| アブストラクト |
The increasing interest in low-mass planets spurs, at least in part, from the expectation that some of them may be similar to Earth and perhaps habitable. Before we can solve the question of habitability there are several previous steps needed to characterizing these planets. The first one is to determine their composition from the limited data that is currently available for exoplanets: masses and radii. In contrast to the giant planets that are mostly made of hydrogen and helium, low-mass planets are expected to be more complex in their constituents: rocks, metals, water/ices, some H/He. Thus, the problem is inherently degenerate in nature. I will present the current data, the basics behind an internal structure model that is needed to infer composition and our current understanding of the low-mass transiting exoplanets with measured masses.
While the data is restricted for exoplanets, and especially so for super-Earths, as they are challenging to detect, the good news is that they are numerous. Several surveys have shown that the occurrence of super-Earths is larger than massive exoplanets. And while uniquely constraining the composition of these planets is not possible, we can set lower and upper limits to their bulk chemical composition. The composition of a planet reflects the initial chemical inventory of the solar nebula from which they form plus any subsequent formation process (such as giant collisions and atmospheric evaporation). I will discuss possible connections we can draw from the detected super-Earths, and prospects for the future.
In addition, planets develop habitable conditions, thus understanding their thermal evolution is important. So far, there has been a debate about whether or not plate tectonics is a viable mode in which massive rocky planets can transport heat out. I will present the basic ideas behind mantle convection, the different approaches by the different models, and discuss their results. Also, I will discuss the connection between habitability and mode of tectonism. |
