The Search For Extraterrestrial Life On Europa

The search for extraterrestrial life is targeting Jupiter's icy moon Europa. We've known of Europa’s existence for more than four ...

The search for extraterrestrial life is targeting Jupiter's icy moon Europa.

We've known of Europa’s existence for more than four centuries, but for most of that time, Jupiter’s fourth-largest moon was just a pinprick of light in our telescopes—a bright and curious companion to the solar system’s resident giant. Over the last few decades, however, as astronomers have scrutinized it through telescopes and six spacecraft have flown nearby, a new picture has come into focus. Europa is nothing like our moon. 

Observations suggest that its heart is a ball of metal and rock, surrounded by a vast saltwater ocean that contains more than twice as much water as is found on Earth. That massive sea is encased in a smooth but fractured blanket of cracked ice, one that seems to occasionally break open and spew watery plumes into the moon’s thin atmosphere. 

Shrouded in a thick crust of ice, Europa beckons as a tantalizing candidate in the search for extraterrestrial life on the outer space.

For these reasons, Europa has captivated planetary scientists interested in the geophysics of alien worlds. All that water and energy—and hints of elements essential for building organic molecules —point to another extraordinary possibility. In the depths of its ocean, or perhaps crowded in subsurface lakes or below icy surface vents, Jupiter’s big, bright moon could host life. 

“We think there’s an ocean there, everywhere,” says Bob Pappalardo, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “Essentially everywhere on Earth that there’s water, there’s life. Could there be life on Europa?” 

Water plumes could be making it rain on Jupiter's moon, Europa.

Pappalardo has been at the forefront of efforts to send a craft to Europa for more than two decades. Now his hope is finally coming to fruition: later this year, NASA plans to launch Europa Clipper, the largest-­ever craft designed to visit another planet. The $5 billion mission, scheduled to reach Jupiter in 2030, will spend four years analyzing this moon to determine whether it could support life. It will be joined after two years by the European Space Agency’s Juice, which launched last year and is similarly designed to look for habitable conditions, not only on Europa but also on other mysterious Jovian moons. 

Neither mission will beam back a definitive answer to the question of extraterrestrial life. “Unless we get really lucky, we’re not going to be able to tell if there is life there, but we can find out if all the conditions are right for life,” says planetary geologist Louise Prockter at the Johns Hopkins Applied Physics Laboratory, a co-­investigator on the Clipper camera team. 

“Essentially everywhere on Earth that there’s water, there’s life. Could there be life on Europa?” - Bob Pappalardo, planetary scientist, NASA’s Jet Propulsion Laboratory.

What these spacecraft will do is get us closer than ever before to answers, by identifying the telltale chemical, physical, and geological signatures of habitability—whether a place is a suitable environment for life to emerge and thrive. The payoff for confirming these signs on Europa would be huge. Not because humans could settle on its surface—it’s far too harsh and rugged and cold and irradiated for our delicate bodies—but because it could justify future exploration to land there and look for alien life-forms. 

Engineers and technicians install reaction wheels on Europa Clipper at NASA’s Jet Propulsion Laboratory in California / NASA.

Finding something, anything, living on Europa would offer strong evidence for an alternate path through which life could emerge. It would mean that life on Earth is not exceptional. We’d know that we have neighbors close by—even if they’re microbial, which would be the most likely life-form—and that would make it very likely that we have neighbors elsewhere in the cosmos.

“With the prospects of life—the prospects of vast oceans—within reach, you just have to go,” says Nicholas Makris, director of MIT’s Center for Ocean Engineering, who uses acoustics and other innovative methods to observe and explore big bodies of water. He once led a team of scientists who proposed a mission to land a spacecraft on Europa and use sound waves to explore what lies beneath the ice; he still hopes to see a lander go there one day. “You have to find out. Everyone wants to know,” he says. “There isn’t anyone who doesn’t want to know.” 

Long before it became the cosmic destination of the year, Europa played an outsize role in transforming our understanding of the solar system. That began with its discovery, when one night in January 1610, the Italian astronomer Galileo Galilei fixed his occiale—an ingenious homemade telescope—on Jupiter and noted three bright little dots near the side of the gas giant.