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Europe Has Big Plans for Saturn’s Moon Enceladus
Saturn’s moon, Enceladus, is a gleaming beacon that captivates our intellectual curiosity. Its clean, icy surface makes it one of the most reflective objects in the entire Solar System. But it’s what’s below that ice that really gets scientists excited.
Under its icy shell is an ocean of warm, salty water, and the ESA says investigating the moon should be a top priority.
Enceladus is Saturn’s sixth-largest moon. It’s only about 500 km (300 miles) in diameter. But despite its small size, it may harbour a buried ocean containing 15 million cubic km of water. (Earth has about 1.4 billion cubic kilometres of water.)
The Cassini spacecraft spotted plumes of water coming from under the ice, and ever since then, scientists have hungered for a closer look at the moon. The European Space Agency (ESA) aims to give them one.
“The mission concepts that we have recommended would provide tremendous scientific return, driving forward our knowledge, and would be fundamental for the successful detection of biosignatures on icy moons.”
Dr. Zita Martins, astrobiologist at Instituto Superior Técnico.The ESA’s long-term plan for exploring the Solar System is called Voyage 2050. In 2021, the ESA settled on an overarching theme for their Voyage 2050 activities called “Moons of the Giant Solar System Planets.” The ESA struck a committee of top planetary scientists to flesh out their ideas, and that committee laid out the priorities. According to them, the ESA should focus on one of the ocean moons and explore its habitability by investigating links between its environment and its interior. The ESA should also search for signs of life, either extant or ancient, and try to identify any surface chemistry that could enable life.
Dr. Zita Martins, an astrobiologist at Instituto Superior Técnico, chaired the team of planetary scientists. “The mission concepts that we have recommended would provide tremendous scientific return, driving forward our knowledge, and would be fundamental for the successful detection of biosignatures on icy moons,” said Dr. Martins.
“I am very happy to have been part of this process, seeing first-hand the early steps that will potentially lead to the investigation of the moons of the giant planets by ESA,” said Dr. Martins. “The search for habitable conditions and for signatures of life in the Solar System is challenging from a science and technology point of view but very exciting!”
But which moon should the ESA focus on? Candidates include Jupiter’s moon Europa and Saturn’s moons, Enceladus and Titan. Strong scientific cases can be made for each of these, as each one hosts liquid water.
Europa, Enceladus, and Titan all have subsurface oceans, and all three are targets for potential exploration. Image Credits: NASABut each moon is unique, and any mission to either of these moons would be uniquely complex. And expensive. Working alongside the science committee was a team of engineers from the ESA’s Concurrent Design Facility (CDF). Their job was to think ahead to the types of technologies that would be needed, and if they would be possible within a couple of decades.
“We commissioned three CDF studies focused on the most promising moons: Jupiter’s Europa and Saturn’s Enceladus and Titan,” elaborates Dr Frederic Safa, head of ESA’s Future Missions Department. “The team of scientists worked closely with the CDF engineers on the objectives of each study. The outcomes helped pin down what can be done with the resources that we will have in the 2040s.”
One had to be chosen, and the ESA chose Enceladus. Titan is second on the list, and Europa is third. (NASA is launching a mission to Europa in October 2024, and the ESA launched its JUICE mission to Jupiter last year.)
Enceladus has many qualities that attract planetary scientists interested in habitability: it has liquid water, an energy source, and some specific chemicals.
Data from the Cassini spacecraft is behind this global infrared mosaic of Saturn’s moon Enceladus. The intriguing ‘tiger stripes’ feature is prominent. Image Credit: NASA/JPL-Caltech/University of Arizona/LPG/CNRS/University of Nantes/Space Science InstituteEnceladus’ plumes are salty and chemically rich. Along with sodium, chlorine, and carbon trioxide, there are nitrogen, carbon dioxide, and hydrocarbons like methane and formaldehyde. There are also some simple organic compounds and larger organic molecules like benzene.
The water is kept liquid by the warmth from tidal heating. As Enceladus orbits Saturn, the gigantic planet tugs on the moon and deforms it. Each time it does, friction heats the moon. The moon also has a rocky core, and some of that rock is probably melted, creating magma chambers. It all adds up to an icy moon with a liquid ocean where the water interacts with the rock core, a critical part of it all. And it’s all kept warm despite a lack of radionuclides.
Unlike Earth’s core, Enceladus has no radionuclides to generate warmth. Instead, tidal heating keeps the moon warm and drives the movement of water. Image Credit: Surface: NASA/JPL-Caltech/Space Science Institute; interior: LPG-CNRS/U. Nantes/U. Angers. Graphic composition: ESAAnybody who follows planetary science news knows some of this, and they know that Enceladus is begging to be explored. A mission to Enceladus would be great for everybody interested in planetary science but would be especially rewarding for the ESA itself.
“An investigation into signs of past or present life around Saturn has never been achieved before. It would guarantee ESA leadership in planetary science for decades to come,” said ESA Director of Science, Prof. Carole Mundell.
The ESA launched its JUICE (Jupiter Icy Moons Explorer) mission one year ago. It’ll reach the Jovian system in 2031 and explore Jupiter’s moons Europa, Ganymede, and Callisto. Together with an eventual mission to Enceladus and NASA’s Europa Clipper mission, we’re on the cusp of learning an awful lot more about icy ocean moons.
The mission won’t be launched until the early 2040s and would take about a decade to reach its target. It could explore the Saturn system with far more technologically advanced science instruments than its predecessor, Cassini-Huygens. It could mimic that mission by exploring the system before a grand finale took it up close to Enceladus for our best-ever look at the icy ocean moon.
The science team developing the mission concept says that collecting a sample from Enceladus’ plumes is a must. A lander could do it, though that introduces an order of magnitude more complexity and expense. But an orbiter could do it too, by flying through the plumes, collecting a sample, and examining it in an onboard lab.
The discovery of ocean moons with icy shells has changed our understanding of planetary science, our Solar System, habitability, and the search for life. If there are this many ocean moons in our Solar System, how many are there out there in the Milky Way?
Learning more about Enceladus, Europa, and the rest could teach us a lot about life in the Universe and potential exomoon habitability.
The post Europe Has Big Plans for Saturn’s Moon Enceladus appeared first on Universe Today.
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Mars’ Gale Crater was Filled with Water for Much Longer Than Anyone Thought
Even with all we’ve learned about Mars in recent years, it doesn’t stack up against all we still don’t know and all we hope to find out. We know that Mars was once warm and wet, a conclusion that was less certain a couple of decades ago. Now, scientists are working on uncovering the details of Mars’s ancient water.
New research shows that the Gale Crater, the landing spot for NASA’s MSL Curiosity, held water for a longer time than scientists thought.
Life needs water, and it needs stability. So, if Gale Crater held water for a long time, it strengthens the idea that Mars could’ve supported life. We know that Gale Crater is an ancient paleolake, and this research suggests that the region could’ve been exposed to water for a longer duration than thought. But was it liquid water?
The research is titled “Ice? Salt? Pressure? Sediment deformation structures as evidence of late-stage shallow groundwater in Gale crater, Mars.” It’s published in the journal Geology, and the lead author is Steven Banham. Banham is from the Imperial College of London’s Department of Earth, Science, and Engineering.
The research centers on desert sandstone that Curiosity found.
We know that water played a role in shaping the Martian surface. Multiple rovers and orbiters have given us ample evidence of that. Orbital images show clear examples of ancient deltas. We also have many images of sedimentary rock, with its tell-tale layered structure, laid down in the presence of water. But beyond the initial creation of Martian sandstone, the details of the rock can tell scientists about what happened long after it formed.
The Eberswalde delta near Holden Crater on Mars is considered the ‘smoking gun’ for evidence of liquid water on Mars. By NASA/JPL/Malin Space Science SystemsThis research focuses on Gale Crater and the landforms within it. Mount Sharp (aka Aeolis Mons) is the dominant feature in the crater and rises 5.5 km or about 18,000 feet. It’s made up of sedimentary layers that have been eroded over time. But it has substructures that show its detailed history.
One structure overlays Mount Sharp and post-dates Mount Sharp’s erosion. It’s characterized by the accumulation of aeolian strata under arid conditions. That means windborne deposits instead of waterborne deposits. So scientists can tell that there was a wet period during which fluviolacustrine sediments built Mt. Sharp. They can also tell that a dry period followed, during which wind-borne sediment created the overlying structure. That’s what you’d expect to find if the story ended here: Mars was wet, then it wasn’t.
“Surprisingly, we found that these wind-deposited layers were contorted into strange shapes, which suggests the sand had been deformed shortly after being laid down. These structures point to the presence of water just below the surface.”
Amelie Roberts, study co-author, Imperial College London’s Department of Earth Science and Engineering.But scientists found something odd in the overlying windborne sandstone: deformed layers that could only have been formed in the presence of water. “The sandstone revealed that water was probably abundant more recently, and for longer, than previously thought – but by which process did the water leave these clues?” Banham said in a press release.
That’s more difficult to determine.
“This water might have been pressurized liquid, forced into and deforming the sediment; frozen, with the repeat freezing and thawing process causing the deformation; or briny, and subject to large temperature swings,” Banham said.
“What’s clear is that behind each of these potential ways to deform this sandstone, water is the common link.”
There’s a generally accepted understanding of Martian water among scientists. By the middle of Mars’ Hesperian Period, the planet lost its water. The Hesperian’s boundaries in time are uncertain, but it’s generally thought of as the transition from the heavy bombardment period to the dry Mars we know today. The Hesperian could’ve ended between 3.2 and 2.0 billion years ago. The Noachian preceded it, and the Amazonian followed it.
This research presents a new wrinkle. It suggests that Mars had abundant subsurface water toward the end of the Hesperian. The evidence is in MSL Curiosity’s images of different sedimentary rocks on Gale Crater’s Mt. Sharp.
“When sediments are moved by flowing water in rivers, or by the wind blowing, they leave characteristic structures which can act like fingerprints of the ancient processes that formed them,” said Banham.
MSL Curiosity slowly worked its way up Mt. Sharp, studying the rocks at different elevations as it ascended. As expected, it found younger rocks the higher it went. Eventually, it reached the Stimson formation. The Stimson formation is the remnant of an ancient windborne desert dune field.
An analysis of Curiosity’s images shows that Stimson formed after Mt. Sharp when Mars was thought to be dry. But Stimson isn’t entirely uniform. One of its features is named the Feòrachas structure, and it contains features that were clearly influenced by the presence of water.
“Usually, the wind deposits sediment in a very regular, predictable way,” said study co-author Amelie Roberts, a PhD candidate from Imperial College London’s Department of Earth Science and Engineering. “Surprisingly, we found that these wind-deposited layers were contorted into strange shapes, which suggests the sand had been deformed shortly after being laid down. These structures point to the presence of water just below the surface.”
This image from the study shows part of the Feorachas structure with undeformed features. Water played no role in shaping them. B shows wind-ripple laminations. The image also shows cross laminations, which are the result of additional sediments deposited by wind. Image Credit: Banham et al. 2024, NASA/JPL-Caltech/MSSSIn the Brackenberry outcrop feature, the sedimentary rocks show evidence of deformation by water. There are laminations in various states of deformity, becoming more pronounced in the feature geologists call the cusp core. In the cusp core, wind-ripple laminations bend toward the vertical and become incoherent.
This image from the research shows some features that are deformed by the presence of water. Vertical, incoherent sedimentary lines in the cusp core, oversteepened laminations, and vertically deformed laminations are all evidence of the presence of water. Image Credit: Banham et al. 2024, NASA/JPL-Caltech/MSSSThe authors explain that there are three mechanisms that can explain the deformed features, and they all involve water. They’re also not mutually exclusive.
High-pressure water could’ve overcome the strength of the rock and deformed it. Large ice deposits on top of the structure could’ve caused deformation, as could freeze/thaw cycles of water inside the rock. The third explanation involves sediment rock weakly bound together by evaporites. Thermal expansion and contraction of the evaporites can deform the rock.
This image from the research shows more examples of fluidization structures. A shows a feature named Up Helly Aa, and B is a zoomed-in image showing up warping and vertical laminations. C shows the Lamington feature, and D is a zoomed-in image showing more deformed laminations. Image Credit: Banham et al. 2024, NASA/JPL-Caltech/MSSS“The layers of sediment in the crater reveal a shift from a wet environment to a drier one over time – reflecting Mars’ transition from humid and habitable environment to inhospitable desert world,” said co-author Roberts. “But these water-formed structures in the desert sandstone show that water persisted on Mars much later than previously thought.”
Mars is no exoplanet, but it’s inadvertently teaching us a lot about our quest to understand exoplanets and habitability.
“Determining whether Mars and other planets were once able to support life has been a major driving force for planetary research for more than half a century,” said Dr. Banham. “Our findings reveal new avenues for exploration – shedding light on Mars’ potential to support life and highlighting where we should continue hunting for new clues.”
“Our finding extends the timeline of water persisting in the region surrounding Gale crater, and so the whole region could have been habitable for longer than previously thought,” said Amelie.
Maybe one day in the far distant future, one of our rovers on a distant exoplanet will flip over a rock and watch something scuttle away. It’s easy to imagine.
But Mars is an instructive example. If it remained habitable for longer than we thought, it was likely only marginally inhabitable. We can’t say for sure, but complex life seems to be out of the question. This should prepare humanity for what we can expect to find in our quest for habitable exoplanets.
There are a bewildering number of variables that go into making Earth the living oasis that it is. We’re much more likely to stumble on other planets like Mars, which were once habitable and maybe even harboured simple life. If Earth’s long-lived habitability is the outlier, and Mars’ marginal, interrupted habitability is more likely, we can expect to find many planets like it that were once alive but are now long dead.
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Marvel at stunning echo of 800-year-old explosion
In the year 1181 a rare supernova explosion appeared in the night sky, staying visible for 185 consecutive days. Historical records show that the supernova looked like a temporary ‘star’ in the constellation Cassiopeia shining as bright as Saturn.
Ever since, scientists have tried to find the supernova’s remnant. At first it was thought that this could be the nebula around the pulsar (dead star) 3C 58. However closer investigations revealed that the pulsar is older than supernova 1181.
In the last decade, another contender was discovered; Pa 30 is a nearly circular nebula with a central star in the constellation Cassiopeia. It is pictured here combining images from several telescopes. This composite image uses data across the electromagnetic spectrum and shows a new spectacular view of the supernova remnant. Allowing us to marvel at the same object that appeared in our ancestors’ night sky more than 800 years ago.
X-ray observations by ESA’s XMM-Newton (blue) show the full extent of the nebula and NASA’s Chandra X-ray Observatory (cyan) pinpoints its central source. The nebula is barely visible in optical light but shines bright in infrared light, collected by NASA’s Wide-field Infrared Space Explorer (red and pink). Interestingly, the radial structure in the image consists of heated sulphur that glows in visible light, observed with the ground-based Hiltner 2.4 m telescope at the MDM Observatory (green) in Arizona, USA, as do the stars in the background by Pan-STARRS (white) in Hawaii, USA.
Studies of the composition of the different parts of the remnant have led scientists to believe that it was formed in a thermonuclear explosion, and more precisely a special kind of supernova called a sub-luminous Type Iax event. During this event two white dwarf stars merged, and typically no remnant is expected for this kind of explosion. But incomplete explosions can leave a kind of ‘zombie’ star, such as the massive white dwarf star in this system. This very hot star, one of the hottest stars in the Milky Way (about 200 000 degrees Celsius), has a fast stellar wind with speeds up to 16 000 km/h. The combination of the star and the nebula makes it a unique opportunity for studying such rare explosions.
[Image description: A composite image of the remnant of supernova 1181. A spherical bright nebula sits in the middle surrounded by a field of white dotted stars. Within the nebula several rays point out like fireworks from a central star.]