January 9, 2016 | David F. Coppedge

Updates from Outer Planets

Let’s review some of the latest news from missions to the outer planets.


Juno mission: It’s been 13 years since the Galileo orbiter plunged into Jupiter’s atmosphere, ending its mission. This year, the Juno mission is scheduled to arrive at the Jupiter system on July 4; do they plan these things for patriotic reasons? Viking 1 landed on Mars on July 4, 1976 (America’s Bicentennial), and New Horizons flew by Pluto last year just 10 days after Independence Day. Whatever; The Conversation says one of Juno’s aims is to look for water in the atmosphere, and PhysOrg teases with what visual fireworks we can look forward to this July 4:

Juno will get closer to Jupiter than any previous orbiting spacecraft, giving JunoCam the best close-up views yet of the planet’s colorful cloud bands. Every 14 days, the spinning, solar-powered spacecraft will dive past the planet in just a couple of hours, gathering huge amounts of science data, plus about a dozen JunoCam images. At closest approach, Juno will snap photos from only 3,100 miles (5,000 kilometers) above Jupiter’s clouds.

Galilean satellites: A paper in Icarus seeks once again to model the four large Jupiter moons (Io, Europa, Ganymede and Callisto)—each one distinct and different from the others—with a secular bottom-up planetesimal model, only to confess, “However, bodies as massive as Ganymede and those located far away from Jupiter, such as Callisto, are difficult to form with this scenario.” The realities of gas drag and migration make keeping the pieces together very challenging. Another paper in Icarus explores what would be required to plan a mission to fly through the plumes of Europa if they exist. If Europa is shooting water vapor outward from its underground ocean, it might contain life, right? (see hydrobioscopy in the Darwin Dictionary). “The likelihood of capturing at least a single cell, with a log-uniform prior of cell abundances, is proposed as a science value metric for different flyby altitudes.” Lots of assumptions there.

Saturn: The Cassini Mission

Enceladus: The geysering moon Enceladus is losing steam, Space.com says. It’s not clear if this is a long-term trend. Veteran atmospheric scientist Andy Ingersoll doesn’t think the geysers are shutting down, but it’s not clear what is going on. Maybe material is being deposited on the walls of the tiger-stripe canyons, “But why they would all act together is totally beyond me,” he said. Enceladus has been known to turn up the volume. On approach to Saturn in 2004, scientists were astonished to witness a huge influx of oxygen to the E-ring that probably came from an outburst at the geysers (see 7/11/06 and 7/02/04). Space.com also has pretty pictures of the August flyby, and a video featuring planetary scientist Luciano Iess making some fact-free speculations about life there. More seriously, scientists published in Icarus are modeling what created the parallel fractures called tiger stripes.  New Scientist reports that NASA is considering two missions to look for life in the plumes or underground oceans of the little moon. Perennial believer in life in space Jonathan Lunine feels the call of the wild. “The plume of Enceladus is waiting for us. It could be the place where we find out if life had a second genesis in our own solar system.” Big if.

Prometheus got its picture taken again on December 3. This is one of the shepherd moons of Saturn’s F-ring. It periodically contacts the ring particles and scours out patterns in the dust. The photo on PhysOrg of the 53-mile-long potato-shaped moon shows a partly cratered, dusty surface. This was the only other body in the solar system that Guillermo Gonzalez calculated was capable of creating a total eclipse of the sun (The Privileged Planet, pp. 10-11), provided one was floating in Saturn’s cloud tops at the right place and time for a half a second. However, Cassini showed that Prometheus is non-spherical. That leaves one place for the beauty and scientific significance of total solar eclipses, the Earth: the one place we know of with sentient beings who can appreciate them. And Earth’s eclipses can last up to two minutes.

Titan still presents problems keeping its methane for billions of years. Another paper in Icarus tries modeling a methane cycle similar to the hydrological cycle on Earth. Seasonal variation alone, however, cannot explain the one-way conversion to ethane that must accumulate on the surface due to breakdown of atmospheric methane by the solar wind. Only a paucity of ethane was detected when the Huygens Probe landed  11 years ago this month, not the global ocean that planetary scientists had predicted from Voyager data. It doesn’t matter if the methane circulates in the atmosphere. Unless there is a means to replenish it (and these scientists didn’t mention any), all of it should get converted to ethane in far less time than the assumed age of the solar system. The missing ethane is one of the major problems for maintaining that Titan is billions of years old. Other Titan news concerns the discovery of possible evaporites on the surface (PhysOrg). Astrobiologists like to consider Titan as a possible abode for life, but what could live on hills of hydrogen cyanide, acetylene and tar?

Saturn’s magnetic field releases some of its energy in explosive bursts from time to time, Science Daily says. In a remarkable case of the tail wagging the dog, little Enceladus is responsible for pumping excess energy into the vast magnetosphere of Saturn through its geysers.

One of the mysteries this gives us clues to answering is how Saturn’s magnetic bubble, known as its magnetosphere, gets rid of gas from Saturn’s tiny icy moon Enceladus. Through jets at its south pole, this tiny 500 km-sized moon ejects around 100 kg of water into space every second.

Dr Chris Arridge, lead author of the study, said: “Water from the Enceladus plume is trapped in Saturn’s magnetosphere. We know it can’t just stay there for ever and until now we have not been able to work out how it has been ejected from the magnetosphere.”

Pluto: The New Horizons Mission

The big news from Pluto is the discovery of a possible ice volcano. Space.com posted a video clip from Johns Hopkins’ New Horizons team explaining the find, showing close-ups of the candidate mountain, named Wright Mons. It’s 100 miles across and about 13,000 feet high, topped with a crater 35 miles wide. They couldn’t tell if it is active now, but it looks like it was or has been recently. It may not be the only eruptive center on this young-looking dwarf planet; there’s at least one other they’ve identified. Judging from their shape and slopes, “These features look just like volcanoes do on Earth when seen from orbit,” the narrator says, except that these would erupt water ice and a slurry of nitrogen, ammonia and methane ices instead of hot lava. They had to get the E-word in there somehow: “Cryovolcanism could provide an important clue into understanding Pluto’s geologic and atmospheric evolution.”

Another stunning image received Dec. 24 is called “X Marks the Spot.” Space.com says that the X-shaped feature in the smooth plains of Sputnik Planum may be the boundary between four neighboring convection cells. Convection, obviously, indicates flow of fluid material from under the surface—another sign of youthful activity. Here’s the thinking: “Solid nitrogen deep beneath the surface is warmed by Pluto’s mysterious interior heat, rises in huge globs, and then cools and sinks again.” A small body like Pluto should not have any heat; that’s why it’s “mysterious.” Given there are few if any impact craters in that region, the convection must be recent or perhaps ongoing. The article mentions that only 25% of the data from New Horizons has been transmitted to Earth so far, so more surprises are likely in store from Pluto and its moons.

Astrobiology Magazine posted the beautiful montage of high-def images from the July 14 flyby, and shared some of the new findings. There’s still about 8 months’ worth of data to get to the ground. Scientific analysis is bound to take years. What’s the latest and greatest?

Geological evidence has been found for widespread past and present glacial activity, including the formation of networks of eroded valleys, some of which are “hanging valleys,” much like those in Yellowstone National Park, Wyoming. “Pluto has greatly exceeded our expectations in diversity of landforms and processes — processes that continue to the present,” said Alan Howard of the University of Virginia, Charlottesville, a scientific collaborator with the New Horizons’ Geology, Geophysics and Imaging team.

The flyby made Astrobiology Magazine‘s #1 spot on its Top Ten Stories from 2015. Space.com posted the detailed montage, too, and explained some of the diversity of landforms revealed in unprecedented detail. About the same time, Space.com also posted “incredible” high-def images of pits, plains and mountains, often starkly adjacent to one another. The second image shows a set of “intricate pits” in Tombaugh Regio. “Because there are only a few impact craters on top of the pits, scientists can now see that these mysterious indentations, which are usually hundreds of yards across and tens of yards deep, formed relatively recently.” But that’s the mystery. Pluto should have been orbiting in the cold outer regions of the solar system for 4.6 billion years, scientists say. How can there be geological processes going on now?

It’s always astounding that highly intelligent planetary scientists can be so right about designing machines to reach precise locations billions of miles away, yet be so wrong about their expectations, and so flummoxed by what they see (i.e., young phenomena). Maybe that’s why they distract attention away from their headaches to the possibility of life. How, otherwise, can they face the public? “Well, sorry we were so wrong, but look! Here’s some water! Maybe there’s life there!” (See Sidestepping in the Baloney Detector.)

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