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Hi everyone! Sorry that the posts were thin on the ground last week. The head druid told me that I needed to honor the solstice by taking some time to reflect on the meaning of things [citation needed]. Anyway…since I didn’t blog last week, I failed to post these astonishing pictures of Jupiter’s giant moon Ganymede, which were photographed by NASA’s Juno spacecraft as it slaloms though the Jovian system.

Ganymede as imaged by NASA probe Juno

Although its lack of atmosphere and pockmarked plains of dust make it superficially resemble Earth’s moon, Gannymede is a very strange and unique heavenly object Of the 200 known moons in the solar system, it is the largest. Indeed it is 26% larger than the planet Mercury by volume (although it is only 45% as massive as the metalliferous first planet). Ganymede has a diameter of 5,268 km (3,273 mi), so each pixel in the full size image of the Jovian moon is equal to a kilometer (although you may want to check out the NASA image to really savor that scale–since WordPress has a noteworthy penchant for scrunching up my images in incomprehensible ways).

A photo of the dark side of Ganymede taken by Juno’s incredibly light sensitive navigational camera

Alone among moons in the solar system, Ganymede has a magnetic field, albeit a rather meager one compared to Earth or Jupiter. Scientists surmise that the magnetic field is created by convection within the liquid iron core of the moon–although answers are not forthcoming as to why it has a liquid iron core to begin with (these planetary cores seem to be the real determinant of what planets are like, but I feel like we know precious little about them). Thanks to its size (and maybe thanks also to its magnetosphere), Ganymede has a very thin oxygen atmosphere…but that just creates more question, since elemental Oxygen has a tendency to instantly bond to all sorts of other elements. The 20 percent or so of oxygen in Earth’s atmosphere did not become a mainstay until about 1.5 billion years ago when photosynthesizing bacteria finally became so prevalent that they overcame the constant loss of atmospheric oxygen thanks to oxidation. Hopefully Juno’s survey will help us solve atmospheric mysteries on Ganymede. Ganymede is also believed to have a vast subsurface ocean of icy water tucked away somewehere beneath its surface. Astronomers have reasonably speculated that this Ganymede underworld ocean may contain more water than all of Earth’s oceans combined!

This is the largest version of this interesting cross section which I could find

Ganymede is a Galilean moon–which means it was discovered by the great scientist, and is one of the first objects ever discovered to orbiting another planet (I still sometimes imagine the thrill Galileo must have felt when he realized what he was seeing). I wonder what surprises Juno will send back for us!


In 2016 the Japanese Space Agency launched a quarter-of-a-billion dollar x-ray observatory named Hitomi into Earth orbit.  The craft’s mission was to study extremely energetic processes at the far reaches of the universe.  It was hoped that the data Hitomi provided would allow astronomers to understand how the large scale structures of the universe came into being (how galactic superclusters form, for example).  The satellite initially worked perfectly, but, within 38 Earth days, the spacecraft was lost: a failure of attitude control sent it into an uncontrolled spin which caused critical structural elements to break apart.


The full story of what destroyed Hitomi is perhaps of greater immediate interest to living beings on Earth than how the meta-structures the universe came into being.  When everything went wrong for the ill-fated space observatory it was passing over the southern part of the Atlantic ocean.  For spacefarers, this region of the Van Allen Belt is analogous to what the Bermuda Triangle or the Namib Skeleton Coast is for sailors: it is a haunted and dangerous stretch of space.  Astronauts who travel through it report strange phantasmagorical dots and streaks in their vision, even when they close their eyes.   The Hubble Space Telescope does not make observations when it passes over the south Atlantic.  Controllers turn off its delicate systems.  The region is known to the world’s space agencies as “the South Atlantic Anomaly.”  Hitomi was not its first victim–it is surmised that the South Atlantic Anomaly was responsible for the failures of the Globalstar network satellites way back in aught seven.


The existence of the South Atlantic Anomaly was known long before that.  It was discovered in 1958 by Explorer 1, the first American satellite (which was equipped with a Geiger counter).  Perhaps the Soviets would have discovered the anomaly by means of Sputnik, but, because the Cold War made  scientific cooperation difficult, Australia did not hand over Sputnik data to the Soviets until later.  Suffice to say, the South Atlantic Anomaly is an anomaly in the Van Allen Belt, the torus-shaped field of charged particles which are held in place by the magnetic field of Earth.  Earth’s magnetosphere is important. Billions of years ago, Mars and Venus seem to have been exceedingly Earthlike, with water oceans and convivial atmospheres.  But neither Mars nor Venus has a magnetosphere and their oceans have perished and their atmospheres have changed into monstrous things….although we don’t know exactly what happened on either of our neighboring planets (and the present priorities here on Earth are to make Michel Dell and Howard Schultz as rich as possible at everyone else’s expense, not, you know, to understand what planetary scale forces could make worlds uninhabitable).


Um, at any rate, the magnetic field of Earth is created by the mysterious processes beneath our feet at the center of the planet.  The Earth’s inner core is believed to have two layers: an outer core of molten iron and heavy metals and an inner core of solid iron nickel alloy.  The inner core is about 70% of the volume of the moon and it is nearly as hot as the surface of the sun with an estimated temperature of (5,430 °C) or 9806 °F, but the molten outer core is only as hot as the surface of an orange star (2,730–4,230 °C; 4,940–7,640 °F).  Within the outer core, eddy currents form in the superheated metal. The complex relationship between these currents, the spinning planet, and the two core layers creates a geodynamo which produces the planet’s magnetosphere which in turn captures the particles which make up the Van Allen Belts.  However, the eddy currents cause the magnetic poles to invert every few hundred thousand years (we are currently overdue for such a flip).  The South Atlantic Anomaly is a manifestation of the “weather” in the molten outer core of Earth–a prelude to the magnetic polar flip.  First generation spacecraft used solid state components and had big ungainly robust circuitry.  Additionally they were hardened against radiation.  Some of today’s craft make use of delicate & elaborate microcircuitry which is prone to failure when struck by esoteric radiation particles.  This is how what happens far beneath our feet influences what happens to craft in outer space.

Ye Olde Ferrebeekeeper Archives

August 2021