An international team of astronomers discovered that the famous exoplanet orbiting the star GJ 1132 has lost its original atmosphere, but has acquired a new one. Thus, the planet transformed from a mini-Neptune into a rocky world similar to Earth. The discovery, reported in an article published in the arXiv.org preprint repository, allows us to learn more about planetary evolution.
The discovery of the unique rocky planet GJ 1132 b was announced in 2015. Its mass is 1.66 times the mass of the Earth, and in size it is 1.16 times larger. The exoplanet is only 41 light years distant, making it relatively close to the solar system. The period of its revolution around the parent star – the red dwarf Gliese 1132 – is 1.6 days. It always faces the luminary with one side, and the temperature on its surface is 257 degrees Celsius. In addition, the planet is exposed to radiation that is 15 times stronger than what the Earth receives from the Sun. Astronomers believe that the exoplanet originally belonged to the class of mini-Neptune, which represents an intermediate link between rocky planets and Neptune. It had a rather thick atmosphere, but the Gliese radiation “blew off” the gas envelope during the five billion years of the existence of GJ 1132 b. New observations made with the MPG / ESO telescope in Chile have revealed a secondary atmosphere for the planet.
The current gas envelope consists of hydrogen, hydrocyanic acid, methane and ammonia. The atmospheric pressure at the surface is similar to the atmospheric pressure of the Earth, and the atmosphere itself gradually evaporates into space. This does not fit the scenario, according to which it should have already evaporated. Computer simulations showed that the original hydrogen atmosphere of GJ 1132 b was swallowed up by an ocean of molten magma that covered the exoplanet.
Now the surface of the planet has already cooled down, but the interior continues to release hydrogen through volcanic activity. This discovery may explain why there are so many mini-Neptunes, as many of them become rocky planets with an atmosphere.