Potentially habitable exoplanet could broaden search for life beyond Earth

29 Février, 2020, 08:57 | Auteur: Therese Cote
  • The new exoplanet has been likened to a mini Neptune More

"The thermodynamic conditions at the surface of the H2O layer range from the supercritical to liquid phases, with a range of solutions allowing for habitable conditions on K2-18b", the researchers wrote in the study's abstract.

With a bulk density between Earth and Neptune, K2-18b may be expected to possess a H/He envelope.

Discovered in 2015, K2-18b has a radius of 2.6 times that of Earth and is about 8.6 times as massive.

For most of human history, the question of whether or not extraterrestrial life exists has been philosophical.

Last autumn two different teams of astronomers detected water vapour encircling the exoplanet.

The presence of an enormous, Neptune-size exoplanet 90 light-years from Earth has been confirmed after it was first spotted in 2019. If this hydrogen layer is too thick, it would increase the exoplanet's temperature and pressure, making it inhospitable.

It may sound familiar - that's because it made big news past year when astronomers found water vapour in its atmosphere.

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It is, however, too early to determine whether any life exists on K2-18b.

The online publication mentioned above notes that a team of researchers in the United Kingdom describe in The Astrophysical Journal Letters the way in which they were able to calculate a range of possible atmospheres for the planet, "based on its mass, size, and previously measured spectra of light that passed from K2-18b's star through its atmosphere". "To establish the prospects for habitability, it is important to obtain a unified understanding of the interior and atmospheric conditions on the planet", Madhusudhan said. And it's within the habitable zone of its star, or the right distance from the exoplanet to the star that means liquid water can exist on the planet's surface.

The researchers noted that whether these levels can be attributed to biological processes remains to be seen. In the present work, we investigate the atmospheric and interior properties of K2-18b based on its bulk properties and its atmospheric transmission spectrum. "We explored a wide range of possible interior compositions that could explain all the data together, including the measured mass and radius of the planet". Even though the red dwarf star is much cooler than our sun it still emits the same heat and liquid water can be stable as well on the planet's surface.

And they found the maximum amount of hydrogen that could explain the observed properties of the planet was around 6 percent of its mass - although most of the solutions had far less hydrogen.

"We wanted to know the thickness of the hydrogen envelope - how deep the hydrogen goes", said Matthew Nixon, a PhD student at Cambridge University.

This study opens the search for habitable conditions and bio-signatures outside the solar system to exoplanets that are significantly larger than the Earth, beyond Earth-like exoplanets, they said.

The techniques used by the Cambridge experts can be refined further by using future observations from NASA's James Webb Space Telescope. The minimum is similar to Earth.

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