NASA’s Europa Clipper spacecraft will soon be on its way to help solve a quarter-century-old mystery: Could anything live in the ocean that lurks beneath the icy shell of Jupiter’s moon Europa?
“This is a mission we’ve been dreaming of for 25 years now, since I was in graduate school,” says planetary geologist Cynthia Phillips of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “It’s a generational mission.”
An October 10 launch from Kennedy Space Center in Florida has been scrubbed due to Hurricane Milton, but the spacecraft is still expected to launch later this month or in early November.
After a five-and-a-half-year trek to Jupiter, Clipper will settle into orbit around the giant planet in April 2030, repeatedly zipping past the icy moon to get snapshots of its frozen terrain, measure the chemical composition of the surface and deduce the moon’s internal structure.
“We think that ocean worlds might actually be a common type of world outside of our solar system,” said NASA’s head of planetary science Gina DiBraccio in a September 17 news conference. “Clipper will be the first in-depth mission that will allow us to characterize habitability on what could be the most common type of inhabited world in our universe.”
Planetary scientists have grown increasingly certain that Europa hosts a subsurface ocean ever since NASA’s Galileo spacecraft visited Jupiter in the 1990s (SN: 2/18/02).
“During the Galileo mission, it was like a detective story,” Phillips says. The clues built up. A lack of craters, suggesting the surface is always moving and changing. Stripes, cracks and pits, suggesting upwelling from below. Regions known as “chaos terrain,” that look like icebergs tilted in a sloshy sea (SN: 11/16/11).
And finally, the measurement of an internal magnetic field induced by Jupiter’s external one. That was “the coup de grâce,” Phillips says. The only geologically plausible material capable of carrying that magnetic field is saltwater.
On Earth, water means life. But the findings on Europa weren’t enough to declare it a habitable world (SN: 4/19/24). Many mysteries remained: How deep is the ocean? How thick is the ice shell? And crucially, how do they interact? Could material from the surface make it down into the briny deep, to provide food for waiting microbes?
Europa Clipper, named for the speedy clipper ships of the 19th century, is poised to pick up where Galileo left off. The spacecraft is charged with investigating Europa’s habitability by searching for three key ingredients: water, energy and organic compounds.
The spacecraft won’t orbit Europa directly. The moon lies within Jupiter’s punishing radiation environment, where high-energy charged particles accelerated by the planet’s magnetic field could fry spacecraft components (SN: 11/9/20). Instead, Clipper will dip in and out of that zone of radiation to zip past Europa at least 49 times — aiming all nine of its instruments at the moon at once — each time retreating to calmer territory to process the data and send it back to Earth.
One of the first things Clipper will do when it arrives is confirm — or possibly refute — the presence of the subsurface ocean. How the moon gravitationally tugs on the spacecraft will reveal details of its interior immediately, said deputy project scientist Bonnie Buratti of JPL in the news conference.
Next will come the pictures. Galileo’s antenna never deployed properly, so its images were not as sharp as they could have been, Phillips says. Galileo’s spectrometer wasn’t designed to work at Europa either, so scientists struggled to tease out the composition of anything that wasn’t ice on the surface. Clipper’s images and spectra will reveal clues about the chemical components of the surface and possibly the subsurface that Galileo never could.
Finally, Clipper will delve into details like the thickness of the crust, the depth of the ocean and how they interact.
There are some limitations. Clipper’s gaze won’t reach the bottom of the ocean, where rock and water meet. That might be the most likely place for microbial ecosystems to nestle themselves, similar to seafloor vents on Earth. But Clipper won’t be able to sense them directly.
There is, however, strong circumstantial evidence that water sometimes comes to the surface, whether in plumes of vapor or slower seeping streams or lakes, and may deposit any other material it’s carried up onto the ice (SN: 5/14/18). Clipper will search for chemicals on the surface and infer what could be brewing in the murky depths.
“The holy grail would be if we saw something like an amino acid on the surface,” Buratti says. “But just seeing a lot of organic molecules there will be good evidence that we have all the requisites for life.”
What Clipper won’t do is look directly for life. “We don’t have a tricorder we can point at Europa and say, ‘It’s life, Jim!’” like in Star Trek, Phillips says. “It’s going to be multiple lines of indirect evidence, again.”
“To do a life-detection mission,” she says, “you’re going to have to touch that surface.” Or maybe get beneath it (SN: 5/2/14).
With how long she’s had to wait to get to Europa, Phillips doesn’t expect to see that mission herself. But she hopes scientists won’t have to wait another 25 years.
“I hope that momentum will build,” she says. “I accept that I’m probably not going to get to see that Europa submarine, but hopefully my kids or maybe my grandkids will.”