An artist rendering of Europa Clipper over Europa. The spacecraft is scheduled to launch in fall 2024. (NASA/JPL)
“ALL THESE WORLDS ARE YOURS – EXCEPT EUROPA. ATTEMPT NO LANDING THERE.”
These are the words broadcast by the computer HAL as recounted in Arthur C. Clarke’s book “2010: Odyssey Two,” the sequel to the iconic “2001: A Space Odyssey.”
The message had been delivered to the computer by the non-corporeal David Bowman (the focus of the “2001”), but more accurately from the energy-based aliens who control the fate of Bowman, the famous monoliths and much more. The aliens had concluded that Europa, with its subsurface ocean, could support life with the potential to evolve, and so they wanted the Jovian moon to be protected from meddling by humans or anyone else.
Clarke’s “Odyssey Two” was released in 1982, when Europa was not exactly a front-burner destination for NASA or anyone else.
But much has changed, and Clarke’s early focus on Europa as the most potentially habitable object in the solar system has been embraced by NASA and others for some time.
Surface features of Jupiter’s icy moon Europa are revealed in an image obtained by Juno’s Stellar Reference Unit (SRU) during the spacecraft’s flyby in 2022. The spacecraft came within 219 miles of the moon.
(NASA/JPL-Caltech/SwRI)
While the fictional admonition not to land on Europa is (for now, a least) being respected, the pull of Europa has become enormously strong.
Consider:
The NASA spaceship Juno recently performed a flyby of the moon and took some revealing new photos. (See above.)
Just last month, the European Space Agency launched the Jupiter Icy Moons Explorer (JUICE) spacecraft that is headed to Jupiter and three Jovian moons, including Europa.
And now all the parts and instruments of NASA’s Europa Clipper are in a Jet Propulsion Lab clean room for assembly in preparation for an October, 2024 launch. The Clipper will not land on Europa, but it will get closer than any other spacecraft has come.
So while it won’t be until the early 2030s that JUICE and the Clipper have their close encounters with Europa, the moon is very much on the front burner now for astrobiologists, planetary scientists and space (and science fiction) aficionados of all kinds.
This composite includes the four largest moons of Jupiter which are known as the Galilean satellites. These moons were first identified by the Italian astronomer Galileo Galilei in 1610. Shown from left to right in order of increasing distance from Jupiter, Io is closest, followed by Europa, Ganymede, and Callisto. (NASA/JPL/DLR)
Europa is one of 95 moons of Jupiter, with the latest one identified this past February. As might be expected in the surrounds of the largest solar system planet — with a mass more than twice as great as all the other planets combined — there are more moons of Jupiter than of any other planet in the solar system.
Four NASA spacecraft have flown by Europa — Voyager 1 and 2 in the late 1970s, Galileo in the 1990s until 2003 and Juno in more recent days. The Voyager spacecraft flew within thousands of miles of Europa, Galileo within hundreds of miles and Juno the same.
The data recovered from these missions strongly suggest that Europa is unusual and special.
For instance, Voyager images revealed a surface brighter than that of Earth’s moon, crisscrossed with numerous bands and ridges, and with a surprising lack of large impact craters, tall cliffs or mountains (in other words, a very smooth surface, relative to the other icy moons).
Even though the Voyagers did not pass especially close to Europa, their images were of high enough quality that researchers saw that some of the dark bands had opposite sides that matched each other extremely well, like pieces of a jigsaw puzzle. These cracks had separated and dark, icy material appeared to have flowed into the opened gaps, suggesting that the surface had been active at some time in the past.
This enhanced color image shows the region surrounding Pwyll, an 18-mile wide impact crater thought to be one of the youngest features on the surface of Europa. The surface has been estimated to be 40 to 90 million years old, much younger than the moon itself. (NASA)
Voyager images showed only a handful of impact craters, which are expected to build up over time as a planetary surface is constantly bombarded by meteorites over billions of years. The lack of these impact craters suggested that the moon’s surface was relatively young and implied that something had erased them – such as icy, volcanic flows, or the settling of the icy crust under its own weight.
The tantalizing discoveries by Voyager led to the Galileo mission to the moons of Jupiter, and especially Europa. New details about makeup and geometry of the moon’s surface was so intriguing that the mission was extended to make a total of 12 close flybys of Europa.
One of the most important measurements showed that Jupiter’s magnetic field was disrupted in the space around Europa. This measurement strongly implied that a special type of magnetic field is being created within Europa by a deep layer of some electrically conductive fluid beneath the surface. Based on Europa’s icy composition, scientists concluded the most likely material to create this magnetic signature is a global ocean of salty water.
But the surface of Europa is beyond frigid — a high of minus 210 degrees Fahrenheit at the equator and a low of minus 370 degrees F. at the poles. So how could the moon house a global ocean of liquid water, and a very large one at that?
Many Worlds looked at this question in 2021, how the moon’s gravitational interactions with Jupiter cause flexing and heat, and here are the results.
Jupiter’s moon Europa has a crust made up of blocks, which are thought to have broken apart and ‘rafted’ into new positions, as shown in the Galileo image on the left. These features are the best geologic evidence to date that Europa had, or has, a subsurface ocean. Combined with the geologic data, the presence of a magnetic field leads scientists to believe an ocean is most likely present at Europa today. In this false color image, reddish-brown areas represent non-ice material resulting from geologic activity. Long, dark lines are ridges and fractures in the crust, some of which are more than 1,850 miles long. (NASA/JPL/University of Arizona)
An early task of the Europa Clipper is to confirm, once and for all, the presence of its ocean. The spacecraft can do so, in part, with measurements of the amount of that surface flexing due to the tides created by the gravitational pulls and tugs of Jupiter and other moons. If the ocean exists, the tides should deform the surface by about 100 feet; if the moon is frozen through, the tides should stretch the surface by only 3 feet.
Also of great interest will be the composition of the reddish material on the surface. Scientists would like to know if this material holds clues to the composition of the ocean — if it contains some of the chemical building blocks of life — and whether material is cycling between the surface and the interior.
But the science goals for the Europa Clipper reach much further.
For instance, scientists are hoping to determine the thickness of Europa’s icy shell – the moon’s outer layer that includes its surface. Researchers will estimate the size, saltiness and other qualities of Europa’s ocean. They also will determine how the ocean interacts with the surface: Does anything in the ocean rise up through the shell to the top? Does any material from the surface work its way down into the ocean?
They will look as well for possibly detached, though connected, lakes or seas between the global ocean and the surface. And they will examine surface features of the moon in search of signs of recent activity such as sliding crust plates or plumes that may be venting water into space, rather like Saturn’s moon Enceladus.
The instruments to do all this will be onboard and the spacecraft will get remarkably close to Europa, making the measurements far more exact than ever before.
When it arrives at Jupiter, the Clipper will be maneuvered into a highly elliptical orbit of the moon that will take it almost 2,000 miles away and then return to within an unprecedented 16 miles. NASA is planning for as many as 50 flybys of Europa and is widely expected to revolutionize our understanding of the moon.
The European Space Agency’s Jupiter Icy Moons Explorer (JUICE) lifted off on April 14 from the Guiana Space Centre in French Guiana atop an Ariane-5 rocket. The spacecraft will study Europa, but also Jupiter and two other of its moons. (ESA)
The Clipper and its team of scientists and engineers will also have outside help in their efforts to better understand Europa.
The European JUICE spacecraft will fly as close as 300 miles from Europa as it explores the Jupiter system . While investigating Europa is a central part of the mission, JUICE will also visit the moons Ganymede and Callisto as part of the larger mission to investigate Jovian moons known, or strongly suspected, to have water under their ice shells.
JUICE will be the first spacecraft to orbit Ganymede, the largest Jovian moon, and it will do so for more than one year. Better understanding the composition and potential subsurface ocean dynamics of Ganymede and Callisto will help better understand Europa as well.
Although JUICE will have launched 18 months before the Clipper (if it departs on schedule), the Clipper will actually make it to Jupiter and its moons a few months before JUICE due to its liftoff push and its pathway.
The Clipper is scheduled to arrive at Jupiter in April, 2030. JUICE, which is also supported by the Japanese and Israeli space agencies, will arrive at Jupiter in 2031, will fly by Europa, Ganymede and Callisto from 2031 to 2034 and then will orbit Ganymede through 2035.
The Clipper will enter an orbit around Jupiter rather than Europa. A Jupiter orbit is necessary due to the belts of intense radiation that surround the planet, which can damage electronics. Initial Clipper mission concept studies showed that a spacecraft orbiting Europa — which circles Jupiter in 3.5 days — might only be able to survive for months, while a Jupiter-orbiting mission should have a multi-year lifetime.
The design of the Europa Clipper trajectory allows up to 50 flybys of Europa, each with a different close approach location, to allow almost the complete moon to be mapped at high resolution. After each close approach, the spacecraft travels outside of Jupiter’s radiation belts to downlink data, uplink new commands, and prepare for the next flyby.
NASA commissioned a study for a lander on Europa and in 2016 the study team reported that it was feasible. But the agency declined to add the lander to the Clipper mission. (NASA)
While the Clipper will not land on Europa, it’s broadest goal is to learn far more about whether the moon may be habitable. In that core ambition, it is unique.
If the answer that comes back is that the ocean beneath Europa’s crust may well be habitable — with the necessary water, chemicals and energy sources — then the next logical step is to send a lander to the moon to determine whether it is actually inhabited.
Indeed, thinking and planning for such a possible NASA landing mission on Europa has been going on for some time and a lander to complement the Clipper mission was considered but never approved and funded. Our understanding of the moon and our technology to investigate it in situ was considered insufficiently mature. And information coming back from the Clipper about possible landing sites was considered a prerequisite for a lander mission.
And then there is the question of planetary protection — the necessity to make sure we don’t bring Earthly contaminants to the moon. The lander concept includes tools to dig up to 4 inches into the surface ice, so it would not just monitor the moon but also interact with it.
This is precisely what the aliens in “2010: Odyssey Two” had in mind as the kind of danger that humans posed to Europa. Might we bring bacteria or other lifeforms to Europa that would reach the subsurface ocean where life might be present? Would those Earthly lifeforms kill off Europan life or stunt its evolution?
In Arthur C. Clarke’s imagined universe, that did not happen and Europan life did evolve and an epilogue to Odyssey features a primitive Europan civilization in AD 20,001. In other words, humans did not interfere with Europa.
But in our real world, a future landing on Europa is seemingly inevitable if the moon is deemed habitable after the Clipper and JUICE missions. The pull of searching for potential extraterrestrial life is just too strong to stay away.
