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takyon writes:

A NASA report on the potential for future exploration of the Jovian moon Europa has been published:

A report on the potential science value of a lander on the surface of Jupiter's icy moon Europa has been delivered to NASA, and the agency is now engaging the broader science community to open a discussion about its findings.

[...] The report lists three science goals for the mission. The primary goal is to search for evidence of life on Europa. The other goals are to assess the habitability of Europa by directly analyzing material from the surface, and to characterize the surface and subsurface to support future robotic exploration of Europa and its ocean. The report also describes some of the notional instruments that could be expected to perform measurements in support of these goals.

Scientists agree that the evidence is quite strong that Europa, which is slightly smaller than Earth's moon, has a global saltwater ocean beneath its icy crust. This ocean has at least twice as much water as Earth's oceans. While recent discoveries have shown that many bodies in the solar system either have subsurface oceans now, or may have in the past, Europa is one of only two places where the ocean is understood to be in contact with a rocky seafloor (the other being Saturn's moon Enceladus). This rare circumstance makes Europa one of the highest priority targets in the search for present-day life beyond Earth.

Executive summary:

The Europa Lander Science Definition Team Report presents the integrated results of an intensive science and engineering team effort to develop and optimize a mission concept that would follow the Europa Multiple Flyby Mission and conduct the first in situ search for evidence of life on another world since the Viking spacecraft on Mars in the 1970s. The Europa Lander mission would be a pathfinder for characterizing the biological potential of Europa's ocean through direct study of any chemical, geological, and possibly biological, signatures as expressed on, and just below, the surface of Europa. The search for signs of life on Europa's surface requires an analytical payload that performs quantitative organic compositional, microscopic, and spectroscopic analysis on five samples acquired from at least 10 cm beneath the surface, with supporting context imaging observations. This mission would significantly advance our understanding of Europa as an ocean world, even in the absence of any definitive signs of life, and would provide the foundation for the future robotic exploration of Europa.

Europa Lander Study 2016 Report (264 pages) and older resources.

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takyon writes:

At a NASA press conference on Thursday, scientists from the Jet Propulsion Laboratory, NASA's D.C. Headquarters, and the Space Telescope Science Institute announced new observations about the "ocean worlds" Enceladus and Europa. At Enceladus, one of Saturn's moons, the Cassini spacecraft has measured emissions of hydrogen gas that could indicate a source of chemical energy for life forms. 2016 Hubble observations of Jupiter's moon Europa have found evidence of a water plume emanating from the same location as a plume measured in 2014.

The Cassini spacecraft took a "deep dive" into one of the Enceladus plumes on Oct. 28, 2015. The plume contains about 98% water, 0.4-1.4% hydrogen, and a mixture of carbon dioxide, methane, ammonia, and other molecules. The findings support the conclusion of hot water interacting with rock at hydrothermal vents on the seafloor, a type of habitat known to support life without the need for sunlight. NASA scientists have concluded that Enceladus has all of the conditions and ingredients necessary to support life, although the detection of hydrogen gas does not prove that the internal ocean currently contains life forms, and phosphorus and sulfur have yet to be measured.

The new Hubble images of Europa show that the height of the plume is about twice that of the one measured in 2014. The location of this periodic plume corresponds with a thermal hotspot on Europa's surface found by the Galileo spacecraft in the 1990s, which was once dismissed as an anomaly. The lack of craters on Europa's surface indicates that water is spraying out of the internal ocean through cracks and reshaping the surface. However, Europa's ice shell is thought to be thicker than that of Enceladus, with water vapor escaping the crust less often. NASA is currently developing a Europa Clipper mission that would conduct a series of 45 or more flybys of Europa, with the possibility of flying directly through water vapor plumes for sampling. The European Space Agency's Jupiter Icy Moons Explorer will study Europa and Callisto, but end its mission by orbiting Ganymede.

The same chemistry detected at Enceladus could also be taking place in interior oceans on other icy worlds, such as Ceres, Titan, Ganymede, Callisto, Dione, Rhea, Titania, Triton, Pluto, Eris, Sedna, etc.

Here's the press briefing (48m16s). Also at Science Magazine, BBC, Space.com, and Popular Mechanics (mhajicek's link).

Cassini finds molecular hydrogen in the Enceladus plume: Evidence for hydrothermal processes (open, DOI: 10.1126/science.aai8703) (DX)

Active Cryovolcanism on Europa? (DOI: 10.3847/2041-8213/aa67f8) (DX)

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Phoenix666 writes:

Saturn's icy moon Enceladus is best known for its numerous geysers ejecting plumes of water and ice. These eruptive fountains perplex researchers searching for signs of microbial life beyond Earth. A dedicated spacecraft designed to study the plume-like features spewing from Enceladus could definitely tell us whether or not they contain alien microorganisms.

"We need a spacecraft to travel to Enceladus, fly through a geyser plume, and analyze the water that is immediately accessible," Geoffrey Marcy, a retired professor of astronomy at the University of California, Berkeley, told Astrowatch.net.

Marcy is a renowned exoplanet researcher who discovered many extrasolar worlds. He was one of the co-investigators of NASA's Kepler planet-hunting mission that detected more than 4,000 exoworlds.
...
"The remarkable aspect of the search for microbes in the water spurting from geysers is that the spacecraft only needs to fly through the plume, well above the surface of Enceladus. No lander is needed—just a succession of flybys through the plumes as it orbits Enceladus," Marcy said.

He noted that such spacecraft should be fitted with a mass spectrometer to detect organic compounds that could be signs of microbial life. The spectrometer will look for amino acids and the structure of any organic molecules, especially fatty acids such as those composing cell membranes. It could also measure the relative amounts of isotopes of carbon (12 and 14) to detect non-natural anomalies due to biological processes.

Moreover, the mission to Enceladus would measure the properties of the water such as pH, oxidation and temperature, therefore assessing its suitability for organic life.

Marcy believes assembling "a brilliant team of billionaires" is the key to making such a mission possible. Lucky for him the monolith said nothing about Enceladus.

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Phoenix666 writes:

The hunt for habitable (and already inhabited) worlds has largely focused on a "Goldilocks zone" around a star, where it's neither too hot nor too cold for liquid water to exist. But astrobiologists have begun to broaden their search – thanks to discoveries by NASA's Cassini orbiter.

Saturn sits too far from the sun for its rays to melt ice, and yet Cassini discovered that one of the planet's moons, Enceladus, has a vast ocean sloshing beneath its icy crust. Instead of sunlight, tidal forces keep Enceladus's ocean warm. The gravity of Saturn pulls at Enceladus's core, driving thermal processes that create a new Goldilocks zone inside the moon itself.

"It's definitely been a paradigm shift in where you might find life," says Cassini project scientist Linda Spilker.

Still, it takes a lot more than water to make a place habitable. But here, too, Enceladus delivers. Icy geysers fueled by Enceladus's ocean shoot out from cracks in the moon's surface, allowing the Cassini spacecraft to sample them directly during flybys. What it found is that Enceladus has almost everything required for life as we know it: a source of energy, a source of carbon, and salts and minerals.

Thank goodness for Cassini, after that whole thing about being banned from Europa.

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takyon writes:

Timeline of Cassini–Huygens

NASA's Cassini Spacecraft Ends Its Historic Exploration of Saturn

Telemetry received during the plunge indicates that, as expected, Cassini entered Saturn's atmosphere with its thrusters firing to maintain stability, as it sent back a unique final set of science observations. Loss of contact with the Cassini spacecraft occurred at 7:55 a.m. EDT (4:55 a.m. PDT), with the signal received by NASA's Deep Space Network antenna complex in Canberra, Australia.

[...] As planned, data from eight of Cassini's science instruments was beamed back to Earth. Mission scientists will examine the spacecraft's final observations in the coming weeks for new insights about Saturn, including hints about the planet's formation and evolution, and processes occurring in its atmosphere.

[...] Cassini launched in 1997 from Cape Canaveral Air Force Station in Florida and arrived at Saturn in 2004. NASA extended its mission twice – first for two years, and then for seven more. The second mission extension provided dozens of flybys of the planet's icy moons, using the spacecraft's remaining rocket propellant along the way. Cassini finished its tour of the Saturn system with its Grand Finale, capped by Friday's intentional plunge into the planet to ensure Saturn's moons – particularly Enceladus, with its subsurface ocean and signs of hydrothermal activity – remain pristine for future exploration.

Farewell, Cassini: a 20 year mission to Saturn comes to a life-protecting end

During the Jovian flyby, Cassini performed scientific observations of the planet, showing that Jupiter's cloud belts were areas of "net-rising atmospheric motion."

This observation contradicted previous hypotheses about Jupiter's dark and light belts and served to highlight differences in planetary weather systems.

During the flyby, Cassini was also able to study Jupiter's thin ring system, revealing that Jupiter's rings were composed of irregularly shaped particles that likely originated as ejecta from micrometeorite impacts with the moons Metis and Adrastea.

Cassini: The legend and legacy of one of NASA's most prolific missions

Previously:

takyon writes:

A study has found that a "porous"/sandy/muddy core can increase the energy released by gravitational tidal friction inside Saturn's moon Enceladus. This could explain why the interior of the icy moon has not cooled down after billions of years:

A paper published in Nature Astronomy today presents the first concept that explains the key characteristics of 500 km-diameter Enceladus as observed by the international Cassini spacecraft over the course of its mission, which concluded in September.

This includes a global salty ocean below an ice shell with an average thickness of 20–25 km, thinning to just 1–5 km over the south polar region. There, jets of water vapour and icy grains are launched through fissures in the ice. The composition of the ejected material measured by Cassini included salts and silica dust, suggesting they form through hot water – at least 90ºC – interacting with rock in the porous core.

These observations require a huge source of heat, about 100 times more than is expected to be generated by the natural decay of radioactive elements in rocks in its core, as well as a means of focusing activity at the south pole.

The tidal effect from Saturn is thought to be at the origin of the eruptions deforming the icy shell by push-pull motions as the moon follows an elliptical path around the giant planet. But the energy produced by tidal friction in the ice, by itself, would be too weak to counterbalance the heat loss seen from the ocean – the globe would freeze within 30 million years.

[...] In the new simulations the core is made of unconsolidated, easily deformable, porous rock that water can easily permeate. As such, cool liquid water from the ocean can seep into the core and gradually heat up through tidal friction between sliding rock fragments, as it gets deeper.

Powering prolonged hydrothermal activity inside Enceladus (DOI: 10.1038/s41550-017-0289-8) (DX)

Previously: Hydrogen Emitted by Enceladus, More Evidence of Plumes at Europa
Cassini Finds Evidence of Change in Enceladus's Spin Axis
Could a Dedicated Mission to Enceladus Detect Microbial Life There?
How the Cassini Mission Led a 'Paradigm Shift' in Search for Alien Life

Original Submission

takyon writes:

Saturn moon a step closer to hosting life

Scientists have found complex carbon-based molecules in the waters of Saturn's moon Enceladus.

Compounds like this have only previously been found on Earth, and in some meteorites. They are thought to have formed in reactions between water and warm rock at the base of the moon's subsurface ocean.

Though not a sign of life, their presence suggests Enceladus could play host to living organisms. The discovery came from data gathered by the Cassini spacecraft.

Also at SwRI, ScienceAlert, Space.com, National Geographic, Popular Mechanics, and The Guardian.

Macromolecular organic compounds from the depths of Enceladus (DOI: 10.1038/s41586-018-0246-4) (DX)

Related: Minerals In Plumes of Enceladus Indicate Hydrothermal Activity
Hydrogen Emitted by Enceladus, More Evidence of Plumes at Europa
Could a Dedicated Mission to Enceladus Detect Microbial Life There?
How the Cassini Mission Led a 'Paradigm Shift' in Search for Alien Life
Cassini Spacecraft Post-Mortem
Porous Core Could be Keeping Enceladus Warm
Yuri Milner Considering Privately Funded Mission to Enceladus
Organic Molecules Found on Ceres
NASA Finds Evidence of Water Plume on Europa
Organic Matter Found on Mars
Study Finds Evidence of More Organic Material on Ceres

Original Submission

takyon writes:

NASA to support initial studies of privately funded Enceladus mission

NASA signed an agreement in September with a foundation to support initial studies of a privately funded mission to a potentially habitable moon of Saturn. The unfunded Space Act Agreement between NASA and the Breakthrough Prize Foundation, initiated with little public fanfare, covers NASA support for initial concept studies, known in NASA programmatic parlance as "Pre-Phase A," for a mission to the moon Enceladus, an icy world believed to have a subsurface ocean of liquid water and plumes that eject that water through the surface into space.

The agreement, the seven-page document posted on a NASA website states, "shall be for the purpose of cooperating on the Breakthrough Pre-Phase A activities for Breakthrough's Enceladus Mission." That includes supporting a series of reviews that leads up to what NASA calls Key Decision Point (KDP) A, "to determine progress to Phase A, for further formation of the Enceladus Mission's concept and technology development."

[...] Most of the study work would be done by Breakthrough. NASA, under the agreement, would use "reasonable efforts" to offer scientific and technical consulting for the study, including expertise in a range of scientific fields and in planetary projection. NASA will also advise "in the development of Phase A plans for a life signature mission to Enceladus." The agreement between NASA and Breakthrough involves no exchange of funds. NASA estimates its cost of carrying out its responsibilities under the agreement to be $72,384.

The agreement, first reported by New Scientist, offers few details about the proposed mission itself. A companion document for the agreement notes that the foundation's Breakthrough Watch program "seeks to evaluate near-term missions to objects in the Solar System, including Enceladus," that would search for signs of life there. "The Enceladus Mission is considering novel low-cost approaches, one of which uses solar sail technology to flyby the moon of Saturn to collect scientific data.

However, foundation officials have publicly discussed their interest in an Enceladus mission for a year. "We formed a little workshop around this idea," said Yuri Milner, the Russian billionaire who funds the foundation, at an event in Seattle in November 2017. "Can we design a low-cost privately-funded mission to Enceladus, which can be launched relatively soon and that can look more thoroughly at those plumes to try to see what's going on there?"

Also at Space.com.

Previously: Yuri Milner Considering Privately Funded Mission to Enceladus

Related: Underground Ocean on Enceladus May be Close to the Surface
Hydrogen Emitted by Enceladus, More Evidence of Plumes at Europa
Could a Dedicated Mission to Enceladus Detect Microbial Life There?
How the Cassini Mission Led a 'Paradigm Shift' in Search for Alien Life
Porous Core Could be Keeping Enceladus Warm
Complex Organic Molecules Found on Enceladus

Original Submission