Water found for the first time on a potentially habitable planet

Copyright of the image
ESA / UCL

Astronomers have for the first time discovered water in the atmosphere of a planet orbiting the habitable zone of a distant star.

The discovery makes the world – called K2-18b – a plausible candidate in the quest for extraterrestrial life.

In 10 years, the new space telescopes could determine if the atmosphere of K2-18b contains gases likely to be produced by living organisms.

The details have been published in the scientific journal Nature Astronomy.

The principal scientist, Professor Giovanna Tinetti of University College London (UCL) described the discovery as "hallucinating".

"This is the first time we detect water on a planet in the habitable zone around a star where temperature is potentially compatible with the presence of life," he said. she declared.

The livable area is the region around a star where temperatures are favorable enough that water exists in liquid form on the surface of a planet.

K2-18b is 111 light-years away – about 650 million kilometers – from Earth, too far to send a probe. The only option is therefore to wait for the next generation of space telescopes to be launched in the 2020s and to search for gases in the atmosphere of the planet that could only be produced by living organisms, according to the Dr. Ingo Waldmann of UCL.

"It's one of the biggest scientific issues and we've always wondered if we're alone in the universe," Dr. Waldmann said. "In the next 10 years, we will know if there are chemicals due to life in these atmospheres."

---

What is an exoplanet?

• Planets beyond our solar system are called exoplanets
• The first exoplanet was discovered in 1992, orbiting a pulsar (neutron star emitting electromagnetic radiation).
• More than 4,000 have been detected to date using several techniques
• Many of these worlds are large planets supposed to resemble Jupiter or Neptune.
• Many giant planets have been found in orbit very close to their stars

---

The team behind this discovery examined the planets discovered by the Hubble Space Telescope between 2016 and 2017. Researchers have identified some of the chemicals in their atmosphere by studying changes in starlight when the planets revolved around their suns. The light filtered through the atmospheres of the planets was slightly modified by the composition of the atmosphere.

Only K2-18b has revealed the molecular signature of water, an essential ingredient of life on Earth. Computer modeling of the data suggested that water could account for up to 50% of its atmosphere.

The new planet has a little more than twice the size of the Earth and has a temperature cold enough to have liquid water, between zero and 40 ° C.

Dr. Angelos Tsiaras, a member of the UCL team, said finding water in the atmosphere of a potentially livable exoplanet was "incredibly exciting".

He said, "It brings us closer to the answer to the fundamental question: Is the Earth unique?"

Long-haul

One difficulty with this approach, however, is that astronomers can not agree on the gases that would constitute proof of life. It could be longer.

According to Professor Tinetti, this will probably require a study of the chemical composition of, perhaps, hundreds of worlds and an understanding of how they are created and evolve.

"The Earth really stands out in our own solar system, it contains oxygen, water, and ozone, but if we find all of this around a planet around A distant star, we must be careful in saying that she supports life, "she said.

"That's why we need to understand not a handful of planets in the galaxy, but hundreds of them, and we hope the habitable planets will stand out, that we'll see a big difference between habitable planets and those who are not. "

Copyright of the image
RAL Space ESA / STFC / UCL / Europlanet-Scientific Office

Dr. Beth Biller of the Edinburgh University's Institute of Astronomy said that she thought that evidence of life on a planet around a star far away would eventually be discovered.

"It would be a paradigm shift for all humanity," she told BBC News.

"It will not necessarily be necessary to call AND at home – more likely microbes or a simple life – even if (when that happens) it will be huge."

The eventual launch of NASA's James Webb Space Telescope (JWST) in 2021, and the European Space Agency's Ariel mission seven years later, will allow astronomers to study in detail the atmospheres of various detected worlds. until now.

Water was detected on other planets, but they were too big or too hot to sustain life. The smaller, colder planets are much more difficult to detect. The UCL team was able to achieve this by developing algorithms capable of determining the chemical composition of atmospheres of potentially habitable worlds.

K2-18b was discovered in 2015 and is one of hundreds of super-Earth-planets whose mass is between Earth and Neptune – discovered by the NASA Kepler probe. Nasa 's mission in Tess is expected to detect hundreds of others in the coming years.

The research was funded by the European Research Council and the UK Council for Scientific and Technological Facilities, part of the UK Research and Innovation Agency (UKRI).

Follow Pallab on Twitter