Exoplanet that twice the size of Earth could have right conditions for life, Astronomers have discovered that the exoplanet is more than twice the size of a potentially habitable Earth, opening the search for life on a planet much larger than Earth but smaller than Neptune.
A team at Cambridge University used mass, radius, and atmosphere data from the ex-planet K2-18b and found that the planet could receive liquid water in habitable conditions in a hydrogen-rich atmosphere.
The extrasolar planet K2-18b, which is 124 light years away, has 2.6 times the radius and 8.6 times the mass of the earth and orbits its star in a habitable zone where temperature can allow liquid water. Exoplanet that twice the size of Earth could have right conditions for life.
The planet was the subject of extraordinary media coverage in the fall of 2019, when two different teams announced the detection of water vapor in a hydrogen-rich atmosphere.
The extent of the atmosphere and interior conditions below is unknown.
Water vapor is in the atmosphere of many extrasolar planets, but even if the planet is in the habitable zone, that does not mean that there are habitable conditions on the surface, researchers say.
To create habitat prospects, it is important to gain a general understanding of the internal conditions and atmosphere of the planet, especially whether liquid water can exist under the atmosphere.
Given the size of K2-18b, it is believed to be more like a smaller version of Neptune than a larger version of Earth.
Mini-Neptune is expected to have a significant hydrogen envelope that encloses a layer of high-pressure water with the inner core of rock and iron. If the hydrogen envelope is too thick, the temperature and surface pressure of the underlying water layer will be too high to maintain life. Exoplanet that twice the size of Earth could have right conditions for life.
Madhusudhan and his team have shown that despite the size of K2-18b, the hydrogen envelope is not necessarily too thick and the water layer has suitable conditions for the maintenance of life.
They use observations of the existing atmosphere, as well as mass and radius, to determine the composition and structure of the atmosphere and interior, and use detailed numerical models and statistical methods to explain the data.
Researchers have confirmed that the atmosphere is rich in hydrogen with large amounts of water vapor.
They also found that levels of other chemicals, such as methane and ammonia, were lower than expected for such an atmosphere. It remains to be seen whether these values are caused by biological processes.
The team then used the nature of the atmosphere as a boundary condition for the interior models of the planet. They examined various models that could explain the nature of the planet’s atmosphere, mass, and radius.
This allows them to obtain a number of possible internal conditions, including the level of the hydrogen envelope and the temperature and pressure in the water layer.
Researchers have found that the maximum amount of hydrogen shell allowed by the data is around 6% of the mass of the planet, although most solutions require far less.
The minimum amount of hydrogen is about one millionth of a mass, similar to the mass of the Earth’s atmosphere. Exoplanet that twice the size of Earth could have right conditions for life.
In particular, a number of scenarios allow the ocean world with liquid water under the atmosphere at pressures and temperatures similar to those in the oceans on Earth.
This research opens exoplanets that are significantly larger than Earth, outside Earth-like extraterrestrials, to search for habitable conditions and biosignature outside the solar system. In addition, planets like K2-18b are more accessible for atmospheric observations with current and future observation options.
The atmospheric constraints obtained in this study can be improved by future observations from large facilities such as the upcoming James Web Space Telescope.