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The North Pole of Enceladus during the October 30th, 2015 Cassini Flyby (NASA/ESA/ASI)

The North Pole of Enceladus during the October 30th, 2015 Cassini Flyby (NASA/ESA/ASI)

Since 2004, the Cassini spacecraft has been in orbit around Saturn. The robot probe (a joint effort of NASA, ESA, and the Italian space agency) received the most press when it launched a flying saucer lander onto Saturn’s planet-like moon Titan, but it is still out there doing amazing work. Last week, while I was busy writing about Halloween themes, the probe made its closest pass yet to Saturn’s ice moon, Enceladus. Enceladus is only 500 kilometers in diameter and it is coated in ice, but it is of great interest to scientists because ice plumes venting from the moon’s south pole seem to indicate a large polar subsurface ocean of liquid water. Warmed above freezing by tidal flux, this ocean beneath the ice probably has a thickness of around 10 km.

View of Enceladus’ south pole geyser, backlit by Saturn

View of Enceladus’ south pole geyser, backlit by Saturn

On October 30th, Cassini flew by the icy moon at the dangerously close distance of 30 kilometers (18.6 miles). The probe was directly above the south pole of Enceladus and it collected a little flake of ice to analyze (which strikes me as incredibly amazing and beautiful). It will take some time for the ship’s devices to assay the drop of water from an alien ocean, but Cassini also snapped some photos which we already have. These are taken from point blank range above the south pole. The ocean is down there beneath the scratches and scars. What is the nature of this icy ocean? How long has it been there? Could it possibly harbor life?

c_gariepinus2

Here is a stamp which combines two of my fascinations—catfish and Namibia.  Of course Namibia is a vast and profoundly arid desert—literally a sea of sand—so perhaps you are wondering how a catfish made it onto their postage.  Well the African sharptooth catfish (Clarias gariepinus) has a habit of getting everywhere.  It lives throughout most of Africa and the Middle East and (though ill-conceived aquaculture) has established colonies in Vietnam, India, Brazil, and Indonesia.  The catfish is an air breather.  It can sip pure air without the use of its gills, so it can survive in puddles, mud wallows, and even in filthy anaerobic water.  Some of them have moved into the sewers of big cities.  Speaking of big it is arguably Africa’s largest catfish with an average adult length of 1–1.5 m (3 ft 3 inches –4 ft 11 inches).  Even in a dry land like Namibia this tough persistent catfish manages to find watercourses of one sort or another.  Like its close cousin, the walking catfish of Asia, the African sharptooth catfish is a remarkable creature.

African sharptooth catfish (C. gariepinus)

African sharptooth catfish (C. gariepinus)

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