How studying climate patterns in distant worlds can help in the search for 'alien life'

Detecting gases like oxygen and methane can offer clues on whether an exoplanet is habitable

The landmark discovery of Trappist-1 set off a wave of excitement across the space community. It was the first time multiple Earth-sized planets were found in a habitable zone and were orbiting the same star – Trappist-1. Courtesy: Nasa

All seven planets orbiting Trappist-1 are believed to be rocky and have potential for water on the surface. Courtesy: Nasa

Located in a habitable zone, Kepler-22b was labelled by Nasa as ‘super Earth’. Researchers believe the planet, which is larger than Earth, could be another ocean world. However, because of the planet’s extreme tilt, the north and south poles would experience sunlight and darkness for half a year each. Courtesy: Nasa

Discovered in 2020, Toi 700 d is only 20 per cent larger than Earth and orbits an M Dwarf star – a cool and stable type of star that do not release killer stellar flares, or radiation. Located 100 million light years away from Earth, one year on the planet is 37.4 days. Courtesy: Nasa

Discovered in 2011, KEPLER-20e is an Earth-size planet that orbits a sun-like star outside of the solar system. It is too close to its star to be in the habitable zone, so it cannot hold liquid water. However, the discovery was still groundbreaking because it was the first time small exoplanets were found to be orbiting around a star that was similar to the Sun. Courtesy: Nasa

Kepler-20f was discovered along with Kepler-20e. A year on the planet is19.6 days. Courtesy: Nasa

The search for alien life has always fascinated humanity, driving scientists to explore beyond our solar system.

One of the most promising methods in this quest involves studying the climates of exoplanets, or planets that orbit stars outside our solar system.

Climate patterns on these distant worlds can offer clues about their potential to harbour life, particularly by examining their atmospheric composition.

Stanimir Metchev, a professor at the Institute for Earth and Space Exploration at Western University, Canada, said that certain gases in the atmosphere suggest whether or not that planet possibly hosts life.

“For life as we know it on Earth, we look for gases that support life or indicate its presence: oxygen or ozone, water vapour, methane (produced by biological decay), and carbon dioxide,” he told The National.

“Among these, the most telling pair is oxygen plus methane. Normally, they react very efficiently, until one of them is completely depleted from the atmosphere.

“If both are observed to exist at the same time, as they do in Earth’s atmosphere, then both are being produced at present: oxygen through photosynthesis and methane through decay.”

He said that the combination of oxygen and methane in an exoplanet’s atmosphere is “perhaps the strongest indicator of life as we know it”.

Insights from the TRAPPIST-1 System

The TRAPPIST-1 system, located about 39 light-years from Earth, has become a focal point in the search for habitable exoplanets.

This system features seven Earth-sized planets, three of which are in the habitable zone, where conditions might be right for liquid water to exist.

“TRAPPIST-1 has multiple rocky planets, three of which are potentially habitable. Similar, cool, and small stars, called red dwarfs, may be the best chance for us to find life in the near future,” Prof Metchev said.

“These kinds of stars account for three-quarters of all stars in our galaxy and are now also known to commonly host multiple rocky planets.

“So, most Earth-sized planets in our galaxy reside around stars like TRAPPIST-1.”

Scientists have been using the James Webb Space Telescope – the most powerful space observatory launched in 2021 – to study the TRAPPIST-1 system.

Recent findings from the telescope have shown that the inner planets in TRAPPIST-1 likely do not have thick, hydrogen-rich atmospheres, suggesting that they are more like terrestrial planets with thin atmospheres, similar to Venus and Mars​.

However, the outer planets could have water, either as atmospheric vapour or ice, depending on their distance from the star​.

Powerful Telescopes

The James Webb Space Telescope has unique instruments that help measure the light that passes through exoplanets or that is emitted by them when they pass in front of or eclipse their host stars.

This planet transiting technique allows scientists to study the atmospheres of the planets.

“It may even offer us the first chance to detect biosignature gases on an exoplanet: it could be one of the TRAPPIST-1 planets or another Earth-sized planet in the habitable zone of a similar nearby red dwarf star,” said Prof Metchev.

“Webb is also allowing us to study some very bright and widely separated giant exoplanets directly, and we are now finding that they have clouds (although made of hot sand, rather than water vapour).

“However, Webb cannot yet give us the much-desired direct image of an Earth-like exoplanet.”

He said that the Habitable Worlds Observatory will allow scientists to directly study the atmospheres of Earth-like planets, without having to rely on the transiting planet technique.

The observatory, which is being planned by Nasa, aims to study 25 potentially habitable worlds.

It will use spectroscopy to search for chemical biosignatures in these planets’ atmospheres, such as oxygen and methane.

Each discovery will help scientists get closer to answering one of humanity’s most profound questions: are we alone in the universe?