Water discovered for first time in habitable exoplanet
- Most exoplanets with atmospheres are giant balls of gas, and the handful of rocky planets for which data is available seem to have no atmosphere at all.
- Even if they did, most Earth-like planets are too far from their stars to have liquid water or so close that any H2O has evaporated.
- Discovered in 2015, K2-18b is one of hundreds of so-called "super-Earths" -- planets with less than ten times the mass of ours -- spotted by NASA's Kepler spacecraft. Future space missions are expected to detect hundreds more in the coming decades.
- Working with spectroscopic data captured in 2016 and 2017 by the Hubble Space Telescope, Tsiaras and his team used open-source algorithms to analyse the starlight filtered through K2-18b's atmosphere.
- They found the unmistakable signature of water vapour. Exactly how much remains uncertain, but computer modelling suggested concentrations between 0.1 and 50 per cent.
- By comparison, the percentage of water vapour in Earth's atmosphere varies between 0.2 percent above the poles, and up to four per cent in the tropics.
- There was also evidence of hydrogen and helium as well. Nitrogen and methane may also be present but with current technology remain undetectable.
- K2-18b orbits a red dwarf star about 110 light years distant -- a million billion kilometres -- in the Leo constellation of the Milky Way, and is probably bombarded by more destructive radiation than Earth.
- This is not only because super-Earths like K2-18b are the most common planets in our galaxy, but also because red dwarfs -- stars smaller than our Sun -- are the most common stars."
- The new generation of space-based star gazing instruments led by the James Webb Space Telescope and the European Space Agency's ARIEL mission will be able to describe exoplanet atmospheres in far greater detail.
- ARIEL, slated for a 2028 launch, will canvas some 1,000 planets, a large enough sampling to look for patterns and identify outliers.