Astronomers Develop Methods to Detect Signs of Alien Life in Distant Planet Atmospheres

Astronomers are exploring innovative methods to detect signs of alien life by analysing the atmospheres of over 6,000 known exoplanets. By assessing factors like temperature and atmospheric composition, they aim to identify potentially habitable worlds.

We are in an era where answers to age-old questions are within reach, including whether Earth is the only planet with life. Over the past three decades, it has been confirmed that our Sun is not unique in having a planetary system. Thousands of exoplanets orbit other stars, raising the question of whether any of these distant worlds also support life.

One method to explore this is by analysing gases in exoplanet atmospheres. More than 6,000 exoplanets have been catalogued, allowing astronomers to identify those most likely to support life. A planet's distance from its star helps determine its temperature, which is crucial for habitability.

Exoplanet Atmospheres and Detection Techniques

Earth is the only Solar System planet with liquid water oceans, suggesting mild temperatures might be necessary for habitability. A planet's atmosphere significantly influences its temperature and potential for liquid water. Quantum mechanics allows us to identify atmospheric molecules by their unique barcode-like patterns on light passing through them.

Telescopes can detect these molecular barcodes when a planet transits its star from our viewpoint. This technique works for a small fraction of known exoplanets. The signal strength depends on the molecule's abundance: more abundant molecules produce stronger signals, though some barcodes are inherently strong or weak.

For instance, Earth's atmosphere is mostly diatomic nitrogen (N₂), but this has a weaker barcode compared to less abundant diatomic oxygen (O₂), ozone (O₃), carbon dioxide (CO₂), and water (H₂O). The James Webb Space Telescope (JWST) collects infrared light to study various exoplanet atmospheres.

Challenges and Discoveries in Molecular Detection

Detecting molecular imprints in exoplanet atmospheres is complex. Different research teams may interpret data differently due to varying methodologies. Despite these challenges, robust detections of simple molecules like methane, carbon dioxide, and water have been achieved.

Sub-Neptunes, larger than Earth but smaller than Neptune, are the most common exoplanets. In 2025, a bold claim was made about detecting a biosignature on one such planet, K2-18b. Dimethyl sulphide was detected with a claimed less-than-once-in-1,000 chance of error.

On Earth, dimethyl sulphide is produced by oceanic phytoplankton but breaks down quickly in sunlight-exposed seawater. If K2-18b is covered by an ocean, this detection might suggest microbial marine life there. However, further analysis by Arizona State University's Luis Welbanks and colleagues questioned this claim.

Future Missions and Their Potential

Their 2025 study showed that different molecular barcode choices could alter results significantly. They found many alternatives that matched or exceeded the original data fit. Detecting atmospheres on Earth-sized rocky planets with JWST remains challenging.

However, upcoming missions promise advancements. The European Space Agency's Plato telescope will launch in 2026 to find Earth-like planets suitable for transmission spectroscopy. NASA's Nancy Grace Roman space telescope will launch in 2029 to use coronagraphic techniques for direct study of dimmer planets near stars.

The European Space Agency's Ariel telescope will also launch in 2029 for dedicated transmission spectroscopy to determine exoplanet atmospheric compositions. NASA's Habitable Worlds Observatory (HWO) is being planned to study around 25 Earth-like planets using a coronagraph.

The Promise of Upcoming Spacecraft

HWO will cover wavelengths from ultraviolet to near-infrared. If an Earth twin orbits one of HWO’s target stars, it would capture starlight reflected from the planet, revealing diatomic oxygen and other gases typical of Earth's atmosphere.

This starlight would also show signs of photosynthesising plants through the "vegetation red edge." Earth's surface reflects light differently from land and oceans; HWO could map these features as they rotate into view.

The future holds promise as upcoming spacecraft may help answer if Earth uniquely hosts life. With new missions set to launch soon, we may soon find out if we are alone in the universe or not.

With inputs from PTI