Next, they’ll use the spectrograph to attempt to discover key molecules like oxygen or methane. How a lot they discover of every determines what they’ll search for subsequent, like carbon dioxide or ozone. (Photosynthesis, which might come up on different worlds, produces oxygen. Organisms that use oxygen usually produce carbon dioxide and water, whereas some sorts of microbes, like micro organism, produce methane.)

It’s greatest to estimate all of those potential biosignatures, if doable, and never only one. But relying on the wavelength vary a telescope’s spectrograph is delicate to, it is going to be capable of measure the abundance of some molecules higher than others. Charting all these paths on Young’s resolution tree will inform astronomers whether or not they’re a world resembling trendy Earth, or a previous model of our planet, or one thing else solely. 

You is likely to be questioning why the search for alien life is so targeted on … effectively, Earth, quite than, say, gasoline giants like Jupiter or ocean worlds like Saturn’s largest moon, Titan, or its sibling satellite tv for pc, Enceladus. “Strategically, it makes sense to look for life as we know it. We only have one example of an inhabited planet, despite tantalizing hints here and there,” says Ken Williford, an astrobiologist on the Blue Marble Space Institute of Science in Seattle. 

He works with NASA’s Perseverance rover, which is looking for signs of past life on Mars and can later be headed for what scientists assume is the shore of a former physique of water. If Mars was something like historic Earth, the remnants of a shallow marine atmosphere might give the rover a shot at digging up a fossilized “microbial mat,” a layered neighborhood of microorganisms.

But, inevitably, anybody who follows Young’s flowchart will discover some planets that return ambiguous outcomes: some encouraging indicators but additionally uncertainties. It’s essential to keep away from false positives, if the obvious life-friendly signatures are literally resulting from nonbiological origins, akin to methane-generating volcanoes, says Maggie Thompson, an astronomer at UC Santa Cruz who additionally offered her work on the astronomy convention this week. 

For instance, Titan has an atmosphere smogged with methane, however it’s most likely lifeless, because of its frigid temperatures and lack of water. (That’s only a “probably,” although. Titan might conceivably host actually bizarre microbes we’ve by no means seen earlier than, able to surviving in methane lakes, consuming acetylene, and respiration hydrogen quite than oxygen. But we received’t know extra till NASA sends its Dragonfly rotorcraft to analyze.)

Nevertheless, methane might nonetheless be a key biosignature on extra hospitable exoplanets, particularly hotter ones with water. “The exciting thing about methane is that it could be a relatively simple thing that life uses and produces,” Thompson says. The Webb telescope, which simply noticed its first exoplanet, will show helpful on this endeavor, because of its near-infrared spectrograph. “Methane is one of the few gases that JWST can actually detect, but JWST alone probably won’t find a planet with a definitive biosignature,” she says. 

Young’s looking forward to Webb’s successor, the Habitable Worlds Observatory, which shall be tasked with looking for indicators of life on Earth-size planets round sun-like stars. (So far, it has been simpler for astronomers to search out gasoline big planets orbiting extra dangerously lively crimson dwarf stars.) In December, NASA chief Bill Nelson announced plans to develop the observatory within the 2030s. Depending on precisely how delicate the brand new telescope is, Young’s modeling reveals that it might scope out dozens of Earth-like worlds.

She’s additionally maintaining an open thoughts for all times as we don’t comprehend it. The resolution tree consists of branches for planets that don’t appear to resemble any stage of Earth historical past. “We want to be prepared for surprises, the weird cases that we might not be able to categorize,” she says. “Let’s put those in the ‘ambiguous planet’ category, and flag them as interesting targets.”