Since humans do not possess a spacecraft capable of navigating to planets outside our solar system, researchers are compelled to devise creative strategies to seek evidence of life light-years away.
A group of scientists has introduced a novel technique for astronomers to identify prospective extraterrestrial life utilizing the **James Webb Space Telescope**—a partnership among NASA, the European Space Agency, and the Canadian Space Agency. Their strategy emphasizes searching for **methyl halides**, which are gases made up of carbon, hydrogen, and a halogen such as chlorine. These substances are mainly generated by bacteria, algae, fungi, and plants on Earth.
Methyl halides hold particular promise as biosignatures because they can be identified in **infrared light**, an area of expertise for Webb. Moreover, researchers suspect that these gases may be more prevalent around planets with **hydrogen-rich atmospheres**, a category of planets that Webb is currently investigating. Known as **Hycean worlds** (a blend of “hydrogen” and “ocean”), these planets are believed to possess extensive bodies of water and fit into the **sub-Neptune** category—oversized compared to Earth but smaller than Neptune. Their dimensions render them more observable than small, terrestrial planets like Earth.
As stated by **Michaela Leung**, a planetary scientist at the University of California, Riverside, identifying methyl halides could require as little as **13 hours** with Webb, significantly quicker than searching for gases like oxygen or methane. “Less time with the telescope implies reduced costs,” Leung remarked.
### A Controversial Precedent
This proposal follows a **2023 study** that ignited discussion among scientists. In that investigation, experts utilized Webb to examine the atmosphere of **exoplanet K2-18 b** and identified a faint, unverified signal of **dimethyl sulfide**—a gas generated by phytoplankton on Earth. Because this molecule is thought to be exclusively biological in nature, the researchers proposed that it could signify the presence of life.
Nonetheless, the assertion was met with doubt. Critics challenged the **faintness of the signal** and the presumption that K2-18 b constitutes a **water world** with a hydrogen-rich atmosphere. While Webb detected methane and carbon dioxide (which correspond to predictions for Hycean planets), the evidence remained inconclusive.
### The Potential of Methyl Halides
The discussion underscored the necessity for additional exploration into which gases Webb can dependably identify and which ones serve as reliable indicators of biological activity. For instance, detecting oxygen might be unfeasible with current technology.
The recent study from UC Riverside proposes that Webb could spot **methyl chloride**, a particular variant of methyl halide, on Hycean planets. The necessary concentration for identification is approximately **10 parts per million**, akin to levels observed in various locations on Earth. Computer simulations suggest that Webb could affirm its existence in as few as **14 observations**.
### How Webb Detects Exoplanet Atmospheres
Webb investigates exoplanet atmospheres employing a method known as **transmission spectroscopy**. When a planet transits in front of its star, the starlight traverses through its atmosphere. Molecules present in the atmosphere absorb specific wavelengths of light, creating a distinctive chemical signature. By examining the missing segments of the light spectrum, astronomers can discern the atmospheric makeup of distant planets.
### What This Means for the Search for Life
Although Hycean planets might not support human life, researchers are captivated by the potential that **microbial life** could flourish in such environments. If astronomers start detecting methyl halides across various exoplanet atmospheres, it might indicate that microbial life is **prevalent** in the galaxy.
“That would transform our understanding of life’s distribution and the mechanisms that lead to the origins of life,” Leung expressed.