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Europa Clipper, the biggest interplanetary spacecraft that NASA has ever built, lifted off from the Kennedy Space Center in Florida early Monday afternoon.
The mission will tackle one of biology’s core questions: Can life exist anywhere else in our solar system?
The spacecraft’s destination is Europa, a moon of Jupiter, where water sloshes beneath a shell of ice that could be more than 10 miles thick. Such ocean worlds are fairly common in the outer solar system. That has created speculation: Could there be life swimming in any of those oceans?
For now, the answer is an intriguing maybe.
The $5.2 billion Europa Clipper mission is the first by NASA devoted to filling in the blanks to the question of habitability on these ocean worlds.
“I think Europa is certainly the most likely place for life beyond Earth in our solar system,” said Robert Pappalardo, the project scientist for Europa Clipper. “And that’s because it is the most likely to have the ingredients for life in abundance and for there to be enough time for life to get going.”
At liftoff, Europa Clipper weighed about 12,500 pounds, nearly half of which was propellant. After the two solar panels unfurled, the spacecraft stretched more than 100 feet across — a bit longer than a basketball court.
A powerful SpaceX Falcon Heavy rocket carried the spacecraft from Earth into an orbit around the sun. A flyby of Mars next February will give it a gravitational boost, and then it will swing back around Earth in December 2026 for an additional slingshot acceleration toward its destination.
After a journey of five and a half years and 1.8 billion miles, Europa Clipper is scheduled to enter orbit around Jupiter on April 11, 2030. It will then make 49 flybys of Europa over four years.
Because Earth is the only place where life is known to exist, scientists, not surprisingly, think that the most promising place to look for life would be somewhere similar: an earthlike planet that would be not too cold and not too warm, with temperatures that would allow liquid water, essential for life as we know it, to flow at the surface.
The region around a star with such temperate conditions is known as the habitable zone, or, for fans of fairy tales, the Goldilocks zone.
In our solar system, only Earth fits the criteria for “just right.” But liquid water turns out to be pretty common in the outer solar system, hidden beneath icy shells. Europa was the first world where planetary scientists found compelling evidence for an unseen ocean — indeed, they now think it could have twice as much water as all of Earth’s oceans combined.
Other worlds believed to possess oceans include Callisto and Ganymede, two other large icy moons of Jupiter; Enceladus and Mimas orbiting Saturn; Triton around Neptune; and even Pluto, the dwarf planet.
In addition to water, the other essential ingredients of life are thought to be energy and carbon-based molecules. This mission is to study whether those are present on Europa too.
To do that, the spacecraft is carrying nine instruments, including cameras, spectrometers, a magnetometer and radar. With its observations, scientists expect to measure the depth of the ocean, identify some of the compounds at Europa’s surface and precisely map the moon’s magnetic field, which will provide additional clues about what lies within.
None of the instruments will directly look for anything living, just whether the conditions within Europa could support life.
Jupiter’s immense gravity squeezes and pulls on Europa’s insides, and the heat of friction could power hydrothermal vents on its seafloor. The vents could spew chemicals known as reductants into the ocean.
At the surface, the bombardment of radiation from Jupiter on ice produces oxidants. When oxidants and reductants combine, energy is released — potentially the chemical reactions that could power life.
But for that to occur, the oxidants sitting on the surface of Europa have to somehow move down through miles of ice into the ocean.
The key is that ice on Europa is not a simple solid shell, just as the Earth’s crust is not a simple, solid piece of rock.
Under pressure far below the surface, ice becomes bendable. Warm blobs of ice rise to the surface and cold, denser blobs sink, potentially carrying the oxidants downward — a pattern of convection similar to how the mantle rises and falls within Earth.
That could be the conveyor belt taking chemicals at the surface to the ocean.
“Very much anticipated to be a lava lamp,” said Donald Blankenship, who is a research professor at the University of Texas Institute for Geophysics and the principal investigator for Europa Clipper’s ice-penetrating radar instrument.
Pings from the spacecraft’s radar will pass almost effortlessly through ice and snow but bounce back off salty water. So Europa Clipper may be able to see all the way through the ice to the ocean.
The radar could also detect lakes embedded within the ice, and cryovolcanoes that erupt water, not molten rock.
A thermal imager onboard will look for warm spots, which could indicate places where the ice is thinner and the ocean is closer to the surface.
A tube-shaped instrument about the length of a baguette will scoop up and identify molecules from the thin atmosphere, including carbon-based molecules that could serve as the building blocks for life.
The Hubble Space Telescope has spotted what could be plumes of water vapor sporadically erupting from Europa’s surface. With luck, Europa Clipper could fly through an erupting plume, which could be material from the ocean.
Another instrument, an ultraviolet spectrometer, could also identify molecules within a plume when a distant star passes behind Europa. Stars are expected to be eclipsed by Europa in this way about 100 times during the mission. Looking at how the colors of ultraviolet light from the star dim will tell the density of the gases and what they are made of.
It has been a long, slow journey to get the Europa Clipper mission to the launchpad.
When Voyager 2 flew past Jupiter in 1979, its pictures of Europa showed something that looked like a scuffed-up cue ball — a bright, but fractured surface almost devoid of craters, which indicated some geological process was erasing them.
That made scientists curious to find out more, especially after measurements of Europa’s magnetic fields that NASA’s Galileo spacecraft made a couple of decades ago offered compelling evidence for a layer of salty water.
“We started planning the mission in about 1995, 30 years ago," said Tom McCord, a senior scientist at the Planetary Science Institute who is working on the mission. “And it’s taken that long to get to the point where we have a chance to send the instrument and others on their way on a six-year journey to actually start making measurements.”
For a long time, the top officials at NASA headquarters in Washington were not particularly interested in Europa.
However, John Culberson, a Texas Republican elected to Congress in 2000, was very interested.
Mr. Culberson recalled visiting NASA’s Jet Propulsion Laboratory in California when the Opportunity rover landed on Mars in 2004. Engineers at the lab provided briefings about what they were working on, and a mission that caught his curiosity would visit several of Jupiter’s large moons, including Europa.
“I discovered they had no support from headquarters,” Mr. Culberson said. So, as a member of the appropriations committee, he added money for the mission.
He was annoyed and frustrated when NASA officials spent the money on a different project. “We put the money in for Europa year after year,” he said, “and NASA figured out ways around it.”
Part of NASA’s reluctance was the fear that the price tag of an ambitious Europa mission would soar out of control.
In 2010, Dr. Pappalardo convened scientists and engineers from inside and outside NASA to brainstorm how to make the mission smaller and more affordable. Half of the small team were people who had previously worked on the mission design. The other half were people who had been critical of it, Dr. Pappalardo said.
He recalled that he began the first meeting by showing a blank slide. “We started with a blank sheet of paper,” Dr. Pappalardo said.
Originally, the spacecraft was to enter orbit around Europa. An analysis eventually showed that almost all of the science could be achieved through multiple flybys instead, reducing the amount of shielding and fuel a spacecraft would need.
Serving on the appropriations subcommittee that finances NASA, Mr. Culberson championed Europa Clipper and its potential for the discovery of extraterrestrial life. He also wanted NASA to include a lander.
“It’s got a real shot of reigniting the public passion for the space program,” he said.
The Obama administration, however, had other priorities for NASA. Its budget request for 2014 not only did not include money for a Europa mission. It flatly stated that NASA could not afford one “in the foreseeable future.”
The Planetary Society, a nonprofit that advocates exploring space, also campaigned for Europa. “We’ve never had a member outreach like this,” said Casey Dreier, the society’s chief of space policy. “I think we just helped establish it as something that needed to be done, something that had support.”
It was during the Trump administration that the Europa Clipper mission finally gained momentum and sizable budgets.
Mr. Culberson lost his re-election bid in 2018. Europa Clipper survived. The lander proposal, which could have added billions of dollars to the price tag, did not.
The mission faced additional hurdles. Originally, Mr. Culberson and Congress mandated that it had to fly on the Space Launch System, a massive NASA-developed rocket that costs an estimated $4 billion per launch.
Congress relented on that requirement, and in 2021 NASA awarded SpaceX the Falcon Heavy launch contract for only $178 million.
This year, Europa Clipper again seemed to be in peril when it appeared that transistors on the spacecraft might be defective and therefore unable to survive the harsh radiation around Jupiter. But engineers found that when the spacecraft swings farther out, the transistors recover, and NASA moved ahead with the launch.
Hurricane Milton caused another brief delay as it passed over the Kennedy Space Center on Thursday, the original launch date.
On Monday, Mr. Culberson watched from a balcony at the launch site as the rocket carrying Europa Clipper arced upward across a clear, azure Florida sky.
“I’m still walking on Cloud Nine,” he said afterward. “A flawless beginning to a potentially civilization-changing mission.”
Some recent research has cast doubts on the hopes for life on Europa.
Two studies presented at the Lunar and Planetary Science Conference this year suggest that there may not be any volcanism on Europa’s seafloor. The rocks there also may not easily fracture, minimizing the chemical reactions between the ocean water and the rocks that could provide energy for living organisms.
Although there may be molten rock deep inside Europa, “it seems very difficult for that magma to be able to ascend anywhere close to the ocean floor,” said Paul Byrne, a planetary scientist at Washington University in St. Louis who was an author on both papers.
Even if life did arise in Europa’s ocean long ago, “It seems challenging to sustain that life today,” Dr. Byrne said. “That’s really what I think these studies are beginning to tell us.”
That does not mean Dr. Byrne thinks that Europa Clipper is a waste of $5 billion.
“Clipper is exactly the kind of mission we need to begin to incrementally build on our understanding of habitability,” he said, adding that he hopes it is the first in a “series of missions, not just to Europa, but so many of these so-called ocean worlds.”
It has been a long wait. Dr. McCord, the scientist who started working on Europa plans around 1995, is now 85.
“I’ll be 91 or something like that” when Europa Clipper reaches its destination, he said. “This is an endeavor that more than spans people’s lives.”
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