Cassini Plunges Through Enceladus Geyser, and Other Saturn News
Yesterday’s daring plunge through a plume of an Enceladus geyser is the highlight of recent Saturn news.
Deepest-Ever Dive Through Enceladus Plume Completed (JPL): Two-way communication with Cassini after the geyser plunge shows that the spacecraft survived, JPL reported. Come back to this spot for latest news and links to photos after the data are downloaded. PhysOrg posted a list of preview facts before the event.
Update 10/30/15: Spectacular close-ups as well as wide-angle shots have been posted by the Cassini Imaging Team website. Photos are not the only purpose of the event. Data on the composition of plume particles will provide important clues about what lies below. Principle investigators for Cassini’s other instruments such as the Cosmic Dust Analyzer (CDA) will have a lot to say when the data are presented at a future date. Science Magazine says that could take months.
Closest Northern Views of Saturn’s Moon Enceladus (NASA-JPL): After the October 10 flyby that skimmed over the north pole, NASA released images showing that the mysterious lines cutting across craters at the equator continue over the north pole.
Aggregate particles in the plumes of Enceladus (Icarus): Atmospheric scientists tried modeling the particles in the Enceladus geyser plumes, but did not come to definitive conclusions about the size of the aggregates or where they form in the vapor column. “Estimates of the total particulate mass of the plumes of Enceladus are important to constrain theories of particle formation and transport at the surface and interior of the satellite.” This is an updated paper from the 2011 model. Yesterday’s flyby will undoubtedly provide more constraints for the models.
The chemistry that could feed life within Saturn’s moon Enceladus: study gives clue ahead of flyby (The Conversation): David Rothery, planetary scientist at The Open University, rang the hydrobioscopy bell before the flyby, equating water with life. Without explaining how, he claims that “The power to drive the plumes must come from heat generated by the varying tidal stresses experienced by Enceladus as it orbits Saturn.” Then he rang the hydrobioscopy bell longer and louder.
High-temperature water–rock interactions and hydrothermal environments in the chondrite-like core of Enceladus (Nature Communications): This paper by primarily Japanese researchers tries to constrain the conditions for a global ocean at Enceladus. To account for silica nanoparticles, they say, the crustal composition must resemble that of carbonaceous chondrites, a type of melted meteor. The silica would have dissolved over geological timescales, they say; “Accordingly, the formation of silica nanoparticles is most likely sustained by geologically recent or ongoing hydrothermal activity.” What happened to cause that? The combination of factors required to keep Enceladus warm for 4.5 billion years seem improbable (radiogenic heat followed by episodic tidal flexing and serpentinization, etc.), so they entertain a more recent chain of events. Unfortunately, it also has a high perhapsimaybecouldness index:
However, given that a porous rocky core tends to lose remnant heat rapidly, especially if it is percolated by the oceanic water, it may be more likely that hydrothermal activity on Enceladus was triggered by a recent incidental heating event (for example, a catastrophic crustal overturn, an orbital evolution or an impact). The thickness of plume particles deposits on the small Saturnian satellites also implies that the duration of cryovolcanic activities on Enceladus would be as short as 10 Myrs (ref. 44). These incidental heating event [sic] could have increased the temperature near the ocean–rock interface (Fig. 4b). It is highly uncertain whether this event alone could have produced a sufficient amount of heat to cause hydrothermal activity, because such an event provides heat mainly in the icy shell rather than in the rocks of the seafloor. However, if Enceladus’ rocky core is fragmented, the incidental events would have triggered effective tidal dissipation within the core, especially near the ocean–rock interface. In addition, if the ocean–rock interface had contained pristine minerals, such an event might have initiated ice melting and subsequent exothermic serpentinization. This in turn could have triggered a positive feedback between serpentinization, temperature increase and large tidal dissipation, possibly leading to hydrothermal reactions.
Something Strange Is Happening Inside Saturn (Space.com): “Unusual ripples in Saturn’s rings are revealing the mysterious inner workings of the great gas giant,” this article on ‘kronoseismology’—the study of oscillations within Saturn— begins. “Planetary scientists and modelers are slowly picking apart that mystery.” Here’s a caution for people who think gas giants are simple objects that form easily:
“There’s a paradigm of giant planets being pretty simple objects, where they have a core of ice and rock, and this tremendous envelope of hydrogen/helium on top of that,” Fortney told Space.com. “That’s how people have mostly modeled giant planets for 50 years. But what the kronoseismology tells us is, there’s some region that is strange, there’s some part of the bottom of the envelope that’s not simple, that’s not convective. It tells us that Saturn is not a simple object; there’s something more going on there.“
At Saturn, One of These Rings is not like the Others (Astrobiology Magazine): Cassini’s Composite Infrared Spectrometer (CIRS) shows anomalously high temperatures in part of the A ring. Scientists infer from it something about the composition of the orbiting particles that raises an age issue:
“A high concentration of dense, solid ice chunks in this one region of Saturn’s rings is unexpected,” said Morishima. “Ring particles usually spread out and become evenly distributed on a timescale of about 100 million years.”….
“This particular result is fascinating because it suggests that the middle of Saturn’s A ring may be much younger than the rest of the rings,” said Linda Spilker, Cassini project scientist at JPL and a co-author of the study. “Other parts of the rings may be as old as Saturn itself.”
The 2013 Saturn auroral campaign (Icarus): The planetary science journal Icarus published a suite of papers about Saturn’s aurora observations from two years ago, for those interested in planetary physics and magnetospheres.
Inside Cassini’s Multi-Year Saturn Mission (Space.com): This article by graphic artist Karl Tate includes a colorful infographic showing highlights of the Cassini mission and its major findings, such as the Enceladus geysers, Titan and the Huygens landing, the solution to the Iapetus dark-light dichotomy, Saturn’s rings and the polar hexagon (see Evolution News & Views, “Are Hexagons Natural?”).
Saturn’s moon Titan (Universe Today via PhysOrg): Matt Williams shares the current knowledge of Titan. He doesn’t shy away from age problems:
The surface of Titan is relatively young – between 100 million and 1 billion years old – despite having been formed during the early solar system. In addition, it appears to be relatively smooth, with impact craters having been filled in. Height variation is also low, ranging by little more than 150 meters, but with the occasional mountain reaching between 500 meters and 1 km in height….
Energy from the sun should have converted all traces of methane in Titan’s atmosphere into more complex hydrocarbons within 50 million years—a short time compared to the age of the solar system. This suggests that methane must be replenished by a reservoir on or within Titan itself.
Saturn’s largest moon Titan could have sun-warmed swirling seas (New Scientist): Solar heating may stir up currents in the oily lakes of Titan, this article says. “What we found is that it can cause currents that are comparable with tidal and wind-driven currents.” Future landings in the lakes will need to take this into account. “Extraterrestrial oceanography is still in its early days,” remarks Ralph Lorenz (Johns Hopkins APL).
Congratulations to the engineers whose intelligent design built and guided this amazing spacecraft and aimed it into a narrow plume of gas around a tiny moon. That’s impressive.
We are now 11 years into Cassini’s mission to Saturn, and scientists still are puzzled about the youth of Titan and Enceladus. Obtaining data is a wonderful achievement for all who contributed, but understanding what they are seeing is a completely different matter. Much of their puzzlement would vanish if they kicked some A.S.S. out there.