13:45 〜 15:15
[PEM11-P06] Searching for exoplanets with oceans: the ExTerrO initiative
キーワード：exoplanets, planetary science, oceanology, exoplanet habitability
Finding planetary bodies in the Solar system and beyond, with surface or subsurface oceans, which may harbor life, is one of the main goals of planetary studies. As a result of this search, an exponentially growing number of exoplanets have been discovered in the last decades (Kepler, K2, TESS, and COROT missions). Databases, built on the astronomical and planetary characteristics of the approximately 5100 discovered exoplanets, provide us a unique opportunity to build and test new theories which may lead to the development of ocean-indicating proxies in the case of exoplanets with limited information about their atmosphere or surface.
The ExTerrO (Extraterrestrial Oceanography) framework, introduced in this study, uses astronomical and planetary data, stored in exoplanetary datasets, and the same parameters of Earth and Mars as an analog. The theory, behind the research, is based on the geological evidence of the ocean formation on Earth (from “Aquatic Earth”, Hadean) and the appearance of the putative early ocean on Mars (“Oceanus Borealis”, Noachian) and their planetary history (from ca. 4 Ga). We use these planetary analogs as roots of our theory, to find similar or partially similar exoplanets in the modified NASA Exoplanet Archive.
From the basic dataset (NASA Exoplanet Archive), filtering to the Sun’s spectral type (G-type stars) is necessary: it leaves a dataset, which contains similar star systems to the Solar System, supposedly with a close stellar evolutionary path and lifetime (Fig. 1a). There are currently around 2000 confirmed planets around various G-type stars, some of them in the same star system. The G-type star dataset must be filtered further, to find exoplanets between the minimum (the estimated time of ocean formation on the analog planets) and the current age of Earth, when the Global Ocean still exists on its surface (0.5 – 4.5 Ga). Their resemblance to these analogs can be assessed from the aspect of their astronomical and planetary parameters (Figs. 1b and c).
Theoretically surface ocean formation in planets may be influenced by the combination of various parameters, thus our theory suggests that along the stellar, orbital, and planetary parameters, the more of them applicable to an exoplanet with only a small divergence from Earth and/or early Mars, the greater the possibility of ocean formation (Fig. 1c). The number of the applied astronomical/planetary parameters (such as planetary mass, semi-major axis, and insolation flux) and their order of importance in ocean forming are yet to be decided (P1, P1,2…Pn; Fig. 1c). Also, further fine-tuning and different combinations of these parameters are required.
Due to the currently operating (TESS, CHEOPS, JWST) and planned (PLATO, ARIEL) exoplanet search missions, more confirmed targets, and more precise measurements are expected in the coming years. Following its development from theory to a tool, the proposed framework of the ExTerrO initiative may help the evaluation of the continuously growing exoplanet data regarding the possibility of ocean formation in exoplanetary systems. If the ExTerrO framework provides proxy(ies) (combination of parameters) for the indication of ocean forming, it can contribute to the selection of prime candidates for future individual exoplanet research.
Figure 1. The flowchart and theory behind the introduced ExTerrO framework, for analyzing the probability of ocean formation on exoplanets. *: During our approach, only the past (from the first ocean formation, 0.5 Ga) to the current statuses of Earth and Noachian to Hesperian Mars were considered.
The ExTerrO (Extraterrestrial Oceanography) framework, introduced in this study, uses astronomical and planetary data, stored in exoplanetary datasets, and the same parameters of Earth and Mars as an analog. The theory, behind the research, is based on the geological evidence of the ocean formation on Earth (from “Aquatic Earth”, Hadean) and the appearance of the putative early ocean on Mars (“Oceanus Borealis”, Noachian) and their planetary history (from ca. 4 Ga). We use these planetary analogs as roots of our theory, to find similar or partially similar exoplanets in the modified NASA Exoplanet Archive.
From the basic dataset (NASA Exoplanet Archive), filtering to the Sun’s spectral type (G-type stars) is necessary: it leaves a dataset, which contains similar star systems to the Solar System, supposedly with a close stellar evolutionary path and lifetime (Fig. 1a). There are currently around 2000 confirmed planets around various G-type stars, some of them in the same star system. The G-type star dataset must be filtered further, to find exoplanets between the minimum (the estimated time of ocean formation on the analog planets) and the current age of Earth, when the Global Ocean still exists on its surface (0.5 – 4.5 Ga). Their resemblance to these analogs can be assessed from the aspect of their astronomical and planetary parameters (Figs. 1b and c).
Theoretically surface ocean formation in planets may be influenced by the combination of various parameters, thus our theory suggests that along the stellar, orbital, and planetary parameters, the more of them applicable to an exoplanet with only a small divergence from Earth and/or early Mars, the greater the possibility of ocean formation (Fig. 1c). The number of the applied astronomical/planetary parameters (such as planetary mass, semi-major axis, and insolation flux) and their order of importance in ocean forming are yet to be decided (P1, P1,2…Pn; Fig. 1c). Also, further fine-tuning and different combinations of these parameters are required.
Due to the currently operating (TESS, CHEOPS, JWST) and planned (PLATO, ARIEL) exoplanet search missions, more confirmed targets, and more precise measurements are expected in the coming years. Following its development from theory to a tool, the proposed framework of the ExTerrO initiative may help the evaluation of the continuously growing exoplanet data regarding the possibility of ocean formation in exoplanetary systems. If the ExTerrO framework provides proxy(ies) (combination of parameters) for the indication of ocean forming, it can contribute to the selection of prime candidates for future individual exoplanet research.
Figure 1. The flowchart and theory behind the introduced ExTerrO framework, for analyzing the probability of ocean formation on exoplanets. *: During our approach, only the past (from the first ocean formation, 0.5 Ga) to the current statuses of Earth and Noachian to Hesperian Mars were considered.