The Hunt for Life Beyond Earth (Europa) - Original

By: Michael D. Lemonick | Modified by: Joshua Gaither NASA’s BRUIE (Buoyant Rover for Under-Ice Exploration) scans the depths of an Alaskan lake An electronic signal travels from NASA’s Jet Propulsion Lab (JPL) in Pasadena, California, to a robotic rover clinging to the underside of foot-thick ice on an Alaskan lake. The rover’s spotlight begins to glow. “It worked!” exclaims John Leichty, a young JPL engineer huddled in a tent on the lake ice nearby. It may not sound like a technological tour de force, but this could be the first small step toward the exploration of a distant moon.More than 4,000 miles to the south, geo-microbiologist Penelope Boston sloshes through murky, calf-deep water in a pitch-dark cavern in Mexico, more than 50 feet underground. Like the other scientists with her, Boston wears an industrial-strength respirator and carries a canister of spare air to cope with the poisonous hydrogen sulfide and carbon monoxide gases that frequently permeate the cave. The rushing water around her feet is laced with sulfuric acid. Suddenly her headlamp illuminates an elongated droplet of thick, semi-transparent fluid oozing from the chalky, crumbling wall. “Isn’t it cute?” she exclaims. Why would searching for life in these two locations help scientists to discover life on other planets? These two sites—a frozen Arctic lake and a toxic tropical cave—could provide clues to one of the oldest, most compelling mysteries on Earth: Is there life beyond our planet? Life on other worlds, whether in our own solar system or orbiting distant stars, might have to survive in ice-covered oceans, like those on Jupiter’s moon Europa, or in sealed, gas-filled caves, which could be plentiful on Mars. If you can figure out how to isolate and identify life forms that thrive in similarly extreme surroundings on earth, you’re a step ahead in searching for life elsewhere.To date, astronomers have confirmed nearly two thousand so-called exoplanets, ranging in size from smaller than Earth to bigger than Jupiter; thousands more—most found by the exquisitely sensitive Kepler space telescope, which went into orbit in 2009—await confirmation. None of these planets is an exact match for Earth, but scientists are confident they’ll find one that is before too long. Based on the discoveries of somewhat larger planets made to date, astronomers recently calculated that more than a fifth of stars like the sun harbor habitable, Earthlike planets. What factors do you think would make a planet “habitable” or “Earthlike"? That’s good news for astrobiologists. But in recent years planet hunters have realized that there’s no reason to limit their search to stars just like our sun. If the star is smaller and dimmer—and therefore, colder—the planet will just have to be positioned closer. Moreover, scientists now believe a planet doesn’t even have to be the same size as Earth to be habitable, but simply must fall in a range from 1-5 times the size of Earth. In short, the variety of habitable planets and the stars they might orbit is likely to be far greater than what scientists conservatively once assumed. Jupiter’s moon, Europa, showing the criss-crossing of cracking ice The one factor that biologists argue is critical for life as we know it is water in liquid form—a powerful solvent capable of transporting dissolved nutrients to all parts of an organism. In our own solar system we’ve known since the Mariner 9 Mars orbiter mission in 1971 that water once likely flowed freely on the red planet. So life might have existed there, at least in microbial (microscopic) form—and it’s plausible that remnants of that life could still endure underground, where liquid water may linger. Jupiter’s moon Europa also shows cracks in its relatively young, ice-covered surface—evidence that beneath the ice lies an ocean of liquid water. At a half billion miles or so from the sun, Europa’s water should be frozen solid. But this moon is constantly flexing under the gravitational push and pull of Jupiter and several of its other moons, generating heat that could keep the water below liquid. In theory, life could exist in that water too. Why is water essential to life? How, in spite of its great distance form the sun, is Europa able to maintain at least some liquid water? A cave in Mexico isn’t Mars, of course, and a lake in northern Alaska isn’t Europa. But it’s the search for extraterrestrial life that has taken JPL astrobiologist Kevin Hand and the other members of his team to Sukok Lake, 20 miles from Barrow, Alaska. The same quest has lured Penelope Boston and her colleagues multiple times to the poisonous Cueva de Villa Luz, a cave near Tapijulapa in Mexico. Both sites let the researchers test new techniques for searching for life in environments that are at least broadly similar to what space probes might encounter. In particular, they’re looking for bio-signatures—visual or chemical clues that signal the presence of life, past or present, in places where scientists won’t have the luxury of doing sophisticated laboratory experiments. What would be an example of a bio-signature? Europa certainly seems to have the basic ingredients for life. Liquid water is abundant, and the ocean floor may also have hydrothermal vents, similar to Earth’s, that could provide nutrients for any life that might exist there. Up at the surface, comets periodically crash into Europa, depositing organic chemicals that might also serve as building blocks of life. Particles from Jupiter’s radiation belts split apart the hydrogen and oxygen that makes up the ice, forming a whole suite of molecules that living organisms could use to metabolize chemical nutrients from the vents. In short: Europa at least poses a potential site for life forms to be discovered. Do you believe that scientists will ever find life on another planet or moon? Defend your response with evidence.