 18 pages; 6 figures; published in ApJ

Near-Earth asteroids present promising opportunities for future human spaceflight missions. Many of these objects have orbits that come within close proximity to the Earth, allowing a significantly lower cost in comparison to missions to Mars or even the Moon. This cost is directly related to the change in velocity (Delta-V) necessary to move a vehicle from low-Earth orbit to the orbit of a near-Earth asteroid. This paper will discuss the merits of asteroid rendezvous missions in the near future and assess the validity of Delta-V approximations for ~1200 known asteroids candidates. A 1979 paper by Shoemaker and Helin suggested a class-specific set of equations for approximating the Delta-V for these objects. Modern numerical calculations provide accurate measurements for these values and will serve as a test to the strength of the Shoemaker-Helin equations.