Artist's concept of a Europa Clipper mission. Credit: NASA/JPL
Since 1979, when the Voyager probes flew past Jupiter and its system of moons, scientists have speculated about the possibility of life within Europa. Based on planetary modeling, Europa is believed to be differentiated between a rocky and metallic core, an icy crust and mantle, and a liquid-water ocean that could be 100 to 200 km (62 to 124 mi) deep. Scientists theorize that this ocean is maintained by tidal flexing, where interaction with Jupiter’s powerful gravitational field leads to geological activity in Europa’s core and hydrothermal vents at the core-mantle boundary.
Investigating the potential habitability of Europa is the main purpose of NASA’s Europa Clipper mission, which will launch on October 10th, 2024, and arrive around Jupiter in April 2030. However, this presents a challenge for astrobiologists since the habitability of Europa is dependent on many interrelated parameters that require collaborative investigation. In a recent paper, a team of NASA-led researchers reviewed the objectives of the Europa Clipper mission and anticipated what it could reveal regarding the moon’s interior, composition, and geology.
NASA’s Europa Clipper is one of the most anticipated missions of the coming decade, in large part because its target, the large Jovian moon Europa, is considered one of the most likely places in our solar system that extraterrestrial life might exist. If Europa is harboring alien microbes, however, they’re likely to be buried deep beneath the moon’s thick icy crust in a vast subsurface ocean. Unlocking the secrets of this water world isn’t going to be easy, but the Clipper team has a plan to make the most of the opportunity they have: If you can’t get to the ocean, let the ocean come to you.
Observations by the NASA/ESA Hubble Space Telescope recently revealed water vapour in the atmosphere of Ganymede, one of Jupiter’s moons. A new analysis of archival images and spectra has now revealed that water vapour is also present in the atmosphere of Jupter’s icy moon Europa. The analysis found that a water vapour atmosphere is present only on one hemisphere of the moon. This result advances our understanding of the atmospheric structure of icy moons, and helps lay the groundwork for upcoming science missions which will explore Jupiter’s icy moons.
Since the Voyager probes passed through the Jupiter system in 1979, scientists have been intrigued and mystified by its moon Europa. Once the images these probes acquired of the moon’s icy surface returned to Earth, scientists began to speculate about the possibility of a subsurface ocean. Since then, the detection of plume activity and other lines of evidence have bolstered this theory and fed speculation that there could be life beneath Europa’s icy surface.
According to new research, another critical piece of evidence of Europa’s watery nature has at least been confirmed. Using a similar technique that confirmed the presence of atmospheric water vapor in Jupiter’s moon Ganymede, Lorenz Roth of the KTH Royal Institute of Technology confirmed that Europa has water vapor in its atmosphere. This discovery could lead to a greater understanding of Europa’s atmosphere and surface environment, informing missions headed there in the near future.
An artist's rendering of Europa and Jupiter based on images sent by visiting spacecraft. Credit: NASA/JPL-Caltech
In the coming decade, NASA and the ESA will be sending two dedicated missions that will explore Jupiter’s moon Europa. These missions are known as the Europa Clipper and the JUpiter ICy moons Explorer (JUICE) missions, which will fulfill a dream that has been decades in the making – searching for possible evidence of life inside Europa. Since the 1970s, astronomers have theorized that this satellite contains a warm-water ocean that could support life.
The case for life in Europa has only been bolstered thanks to multiple flybys and observation campaigns that have been mounted since. According to new research led by the University of Hawaii at Manoa, the best way to look for potential signs of life (aka. biosignatures) would be to analyze small impact craters on Europa’s surface. These patches of exposed subsurface ice could point the way towards life that might exist deeper in the moon’s interior.
Artist's conception of a cryovolcanic eruption on Europa.
Credit: Justice Blaine Wainwright
Observations have already confirmed the existence of a sub-surface ocean on Europa, and there has been rampant speculation about whether they could contain life. While there have been tentative plans to send a submersible spacecraft to this ocean, we are still a long way from uncovering what lies in those depths.
Which is one big reason why the geysers that occasionally shoot out of Europa’s ice sheet have garnered such interest. Scientists hoped that some of the ejected water could come from that ocean. It could then be sampled with a simple fly-by mission, such as Europa Clipper, rather than a submersible craft. However, a new paper published in Geophysical Research Letters suggests a much more mundane source of the geysers – local liquid water buried in the moon’s thick ice shelf.
The fascinating surface of Jupiter’s icy moon Europa looms large in this newly-reprocessed color view, made from images taken by NASA's Galileo spacecraft in the late 1990s. This is the color view of Europa from Galileo that shows the largest portion of the moon's surface at the highest resolution. Credits: NASA/JPL-Caltech/SETI Institute
What’s been long-suspected has now been confirmed: Jupiter’s moon Europa has water. As we’ve learned more about the outer Solar System in recent years, Europa has become a high-priority target in the search for life. With this discovery, NASA has just painted a big red bulls-eye on Jupiter’s smallest Galilean moon.
Radiation from Jupiter can destroy molecules on Europa's surface. Material from Europa's ocean that ends up on the surface will be bombarded by radiation, possibly destroying any biosignatures, or chemical signs that could imply the presence of life. Credit: NASA/JPL-Caltech
Ever since the Galileo probe provided compelling evidence for the existence of a global ocean beneath the surface of Europa in the 1990s, scientists have wondered when we might be able to send another mission to this icy moon and search for possible signs of life. Most of these mission concepts call for an orbiter or lander than will study Europa’s surface, searching the icy sheet for signs of biosignatures turned up from the interior.
Unfortunately, Europa’s surface is constantly bombarded by radiation, which could alter or destroy material transported to the surface. Using data from the Galileo and Voyager 1 spacecraft, a team of scientists recently produced a map that shows how radiation varies across Europa’s surface. By following this map, future missions like NASA’s Europa Clipper will be able to find the spots where biosignatures are most likely to still exist.
As many missions have revealed by studying Europa’s surface, the moon experiences periodic exchanges between the interior and the surface. If there is life in its interior ocean, then biological material could theoretically be brought to the surface where it could be studied. Since radiation from Jupiter’s magnetic field would destroy this material, knowing where it is most intense, how deep it goes, and how it could affect the interior are all important questions.
Artist’s impression of water bubbling up from Europa’s interior ocean and breaching the surface ice. Credit: NASA/JPL-Caltech
As Tom Nordheim, a research scientist at NASA’s Jet Propulsion Laboratory, explained in a recent NASA press release:
“If we want to understand what’s going on at the surface of Europa and how that links to the ocean underneath, we need to understand the radiation. When we examine materials that have come up from the subsurface, what are we looking at? Does this tell us what is in the ocean, or is this what happened to the materials after they have been radiated?”
To address these question, Nordheim and his colleagues examined data from Galileo‘s flybys of Europa and electron measurements from NASA’s Voyager 1 spacecraft. After looking closely at the electrons blasting the moon’s surface, Nordheim and his team found that the radiation doses vary by location. The harshest radiation is concentrated in zones around the equator, and the radiation lessens closer to the poles.
Artist’s concept of a Europa Clipper mission. Credit: NASA/JPL
“This is the first prediction of radiation levels at each point on Europa’s surface and is important information for future Europa missions,” said Paranicas. Now that scientists know where to find regions least altered by radiation, they will be able to designate areas of study for the Europa Clipper, a JPL-led mission that is expected to launch as early as 2022.
For the sake of their study, Nordheim and his team went beyond a conventional two-dimensional map to build 3D models that examined how far below the surface the radiation penetrates. To test how deep organic material would have to be buried in order to survive, Nordheim and his team tested the effect of radiation on amino acids (the basic building blocks for proteins) to figure out how Europa’s exposure to radiation would affect potential biosignatures.
The results indicate how deep scientists will need to dig or drill during a potential future Europa lander mission in order to find any biosignatures that might be preserved. In the highest-radiation zones around the equator, the depth at which biosignatures could be found ranged from 10 to 20 cm (4 to 8 inches). At the middle- and high-latitudes, closer to the poles, the depths decrease to about 1 cm (0.4 inches). As Hand indicated:
“The radiation that bombards Europa’s surface leaves a fingerprint. If we know what that fingerprint looks like, we can better understand the nature of any organics and possible biosignatures that might be detected with future missions, be they spacecraft that fly by or land on Europa.”
Artist’s impression of a water vapor plume on Europa. Credit: NASA/ESA/K. Retherford/SwRI
When the Europa Clipper mission reaches the Jovian system, the spacecraft will orbit Jupiter and conducting about 45 close flybys of Europa. It’s advanced suite of scientific instruments will include cameras, spectrometers, plasma and radar instruments which will investigate the composition of the moon’s surface, its ocean, and material that has been ejected from the surface.
“Europa Clipper’s mission team is examining possible orbit paths, and proposed routes pass over many regions of Europa that experience lower levels of radiation,” Hand said. “That’s good news for looking at potentially fresh ocean material that has not been heavily modified by the fingerprint of radiation.”
With this new radiation map, the mission team will be able to narrow the range of possible research sites. This, in turn, will increase the likelihood that the orbiter mission will be able to settle the decades-old mystery of whether or not there is life in the Jovian system.
Based on new evidence from Jupiter's moon Europa, astronomers hypothesize that chloride salts bubble up from the icy moon's global liquid ocean and reach the frozen surface where they are bombarded with sulfur from volcanoes on Jupiter's innermost large moon Io. The new findings propose answers to questions that have been debated since the days of NASA's Voyager and Galileo missions. This illustration of Europa (foreground), Jupiter (right) and Io (middle) is an artist's concept. Credit: NASA/JPL-Caltech
In the 1970s, the Jupiter system was explored by a succession of robotic missions, beginning with the Pioneer 10 and 11 missions in 1972/73 and the Voyager 1 and 2 missions in 1979. In addition to other scientific objectives, these missions also captured images of Europa’s icy surface features, which gave rise to the theory that the moon had an interior ocean that could possibly harbor life.
Since then, astronomers have also found indications that there are regular exchanges between this interior ocean and the surface, which includes evidence of plume activity captured by the Hubble Space Telescope. And recently, a team of NASA scientists studied the strange features on Europa’s surface to create models that show how the interior ocean exchanges material with the surface over time.
The study, which recently appeared in the the Geophysical Research Letters under the title “Band Formation and Ocean-Surface Interaction on Europa and Ganymede“, was conducted by Samuel M. Howell and Robert T. Pappalardo – two researchers from the NASA Jet Propulsion Laboratory. For their study, the team examined both Ganymede and Europa to see what the moons surface features indicated about how they changed over time.
Images from NASA’s Galileo spacecraft show the intricate detail of Europa’s icy surface. Image: NASA/JPL-Caltech
Using the same two-dimensional numerical models that scientists have used to solve mysteries about motion in the Earth’s crust, the team focused on the linear features known as “bands” and “groove lanes” on Europa and Ganymede. The features have long been suspected to be tectonic in nature, where fresh deposits of ocean water have risen to the surface and become frozen over previously-deposited layers.
However, the connection between this band-forming processes and exchanges between the ocean and the surface has remained elusive until now. To address this, the team used their 2-D numerical models to simulate ice shell faulting and convection.Their simulations also produced a beautiful animation that tracked the movement of “fossil” ocean material, which rises from the depths, freezes into the base of the icy surface, and deforms it over time.
Whereas the white layer at the top is the surface crust of Europa, the colored band in the middle (orange and yellow) represents the stronger sections of the ice sheet. Over time, gravitational interactions with Jupiter cause the ice shell to deform, pulling the top layer of ice apart and creating faults in the upper ice. At the bottom is the softer ice (teal and blue), which begins to churn as the upper layers pull apart.
This causes water from Europa’s interior ocean, which is in contact with the softer lower layers of the icy shell (represented by white dots), to mix with the ice and slowly be transported to the surface. As they explain in their paper, the process where this “fossil” ocean material becomes trapped in Europa’s ice shell and slowly rises to the surface can take hundreds of thousands of years or more.
Artist’s concept of a Europa Clipper mission. Credit: NASA/JPL
As they state in their study:
“We find that distinct band types form within a spectrum of extensional terrains correlated to lithosphere strength, governed by lithosphere thickness and cohesion. Furthermore, we find that smooth bands formed in weak lithosphere promote exposure of fossil ocean material at the surface.”
In this respect, once this fossil material reaches the surface, it acts as a sort of geological record, showing how the ocean was millions of years ago and not as it is today. This is certainly significant when it comes to future missions to Europa, such as NASA’s Europa Clipper mission. This spacecraft, which is expected to launch sometime in the 2020s, will be the first to study Europa exclusively.
In addition to studying the composition of Europa’s surface (which will tell us more about the composition of the ocean), the spacecraft will be studying surface features for signs of current geological activity. On top of that, the mission intends to look for key compounds in the surface ice that would indicate the possible presence of life in the interior (i.e. biosignatures).
Artist’s impression of a hypothetical ocean cryobot (a robot capable of penetrating water ice) in Europa. Credit: NASA
If what this latest study indicates is true, then the ice and compounds the Europa Clipper will be examining will essentially be “fossils” from hundreds of thousands or even millions of years ago. In short, any biomarkers the spacecraft detects – i.e. signs of potential life – will essentially be dated. However, this need not deter us from sending missions to Europa, for even evidence of past life would be groundbreaking, and a good indication that life still exists there today.
If anything, it makes the case for a lander that can explore Europa’s plumes, or perhaps even a Europa submarine (cryobot), all the more necessary! If there is life beneath Europa’s icy surface, we are determined to find it – provided we don’t contaminate it in the process!
Artist's impression of a water vapor plume on Europa. Credit: NASA/ESA/K. Retherford/SWRI
Since the 1970s, when the Voyager probes captured images of Europa’s icy surface, scientists have suspected that life could exist in interior oceans of moons in the outer Solar System. Since then, other evidence has emerged that has bolstered this theory, ranging from icy plumes on Europa and Enceladus, interior models of hydrothermal activity, and even the groundbreaking discovery of complex organic molecules in Enceladus’ plumes.
However, in some locations in the outer Solar System, conditions are very cold and water is only able to exist in liquid form because of the presence of toxic antifreeze chemicals. However, according to a new study by an international team of researchers, it is possible that bacteria could survive in these briny environments. This is good news for those hoping to find evidence of life in extreme environments of the Solar System.
The study which details their findings, titled “Enhanced Microbial Survivability in Subzero Brines“, recently appeared in the scientific journal Astrobiology. The study was conducted by Jacob Heinz from the Center of Astronomy and Astrophysics at the Technical University of Berlin (TUB), and included members from Tufts University, Imperial College London, and Washington State University.
Based on new evidence from Jupiter’s moon Europa, astronomers hypothesize that chloride salts bubble up from the icy moon’s global liquid ocean and reach the frozen surface. Credit: NASA/JPL-Caltech
Basically, on bodies like Ceres, Callisto, Triton, and Pluto – which are either far from the Sun or do not have interior heating mechanisms – interior oceans are believed to exist because of the presence of certain chemicals and salts (such as ammonia). These “antifreeze” compounds ensure that their oceans have lower freezing points, but create an environment that would be too cold and toxic to life as we know it.
For the sake of their study, the team sought to determine if microbes could indeed survive in these environments by conducting tests with Planococcus halocryophilus, a bacteria found in the Arctic permafrost. They then subjected this bacteria to solutions of sodium, magnesium and calcium chloride as well as perchlorate, a chemical compound that was found by the Phoenix lander on Mars.
They then subjected the solutions to temperatures ranging from +25°C to -30°C through multiple freeze and thaw cycles. What they found was that the bacteria’s survival rates depended on the solution and temperatures involved. For instance, bacteria suspended in chloride-containing (saline) samples had better chances of survival compared to those in perchlorate-containing samples – though survival rates increased the more the temperatures were lowered.
For instance, the team found that bacteria in a sodium chloride (NaCl) solution died within two weeks at room temperature. But when temperatures were lowered to 4 °C (39 °F), survivability began to increase and almost all the bacteria survived by the time temperatures reached -15 °C (5 °F). Meanwhile, bacteria in the magnesium and calcium-chloride solutions had high survival rates at –30 °C (-22 °F).
Artist rendering showing an interior cross-section of the crust of Enceladus, which shows how hydrothermal activity may be causing the plumes of water at the moon’s surface. Credits: NASA-GSFC/SVS, NASA/JPL-Caltech/Southwest Research Institute
The results also varied for the three saline solvents depending on the temperature. Bacteria in calcium chloride (CaCl2) had significantly lower survival rates than those in sodium chloride (NaCl) and magnesium chloride (MgCl2)between 4 and 25 °C (39 and 77 °F), but lower temperatures boosted survival in all three. The survival rates in perchlorate solution were far lower than in other solutions.
However, this was generally in solutions where perchlorate constituted 50% of the mass of the total solution (which was necessary for the water to remain liquid at lower temperatures), which would be significantly toxic. At concentrations of 10%, bacteria was still able to grow. This is semi-good news for Mars, where the soil contains less than one weight percent of perchlorate.
However, Heinz also pointed out that salt concentrations in soil are different than those in a solution. Still, this could be still be good news where Mars is concerned, since temperatures and precipitation levels there are very similar to parts of Earth – the Atacama Desert and parts of Antarctica. The fact that bacteria have can survive such environments on Earth indicates they could survive on Mars too.
In general, the research indicated that colder temperatures boost microbial survivability, but this depends on the type of microbe and the composition of the chemical solution. As Heinz told Astrobiology Magazine:
“[A]ll reactions, including those that kill cells, are slower at lower temperatures, but bacterial survivability didn’t increase much at lower temperatures in the perchlorate solution, whereas lower temperatures in calcium chloride solutions yielded a marked increase in survivability.”
This full-circle view from the panoramic camera (Pancam) on NASA’s Mars Exploration Rover Spirit shows the terrain surrounding the location called “Troy,” where Spirit became embedded in soft soil during the spring of 2009. Credit: NASA/JPL
The team also found that bacteria did better in saltier solutions when it came to freezing and thawing cycles. In the end, the results indicate that survivability all comes down to a careful balance. Whereas lower concentrations of chemical salts meant that bacteria could survive and even grow, the temperatures at which water would remain in a liquid state would be reduced. It also indicated that salty solutions improve bacteria survival rates when it comes to freezing and thawing cycles.
Of course, the team emphasized that just because bacteria can subsist in certain conditions doesn’t mean they will thrive there. AsTheresa Fisher, a PhD student at Arizona State University’s School of Earth and Space Exploration and a co-author on the study, explained:
“Survival versus growth is a really important distinction, but life still manages to surprise us. Some bacteria can not only survive in low temperatures, but require them to metabolize and thrive. We should try to be unbiased in assuming what’s necessary for an organism to thrive, not just survive.”
As such, Heinz and his colleagues are currently working on another study to determine how different concentrations of salts across different temperatures affect bacterial propagation. In the meantime, this study and other like it are able to provide some unique insight into the possibilities for extraterrestrial life by placing constraints on the kinds of conditions that they can survive and grow in.
These studies also allow help when it comes to the search for extraterrestrial life, since knowing where life can exist allows us to focus our search efforts. In the coming years, missions to Europa, Enceladus, Titan and other locations in the Solar System will be looking for biosignatures that indicate the presence of life on or within these bodies. Knowing that life can survive in cold, briny environments opens up additional possibilities.
Artist’s illustration of Jupiter and Europa (in the foreground) with the Galileo spacecraft after its pass through a plume erupting from Europa’s surface. Credits: NASA/JPL-Caltech/Univ. of Michigan
Jupiter’s moon Europa continues to fascinate and amaze! In 1979, the Voyager missions provided the first indications that an interior ocean might exist beneath it’s icy surface. Between 1995 and 2003, the Galileo spaceprobe provided the most detailed information to date on Jupiter’s moons to date. This information bolstered theories about how life could exist in a warm water ocean located at the core-mantle boundary.
Even though the Galileo mission ended when the probe crashed into Jupiter’s atmosphere, the spaceprobe is still providing vital information on Europa. After analyzing old data from the mission, NASA scientists have found independent evidence that Europa’s interior ocean is venting plumes of water vapor from its surface. This is good news for future mission to Europa, which will attempt to search these plumes for signs of life.
The study which describes their findings, titled “Evidence of a plume on Europa from Galileo magnetic and plasma wave signatures“, recently appeared in the journal Nature Astronomy. The study was led by Xianzhe Jia, a space physicist from the Department of Climate and Space Sciences and Engineering at the University of Michigan, and included members from UCLA and the University of Iowa.
Artist’s concept of the Galileo space probe passing through the Jupiter system. Credit: NASA
The data was collected in 1997 by Galileo during a flyby of Europa that brought it to within 200 km (124 mi) of the moon’s surface. At the time, its Magnetometer (MAG) sensor detected a brief, localized bend in Jupiter’s magnetic field, which remained unexplained until now. After running the data through new and advanced computer models, the team was able to create a simulation that showed that this was caused by interaction between the magnetic field and one of the Europa’s plumes.
This analysis confirmed ultraviolet observations made by NASA’s Hubble Space Telescope in 2012, which suggested the presence of water plumes on the moon’s surface. However, this new analysis used data collected much closer to the source, which indicated how Europa’s plumes interact with the ambient flow of plasma contained within Jupiter’s powerful magnetic field.
In addition to being the lead author on this study, Jia is also the co-investigator for two instruments that will travel aboard the Europa Clipper mission – which may launch as soon as 2022 to explore the moon’s potential habitability. Jia’s and his colleagues were inspired to reexamine data from the Galileo mission thanks to Melissa McGrath, a member of the SETI Institute and also a member of the Europa Clipper science team.
During a presentation to her fellow team scientists, McGrath highlighted other Hubble observations of Europa. As Jiang explained in a recent NASA press release:
“The data were there, but we needed sophisticated modeling to make sense of the observation. One of the locations she mentioned rang a bell. Galileo actually did a flyby of that location, and it was the closest one we ever had. We realized we had to go back. We needed to see whether there was anything in the data that could tell us whether or not there was a plume.”
Artist’s impression of a water vapor plume on Europa. Credit: NASA/ESA/K. Retherford/SWRI
When they first examined the information 21 years ago, the high-resolution data obtained by the MAG instrument showed something strange. But it was thanks to the lessons provided by the Cassini mission, which explored the plumes on Saturn’s moon Enceladus, that the team knew what to look for. This included material from the plumes which became ionized by the gas giant’s magnetosphere, leaving a characteristic blip in the magnetic field.
After reexamining the data, they found that the same characteristic bend (localized and brief) in the magnetic field was present around Europa. Jia’s team also consulted data from Galileo’sPlasma Wave Spectrometer (PWS) instrument to measure plasma waves caused by charged particles in gases around Europa’s atmosphere, which also appeared to back the theory of a plume.
This magnetometry data and plasma wave signatures were then layered into new 3D modeling developed by the team at the University of Michigan (which simulated the interactions of plasma with Solar system bodies). Last, they added the data obtained from Hubble in 2012 that suggested the dimensions of the potential plumes. The end result was a simulated plume that matched the magnetic field and plasma signatures they saw in the Galileo data.
As Robert Pappalardo, a Europa Clipper project scientist at NASA’s Jet Propulsion Laboratory (JPL), indicated:
“There now seem to be too many lines of evidence to dismiss plumes at Europa. This result makes the plumes seem to be much more real and, for me, is a tipping point. These are no longer uncertain blips on a faraway image.”
Artist’s concept of a Europa Clipper mission, which will study Europa in 2022-2025 to search for signs of life. Credit: NASA/JPL
The findings are certainly good news for the Europa Clipper mission, which is expected to make the journey to Jupiter between 2022 and 2025. When this probe arrives in the Jovian system, it will establish an orbit around Jupiter and conduct rapid, low-altitude flybys of Europa. Assuming that plume activity does take place on the surface of the moon, the Europa Clipper will sample the frozen liquid and dust particles for signs of life.
“If plumes exist, and we can directly sample what’s coming from the interior of Europa, then we can more easily get at whether Europa has the ingredients for life,” Pappalardo said. “That’s what the mission is after. That’s the big picture.”
At present, the mission team is busy looking at potential orbital paths for the Europa Clipper mission. With this new research in hand, the team will choose a path that will take the spaceprobe above the plume locations so that it is in an ideal position to search them for signs of life. If all goes as planned, the Europa Clipper could be the first of several probes that finally proves that there is life beyond Earth.
And be sure to check out this video of the Europa Clipper mission, courtesy of NASA:
