Monday, May 31, 2021

A cold exoplanet

Most of the exoplanets that have been discovered to date have very high temperatures, much higher than those we are used to on our planet.

On the contrary, there are only a few exoplanets with very low temperatures: among these stands OGLE-2005-BLG-390L b, which according to the most recent estimates should have a temperature of just 50 degrees above absolute zero (-220 Celsius degrees)!

The reason why the exoplanet is so cold is very simple: it orbits a faint red dwarf that has a mass of just 0.22 solar masses and a brightness just 0.5% that of our star.

Furthermore, the distance between the exoplanet and the red dwarf is very large: 2.6 AU. At first glance this distance may seem small, especially when compared to those of the Solar System, where the 2.6 AU are located about halfway between Mars and the Main Asteroid Belt. However, it must be taken into account that the radiant energy emitted by the red dwarf is much lower than that of the Sun. Consequently, the radiation that reaches the orbit of the exoplanet is almost zero and this implies a temperature of only 50 Kelvin.

The physical characteristics of OGLE-2005-BLG-390L b are not yet known precisely: it is believed it os a Super Earth with a mass about five times that of our planet.

Credit: ESO.

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