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

“We predict there’s an ocean there, in every single place,” says Bob Pappalardo, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “Primarily in every single place on Earth that there’s water, there’s life. Might there be life on Europa?” 

Pappalardo has been on the forefront of efforts to ship a craft to Europa for greater than twenty years. Now his hope is lastly coming to fruition: later this 12 months, NASA plans to launch Europa Clipper, the largest-­ever craft designed to go to one other planet. The $5 billion mission, scheduled to succeed in Jupiter in 2030, will spend 4 years analyzing this moon to find out whether or not it may help life. Will probably be joined after two years by the European Area Company’s Juice, which launched final 12 months and is equally designed to search for liveable circumstances, not solely on Europa but in addition on different mysterious Jovian moons. 

Neither mission will beam again a definitive reply to the query of extraterrestrial life. “Except we get actually fortunate, we’re not going to have the ability to inform if there’s life there, however we will discover out if all of the circumstances are proper for all times,” says planetary geologist Louise Prockter on the Johns Hopkins Utilized Physics Laboratory, a co-­investigator on the Clipper digital camera crew. 

“Primarily in every single place on Earth that there’s water, there’s life. Might there be life on Europa?”
Bob Pappalardo, planetary scientist, NASA’s Jet Propulsion Laboratory

What these spacecraft will do is get us nearer than ever earlier than to solutions, by figuring out the telltale chemical, bodily, and geological signatures of habitability—whether or not a spot is an appropriate surroundings for all times to emerge and thrive.

The payoff for confirming these indicators on Europa can be big. Not as a result of people may choose its floor—it’s far too harsh and rugged and chilly and irradiated for our delicate our bodies—however as a result of it may justify future exploration to land there and search for alien life-forms. Discovering one thing, something, dwelling on Europa would supply robust proof for an alternate path via which life may emerge. It might imply that life on Earth will not be distinctive. We’d know that we’ve got neighbors shut by—even when they’re microbial, which might be the most definitely life-form—and that might make it very possible that we’ve got neighbors elsewhere within the cosmos.

Engineers and technicians set up response wheels on Europa Clipper at NASA’s Jet Propulsion Laboratory in California


“With the prospects of life—the prospects of huge oceans—inside attain, you simply must go,” says Nicholas Makris, director of MIT’s Middle for Ocean Engineering, who makes use of acoustics and different modern strategies to look at and discover massive our bodies of water. He as soon as led a crew of scientists who proposed a mission to land a spacecraft on Europa and use sound waves to discover what lies beneath the ice; he nonetheless hopes to see a lander go there sooner or later. “You need to discover out. Everybody desires to know,” he says. “There isn’t anybody who doesn’t need to know.” 

From a spot within the sky to a dynamic moon

Lengthy earlier than it turned the cosmic vacation spot of the 12 months, Europa performed an outsize position in reworking our understanding of the photo voltaic system. That started with its discovery, when one evening in January 1610, the Italian astronomer Galileo Galilei fastened his occiale—an ingenious do-it-yourself telescope—on Jupiter and famous three shiny little dots close to the aspect of the fuel large. 

Galileo assumed it was an phantasm, that they have been distant stars that solely gave the impression to be shut. However the subsequent evening, he noticed those self same three shiny little stars now on the different aspect of the planet. Additional observations revealed one more shiny gentle, additionally wandering close by however refusing to go away Jupiter’s aspect. In a brief treatise known as Sidereus Nuncius (Starry Messenger), revealed in March 1610, Galileo reported that he’d discovered 4 worlds orbiting Jupiter, much like how Mercury and Venus orbit the solar. (Astronomers nonetheless regard Jupiter and its satellites as a type of mini photo voltaic system.) Galileo named the worlds I, II, III, and many others., and referred to them because the “Medicean planets,” although they’re now known as the “Galilean moons.” His discovery was the primary time scientists had immediately noticed small worlds orbiting one thing apart from Earth or the solar, giving robust proof to the argument, nonetheless controversial on the time, that planets circled the solar and never the opposite manner round. 

In 1614, German astronomer Simon Marius instructed that Jupiter’s 4 newly found moons be named Io (high), Callisto (center), Ganymede (backside), and Europa, after 4 “irregular loves” pursued by the god for whom the planet is called. Astronomers have since recognized 91 others, and there are possible extra.


Naming rights for these 4 Jovian moons in the end went to the German astronomer Simon Marius, who claimed (however couldn’t show) that he’d really found them just a few weeks earlier than Galileo. In 1614, on a suggestion from Johannes Kepler, Marius proposed naming the moons Io, Callisto, Europa, and Ganymede—after 4 “irregular loves” pursued by Zeus (Jupiter) in historical mythology. It took 200 years for these names to achieve widespread adoption, however they have been positively an improve. Had Galileo’s naming scheme caught, you’d now be studying concerning the “II Clipper,” which doesn’t have the identical ring.

These moons have been solely the primary to be found orbiting Jupiter. As of December 2023, astronomers had formally confirmed the existence of 91 others—and there are possible many extra. The place the primary 4 are spherical and observe stately, easy orbits, the newer discoveries are extra various. Some orbit in erratic swarms or go the other manner round; some have been asteroids captured in passing; others resulted from collisions. There are such a lot of objects round Jupiter, in reality, that the Worldwide Astronomical Union not confers names on Jovian satellites until they’re deemed to have important scientific worth.

The extra we’ve discovered about Europa, the extra fascinating it has turn into. For hundreds of years, it was little greater than a spot showing to maneuver from one aspect of Jupiter to the opposite. However by the early twentieth century, stargazers had made cheap estimates of Europa’s diameter and mass (revealing that it was barely smaller than Mercury or Earth’s moon, however bigger than Pluto). They’d additionally studied the sunshine reflecting from its floor and located that Europa was unexpectedly shiny. Have been it to exchange our moon within the evening sky, Europa can be a bit of smaller however shine 5 occasions brighter.   

Within the Nineteen Fifties, when scientists started relating to distant objects not as shiny cosmic curiosities however as actual worlds, every with a definite origin story, they started to ask questions on composition and formation. In The Planets, a guide revealed in 1952, the astronomer Harold Urey instructed that water ice was considerable within the outer photo voltaic system as a result of the our bodies there fashioned removed from the solar and by no means turned heat sufficient for his or her ice to evaporate. By the Sixties, astronomers and astrophysicists had begun to take a position, partly on the idea of early measurements of its infrared spectrum, that Europa’s extraordinary reflectance was certainly as a result of presence of ice. However proving it was tough.

Stephen Ridgway, now an astronomer on the Nationwide Science Basis’s NOIRLab in Tucson, Arizona, first heard about the issue of probably icy moons within the outer photo voltaic system within the early Nineteen Seventies, as a graduate scholar. Carl Pilcher, a postdoctoral researcher he’d met at a convention, advised him about it. “We predict they need to have ice on them as a result of they’re chilly and reflective, however is it water? Is it carbon dioxide ice? Is it another form, or some combination?” Ridgway remembers him asking. 

It turned out that Ridgway, who describes himself as a tinkerer in addition to a physicist, was effectively positioned to reply these questions. Utilizing an previous mathematical trick, he had devised an modern instrument that might seize the spectrum of a distant gentle supply, and he was utilizing it throughout nighttime observations at a telescope at Kitt Peak Observatory, in Arizona. Each factor and molecule absorbs and emits a novel assortment of wavelengths of vitality, and astronomers can learn these spectra as fingerprints that reveal the composition of cosmic our bodies. Pilcher instructed that he use the instrument to look at Europa.

They thought it could take every week to get a helpful spectrum of one in every of Jupiter’s moons. “I went and acquired it in a single evening, perhaps two,” Ridgway remembers. Ridgway confirmed the information to Pilcher, who confirmed it to his advisor, Tom McCord. Their analyses, revealed in Science in December 1972, instructed that water ice lined at the least half, and probably all, of the floor of Europa. (In addition they confirmed that the Jovian moons Ganymede and Callisto, each of that are bigger than Europa, additionally had ice on their surfaces.) 

In a 1980 paper, scientists reported that Europa seemed “cracked like a damaged eggshell” and in contrast it to a white pool ball fouled by a felt-tip pen.

One 12 months later, the Pioneer 10 spacecraft, which had launched in March 1972, handed shut sufficient to Europa to take a photograph. The grainy picture was provocative sufficient to justify sending Pioneer 11—which launched in 1973—to swing by on its solution to Saturn after which out of the photo voltaic system. 

Different doubtlessly liveable areas within the photo voltaic system embrace two moons of Saturn: Titan (high) and Enceladus (backside). Enceladus boasts liquid water beneath its floor and spews icy geysers into area. Titan has a floor wealthy in natural molecules and certain additionally has a liquid-water ocean beneath its crust.


However Europa actually began to come back into focus in 1979, after the Voyager 2 spacecraft sped previous the moon on July 9. (Voyager 1 additionally handed close to Europa, however Voyager 2 had higher pictures.) The pictures the spacecraft beamed again revealed a easy, shiny floor, crisscrossed by lengthy linear marks and low ridges; they could have been cracks or cliffs. In a 1980 NASA paper describing the commentary, scientists reported that Europa seemed “cracked like a damaged eggshell” and in contrast it to a white pool ball fouled by a felt-tip pen. A 1983 Nature paper fueled curiosity in Europa by proposing that these options have been per liquid water and common resurfacing, just like the work of a pure Zamboni machine.   

The Galileo mission, which launched in 1989 to review Jupiter’s environment and the composition of Europa and different moons, encountered issues: the spacecraft’s main antenna uncared for to increase, which severely restricted the information that may very well be transmitted to Earth. 

However what did come again, after Galileo reached the system in 1995, additional highlighted the moon’s extraordinary options and continues to energise scientists. “Now we have quite a lot of tantalizing glimpses of issues,” Prockter says. 

Amongst different issues, Galileo’s magnetometer revealed a wildly various magnetic area. Ice is a poor conductor, however liquid salt water isn’t, and Europa’s magnetic oscillations pointed to one thing transferring beneath the floor. Its readings match the thought of a world ocean being pushed, pulled, and heated by the tidal forces of Jupiter and its moon companions. In addition they lined up with earlier theoretical predictions of liquid water close to the floor of icy moons. “We’re fairly sure there’s an ocean there,” Prockter says, “however there’s a likelihood that it could be one thing actually unique we don’t perceive.” The one solution to know for certain, she says, is to return. 

Different pictures from Galileo confirmed what telescope observations had lengthy instructed: that Europa sports activities a youthful look regardless of its superior age. It possible fashioned similtaneously Jupiter and the remainder of the photo voltaic system, about 4.5 billion years in the past, but its floor—as dated by the oldest craters—is lower than 100 million years previous. “That’s a very long time for us mere mortals,” says Prockter, “however in geological phrases, it was born yesterday. The floor could be very, very younger.” The cracks and crevices on Europa counsel that big ice plates on its floor collide, break aside, shove underneath and over one another, and refreeze. 

The Pioneer 10 spacecraft, which launched in March 1972, handed shut sufficient to take the primary flyby photograph
of Europa.
{A photograph} beamed
again by the Voyager 2
spacecraft, taken on the
morning of July 9, 1979,
illuminated Europa’s
mysterious nature in
higher element.
The Galileo mission, which launched in 1989 to review Jupiter’s environment and the composition of its moons, together with Europa, introduced the moon’s extraordinary
options into focus.
This placing picture of
Europa, captured in
September 2022 by a digital camera on the Juno spacecraft, reveals lots of the options which can be driving scientists to need to return.

The longer scientists stared at Europa, the extra mysteries emerged—just like the questions round these ubiquitous darkish ridges, usually in pairs, that splatter the floor like a Jackson Pollock portray. Theorists have been busy devising explanations. Maybe they’re made by ice volcanoes or geysers, or cracks the place liquid water from subsurface swimming pools rose, froze, and crumbled because the opening closed once more. Perhaps they resulted from subduction, which happens on Earth in plate tectonics, as one large sheet of ice slid and crumpled underneath one other. “I’ve misplaced depend of the variety of totally different fashions for forming these landforms, however we actually don’t understand how they kind,” Prockter says. “A part of the reason being that geology is predicated on Earth geology, but it surely’s not like Earth.” 

One notably placing picture of Europa, captured in September 2022 by a digital camera on the Juno spacecraft, which is at present exploring Jupiter, reveals lots of the options which can be driving scientists to need to take a more in-depth look. It reveals the aspect of Europa that at all times faces Jupiter, bathed in daylight. The moon’s floor is roofed with cracks, streaks, and ridges the place water might rise from the ocean beneath, or the place irradiated floor materials might sink decrease. It additionally reveals the “chaos terrains”—remarkably messy areas suggesting that big items of ice have damaged off, moved round, and refrozen, bolstering the case for geological exercise much like plate tectonics on Earth. 

Nonetheless, Juno’s temporary two-hour flyby didn’t reply questions on how these options fashioned or to substantiate the existence of a buried ocean. For planetary scientists and astrophysicists, Clipper’s knowledge might help fill within the lacking information. It would additionally push our relationship with Europa into new, unexplored territory. 

What all these earlier missions did do was assist construct enthusiasm for the plan to get to Europa, a plan that has developed dramatically during the last 20 years. Initially, scientists wished orbiters and landers, and NASA and ESA have been working collectively on a joint mission with a number of spacecraft. These plans fizzled, however in 2013—on account of the 2011 Decadal Survey, a report that units the priorities for area exploration for the following 10 years—NASA accredited a plan to ship an orbiter. By 2015, the company had chosen the devices on board. Independently, the ESA moved ahead with its personal mission, with a broader aim of finding out Jupiter’s icy moons. 

“The Voyager mission reworked Europa from a light-weight within the sky to a geologic world, after which the Galileo mission did the transformation to an ocean world,” says Diana Blaney, a JPL geophysicist who leads the Clipper crew charged with utilizing a mapping picture spectrometer to determine molecules on Europa’s floor. “Hopefully, Clipper will convey the transformation to a liveable world.” 

Getting in shut

Researchers have lengthy looked for indicators of habitability within the photo voltaic system. Landers and rovers on Mars have discovered proof of liquid water, largely lengthy gone, and natural molecules, which include carbon, usually in chains or rings. The constructing blocks of organic organisms—together with nucleic acids and proteins—all include carbon, which is why scientists get excited after they discover natural molecules. Their presence may point out that it’s potential for the precursors of life to kind. 

Nevertheless it’s not sufficient simply to have promising items in place. Any alien species would additionally must discover a solution to develop and survive. That removed from the solar, photosynthesis is probably going unattainable. Organisms would essentially be fueled by chemical vitality, a lot as microbial extremophiles close to the black people who smoke and hydrothermal vents on the seafloor reside off the minerals and methane. 

The chance for Europan life is on the mercy of the moon’s geophysics, says Lynnae Fast, a planetary geophysicist at NASA’s Goddard Area Flight Middle. Actually, she argues that you would be able to’t have one with out the opposite. Europa appears to host the mandatory elements for all times. However elements alone, on Europa as within the kitchen, received’t spontaneously mix in the fitting manner on their very own. Different forces must intervene: the moon must shift and squeeze, with warmth, to combine the minerals from the seafloor with the salt water and any irradiated particles that seep down from the icy floor. “We want one thing to stir the pot, and I believe the geophysical processes try this,” says Fast, whose graduate work on cryovolcanism in alien worlds led to her recruitment to hitch Clipper. She’s notably enthusiastic about the potential for discovering pockets of heat salty water, trapped simply beneath the floor, that may very well be abodes for all times. 

 “Europa is my favourite physique within the photo voltaic system,” Fast confesses. However she notes that different ocean worlds additionally supply promising locations to search for indicators of life. These embrace Enceladus, a small moon of Saturn that, like Europa, has an icy crust with an ocean beneath. Pictures from the Cassini mission in 2005 revealed that geysers on the south pole of Enceladus spew water and natural molecules into area, feeding Saturn’s outermost ring. 

Nonetheless, Europa is greater than Enceladus and is extra more likely to have a floor lined in icy plates that transfer in a manner much like Earth’s plate tectonics. This type of exercise would assist mix the elements for all times. Ganymede, one other Jovian moon and the photo voltaic system’s largest, additionally possible has a liquid ocean, however sandwiched between two ice layers; with out an interface between water and minerals, life is much less possible. Different potential locations to look embrace Titan, Saturn’s greatest moon, which additionally in all probability hides a liquid-water ocean beneath an ice crust. (Fast is an investigator on Dragonfly, a mission to discover Titan, scheduled to launch in 2028.) 

Most of the challenges dealing with mission engineers
revolve round vitality: Europa receives solely a fifth as a lot daylight as Earth. Clipper addresses the issue with gargantuan photo voltaic panels, spanning 30 meters when absolutely prolonged.

To search for the indicators and alerts of habitability, Clipper will use 9 main devices. These will take photos of the floor, search for water plumes, use ground-penetrating radar to measure the icy shell and seek for the ocean under, and take exact measurements of the magnetic area. 

The spacecraft will go shut sufficient to the moon to pattern its skinny environment, and it’ll use mass spectrometry to determine molecules within the gases it finds there. One other instrument will allow scientists to investigate mud from the floor that has been kicked into the environment by meteorite collisions. With a bit of luck, they’ll be capable of inform if that mud originated from under—from the enclosed ocean or subsurface lakes trapped within the ice—or from above, as fragments that migrated from the violent volcanoes on the close by moon Io. Both state of affairs can be attention-grabbing to planetary geologists, but when the molecules have been natural and got here from under, they might assist construct the case that life may exist there.

ESA’s Juice mission has an analogous suite of devices, and scientists from the 2 groups meet frequently to plan for methods to collectively exploit the information when it begins coming in—5 or 6 years from now. “That is actually superb for scientists within the planetary neighborhood,” says Lorenzo Bruzzone, a telecommunications engineer on the College of Trento who leads the Juice mission’s radar software crew. He’s lengthy been concerned in efforts to get to Europa and the remainder of the Jovian system. 

As a result of Juice will go to the opposite ocean-bearing Galilean moons, Bruzzone says, knowledge from that mission will be mixed with Clipper’s to generate a extra complete image of the geological processes and potential habitability of all of the ocean worlds. “We are able to analyze the variations in subsurface geology to higher perceive the evolution of the Jupiter system,” he says. These variations might assist clarify, for instance, why three of the Galilean moons fashioned as icy worlds whereas the fourth, Io, turned a volcanic hellscape. 

Jupiter’s radiation has the potential to intrude with each measurement, turning a significant sign into a multitude of digital snow, like static on a tv display screen.

To verify these devices work after they get there, engineers and designers for each missions have needed to deal with a raft of challenges. Lots of them revolve round vitality: Europa receives solely a fifth as a lot daylight as Earth. Clipper addresses the issue with gargantuan photo voltaic panels, which is able to span 30 meters when absolutely prolonged. (An earlier proposal for a mission to Europa included nuclear batteries, however that concept was costly, and it was in the end scrapped.) 

As well as, Jupiter’s magnetic area is greater than 10,000 occasions extra highly effective than Earth’s, accelerating already-­energetic particles across the planet to create an intense radiation surroundings. The radiation has the potential to intrude with each measurement—turning a significant sign into a multitude of digital snow, like static on a tv display screen—and might threaten the integrity of the devices. 

To sluggish the buildup of radiation injury, Clipper received’t orbit Europa when it reaches the moon in 2030; as an alternative, it’ll make about 50 flybys over 4 years, swooping nearer and farther from the damaging radiation area. At its closest, it’ll go simply 16 miles above the floor. The title factors again to quick Nineteenth-century crusing vessels, but it surely additionally describes the journey. The craft will sail previous the world, time and again. In between passes, its distance from Jupiter will give it openings to transmit knowledge again to Earth. 

These first transmissions could have been generations—if not centuries—within the making. A few of the individuals who laid the groundwork for the mission, many years in the past, have already died. Makris, at MIT, says that when scientists have been first discussing find out how to get to Europa, he was advised by Ron Greeley, a planetary geologist and NASA advisor who proposed and fiercely advocated for missions to the moon, that area journey spans generations: “He likened it to constructing a cathedral.” Prockter notes that by the point Clipper’s knowledge is available in, she’ll be in her late 60s. “I’ll have spent my total profession on Clipper,” Prockter says. Fast, at 39, is likely one of the youngest members of the science crew. 

In April 2023, the European Area Company
launched Juice to discover a number of ocean-bearing moons of Jupiter. In July 2032, it’ll fly 400 kilometers above Europa’s floor, twice.


Most of the scientists concerned in Clipper—together with Pappalardo, Prockter, and Fast—are already planning methods to make use of its insights for future missions to different worlds. Nevertheless it’s Europa that holds essentially the most promise, at the least for the second. 

Pappalardo thrills on the prospect of discovering a Europan neighborhood that could be good for all times. “What if we discover a place that’s type of an oasis, the place there are sizzling spots or heat spots that we detect with a thermal imager?” he says. 

In the end, Pappalardo says, his hope is that Clipper finds sufficient proof to make a powerful case for sending a lander sometime. The mission’s observations may additionally inform scientists the place to land it: “That might be a spot the place we’d say, effectively, we actually have to go and scoop up a few of that stuff from under the floor, have a look at it with a microscope, put it in a mass spectrometer, and do the following step, which is to seek for life.” 

Stephen Ornes is a science author based mostly in Nashville, Tennessee.


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