Phosphine could be a key molecule in the understanding of exotic chemistry that occurs in (exo)planetary atmospheres. While phosphine has been detected in the Solar System's giant planets, it has not ...been observed in exoplanets to date. In the exoplanetary context, however, it has been theorized to be a potential biosignature molecule. The goal of our study was to identify which illustrative science cases for PH
chemistry are observable with a space-based mid-infrared nulling interferometric observatory like the Large Interferometer for Exoplanets (LIFE) concept. We identified a representative set of scenarios for PH
detections in exoplanetary atmospheres that vary over the whole dynamic range of the LIFE mission. We used chemical kinetics and radiative transfer calculations to produce forward models of these informative, prototypical observational cases for LIFEsim, our observation simulator software for LIFE. In a detailed, yet first order approximation, it takes a mission like LIFE: (i) about 1 h to find phosphine in a warm giant around a G star at 10 pc, (ii) about 10 h in H
or CO
dominated temperate super-Earths around M star hosts at 5 pc, (iii) and even in 100 h it seems very unlikely that phosphine would be detectable in a Venus-Twin with extreme PH
concentrations at 5 pc. Phosphine in concentrations previously discussed in the literature is detectable in 2 out of the 3 cases, and it is detected about an order of magnitude faster than in comparable cases with James Webb Space Telescope. We show that there is a significant number of objects accessible for these classes of observations. These results will be used to prioritize the parameter range for the next steps with more detailed retrieval simulations. They will also inform timely questions in the early design phase of a mission like LIFE and guide the community by providing easy-to-scale first estimates for a large part of detection space of such a mission.
Abstract
The James Webb Space Telescope’s Near Infrared Imager and Slitless Spectrograph (JWST-NIRISS) flies a 7-hole non-redundant mask (NRM), the first such interferometer in space, operating at ...3–5
μ
m wavelengths, and a bright limit of ≃4 mag in W2. We describe the NIRISS Aperture Masking Interferometry (AMI) mode to help potential observers understand its underlying principles, present some sample science cases, explain its operational observing strategies, indicate how AMI proposals can be developed with data simulations, and how AMI data can be analyzed. We also present key results from commissioning AMI. Since the allied Kernel Phase Imaging (KPI) technique benefits from AMI operational strategies, we also cover NIRISS KPI methods and analysis techniques, including a new user-friendly KPI pipeline. The NIRISS KPI bright limit is ≃8 W2 (4.6
μ
m) magnitudes. AMI NRM and KPI achieve an inner working angle of ∼70 mas, which is well inside the ∼400 mas NIRCam inner working angle for its circular occulter coronagraphs at comparable wavelengths.
Detecting Earth-like exoplanets in direct images of nearby Sun-like systems
brings a unique set of challenges that must be addressed in the early phases of
designing a space-based direct imaging ...mission. In particular, these systems
may contain exozodiacal dust, which is expected to be the dominant source of
astrophysical noise. Previous work has shown that it may be feasible to
subtract smooth, symmetric dust from observations; however, we do not expect
exozodiacal dust to be perfectly smooth. Exozodiacal dust can be trapped into
mean motion resonances with planetary bodies, producing large-scale structures
that orbit in lock with the planet. This dust can obscure the planet,
complicate noise estimation, or be mistaken for a planetary body. Our ability
to subtract these structures from high-contrast images of Earth-like exoplanets
is not well understood. In this work, we investigate exozodi mitigation for
Earth--Sun-like systems with significant mean motion resonant disk structures.
We find that applying a simple high-pass filter allows us to remove structured
exozodi to the Poisson noise limit for systems with inclinations $< 60^\circ$
and up to 100 zodis. However, subtracting exozodiacal disk structures from
edge-on systems may be challenging, except for cases with densities $<5$ zodis.
For systems with three times the dust of the Solar System, which is the median
of the best fit to survey data in the habitable zones of nearby Sun-like stars,
this method shows promising results for mitigating exozodiacal dust in future
HWO observations, even if the dust exhibits significant mean-motion resonance
structure.
Biosignature detection in the atmospheres of Earth-like exoplanets is one of
the most significant and ambitious goals for astronomy, astrobiology, and
humanity. Molecular oxygen is among the ...strongest indicators of life on Earth,
but it will be extremely difficult to detect via transmission spectroscopy. We
used the Bioverse statistical framework to assess the ability to probe
Earth-like O$_{\mathrm{2}}$ levels on hypothetical nearby habitable zone
exoplanets (EECs) using direct imaging and high-resolution spectroscopy on the
Giant Magellan Telescope (GMT) and the Extremely Large Telescope (ELT). We
found that O$_{\mathrm{2}}$ could be probed on up to $\sim$5 and $\sim$15 EECs
orbiting bright M dwarfs within 20 pc in a 10-year survey on the GMT and ELT,
respectively. Earth-like O$_{\mathrm{2}}$ levels could be probed on four known
super-Earth candidates, including Proxima Centauri b, within about one week on
the ELT and a few months on the GMT. We also assessed the ability of the ELT to
test the habitable zone oxygen hypothesis $\unicode{x2013}$ that habitable zone
Earth-sized planets are more likely to have O$_{\mathrm{2}}$ $\unicode{x2013}$
within a 10-year survey using Bioverse. Testing this hypothesis requires either
$\sim$1/2 of the EECs to have O$_{\mathrm{2}}$ or $\sim$1/3 if $\eta_{\oplus}$
is large. A northern hemisphere large-aperture telescope, such as the Thirty
Meter Telescope (TMT), would expand the target star pool by about 25%, reduce
the time to probe biosignatures on individual targets, and provide an
additional independent check on potential biosignature detections.
This study aims to identify exemplary science cases for observing N$_2$O,
CH$_3$Cl, and CH$_3$Br in exoplanet atmospheres at abundances consistent with
biogenic production using a space-based ...mid-infrared nulling interferometric
observatory, such as the LIFE (Large Interferometer For Exoplanets) mission
concept. We use a set of scenarios derived from chemical kinetics models that
simulate the atmospheric response of varied levels of biogenic production of
N$_2$O, CH$_3$Cl and CH$_3$Br in O$_2$-rich terrestrial planet atmospheres to
produce forward models for our LIFEsim observation simulator software. In
addition we demonstrate the connection to retrievals for selected cases. We use
the results to derive observation times needed for the detection of these
scenarios and apply them to define science requirements for the mission. Our
analysis shows that in order to detect relevant abundances with a mission like
LIFE in it's current baseline setup, we require:
(i) only a few days of observation time for certain very near-by "Golden
Target" scenarios, which also motivate future studies of "spectral-temporal"
observations
(ii) $\sim$10 days in certain standard scenarios such as temperate,
terrestrial planets around M star hosts at 5 pc,
(iii) $\sim$50 - 100 days in the most challenging but still feasible cases,
such as an Earth twin at 5pc. A few cases for very low fluxes around specific
host stars are not detectable.
In summary, abundances of these capstone biosignatures are detectable at
plausible biological production fluxes for most cases examined and for a
significant number of potential targets.
While previous studies have shown a strong preference for a future mid-infrared nulling interferometer space mission to detect planets within the HZ around M dwarfs, we here focus on a more ...conservative approach toward the concept of habitability and present yield estimates for two stellar samples consisting of nearby (d<20 pc) Sun-like stars (4800-6300 K) and nearby FGK-type stars (3940-7220 K) accessible to such a mission. Our yield estimates are based on recently derived occurrence rates of rocky planets from the Kepler mission and our LIFE exoplanet observation simulation tool LIFEsim, which includes all main astrophysical noise sources, but no instrumental noise sources as yet. Depending on a pessimistic or optimistic extrapolation of the Kepler results, we find that during a 2.5-year search phase, LIFE could detect between ~10-16 (average) or ~5-34 (including 1\(\sigma\) uncertainties) rocky planets (0.5-1.5 R\({}_\rm{Earth}\)) within the optimistic HZ of Sun-like stars and between ~4-6 (average) or ~1-13 (including 1\(\sigma\) uncertainties) exo-Earth candidates (EECs) assuming four collector spacecraft equipped with 2 m mirrors and a conservative instrument throughput of 5%. With D=3.5 m or 1 m mirrors, the yield \(Y\) changes strongly, following approximately \(Y \propto D^{3/2}\). With the larger sample of FGK-type stars, the yield increases to ~16-22 (average) rocky planets within the optimistic HZ and ~5-8 (average) EECs. Furthermore, we find that in addition to the mirror diameter, the yield depends strongly on the total throughput, but only weakly on the exozodiacal dust level and the accessible wavelength range of the mission. When the focus lies entirely on Sun-like stars, larger mirrors (~3 m with 5% total throughput) or a better total throughput (~20% with 2 m mirrors) are required to detect a statistically relevant sample of ~30 rocky planets within the optimistic HZ.
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