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The Detection, Characterization, and Retrieval of Terrestrial Exoplanet Atmospheres.

Record Type:	Electronic resources : Monograph/item
Title/Author:	The Detection, Characterization, and Retrieval of Terrestrial Exoplanet Atmospheres./
Author:	Lustig-Yaeger, Jacob.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
Description:	405 p.
Notes:	Source: Dissertations Abstracts International, Volume: 82-05, Section: B.
Contained By:	Dissertations Abstracts International82-05B.
Subject:	Astronomy. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28088033
ISBN:	9798684661327

The Detection, Characterization, and Retrieval of Terrestrial Exoplanet Atmospheres.
Lustig-Yaeger, Jacob.

The Detection, Characterization, and Retrieval of Terrestrial Exoplanet Atmospheres. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 405 p.

Source: Dissertations Abstracts International, Volume: 82-05, Section: B.

Thesis (Ph.D.)--University of Washington, 2020.

This item must not be sold to any third party vendors.

With the upcoming launch of the James Webb Space Telescope (JWST), the first light of thirty-meter class ground based telescopes in the 2020s, and plans in the works for a next-generation space-based telescope designed from the outset to probe exoplanet habitability and biosignatures, we are entering the era of terrestrial exoplanet science. Soon we will have the opportunity to study the presence, composition, habitability, and biosignatures of terrestrial exoplanet atmospheres, enabling new perspectives on comparative planetology, astrobiology, and our place as humans within the cosmos. In this dissertation, we explore optimal astronomical observations and theoretical modeling approaches for constraining terrestrial exoplanet environments. In the first part of this dissertation, we investigate the extent of terrestrial exoplanet science that may be achievable in the JWST era. We begin by studying the feasibility and observational cost of detecting and characterizing the composition of the seven Earth-sized TRAPPIST-1 exoplanets with JWST. By positing several terrestrial atmospheric compositions that are plausible given the tumultuous history of atmospheric escape expected for this late M dwarf system, we use JWST noise models to determine the optimal observing modes and number of transits/eclipses necessary to detect the planet's atmospheres. We show that the likely common presence of CO2 in terrestrial atmospheres should drive our ability to detect all seven TRAPPIST-1 planet atmospheres with JWST's NIRSpec Prism, although as many as 30 transits may be required if the planets are cloudy Venus-like worlds. We find that water may be prohibitively difficult to detect in both Venus-like and habitable atmospheres due to its presence lower in the atmosphere where transit transmission spectra are less sensitive. Although the presence of biogenic O2 and O3 will be extremely challenging to detect, abiotically produced oxygen from past ocean loss may be detectable for all of the TRAPPIST-1 planets via O2-O2 collisionally induced absorption features at 1.06 and 1.27 µm, or via NIR O3 features for the outer three planets. These results constitute a suite of hypotheses on the nature and detectability of highly evolved terrestrial exoplanet atmospheres that may be tested with JWST. Although the presence of clouds in the TRAPPIST-1 planet atmospheres are not expected to prevent the atmospheres from being detected, we use models of cloudy Venus-like exoplanets to demonstrate that their atmospheres may remain significantly misunderstood. We find that JWST/Mid-IR Instrument (MIRI) Low Resolution Spectrometer (LRS) secondary eclipse emission spectroscopy in the 6 µm opacity window could probe at least an order of magnitude deeper pressures than transmission spectroscopy, potentially allowing access to the sub-cloud atmosphere for the two hot innermost TRAPPIST-1 planets. In addition, we identify two confounding effects of sulfuric acid aerosols that may carry strong implications for the characterization of terrestrial exoplanets with transmission spectroscopy: (1) there exists an ambiguity between cloud-top and solid surface in producing the observed spectral continuum; and (2) the cloud-forming region drops in altitude with semimajor axis, causing an increase in the observable cloud-top pressure with decreasing stellar insolation. Taken together, these effects could produce a trend of thicker atmospheres observed at lower stellar insolation--a convincing false positive for atmospheric escape and a "mirage" of the cosmic shoreline. These studies emphasize that JWST should be able to detect terrestrial exoplanet atmospheres around the smallest of stars, but characterizing the unique nature of secondary atmospheres, including habitability and biosignature detection, may be beyond JWST's capabilities. In the second part of this dissertation, we investigate terrestrial exoplanet science cases that a future space telescope could undertake. A future coronagraph-equipped, direct-imaging telescope may offer the best chance to directly search for oceans on the surface of exoplanets. To explore the depths of ocean detection, we introduce a novel approach for exoplanet ocean detection that combines two previously distinct techniques--rotational mapping and ocean glint--into the most rigorous approach to date for determining exoplanet habitability. We demonstrate that time-series observations of Earth-like exoplanets at crescent phase can be used to search for the "blinking" of ocean glint as continents, which interrupt the ocean glint spot, rotate into and out of the illuminated planet crescent. This effect causes large-amplitude, time-varying signals in the reflected light, which can be used to longitudinally map the ocean glint. In our simulations, we find that the retrieved apparent albedo of ocean-bearing longitudes is increased by a factor of 5 at crescent phase due to the contribution from glint, compared to the albedo of the same longitudes at quadrature phase. Meanwhile, the predominately land-bearing longitudes exhibit no significant change in apparent albedo with phase. Thus, by using time-dependent information we can. (Abstract shortened by ProQuest).

ISBN: 9798684661327Subjects--Topical Terms:

517668
Astronomy.
Subjects--Index Terms:

Astrobiology

The Detection, Characterization, and Retrieval of Terrestrial Exoplanet Atmospheres.
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500 $a Source: Dissertations Abstracts International, Volume: 82-05, Section: B.
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506 $a This item must not be sold to any third party vendors.
520 $a With the upcoming launch of the James Webb Space Telescope (JWST), the first light of thirty-meter class ground based telescopes in the 2020s, and plans in the works for a next-generation space-based telescope designed from the outset to probe exoplanet habitability and biosignatures, we are entering the era of terrestrial exoplanet science. Soon we will have the opportunity to study the presence, composition, habitability, and biosignatures of terrestrial exoplanet atmospheres, enabling new perspectives on comparative planetology, astrobiology, and our place as humans within the cosmos. In this dissertation, we explore optimal astronomical observations and theoretical modeling approaches for constraining terrestrial exoplanet environments. In the first part of this dissertation, we investigate the extent of terrestrial exoplanet science that may be achievable in the JWST era. We begin by studying the feasibility and observational cost of detecting and characterizing the composition of the seven Earth-sized TRAPPIST-1 exoplanets with JWST. By positing several terrestrial atmospheric compositions that are plausible given the tumultuous history of atmospheric escape expected for this late M dwarf system, we use JWST noise models to determine the optimal observing modes and number of transits/eclipses necessary to detect the planet's atmospheres. We show that the likely common presence of CO2 in terrestrial atmospheres should drive our ability to detect all seven TRAPPIST-1 planet atmospheres with JWST's NIRSpec Prism, although as many as 30 transits may be required if the planets are cloudy Venus-like worlds. We find that water may be prohibitively difficult to detect in both Venus-like and habitable atmospheres due to its presence lower in the atmosphere where transit transmission spectra are less sensitive. Although the presence of biogenic O2 and O3 will be extremely challenging to detect, abiotically produced oxygen from past ocean loss may be detectable for all of the TRAPPIST-1 planets via O2-O2 collisionally induced absorption features at 1.06 and 1.27 µm, or via NIR O3 features for the outer three planets. These results constitute a suite of hypotheses on the nature and detectability of highly evolved terrestrial exoplanet atmospheres that may be tested with JWST. Although the presence of clouds in the TRAPPIST-1 planet atmospheres are not expected to prevent the atmospheres from being detected, we use models of cloudy Venus-like exoplanets to demonstrate that their atmospheres may remain significantly misunderstood. We find that JWST/Mid-IR Instrument (MIRI) Low Resolution Spectrometer (LRS) secondary eclipse emission spectroscopy in the 6 µm opacity window could probe at least an order of magnitude deeper pressures than transmission spectroscopy, potentially allowing access to the sub-cloud atmosphere for the two hot innermost TRAPPIST-1 planets. In addition, we identify two confounding effects of sulfuric acid aerosols that may carry strong implications for the characterization of terrestrial exoplanets with transmission spectroscopy: (1) there exists an ambiguity between cloud-top and solid surface in producing the observed spectral continuum; and (2) the cloud-forming region drops in altitude with semimajor axis, causing an increase in the observable cloud-top pressure with decreasing stellar insolation. Taken together, these effects could produce a trend of thicker atmospheres observed at lower stellar insolation--a convincing false positive for atmospheric escape and a "mirage" of the cosmic shoreline. These studies emphasize that JWST should be able to detect terrestrial exoplanet atmospheres around the smallest of stars, but characterizing the unique nature of secondary atmospheres, including habitability and biosignature detection, may be beyond JWST's capabilities. In the second part of this dissertation, we investigate terrestrial exoplanet science cases that a future space telescope could undertake. A future coronagraph-equipped, direct-imaging telescope may offer the best chance to directly search for oceans on the surface of exoplanets. To explore the depths of ocean detection, we introduce a novel approach for exoplanet ocean detection that combines two previously distinct techniques--rotational mapping and ocean glint--into the most rigorous approach to date for determining exoplanet habitability. We demonstrate that time-series observations of Earth-like exoplanets at crescent phase can be used to search for the "blinking" of ocean glint as continents, which interrupt the ocean glint spot, rotate into and out of the illuminated planet crescent. This effect causes large-amplitude, time-varying signals in the reflected light, which can be used to longitudinally map the ocean glint. In our simulations, we find that the retrieved apparent albedo of ocean-bearing longitudes is increased by a factor of 5 at crescent phase due to the contribution from glint, compared to the albedo of the same longitudes at quadrature phase. Meanwhile, the predominately land-bearing longitudes exhibit no significant change in apparent albedo with phase. Thus, by using time-dependent information we can. (Abstract shortened by ProQuest).
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