Detecting Biosignatures in the Atmospheres of Gas Dwarf Planets with the James Webb Space Telescope

Abstract Exoplanets with radii between those of Earth and Neptune have stronger surface gravity than Earth, and can retain a sizable hydrogen-dominated atmosphere. In contrast to gas giant planets, we call these planets gas dwarf planets. The James Webb Space Telescope (JWST) will offer unprecedented insight into these planets. Here, we investigate the detectability of ammonia (NH3, a potential biosignature) in the atmospheres of seven temperate gas dwarf planets using various JWST instruments. We use petitRadTRANS and PandExo to model planet atmospheres and simulate JWST observations under different scenarios by varying cloud conditions, mean molecular weights (MMWs), and NH3 mixing ratios. A metric is defined to quantify detection significance and provide a ranked list for JWST observations in search of biosignatures in gas dwarf planets. It is very challenging to search for the 10.3–10.8 μm NH3 feature using eclipse spectroscopy with the Mid-Infrared Instrument (MIRI) in the presence of photon and a systemic noise floor of 12.6 ppm for 10 eclipses. NIRISS, NIRSpec, and MIRI are feasible for transmission spectroscopy to detect NH3 features from 1.5–6.1 μm under optimal conditions such as a clear atmosphere and low MMWs for a number of gas dwarf planets. We provide examples of retrieval analyses to further support the detection metric that we use. Our study shows that searching for potential biosignatures such as NH3 is feasible with a reasonable investment of JWST time for gas dwarf planets given optimal atmospheric conditions.

Download Full-text

Modeling Synthetic Spectra for Transiting Extrasolar Giant Planets: Detectability of H2S and PH3 with the James Webb Space Telescope

The Astrophysical Journal ◽

10.3847/1538-4357/aa978e ◽

2017 ◽

Vol 850 (2) ◽

pp. 199 ◽

Cited By ~ 6

Author(s):

Dong Wang ◽

Yamila Miguel ◽

Jonathan Lunine

Keyword(s):

Giant Planets ◽

Space Telescope ◽

Synthetic Spectra ◽

James Webb Space Telescope

Download Full-text

Search for giant planets around seven white dwarfs in the Hyades cluster with the Hubble Space Telescope

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3422 ◽

2020 ◽

Vol 500 (3) ◽

pp. 3920-3925

Author(s):

Wolfgang Brandner ◽

Hans Zinnecker ◽

Taisiya Kopytova

Keyword(s):

White Dwarfs ◽

Near Infrared ◽

Hubble Space Telescope ◽

Infrared Camera ◽

Detection Limits ◽

Giant Planets ◽

High Angular Resolution ◽

Mass Detection ◽

Space Telescope ◽

Hyades Cluster

ABSTRACT Only a small number of exoplanets have been identified in stellar cluster environments. We initiated a high angular resolution direct imaging search using the Hubble Space Telescope (HST) and its Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) instrument for self-luminous giant planets in orbit around seven white dwarfs in the 625 Myr old nearby (≈45 pc) Hyades cluster. The observations were obtained with Near-Infrared Camera 1 (NIC1) in the F110W and F160W filters, and encompass two HST roll angles to facilitate angular differential imaging. The difference images were searched for companion candidates, and radially averaged contrast curves were computed. Though we achieve the lowest mass detection limits yet for angular separations ≥0.5 arcsec, no planetary mass companion to any of the seven white dwarfs, whose initial main-sequence masses were >2.8 M⊙, was found. Comparison with evolutionary models yields detection limits of ≈5–7 Jupiter masses (MJup) according to one model, and between 9 and ≈12 MJup according to another model, at physical separations corresponding to initial semimajor axis of ≥5–8 au (i.e. before the mass-loss events associated with the red and asymptotic giant branch phase of the host star). The study provides further evidence that initially dense cluster environments, which included O- and B-type stars, might not be highly conducive to the formation of massive circumstellar discs, and their transformation into giant planets (with m ≥ 6 MJup and a ≥6 au). This is in agreement with radial velocity surveys for exoplanets around G- and K-type giants, which did not find any planets around stars more massive than ≈3 M⊙.

Download Full-text