by The question of our solitude in the vast cosmos has been a contemplative theme throughout our existence.
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In 1977, the New York Times published an article titled “The Quest Ends for Solitude in Space,” detailing physicists’ efforts to capture extraterrestrial radio signals in the Search for Extraterrestrial Intelligence (SETI). Though in its early stages, SETI aimed to secure congressional support as a worthwhile investment.
Since then, the pursuit to determine if anything exists beyond our earthly domain has made significant strides. Back then, astronomers had yet to discover planets beyond our solar system. Today, we know the Milky Way alone houses countless diverse worlds. Our understanding of life-sustaining environments has broadened with the discovery of extremophiles thriving in conditions hotter, saltier, more acidic, and more radioactive than previously thought.
Presently, we are closer than ever to comprehending the prevalence of life-sustaining worlds in the universe. New tools, including machine learning and artificial intelligence, may help scientists reassess past assumptions about life’s building blocks. Future instruments could detect atmospheres of distant planets and collect samples from our solar system’s bodies to determine if they contain chemicals suitable for life.
“I think in our era, we can achieve this. We will know if there is life on other planets,” says Ravi Kopparapu, a planetary scientist at NASA’s Goddard Space Flight Center.
While humans have long speculated about distant worlds, concrete evidence has been sparse. The first planets around stars, called exoplanets, were discovered in the early 1990s. However, it wasn’t until NASA launched the Kepler Space Telescope into orbit that astronomers realized how prevalent such planets are. Kepler monitored hundreds of thousands of stars, searching for the faint light dips that indicated planets passing in front of them. This mission increased the known count of exoplanets from just a few to over 5,500.
Kepler aimed to determine the prevalence of Earth-like planets orbiting Sun-like stars at distances suitable for liquid water. While the quest to find an exact Earth replica is ongoing, researchers can use the discoveries made to make predictions about the potential habitability of planets. Current estimates suggest that 10-50% of Sun-like stars may host Earth-like planets.
“There are billions of Sun-like stars in the Milky Way, and if half of them have Earth-like planets, there could be billions of rocky planets capable of sustaining life,” estimates Jessie Christiansen, an astrophysicist at Caltech in Pasadena, California.
The Search for Extraterrestrial Life
Determining whether these planets indeed harbor life is a challenging task. While astronomers focus on Sun-like stars, there are technological challenges. The James Webb Space Telescope, currently in orbit, is observing smaller, cooler, and redder stars known as dim M-dwarfs. These stars may host life, but as of now, certainty remains elusive.
To sustain liquid water on the surface, planets around M-dwarfs will need to orbit close to their stars. James Webb is studying Trappist-1, an M-dwarf star 40 light-years away with seven small rocky planets. Four of them are at suitable distances for liquid water. Two of the planets closest to the primary star are thought to lack atmospheres, but scientists await results from James Webb observations for the third planet.
Notably, James Webb recently detected dimethyl sulfide, a molecule on Earth only produced by living organisms, on an exoplanet nearly nine times the size of Earth and 120 light-years away. However, these results remain unconfirmed and require further investigation.
Almost throughout human history, we believed we were not alone. We filled the skies with gods, mythical creatures, and wonders. Only in modern times have we begun to ponder our place in the universe. Regardless of the existence of extraterrestrial life, the universe remains our home. We can choose solitude or embrace the beauty of it all and question everything around us.
