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The Great Basin on Saturn's Tethys  (Credit: Cassini Imaging Team)

The Great Basin on Saturn’s Tethys (Credit: Cassini Imaging Team)

It’s been too long since we headed out to space.  This is true of humankind, but it is also true of this blog…so today we are going to cast our eyes across the solar system to Tethys a mid-sized moon of Saturn. In 1684 the Italian astronomer Giovanni Domenico Cassini discovered Tethys. He initially named the moon in honor of Louis XIV, but his choice was later changed so that the moon is named for a first generation Greek titan-goddess.  The moon has been approached by several human spacecraft, most notably…Cassini, which has dropped by several times (the robot space probe is named after the astronomer—the poor fellow has not been drifting in space since the 17th century).

Giovanni Domenico Cassini

Giovanni Domenico Cassini

Of all the major moons in the solar system, Tethys has the lowest density: 0.98 g/cm3 ! This means that almost the entire moon is made of frozen water—it is essentially a huge round ice cube floating around Saturn. Tethys has two extremely prominent features—a giant crater 450 kilometers (280 miles) across (named Odysseus) and a huge ice canyon 2000 kilometers (1200 miles) long, 100 km (62 miles) wide, and 3 km (1.8 miles) deep, which stretches most of the way across the moon.  Unsurprisingly astronomers speculate that the two features are related and the massive impact which created Odysseus melted a chasm along the entire side of the planetoid.


Although you might be inclined not to expect much activity from a ball of ice in the depths of space, Tethys seems like it may be geologically active, or, at least, it may have been once.  The area around the hemisphere is comparatively flat and free of craters—which suggests that tidal flux from Saturn causes some melting—and possibly cryovolcanoes.

Ithaca Chasma: The Great Rift on Saturn's Tethys  (Credit: Cassini Imaging Team)

Ithaca Chasma: The Great Rift on Saturn’s Tethys
(Credit: Cassini Imaging Team)

Paleontologists and sharp-eyed readers already know the name Tethys.  During the age of Pangaea (when all of the world’s continents joined to form a single land mass), the great ocean in the midst was named the Tethys Ocean. In Greek mythology, Tethys was the daughter of Gaea (the mother earth) and Uranus (the heavens).  She was regarded as the mother of all waters and was married to her brother Oceanus, the first lord of the seas.  The astronomers of the age of enlightenment who renamed the moon, could not have known it was composed mostly of water, but they chose well.


Serpent d'Océan  (Huang Yong Ping, 2012, aluminum sculpture)

Serpent d’Océan (Huang Yong Ping, 2012, aluminum sculpture)

Here is an amazing giant sea serpent sculpture by the Franco-Chinese artist Huang Yong Ping. The 130 meter long artwork is made of aluminum and is appropriately titled Serpent d’Océan (“Sea Serpent”). The sculptor completed the piece in 2012 for the Loire “Estuaire” festival. He erected the monumental work at the mouth of the Loire River where the great waterway empties into the Atlantic Ocean–just west of the port city of Nantes.

Serpent d'Océan (Huang Yong Ping, 2012, aluminum sculpture)

Serpent d’Océan (Huang Yong Ping, 2012, aluminum sculpture)

The head of Serpent d’Océan lies just above the high tide mark and its tail is just below the low tide boundary. Thus, every day the serpent goes from being mostly submerged to mostly on land. At low tide, art enthusiasts can walk around the piece and see it close up like a museum specimen. At high tide it takes on a mythical supernatural character as it appears to writhe through the waves.

Serpent d'Océan (Huang Yong Ping, 2012, aluminum sculpture)

Serpent d’Océan (Huang Yong Ping, 2012, aluminum sculpture)

The artist Huang Yong Ping designed the serpent to straddle all sorts of boundaries. It is neither at sea nor properly on land. Likewise it lies where river meets ocean and the ecosystem is neither fully marine nor riverine. The serpent is a metal sculpture designed to look like a living skeleton of a mythical creature. The sculptor himself self-identifies as neither entirely Chinese nor French: he used myths from both cultures to inform his sculpture. Indeed the serpent takes on even more facets when considered in the light of world trade (where monsters–real and imagined–abound). Additionally, as a youth, Huang studied with the French master of artistic ambiguity Marcel Duchamp. Most of Huang’s artworks blur the lines between art and non-art (though, like Duchamp, he tries to stick to the former category).

Serpent d'Océan (Huang Yong Ping, 2012, aluminum sculpture)

Serpent d’Océan (Huang Yong Ping, 2012, aluminum sculpture)

The artist has expressed his hope that, as the sculpture ages, various tidal plants and animals will begin to colonize it and live within—or atop–the metal creation. As seabirds build their nests there and living amphibious beasts hide and feed within the snake, it will stretch across even more boundaries.

Gibbous Europa (Credit: Galileo Project, JPL, NASA)

Gibbous Europa
(Credit: Galileo Project, JPL, NASA)

Tonight is Yuri’s Night, when space enthusiasts around the world celebrate the first human trip to outer space made by Yuri Gagarin fifty two years ago.  You can read about Yuri here.   It is an excellent occasion to assess what is most exciting in space exploration.  Unfortunately nobody has jumped forward to build a floating colony on Venus.  Indeed NASA seems rather flat footed lately—building a series of colorless rockets and sending successive similar rovers to Mars.  Fortunately there is one exciting mission which still has not definitively been cancelled because of budget stalemate.

Proposed Europa Clipper (NASA)

Proposed Europa Clipper (NASA)

The Europa Clipper mission is a $2bn dollar project to launch a probe to Jupiter’s moon Europa, a large icy satellite covered in cracked ice.  Europa is slightly smaller than Earth’s moon and has a thin oxygen atmosphere.  It is one of the smoothest items in the solar system.   Astronomers believe that an ocean of liquid water lies beneath Europa which is warmed by tidal flexing (a process which causes orbital and rotational energy to be converted into heat).   The surface of Europa is bathed in exotic radiation which rips apart water molecules and leaves oxidants like hydrogen peroxide.  All of this means that Europa is the most likely planet in the solar system to harbor unknown life.  It has even been theorized that beneath the ice the ocean could have black smoker type environments–and just possibly thermal vent or “cold seep” ecosystems.

Artist's concept of the cryobot and hydrobot probes (NASA)

Artist’s concept of the cryobot and hydrobot probes (NASA)

Because of this, scientists have been anxious to get a closer look at the intriguing moon.  Various proposals have been put forward for missions directly to the moon. The Pioneer and Voyager spacecraft took pictures of it as they flew through the solar system and subsequent missions also took readings and photos—but there has been no Europa-centric mission to really find out about the oceans below the cracked ice.  One (amazing!) proposal was to send a nuclear powered melt probe to melt through the ice and sink to the bottom of the ocean, whereupon a mini-sub probe would emerge and explore the extraterrestrial ocean!  That plan was shelved because it was too expensive (and nobody could figure out how to sterilize the probe).  The proposed Europa Clipper mission is more modest but still quite amazing. Here’s how the Jet Propulsion Laboratory describes it:

The Europa Clipper mission would send a highly capable, radiation-tolerant spacecraft into a long, looping orbit around Jupiter to perform repeated close flybys of Europa.

The possible payload of science instruments under consideration includes radar to penetrate the frozen crust and determine the thickness of the ice shell, an infrared spectrometer to investigate the composition of Europa’s surface materials, a topographic camera for high-resolution imaging of surface features, and an ion and neutral mass spectrometer to analyze the moon’s trace atmosphere during flybys…The nominal Europa Clipper mission would perform 32 flybys of Europa at altitudes varying from 2700 km to 25 km.

That sounds amazing!  Join me in lifting a glass to Yuri Gagarin and also join me in hoping that our moribund government funds this far-sighted mission to what might be life’s other home in the solar system!

Yuri Gagarin--the first human to go to space

Yuri Gagarin–the first human to go to space

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