A potential water world orbiting a faint red star just 120 light years away just got a little more exciting.

A probe into the atmosphere of K2-18b reveals the presence of carbon dioxide and methane, as scientists had previously predicted for an ocean planet or Hycean world with a hydrogen-rich atmosphere.

Moreover, the observations reveal a tantalising hint of dimethyl sulfide, a signature of biology that scientists had predicted would be detectable on Ocean worlds. On Earth, dimethyl sulphide is produced only by life, and the majority is derived from marine phytoplankton.

"Our findings emphasise the importance of considering a variety of habitable environments in the search for life elsewhere," says astronomer Nikku Madhusudhan from the University of Cambridge.

"Traditionally, the search for life on exoplanets has primarily focused on smaller rocky planets, but larger Hycean worlds are significantly more favourable for atmospheric observations."

Astronomers have had their eyes on K2-18b for some time. This planet was the first habitable zone rocky world to have water detected in its atmosphere in 2019 (unlike gaseous planets like Jupiter and Saturn). The habitable zone is the distance from the host star where liquid water can remain on the surface, neither so far away that it freezes into ice, nor so far away that it evaporates away.

K2-18b is very different from Earth. With a mass of about 8.6 Earth masses and a radius of 2.6 Earth radii, it is significantly heavier and orbits the red dwarf star quite closely every 33 days.

However, red dwarf stars are cooler and dimmer than the Sun, which means that K2-18b receives stellar radiation similar to Earth. Just the right consistency, like Baby Bear's porridge.

Madhusudhan and colleagues evaluated K2-18b in 2020 and found that habitability is possible. They also identified K2-18b as a potential Hycean world in 2021.

"Some conditions in the oceans of these worlds may be similar to habitable conditions in Earth's oceans, i.e. similar temperatures and pressures, the presence of liquid water, and energy from the star," Madhusudhan told ScienceAlert at the time.

"There are many open questions but at this stage this is just a first guess. The hypothesis is that if microbial aquatic life can occur in these oceans, as on Earth, then some biosignatures may also be common."

But the researchers needed more data. They needed the James Webb Space Telescope to take a closer look at the exoplanet's atmosphere and look for signs. And they finally found it.

Using JWST's near-infrared NIRSpec and NIRISS instruments, they tracked K2-18b as it orbited twice between us and its host star. They then studied the difference in the star's light, the result of passing through the exoplanet's atmosphere and being modified by its composition.

When they analysed these changes, the researchers found evidence of carbon molecules, carbon dioxide and methane. The light spectrum also revealed hints - but only hints - of dimethyl sulphide.

This means that the observations are not enough to determine whether K2-18b is habitable. But we are very close.

"Upcoming Webb observations should be able to confirm whether dimethyl sulphide is indeed present at significant levels in the atmosphere of K2-18b," says Madhusudhan.

The next step will be to point JWST's mid-infrared MIRI at the exoplanet, investigate the possibility of dimethyl sulfide in more detail, and look for other possible biosignatures in the exoplanet's atmosphere.

In a broader context, the results show that JWST is capable of detecting biosignatures in exoplanet atmospheres, an important first step towards finding life on another planet.

"Our ultimate goal is the detection of life on a habitable exoplanet, which will transform our understanding of our place in the Universe," says Madhusudhan.

"Our findings are a promising step towards a better understanding of Hycean worlds in this quest."

I'm extremely excited about this news. What do you think?

 

Source: https://www.sciencealert.com/