Europa is one of the most interesting moons in the solar system, it is one of the Galilean moons of Jupiter, along with Io, Ganymede, and Callisto. Astronomer Galileo Galilei is credited with discovering these moons, some of the largest in the solar system. Europa is the smallest of the four, but one of the most interesting. Europa’s surface is covered in ice, but scientists believe that there is an ocean underneath. The icy surface also makes it one of the most reflective moons in the solar system.
In 2012, researchers using the Hubble Space Telescope detected a possible plume of water ejected from Europa’s south polar region. Another team, after repeated attempts to confirm the observations, found clear plumes in 2014 and 2016. The researchers cautioned that the plumes have not yet been fully confirmed, but they suggest that Europa has water in its ocean ejected to the surface.
Several spacecraft have flown past Europa (including Pioneers 10 and 11, and Voyagers 1 and 2 in the 1970s). The Galileo spacecraft carried out a long-duration mission in the vicinity of Jupiter from 1995 to 2003.
Europa is estimated to be about 4.5 billion years old, which is about the same age as Jupiter. On average, Europa is about 485 million miles (or 780 million kilometers) away from the Sun.
Europa is Jupiter’s sixth moon. Its orbital distance from Jupiter is 670,900 km (414,000 mi). Europa orbits Jupiter once every three and a half Earth days. Europa is tidally locked, meaning the same side always faces Jupiter.
Europa has a diameter of 3,100 km (1,900 miles), making it smaller than Earth’s moon but larger than Pluto. It is the smallest of the Galilean satellites.
The surface temperature of Europa at the equator never rises above minus 260 degrees Fahrenheit (minus 160 degrees Celsius). At the satellite’s poles, the temperature never rises above minus 370 degrees Fahrenheit (minus 220 degrees Celsius).
These images show the trailing hemisphere of Jupiter’s moon Europa, taken by the Galileo spacecraft from a distance of about 430,000 miles (677,000 km). Europa is shown in nearly natural color on the left, and enhanced color on the right to bring out detail. The bright feature in the lower right is the 45-km-wide crater Pwyll. NSSDC Photo Gallery
Europa is very similar in size to our Moon. Its diameter is 1/4 of the Earth’s diameter.
Europa is mostly silicate rock (chemical formula SiO_x). The top layer is still made of water ice – H₂O. There are huge amounts of H2O on Europa, and there is evidence that beneath the ice crust, H2O exists in liquid form in a global subsurface ocean.
Europa is one of the most promising candidates for the existence of extraterrestrial life. Under the icy crust is an ocean, which probably has a real ocean floor, that is, it is in contact with silicate rocks on the bottom.
An important feature of Europa is its high reflectivity. Europa’s icy crust gives it an albedo (reflectivity of light) of 0.64, which is one of the highest values among all the moons of the Solar System. Scientists have calculated that the age of Europa’s surface is between 20 and 180 million years, which makes it quite young.
Images and data from the Galileo spacecraft indicate that Europa is made of silicate rock and has an iron core and rocky mantle, like Earth. However, unlike Earth’s interior, Europa’s rocky core is surrounded by a layer of water and/or ice that is 50 to 100 miles (80 to 170 kilometers) thick, according to NASA.
Based on the fluctuations in Europa’s magnetic field, which indicate the presence of some kind of conductor, scientists also suspect the presence of an ocean deep beneath the moon’s surface. Some form of life may exist in this ocean. The possibility of extraterrestrial life is one of the reasons why Europa continues to be of great interest. Moreover, recent studies have given new life to the theory that Europa may be habitable.
Europa’s surface is covered in cracks. Many believe that these cracks are the result of tidal forces acting on the ocean beneath the surface. Perhaps when Europa orbits close to Jupiter, the sea level beneath the ice rises above normal. If so, the constant rise and fall of sea level would be responsible for the many cracks seen on the moon’s surface.
Obtaining ocean water samples may not require drilling into the ice crust if repeated observations of possible plumes prove to be real water jets. Although researchers found evidence of them in 2012, 2014, and 2016, the true nature of the plumes and the reasons for their sporadic appearance require further observation.
This raw image of Jupiter’s icy moon Europa was taken by the Juno spacecraft during its flyby on Sept. 29, 2022. NASA/SWRI/MSSS
In 2014, scientists discovered that Europa may have a type of plate tectonics. Previously, Earth was the only known body in the solar system with a dynamic crust, which is thought to have helped fuel the evolution of life on the planet.
The presence of water beneath Europa’s frozen crust makes it one of the best places in the solar system for life to develop. The moon’s icy depths are thought to contain openings into the mantle, similar to oceans on Earth. These openings could provide the necessary thermal environment for life to develop.
If life exists on the Moon, it could have been triggered by cometary fallout. In the early stages of the Solar System, icy bodies could have delivered organic matter to the Moon.
A 2016 study found that Europa produces 10 times more oxygen than hydrogen, comparable to Earth. This could make its ocean more hospitable to life, and the moon might not need tidal heat to generate enough energy. Instead, chemical reactions would be enough to keep the cycle going.
History of research
Pioneer 10 (Jupiter flyby in 1973) Passed too far from Europa to obtain detailed images, but the mission did record some changes in the albedo (brightness) of the moon’s surface.
Pioneer 11 (Jupiter flyby in 1974) The spacecraft flew past Europa at a distance of almost 600,000 km, which allowed it to only see some changes on its surface.
Voyager 1 (Jupiter flyby in 1979) Performed a long flyby of Europa and also provided insight into how the gravity of one moon in the Jovian system affects the gravity of others. For example, volcanism on Io was partly due to Io’s interactions with its moons, as well as with massive Jupiter.
Voyager 2 (flyby of the Jupiter system in 1979). One of its most important discoveries was the confirmation of brown streaks on the surface of Europa, indicating cracks in the icy surface.
Galileo (orbited Jupiter from 1995 to 2003) made its most famous discovery on Europa, finding compelling evidence of an ocean beneath the moon’s icy surface.
The Jupiter Icy Moons Explorer (JUICE) spacecraft launched on April 14, 2023, and is currently on an eight-year journey to the outskirts of Jupiter, where it is expected to arrive in 2031. JUICE will look for molecules, such as organic ones, that are associated with the processes by which life originated. (Organic substances are common in the solar system, but the molecules themselves are not always a sign of life.)
Europa Clipper (launched in 2024) will fly past Europa dozens of times. One of its main goals is to look for evidence of visible plumes, which Hubble researchers have seen several times.
Europa is one of the most interesting moons in the solar system. Stocktrek/Getty Images
Despite launching after JUICE, the Europa Clipper mission will reach Jupiter ahead of JUICE, on April 11, 2030. The spacecraft will carry nine scientific instruments, including cameras, a radar to probe beneath the ice and determine its thickness, a magnetometer to measure the magnetic field (and therefore the salinity of the ocean), and a thermal instrument to look for signs of eruptions. The flyby altitudes will range from 25 km to 2,700 km. This will allow the spacecraft to penetrate the high-radiation zone on Europa, where survival is difficult. The ability to enter and exit this zone will extend the spacecraft’s life and make it easier to transmit data to Earth.
One of Europa Clipper’s priorities will be to continue observing the plumes made by Hubble. “If the plumes are confirmed to be associated with a subsurface ocean, studying their composition will help scientists understand the chemistry of Europa’s potentially habitable environment while minimizing the need to drill through the ice,” NASA said in a statement.
The European Space Agency’s (ESA) JUICE mission will visit Jupiter and its three icy moons: Europa, Callisto, and Ganymede. JUICE is a single-person orbiter without a lander that will orbit Ganymede, the largest moon in the solar system, making it the first probe to orbit a moon of a planet other than Earth. Once it reaches Europa, the mission will study organic molecules and other components that could make the moon habitable. The spacecraft will also measure the thickness of the crust, particularly in the active regions it discovers.
Galileo Galilei discovered Europe on January 8, 1610.
It is possible that the German astronomer Simon Marius (1573–1624) also discovered the Moon at the same time. However, he did not publish his observations, so Galileo is most often credited with the discovery. For this reason, Europa and Jupiter’s three other largest moons are often called the Galilean moons. Galileo named these moons the Medici planets, after the Medici family.
Galileo may have observed Europa the day before, on January 7, 1610. However, because he used a low-power telescope, he was unable to distinguish Europa from Io, another moon of Jupiter. Only later did Galileo realize that they were two different bodies.
The discovery had not only astronomical but also religious significance. At the time, the Catholic Church supported the idea that everything revolved around the Earth, which had been supported in ancient times by Aristotle and Ptolemy. Galileo’s observations of Jupiter’s moons, as well as the fact that Venus went through “phases” similar to those of our Moon, convincingly proved that not everything revolved around the Earth.
However, with the development of telescopic observations, a new view of the universe emerged. The moons and planets were not fixed and perfect; for example, the mountains observed on the moon indicated that geological processes were occurring elsewhere. In addition, all the planets revolved around the sun. Over time, moons were discovered around other planets, as well as around Jupiter.
Is There Potential for Life on Europa? NASA Expert Answers
That’s a great question. And it’s one that NASA is trying to answer with its Europa Clipper spacecraft. Europa is a moon of Jupiter. It’s about the same size as the Moon, but its surface looks very different. Europa’s surface is covered in a layer of ice, and underneath that ice, we think, is a layer of liquid water that contains more water than all of Earth’s oceans combined.
So, because of this giant ocean, we think that Europa is actually one of the best places in the solar system to look for life beyond Earth.
Life as we know it requires three basic conditions: liquid water – all life on Earth uses liquid water as its base.
The second is the right chemical elements. These are elements like carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. These are the elements that make up life as we know it on Earth. We believe that these elements are present on Europa.
The third component is an energy source. As Europa orbits Jupiter, its strong gravity pulls on it. This effectively stretches the surface. This creates a heat source called tidal heating. So it’s possible that hydrothermal systems could exist on the bottom of Europa’s ocean, and that’s where abundant life could exist.
In 2022, NASA’s Juno spacecraft made a close flyby of Jupiter’s intriguing moon Europa, revealing potential signs of modern activity on its surface.
The spacecraft’s Stellar Reference Unit (SRU), a stellar camera designed to assist in positioning aboard Juno, was used to obtain high-resolution images of Europa’s surface illuminated by Jupiter’s glow, or sunlight scattered by Jupiter.
The image taken by SRU during the flyby is discussed in a paper published in the journal JGR Planets on December 22, 2023. The image shows an unusually shaped patch of ice, 37 by 67 kilometers (23 by 42 miles), resembling a platypus. In other words, it has a “body” in the north and a “beak” in the south. The two regions, connected by a cracked land bridge, contain large ice floes, each about 1 km (0.62 mi) in size, that cast shadows.
Comparisons with similar resolution images taken earlier by NASA’s Galileo spacecraft, which studied Jupiter from 1995 to 2003, show changes in the southern portion of the “platypus,” suggesting that Europa’s surface may have changed since the Galileo images were taken.
Europe. NASA/JPL-Caltech/SETI Institute)
However, a team of authors led by Heidi N. Becker of NASA’s Jet Propulsion Laboratory (JPL) argues that this evidence is not conclusive due to differences in image quality and conditions.
The 2022 image also shows nearby low-albedo deposits that may be associated with underground water, the researchers say. These dark spots may be associated with plumes thought to be spewing water.
However, while not a definitive conclusion, Platypus represents an attractive target for future missions such as NASA’s Europa Clipper and Europe’s JUICE to explore and possibly confirm modern surface activity on Europa. JUICE launched in April 2023 and will arrive at Jupiter in December 2031. Europa Clipper is scheduled to launch on October 6 this year aboard a Falcon Heavy rocket.
Jupiter’s moon may have large amounts of liquid water beneath its icy surface.
Europa, one of Jupiter’s four major moons, has a 20-kilometer-thick crust of ice beneath which scientists believe an ocean sloshes. But a 2022 study that found similarities between the formation of the distant moon’s surface and Earth’s icy Greenland suggests scientific possibilities may lie much closer to the frozen moon’s surface. Kalberg and his colleagues published their work in the journal Nature Communications on April 19, 2022.
Europa’s icy crust is covered in a lattice of so-called double ridges – pairs of long, parallel, raised lines with a trough between them, stretching for hundreds of miles or kilometers. Every patch of the moon’s surface is marked by crisscrossing rows of these double ridges, but scientists still don’t know for sure how they form.
However, a recent analysis of satellite images has revealed that a strikingly similar ridge formed in the ice sheet covering Greenland about 10 years ago.
By studying what lies beneath the double Greenland ridge, Kalberg and his colleagues have proposed that the double ridges — on both Earth and Europa — are formed by groundwater rising through cracks in the surface ice and then refreezing. If the explanation is correct, it’s a hint that Europa may not only have a deep, hidden ocean; Jupiter’s moon may also have water pockets just beneath the surface ice.
Artist’s impression of the water pools that form the double ridges on Jupiter’s moon Europa. Blaine Wainwright
Kalberg, a geophysicist who studies primarily the effects of climate change on the Greenland ice sheet, saw images of Europa’s double ridges and immediately thought of a feature he’d seen in images of Earth’s polar island. Indeed, when scientists adjust their measurements for differences in gravity, the shape of Greenland’s double ridge is strikingly similar to that of Europa’s.
That’s useful because scientists can do something with Greenland that they can’t yet do with Europe: penetrate the ice sheet with radar. And in Greenland, radar scans have shown water rising beneath the double ridge.
Scientists believe that the key to the formation of double ridges is upwelling water. When a pool of water forms inside the ice, it can begin to exert pressure on the surface ice. With enough pressure, the ice can crack and water can begin to rise into the gap. This water quickly freezes, but the pressure created by this entire process cuts double ridges into the surface.
It’s hard to overstate how much of Europa is made up of double ridges. If this explanation is correct, it means that pockets of water beneath the surface have been a feature of Europa for much of the moon’s history. If so, something must be replenishing them.
In this regard, Greenland is an odd comparison, since its double ridge formed over the past decade. Kalberg and his colleagues believe that an unusually warm summer in 2012 melted enough water to create an underground pocket beneath the ridge.
But there is almost no meltwater on Europa’s surface, so Kalberg and his colleagues argue that this new water is coming from even deeper beneath the ice: from tens of miles or kilometers away, where scientists expect to find a global ocean.
The study shows that even weaker impacts can heat and soften ice on Jupiter’s moon Europa enough to cause the material to sink into a subsurface ocean. The discovery explains a new transport mechanism that could deliver important components to the moon’s ocean.
The icy shell of Jupiter’s moon Europa is pockmarked with craters, most of which were formed by small impacts that dent the moon’s surface but weren’t big enough to penetrate the ocean beneath. Researchers have shown that impacts that penetrate even halfway through the ice shell accumulate enough meltwater to seep through the ice and into the ocean beneath. The research is described in a paper published November 28, 2022, in the journal Geophysical Research Letters.
This drainage, which the researchers found could occur over 10,000 to 100,000 years, is a critical mechanism for transporting oxidizers—chemicals that can easily gain electrons from other substances, triggering chemical reactions—from the moon’s surface into its ocean, increasing its chances of habitability.
Previous studies assumed that impacts had to penetrate the ice, which limited the potential for mineral transport to only the largest impacts. The latest research expands this range, showing that much smaller, non-penetrating impacts are, in fact, sufficient to achieve this goal.
The four largest impact craters on Jupiter’s moon Europa: Pwyll, Sylix, Tyre, and Manannan. NASA
“This increases the likelihood that the necessary chemical ingredients for life are present,” Mark Hesse, a geologist at the University of Texas at Austin and a co-author of the study, said in the same statement.
Scientists have long suspected that cometary impacts could be important carriers of organic molecules essential for life, and nearly two dozen craters on Europa’s surface indicate that the moon has certainly been visited by comets and asteroids. In addition, radiation from Jupiter splits water molecules into hydrogen and oxygen, ensuring the presence of oxygen on the moon’s surface.
However, it is still unclear how these essential minerals deposited on the Moon’s surface could have ended up in its underground ocean.
In the new study, the researchers used numerical modeling to simulate the long-term evolution of impact craters. They also looked at how meltwater and mineral-rich water seeps through the ice. Across nine experiments, the researchers simulated meltwater seepage through ice shells of varying thicknesses under impact conditions to better understand when material might be submerged into the ocean.
For Europa, their analysis found that if impacts passed through even half of the moon’s 16- to 24-kilometer (10- to 15-mile) thick surface, 40 percent of the resulting meltwater would sink into its ocean. By comparison, a 0.8-kilometer (0.5-mile) wide comet that passed through half the surface could melt enough surrounding ice to fill a crater lake.
The researchers also show that a molten chamber beneath Manannan, one of Europa’s largest impact craters, would have released more than 6.7 cubic miles (28 cubic kilometers) of meltwater from the moon’s surface into its ocean over 1,000 years.
The researchers said the mechanism is a natural consequence of collisions, meaning it applies not only to Europa but to most icy worlds. Saturn’s moon Titan is also thought to have a hidden ocean beneath its outer shell, which is between 30 and 120 miles (48 and 190 km) thick.
Even with these models, scientists are not yet sure how many minerals present on the surface will survive the impacts, and exactly how many might end up in meltwater and, therefore, in the underground ocean.
Sulfur dioxide was detected on the far side of Europa thanks to Jupiter’s magnetic field.
Researchers have studied material on the far side of Jupiter’s moon Europa and found that sulfur found on its surface likely came from Io, a large and volcanically active moon of Jupiter. The study was published June 2, 2023, in the Planetary Science Journal.
Using the Hubble Space Telescope, a team led by the Southwest Research Institute (SwRI) observed Europa in ultraviolet wavelengths, filling a gap in the different wavelengths used to observe the icy water world.
The results of these studies produced the first near-global map of sulfur dioxide on Europa. Although this is not the first time the compound has been detected on Europa, the map shows the presence of solid sulfur dioxide with better coverage and resolution than previous observations. Concentrations of the substance also correlate with darker regions at large scales in both the visible and ultraviolet ranges.
The results of the study showed that sulfur is likely erupting from Io, the most volcanically active body in the solar system, and is then ionized and captured by Jupiter’s magnetic field. It is then transported to Europa, where it reacts with water in the moon’s icy crust to form sulfur dioxide.
Sulfur dioxide concentrations detected on Europa, Jupiter’s fourth-largest moon (shown below), likely came from Io (top), Jupiter’s ultravolcanic moon. NASA
However, there is also a possibility that this compound is present in the bowels of Europe.
“Europa’s relatively young surface is mostly made of water ice, although other materials have been detected on its surface,” said Tracy Becker, a planetary scientist at SwRI and lead author of a paper describing the ultraviolet observations. “Determining whether these materials are native to Europa is important for understanding its formation and subsequent evolution.”
Higher concentrations of sulfur dioxide detected in Europa’s trailing hemisphere as it orbited Jupiter suggest that the sulfur originated from Io.
“Most of the sulfur dioxide is in Europa’s ‘back’ hemisphere,” said Philippa Molyneux, a scientist at the South Pacific Institute and a co-author of the paper. “It’s likely concentrated there because Jupiter’s unidirectionally rotating magnetic field is trapping sulfur particles emitted by Io’s volcanoes and slamming them onto Europa’s backside.”
SwRI plans to continue these studies using the Europa Ultraviolet Spectrograph, which will observe Jupiter’s fourth-largest moon as part of NASA’s Europa Clipper mission, which is expected to arrive in the Jovian system in 2031.
Scientists are almost certain that beneath Europa’s icy surface lies a salty ocean containing almost twice as much water as all of Earth’s oceans combined. That’s why Jupiter’s moon is considered one of the most promising places to search for life beyond Earth.
A new type of salt could explain the mystery of Europa’s ice cracks. The discovery could explain the red streaks on Jupiter’s moon Europa that don’t match any known substance on Earth.
Scientists on Earth have discovered two new types of hard crystals that form when table salt and water mix at low temperatures and pressures. The discovery could have otherworldly significance because these salts could be found in deep cracks and crevices on the surfaces of moons in the solar system. The team’s research is published in the February 20, 2023 issue of the Proceedings of the National Academy of Sciences.
In particular, the discovery could explain the strange red streaks that crisscross the surface of Jupiter’s moon Europa. The scratch-like lines have a chemical composition that doesn’t match anything found on Earth, but scientists think they could be a frozen mixture of salts and water. The new discovery could finally provide an explanation.
The new substances, a mixture of two of the most common molecules on Earth, have been created by a team of scientists led by the University of Washington, who believe the salts could have formed naturally at the bottom of deep oceans on moons like Europa.
“Fundamental discoveries in science are rare these days,” said Baptiste Journoux, lead author of the study and an associate professor in the Department of Earth and Space Sciences at the University of Washington. “Salt and water are well known in terrestrial settings. But beyond that, we’re in the dark. And now we have these planetary objects that probably contain compounds that we’re familiar with, but in very exotic settings.”
A crystal of a completely new type of salt ice that was previously unknown on Earth but could exist on the icy moons of the solar system. Journo et al./PNAS
When water and salts combine at low temperatures, a rigid lattice called a “hydrate” is formed, held together by hydrogen bonds. Sodium chloride, or table salt, a simple structure in which there is one salt molecule for every two water molecules, was previously the only known hydrate.
These two newly discovered compounds are also hydrates, but they differ significantly from sodium chloride. In one compound, there are two sodium chloride molecules for every 17 water molecules. In the other, there is one sodium chloride molecule for every 13 water molecules.
If these high-water hydrates are found all over Europa, it could explain why the surface of this and other Jupiter moons appears to be more watery than expected. “It has the structure that planetologists have been waiting for,” Journo said.
The team discovered the new hydrates by squeezing a small sample of salty water between tiny diamonds no bigger than a grain of sand. This meant the liquid was subjected to pressures 25,000 times greater than Earth’s normal atmospheric pressure.
Because the diamonds were transparent, the researchers were able to monitor the experiment under a microscope. The team found that after the high pressure was released, one of the hydrate structures remained stable.
“We were trying to measure how adding salt would affect the amount of ice produced, because salt acts as an antifreeze,” Journo said. “Surprisingly, when we increased the pressure, we saw these crystals that we weren’t expecting start to grow. It was a very fortunate discovery.”
While the cold, high-pressure conditions the team created in the lab are not common on Earth, they do occur naturally on Jupiter’s moons. On Jupiter’s moons, conditions are sufficient to form ice sheets 5 to 10 kilometers thick over oceans up to 160 kilometers deep. Even denser ice can form on the bottom of these oceans.
“Pressure simply pushes molecules closer together, so their interactions change – that’s the main driver of the diversity of crystal structures we find,” Journo said.
The James Webb Space Telescope has detected the first traces of carbon on Jupiter’s icy moon Europa. The discovery, made by NASA’s powerful space telescope, brings scientists closer to determining whether Europa’s salty oceans could support life.
NASA’s James Webb Space Telescope has detected carbon dioxide coming from the salty liquid oceans of Jupiter’s icy moon Europa. The research by two teams was published in two papers in the September 21, 2023, issue of Science.
Scientists have long known that Europa has oceans of water beneath its icy shell, but they didn’t know whether those oceans had the right chemical makeup to support life. So the discovery of carbon, an element vital to life, in this subsurface ocean on one of Jupiter’s moons has important implications for the moon’s potential habitability and is a testament to groundbreaking scientific discoveries made possible by the James Webb Space Telescope (JWST).
“On Earth, life values chemical diversity — the more diversity, the better. We are carbon-based life. Understanding Europa’s ocean chemistry will help us determine whether it is hostile to life as we know it, or whether it might be a good place for it,” said lead author of the study and NASA Goddard Space Flight Center scientist Geronimo Villanueva. “This suggests that we can learn some basic information about the ocean’s composition before we drill through the ice to get the full picture.”
This graph shows a map of the surface of Europa obtained with the NIRCam (Near Infrared Camera) in the first panel, and composition maps obtained with data from the Near Infrared Spectrograph Integral Field Unit (NIRSpec/IFU) in the next three panels. In the composition maps, white pixels correspond to carbon dioxide in a large-scale region of disrupted chaos known as the Tara Regio (center and right), with additional concentrations in parts of the chaos region, the Powys Regio (left). The second and third panels show signatures of crystalline carbon dioxide, and the fourth panel shows a complex amorphous form of carbon dioxide. NASA, ESA, CSA, G. Villanueva (NASA/GSFC), S. Trumbo (Cornell Univ.), A. Pagan (STScI)
But even more interestingly, the team was able to use infrared observations from JWST’s Near Infrared Spectrograph (NIRSpec) to determine that the carbon molecules did not arrive on Europa from meteorite impacts or other external sources.
“We now believe we have observational evidence that the carbon we see on Europa’s surface is of oceanic origin. That’s not a trivial fact. Carbon is a biologically important element,” said Samantha Trumbo, a researcher at Cornell University and lead author of a second paper describing the discovery.
JWST found that carbon dioxide around Europa, the smallest of Jupiter’s four large Galilean moons, is most abundant in a geologically young region called Tara Regio. In this region, called “chaotic terrain,” the surface ice has been disturbed, indicating exchanges of matter between Europa’s icy surface and its subsurface ocean.
“Previous observations from the Hubble Space Telescope show evidence of oceanic salt in the Tara region,” Trumbo continued. “Now we see that there are also high concentrations of carbon dioxide there. We think that means the carbon probably originally came from an internal ocean.”
Finding carbon dioxide on Europa will be a bit bittersweet news for Villanueva and his team, as they also used JWST to look for plumes of material shooting off the surface of Jupiter’s moon that the powerful space telescope had failed to detect. The plumes had previously been detected in 2013, 2016, and 2017, and the fact that JWST couldn’t confirm their existence doesn’t mean they aren’t around Europa.
“There’s always the possibility that these jets are variable and only visible at certain times,” said Heidi Hammel, a JWST interdisciplinary scientist at the Association of Universities for Research in Astronomy. “What we can say with 100 percent certainty is that we didn’t detect jets on Europa when we did these observations with JWST.”
Still, the carbon dioxide observations on Europa are a testament to the power and usefulness of the James Webb Space Telescope.
“These observations took only a few minutes of observatory time,” added Hammel, who leads the JWST’s solar system assurance program for the first cycle. “Even in this short period of time, we were able to do some truly massive science. This work gives us a first hint of all the amazing solar system science we will be able to do with JWST.”
These results also have important implications for other future missions. In October 2024, NASA will launch the Europa Clipper spacecraft, which will travel to Jupiter’s moon system to conduct a detailed study of Europa and determine whether its subsurface oceans could support life.
The results obtained by these two teams at JWST could also help to study Jupiter and its moons as part of the European Space Agency’s (ESA) Jupiter Icy Moons Explorer (JUICE) mission. JUICE was launched in April 2023 on a 7.5-year journey to Europa and Jupiter’s large moons, Callisto and Ganymede, which are also covered in vast oceans, as well as to make important observations of Jupiter itself.
“This is an excellent first result of what JWST will bring to the study of Jupiter’s moons,” said study co-author and ESA research scientist Guillaume Cruz-Mermy. “I look forward to learning more about their surface properties from these and future observations.”
A long-standing mystery about the presence of hydrogen peroxide (H2O2) on Jupiter’s icy ocean moon Europa may be close to being solved. A new study was published in the Planetary Science Journal on July 21, 2025.
Hydrogen peroxide is formed as a byproduct when energetic particles split water molecules, resulting in the recombination of OH radicals, highly reactive molecules with unpaired electrons.
Hydrogen peroxide (H₂O₂) was first detected on Europa by the Galileo Near-Infrared Mapping Spectrometer, a scientific instrument aboard NASA’s Galileo Jupiter orbiter. It was designed to study the composition and surface features of the gas giant’s moons and atmosphere using infrared light. NASA’s James Webb Space Telescope (JWST) later found elevated levels of hydrogen peroxide in unexpected areas of the Jupiter moon.
Laboratory studies predicted that higher concentrations of hydrogen peroxide would be found in Europa’s colder polar regions, but JWST observations showed otherwise, finding higher levels in the moon’s warmer equatorial regions. These areas, known as “chaos zones,” are marked by chunks of surface ice that appear to have shifted, drifted, and refrozen.
“The distribution of hydrogen peroxide in Europa does not follow the temperature dependence predicted for pure water ice,” the researchers wrote in their paper. Laboratory studies consistently show that colder ice contains more H₂O₂, while warmer ice contains less.
In a new study, scientists report that they have noticed elevated levels of carbon dioxide (CO2) in the chaos zones, along with elevated levels of H2O2. This is likely due to CO2 leaking from Europa’s subsurface ocean through cracks in the ice, the researchers say.
This visualization of Europa shows the temperature field obtained by modeling the ocean dynamics of Jupiter’s icy moon, with hot plumes (red) rising from the seafloor and cold fluid (blue) sinking from the ice-ocean boundary. More heat enters the ice shell near the equator, consistent with the distribution of chaotic landscapes on Europa. C. M. Soderlund/NASA/JPL/University of Arizona
So the team wondered whether the presence of CO2 might alter the chemical composition of the ice.
“Could the presence of CO2 enhance peroxide formation in Europa’s chaotic regions, indicating a surface composition more favorable for the formation of this radiolytic oxidizer?” they write in their paper. “This hypothesis is supported by preliminary experiments with irradiated H2O-CO2 mixtures, which show increased H2O2 production compared to pure water ice.”
To find a definitive answer, they “simulated the conditions on Europa’s surface inside a vacuum chamber by putting water ice mixed with CO2,” said Bereket Mamo, a graduate student at the University of Texas at San Antonio and a contractor at the Southwest Research Institute. “We then blasted this ice mixture with energetic electrons to see how the peroxide production changed.”
The experiment confirmed the team’s suspicions: Even small amounts of CO2 in water ice can significantly increase hydrogen peroxide production at temperatures similar to those on Europa’s surface, helping to explain JWST’s unexpected observations.
This is because the CO2 molecules act as “molecular scavengers,” capturing any stray electrons that are created when the ice is hit by radiation. By capturing these electrons, the CO2 helps protect the hydrogen peroxide from being destroyed by further impacts or reactions.
“The production of oxidizers like hydrogen peroxide on the surface of Europa is important from an astrobiological perspective,” said study co-author Richard Cartwright of the Johns Hopkins University Applied Physics Laboratory. “In fact, an entire NASA mission, the Europa Clipper, is heading to the Jupiter system right now to study this icy moon and help us understand whether Europa is habitable.”
“Our experiments provide clues to better understanding JWST Europa’s observations and serve as a prelude to upcoming close-up studies with Europa Clipper and the European Space Agency’s JUICE spacecraft,” Cartwright added.
The James Webb Space Telescope has found that there is ‘chaos’ beneath the ice of Jupiter’s moon Europa. New observations from NASA’s James Webb Space Telescope (JWST) paint a new picture of Jupiter’s moon Europa and reveal the hidden chemistry of the icy moon’s interior.
For decades, scientists have imagined Europa’s frozen surface as a motionless, silent shell. But new observations show that it is in fact a dynamic world, far from frozen in time.
“We think the surface is quite porous and warm enough in some areas that ice can quickly recrystallize,” said Richard Cartwright, a spectroscopist at the Johns Hopkins University Applied Physics Laboratory and lead author of the new study.
Perhaps even more exciting is what this surface activity tells us about Europa’s subsurface ocean. The presence of geological activity and the constant exchange of materials between the subsurface and the surface make “chaotic landscapes” – heavily disturbed areas where chunks of ice appear to have broken off, drifted, and refroze – particularly valuable as potential windows into Europa’s interior.
The study focused on two regions in Europa’s southern hemisphere: the Tara and Powys regions. The Tara region in particular stands out as one of the most interesting regions on the moon. Observations from the JWST telescope have found crystalline ice both on the surface and in deeper layers, challenging previous ideas about the distribution of ice on Europa.
NASA’s Jupiter-observing mission Juno has captured the closest image yet of the gas giant Europa’s mysterious ice-covered moon. NASA/JPL-Caltech/SwRI
By measuring the spectral properties of these “chaotic” regions using remote sensing data, scientists can gain valuable insights into Europa’s chemical composition, as well as its potential habitability, they explained in a paper published May 28, 2025, in The Planetary Science Journal.
“Our data strongly suggests that the phenomenon we observe has an internal origin, possibly from a subsurface ocean located nearly 20 miles (30 kilometers) beneath Europa’s thick icy shell,” said Ujjwal Raut, a program director at Southwest Research Institute and a co-author of the study.
Rout and his team conducted laboratory experiments to study how water freezes on Europa, whose surface is constantly bombarded by charged particles from space. Unlike on Earth, where ice naturally forms a hexagonal crystalline structure, the intense radiation on Europa breaks down the structure of the ice, turning it into what’s called amorphous ice — a disordered, non-crystalline form.
The experiments were instrumental in showing how the ice changes over time. By studying how the ice changes from one state to another, scientists can learn more about the dynamics of the moon’s surface. Combined with the new JWST data, these results add to a growing body of evidence that Europa harbors a vast, hidden liquid ocean beneath its icy shell.
“In this same region […] we see a lot of other unusual things, including strong evidence for sodium chloride, similar to table salt, likely from its internal ocean,” Cartwright said. “We also see some of the strongest evidence for CO₂ and hydrogen peroxide on Europa. The chemistry here is really weird and fascinating.”
Simulated view from the surface of Europa, one of Jupiter’s four Galilean moons. NASA
These regions, marked by fractured surface features, may indicate geological activity pushing material out from beneath Europa’s ice shell.
JWST’s NIRSpec instrument is particularly well suited to studying Europa’s surface because it can detect key chemical signatures across a wide range of infrared wavelengths. These include features associated with crystalline water ice and a special form of carbon dioxide called ¹³CO₂, which are important for understanding the moon’s geological and chemical processes.
NIRSpec can measure all of these properties simultaneously, as well as create detailed maps of the distribution of these materials across Europa’s surface. Its high sensitivity and ability to collect both spectral and spatial data make it an ideal tool for studying what lies beneath Europa’s icy crust.
The team found higher levels of carbon dioxide in these areas than in neighbouring areas, leading them to conclude that it likely originated underground rather than from external sources such as meteorites, which would have resulted in a more even distribution.
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What’s more, the carbon dioxide is unstable in Europa’s intense radiation environment, suggesting that these deposits were formed relatively recently and are linked to ongoing geological processes. “There’s growing evidence for a liquid ocean beneath Europa’s ice shell, which makes this study even more exciting as we continue to learn more,” Routt said.
Another intriguing discovery was the presence of carbon-13, an isotope of carbon. “Where does this 13CO2 come from? It’s hard to explain, but every road leads to an internal source, which is consistent with other hypotheses about the origin of the 12CO2 found in the Tara region,” Cartwright said.
The study comes as NASA’s Europa Clipper mission is en route to Jupiter’s moon, with arrival expected in April 2030. The spacecraft will make dozens of flybys, each bringing it closer to Europa’s surface to gather vital data about the ocean hidden beneath the moon’s icy crust.
Regions of “chaos” on Jupiter’s moon Europa may hold clues to the possible existence of life in the ocean beneath the moon’s icy crust.
Another take on an old theory lends more weight to the idea that Europa’s subsurface ocean could be rich in oxygen, which fell out of the Jupiter moon’s icy shell as it formed its rugged surface. What’s more, oxygen levels in Europa’s subsurface oceans could be as high as those on Earth, bolstering arguments that the icy moon could be habitable, according to a new study. The study was published online February 10, 2022, in the Astrophysical Journal Letters.
“This provides a solution to one of the most persistent problems associated with the habitability of Europa’s subsurface ocean,” said lead researcher Mark Hesse, a professor in the Department of Geological Sciences at the University of Texas at Austin.
We already know there is oxygen on Europa’s surface, so the new study focuses on how much oxygen is in the ocean hidden beneath the moon’s 15-kilometer (10-mile) thick icy crust. The icy crust is made up of hydrogen and oxygen. Radiation from nearby Jupiter reacts with the ice to form free oxygen and other compounds with oxidizing agents (such as hydrogen peroxide).
An artist’s illustration showing how liquid water may accumulate beneath the surface of the “chaos terran” on Jupiter’s moon Europa. NASA/JPL-Caltech
A new study involving physics-based computer modeling of Europa’s surface has found that partial melting of the moon’s ice sheet produces a slushy substance known as brine. The force of this slush seeping through the ice creates a “porosity wave” in the ice, causing the pores to temporarily expand. This expansion creates a path for oxygen-rich brine to flow from the surface into the ocean.
The University of Texas said in a statement that saltwater transport “appears to be an efficient way to deliver oxygen through the ice, with 86% of the oxygen absorbed at the surface being carried by the wave all the way to the ocean.”
The speed of delivery appears to correlate with brief moments in Europa’s geological history when so-called chaos regions form. There are five known “chaos” regions on the icy moon, and scientists believe they formed during warmer periods when chunks of melting ice moved across the surface and then became trapped again as fresh ice froze around them.
However, it is not yet clear how much oxygen is entering the ocean. The model suggests a “wide range of oxygen levels” entering Europa’s ocean over time, with a spread of 10,000 times.
The chaotic terrain of Europa as photographed by the Galileo orbiter. NASA/JPL-Caltech/SETI Institute
However, only the highest estimates show that oxygen levels in Europa’s ocean are similar to those on Earth, co-author and researcher Stephen Vance of NASA’s Jet Propulsion Laboratory added in a statement.
But if the highest oxygen levels are indeed observed, Vance said, “it’s tempting to imagine some kind of aerobic organism living just under the ice,” he said. (“Aerobic” is organisms that thrive in oxygen-rich conditions.)
Unrelated studies using the Hubble Space Telescope have shown water vapor rising from the plumes, adding to concerns about the planet’s habitability prospects as new missions such as NASA’s Europa Clipper are expected to visit in the 2030s.
Europa Clipper’s instruments include a radar probe provided by the University of Texas at Austin to search for components that could be critical to life on Europa. The research includes sounding the ocean, measuring the thickness of the ice, and assessing its structure and surface properties, according to NASA’s website.
Vance noted that while Clipper is an orbital mission, the spacecraft may be able to refine estimates of the moon’s oxygen content. However, a landing may be needed to more accurately assess the viability of salt transport.
A 2021 image from NASA’s Juno spacecraft orbiting Jupiter shows a previously unseen region of the icy moon that appears to be producing water vapor from plumes and may have habitable ocean conditions.
The image was taken from a distance of nearly 80,000 kilometers (50,000 miles) while Juno was on its primary mission of studying Jupiter’s atmosphere. The resolution is, of course, quite coarse, as individual pixels are each about 50 to 60 kilometers (31 to 37 miles) away. However, it is possible to see variations in the albedo, or reflectivity of light, on this otherwise very bright moon.
Europa is a popular location, having been photographed many times by spacecraft. The first close-up images were taken in the 1970s by NASA’s Pioneer and Voyager spacecraft, which showed an icy surface riddled with cracks. Even more detailed images were obtained during the Galileo mission, which orbited Jupiter and its moons from 1995 to 2003.
The Juno spacecraft has photographed Europe’s north pole from afar for the first time. NASA officials said it was the first time they had seen the region, and future flybys will provide sharper images. NASA/SwRI/MSSS/Andrea Luck
Many spacecraft have flown past Europa on their way to other destinations, and the Hubble Space Telescope and other telescopes near or on Earth occasionally glance at the Moon. But the limitation of these various views is that they have all been on or near the ecliptic, the plane in which the Sun, the planets of the solar system, and many of its moons orbit.
Juno, on the other hand, has a more polar orbit, which has already produced unique images of Jupiter, such as the scale and stability of its polar cyclones. The Europa image was created by amateur scientist Andrea Luck using data from the JunoCam.
The press conference did not discuss possible scientific research at the poles of Europe, but previous peer-reviewed studies have discussed transient water vapor at the south pole or attempts at geological mapping as close to the poles as possible.
NASA’s Hubble Space Telescope also detected water vapor on Jupiter’s oceanic moon Europa in 2021, which could provide new clues about icy moons in our solar system and beyond.
Hubble has previously detected water vapor on Europa — visible plumes that appear sporadically and temporarily extend perhaps 200 kilometers into space from the moon’s icy shell, which covers a vast, buried ocean of liquid water. But this new discovery is something entirely different.
Lorenz Roth, a researcher at KTH Royal Institute of Technology in Stockholm, Sweden, analyzed archival ultraviolet observations of Europa taken by the Hubble Space Telescope with its Space Telescope Imaging Spectrograph instrument in 1999, 2012, 2014 and 2015.
The analysis revealed the presence of significant amounts of water vapor in Europa’s trailing hemisphere — the one facing away from the moon’s orbital path around Jupiter. This water vapor persisted for long periods of time, unlike short-lived jets, Roth reported in a study published in September 2021 in the journal Geophysical Research Letters.
Recently, Roth and his colleagues used similar technology to detect water vapor on Ganymede, a moon of Jupiter, the largest moon in the solar system.
“Observing water vapor on Ganymede and the far side of Europa expands our understanding of the atmospheres of icy moons,” Roth said. “However, finding stable water content on Europa is somewhat more surprising than on Ganymede, because Europa’s surface temperature is cooler than Ganymede’s.”
Europa reflects sunlight more efficiently than Ganymede, making it about 33 degrees Celsius cooler than the larger moon, NASA officials said. Europa’s maximum temperature is about minus 160 degrees Celsius, but it appears to be sublimating significant amounts of ice, which turns to vapor and escapes into space.
Adding to the intrigue is the fact that this water vapor is concentrated in Europa’s trailing hemisphere. NASA officials say the reason for this is still unclear.
Turbulent, swirling currents in Europa’s underground sea may be affecting the rotation and geology of the moon’s icy crust. Scientists say a huge, churning ocean inside Jupiter’s moon Europa may be affecting the rotation of its icy crust.
New supercomputer simulations show that the waters of the world’s internal ocean may be exerting pressure on Europa’s crust – perhaps strongly enough to affect the speed at which the moon’s icy shell spins over time.
It is already known that Europa’s icy outer crust likely floats freely and rotates at a different rate than the moon’s ocean and rocky core beneath it. But the new model is the first to suggest that Europa’s ocean currents play a role in the rotation rate of the moon’s frozen outer layer.
“It was previously known, through laboratory experiments and modeling, that the heating and cooling of Europa’s ocean could drive currents. Now our results reveal a link between the ocean and the rotation of the ice shell that has never been considered before,” said Hamish Hay, a researcher at the University of Oxford in England and lead author of the new study, published in the journal JGR: Planets in 2023.
Much of the research and discussion about the effects on Europa’s crust has focused on the enormous outward force of Jupiter’s gravitational field. The new study looks at how radioactive decay and tidal heating in Europa’s interior, as well as its overall rotation, could drive currents and create turbulent drag within the icy shell.
“It was a complete surprise to me that what was happening in the ocean circulation could affect the ice sheet so much. It was a huge surprise,” said study co-author Robert Pappalardo of NASA’s Jet Propulsion Laboratory in Southern California.
The model also suggests that Europa’s ocean currents may be responsible for some of the geology seen on the moon’s frozen surface, which is riddled with lines and cracks.
Stunning portraits of Jupiter’s mysterious icy moon Europa taken by NASA’s Juno mission during its close flyby in October 2022 show the moon, which may harbor alien life, in unexpected colors.
The new images were taken by Juno’s JunoCam camera as the probe flew past Europa on September 29, and then sent to enthusiastic image processors, who have given them some almost artistic treatment.
Newly released images reveal previously unexplored surface features that could shed light on what’s happening in the potentially habitable ocean beneath Europa’s thick icy crust. The images, collected over just a few minutes, include a satellite image taken by JunoCam from 1,500 kilometers above Europa’s surface. The image shows a region called Annwn Regio, known for what scientists call chaotic terrain — a maze of ridges, grooves, and cracks that crisscross the icy surface.
A view of Jupiter’s moon Europa taken by NASA’s Juno mission during its close flyby on September 29. The spacecraft was 1,500 kilometers (945 miles) above the moon’s surface when the image was taken. NASA/JPL-Caltech/SwRI/MSSS. Image processing by Björn Jönsson. CC BY-NC-SA 2.0
The image, processed by Björn Jónsson, maps the surface at a resolution of about 1 kilometer per pixel, revealing numerous bright and dark depressions, as well as previously unknown indentations. The Callanish crater, which NASA’s Galileo probe studied in the late 1990s and early 2000s, is visible in the lower right as a circular dark spot.
Two images show the same area of Europa’s surface, comparing different processing approaches: one with minimal processing, and one with enhanced color contrast that highlights surface features. The more processed image shows the shadows cast by the many scars.
Finally, Fernando Garcia Navarro’s highly stylized image gives the rather simple white and brownish moon an extravagant, psychedelic look.
Comparison of minimally processed and heavily processed images of the same area of Europa’s surface. NASA/JPL-Caltech/SwRI/MSSS. Image processing: Navaneet Krishnan S.
“Citizen scientists working with Juno are part of a global collaborative effort that is opening up new perspectives and discovering new ideas,” said Candy Hansen, JunoCam co-principal investigator at the Planetary Science Institute in Arizona. “Often, citizen scientists completely ignore the potential scientific applications of an image, focusing on how Juno inspires their imagination or artistic taste, and we applaud their creativity.”
In October 2022, Juno flew 250 miles (412 kilometers) above Europa’s frozen surface, making its closest approach to the moon and getting closer than any spacecraft has been since Galileo flew by in 2000. Speeding through space at 15 miles (24 kilometers) per second (15 miles) per second (15 miles per second), Juno captured the most detailed image of Europa to date. The maneuver wasn’t just for sightseeing; it also adjusted the probe’s trajectory around Jupiter, cutting the time it takes to orbit the gas giant from 43 days to 38 days, NASA said in a statement.
The image, which covers an area 93 miles (150 kilometers) long and 125 miles (200 kilometers) wide, also shows a strange, quarter-note-shaped depression running 42 miles (67 kilometers) north to south and 23 miles (37 kilometers) east to west in the lower half of the image. Tiny white dots scattered throughout the image are “high-energy particle penetrations from intense radiation around the moon,” the scientists said.
Europe. NASA
Juno took the image using its Stellar Reference Unit (SRU) camera, which normally helps Juno maintain its orientation by determining the spacecraft’s position relative to the stars in the surrounding space, but during the flyby, the SRU also served as a science instrument, capturing the stunning black-and-white image.
The image shows the surface of Europa with a resolution of 256 to 340 meters per pixel. Remarkably, SRU took the image at night, when the only light illuminating the moon was light reflecting off Jupiter’s cloud tops.
SRU previously proved its value in low-light imaging when it captured images of Jupiter’s faint rings and discovered surface lightning in Jupiter’s atmosphere.
Surface of Europa. NASA
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