The model, which refines that presented in an earlier paper by the same researchers, allows the calculation of the amount of water that should be produced through the atmosphere/magma interaction. The authors have created a planetary population synthesis model that tracks the mass and orbital evolution of planets in formation, including among other things the structure of the protoplanetary disk, potential orbital migration, instabilities in multi-planet systems and the effects of water production in the primordial atmosphere. In this scenario, the amount of water present depends on how the planet forms. Credit: National Astronomical Observatory of Japan. The dotted line is the present-day seawater amount on the Earth. ![]() Orange is the result when the model of the present study is used and the effect of water production in the primordial atmosphere is taken into account. Green is the result of calculations following the conventional model and considering only the acquisition of water-bearing rocks. Image: Probability distribution of seawater mass fractions for planets of Earth-like mass (0.3-3 times Earth mass) located in the habitable zone around M-type stars (0.3 solar masses). ![]() The results suggest that including this water production process significantly affects the predicted water amount distribution of exoplanets in the habitable zone around M dwarfs. By assuming effective water production, we recently showed that nearly-Earthmass planets can acquire sufficient amounts of water for their atmospheric vapour to survive in harsh UV environments around pre-main-sequence M stars. …water can be secondarily produced in a primordial atmosphere of nebular origin through reaction of atmospheric hydrogen with oxidising minerals from the magma ocean, which is formed because of the atmospheric blanketing effect, thereby enriching the primordial atmosphere with water. Water is accumulated through the chemical reaction between atmospheric hydrogen and the oxides found in the surface magma – a magma ‘ocean’ – of the young planet. It involves interactions between the hydrogen-rich atmosphere, drawn from the protoplanetary disk, and the magma ocean that would be present from impacts during the early days of planet formation. In a new paper in Nature Astronomy, the authors argue that there is a mechanism beyond the infall of icy planetesimals that can produce water as a young planet accumulates its atmosphere. Are habitable planets around such stars, then, a celestial rarity? According to Tadahiro Kimura, a doctoral student at the University of Tokyo, and Masahiro Ikoma (National Astronomical Observatory of Japan), a number of models suggest that terrestrial planets around M-dwarfs would have either too much water or no water at all. Thus new work on water content in such systems is welcome.įor purposes of reference, Earth’s seawater accounts for 0.023% of the planet’s total mass. Too much of it could suppress weathering in the geochemical carbon cycle, but too little does not allow for the development of a temperate climate. In addition to flare activity, we also have to reckon with the presence of water. But M-dwarfs make challenging homes for life, if indeed it can exist there. ![]() ![]() Soon-to-be commissioned ground-based extremely large telescopes will likewise play a role as we examine nearby transiting systems. Recent studies have shown that the James Webb Space Telescope has the precision to at least partially characterize the atmospheres of Earth-class planets around some M-dwarfs. The small size of these stars and the significant transit depth this allows when an Earth-mass planet crosses their surface as seen from Earth mean that atmospheric analysis by ground- and space-based telescopes should be feasible via transmission spectroscopy. Small M-dwarf stars, the most common type of star in the galaxy, are likely to be the primary target for our early investigations of habitable planets.
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