Astrobiologists are counting on finding signs of life beyond our planet and solar system.
Despite these awe-inspiring possibilities, a more likely scenario is that our first inklings of life in outer space will arrive via tools that can analyze electromagnetic properties, such as the gas composition surrounding a planet. The discovery of gaseous elements like oxygen could be indicators of life-sustaining conditions.
Technology For Seeking Out Life… And Maybe New Civilizations
The first step is to find exoplanets—and we’re doing a pretty good job at this. Astronomers can find planets outside our solar system in several different ways, but the most successful method to date is to capture the planet’s passage between its own star and Earth. As a planet moves in front of its star, the starlight dims by a measurable amount. This transit method has allowed astronomers to map thousands of exoplanets since they discovered the first one 20 years ago. While this discovery blew people’s minds in 1992, NASA expects that our galaxy actually contains trillions of worlds. In March 2022, the number of confirmed exoplanets surpassed 5,000. Many of these planets are a mix of rocky and volatile-rich worlds, potential good news for exobiologists.
Some of the most promising candidates for hosting life are the five worlds around the star K2-384, about 270 light-years from Earth. This star is of a comfortable temperature and brightness, and the planets are rocky. One of the planets in this system is comparable in size to Earth. Another candidate, WASP-17b, is about 1,000 light-years from Earth. Cornell astrophysicist Nikole Lewis is using the James Webb Space Telescope to investigate this “hot Jupiter”; Webb’s array of instruments can measure the temperature, the atmosphere’s chemical composition, and the cloud structure. TRAPPIST-1 is another star supporting a planetary system with potentially suitable conditions for life, about 40 light-years from Earth.
The Webb Telescope’s primary mission is to peer at the earliest, oldest galaxies, but researchers are also using it to learn more about these exoplanets—for example, by identifying the mix of gases in planetary atmospheres. And although Webb will still see faraway planets as no more than bright dots in the visual spectrum, its instruments will help exobiologists imagine what a planet might look or feel like.
Most intriguing will be the onboard instruments’ ability—using a 6.5-meter-diameter primary mirror and infrared spectroscopy tools—to make out atmospheric conditions, such as the presence of oxygen, methane, and carbon dioxide, that could be suitable for life. Once telescopes like Webb—and the now-retired Kepler, Spitzer, and Hubble space telescopes—gather light, astronomers can delve into the rainbow spectrum of light and measure its intensity at different wavelengths. This method, called transit spectroscopy, is a key to unlocking the specific mix of chemicals and elements present in a planet’s atmosphere.
Scientists now have a large enough exoplanet sample size to be able to narrow the search for habitable worlds. They’re looking first to planets in the “habitable zone,” located within the orbital distance from a home star where planetary temperatures could permit liquid water to exist on the surface. But a planet also needs to be the right size, have a suitable atmosphere, and orbit a stable star, according to NASA.
In the future, telescopes might be able to detect even more details of life, such as molecules made by plants or animals or pollution generated by more-intelligent beings.
Alien Life Could Be Like Life on Our Own Planet
In the meantime, exobiologists are taking their cues from some of the more bizarre life forms on our home-world. Our own cushy spot in the Goldilocks Zone (so called because of its perfect placement, about 93 million miles from the Sun) is home to otherworldly creatures that thrive in even the most hellish conditions.
The magma-heated hydrothermal vents deep beneath the ocean is where animals like the Yeti crab and the remarkably heat-resilient Pompeii worm dwell in temperatures above 700°F. A type of bacteria found in deserts may be the champion of surviving brutal conditions. Heat and intense radiation can’t stop it from resurrecting its genome to live again, so it’s understandably dubbed the Lazarus microbe.
On the other end of the temperature scale are psychrophiles, creatures that make the coldest locations on Earth their home, such as deserts in Alaska, Greenland, Svalbard, and Iceland, as well as the Dry Valleys of Antarctica. These bacterial organisms require cold below −4°F to survive, and they make their own protein-based antifreeze.
Then there are tardigrades, microscopic, eight-limbed micro-animals that also don’t seem to care much about environmental conditions on Earth. The little “water bears” are everywhere. Experiments prove that they can experience the cold, dehydrated, irradiated vacuum of space and then, once they return to some moisture and warmth, resume their lives as usual.
These extremophiles, species that flourish beyond the limits of what most life on Earth can withstand, could be the counterparts of life forms on planets we deem too harsh to support life. “Extremophile research also has implications for origin-of-life studies and the search for life on other planetary and celestial bodies,” write the authors of a 2019 study about these rarefied creatures. Extremophiles have probably been the dominant form of life for most of Earth’s history, the authors note, because life existed long before our current oxygen levels and temperate conditions developed.
Living on a planet replete with life in every corner, we can only imagine how many other planets may offer ideal homes. Though 5,000 exoplanets are plenty to start with, there are still 100 billion to 200 billion planets in our galaxy waiting to be explored.