1:45 PM - 3:15 PM
[PEM11-P04] Simulation of Exoplanetary Oxygen Exospheres for Ultraviolet Transit Observation
Keywords:Exoplanet, Transit method, Exosphere
To date, many exoplanets have been discovered, some of which are Earth-like planets in their respective habitable zones, and JWST is expected to expand our understanding of the lower atmospheres of these terrestrial exoplanets. Low-mass stars emit strong X-ray and extreme ultraviolet radiation (XUV) because of their slow evolution. Thus, their terrestrial exoplanets can be exposed to this strong radiation, which would expand their atmospheres by heating. Because such an expanded atmosphere would absorb considerable amounts of ultraviolet radiation, these stellar ultraviolet emissions appear greatly attenuated during a planetary transit.
We develop an ultraviolet spectrometer for observing the atmospheres of terrestrial planets in the habitable zone around low-mass stars, which will be used to perform transit spectroscopy of the atomic absorption lines of oxygen (triplet lines at approximately 130.5 nm) because oxygen is a major component of the lower and upper atmosphere on Earth. When attenuation of oxygen lines is detected, it indicates that the planetary atmosphere contains oxygen. Furthermore, since the oxygen density in the upper atmosphere and exosphere strongly depends on temperature and dynamical state in addition to the atmospheric composition, the transit depth could reveal insight into the heating and cooling processes in the upper atmospheres. Thus, observations with the spectrometer can help us discover exoplanets with Earth-like environments and approximate their evolution.
In this study, we estimated the transit depth of the atmospheric absorption lines of oxygen during the transit of an Earth-like planet in the habitable zone around TRAPPIST-1. We focused on the emission lines at 130.4 and 130.6 nm because of weak interstellar absorption. We assumed that the planet has a spherically symmetric atmosphere, for which we adopted the temperature and compositional structure consistent with a transonic atmosphere (Johnstone et al., 2019). We extrapolated their results to higher altitudes beyond the exobase. These results showed that an integrated transit depth at wavelengths becomes 44.3% at the center of the transit. Finally, we discuss whether oxygen atoms in exoplanetary atmospheres can be detected considering the performance of the instrument.
We develop an ultraviolet spectrometer for observing the atmospheres of terrestrial planets in the habitable zone around low-mass stars, which will be used to perform transit spectroscopy of the atomic absorption lines of oxygen (triplet lines at approximately 130.5 nm) because oxygen is a major component of the lower and upper atmosphere on Earth. When attenuation of oxygen lines is detected, it indicates that the planetary atmosphere contains oxygen. Furthermore, since the oxygen density in the upper atmosphere and exosphere strongly depends on temperature and dynamical state in addition to the atmospheric composition, the transit depth could reveal insight into the heating and cooling processes in the upper atmospheres. Thus, observations with the spectrometer can help us discover exoplanets with Earth-like environments and approximate their evolution.
In this study, we estimated the transit depth of the atmospheric absorption lines of oxygen during the transit of an Earth-like planet in the habitable zone around TRAPPIST-1. We focused on the emission lines at 130.4 and 130.6 nm because of weak interstellar absorption. We assumed that the planet has a spherically symmetric atmosphere, for which we adopted the temperature and compositional structure consistent with a transonic atmosphere (Johnstone et al., 2019). We extrapolated their results to higher altitudes beyond the exobase. These results showed that an integrated transit depth at wavelengths becomes 44.3% at the center of the transit. Finally, we discuss whether oxygen atoms in exoplanetary atmospheres can be detected considering the performance of the instrument.