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One of the smaller moons in the Saturn system is Daphnis, a little 8 km (5 mile) irregular satellite which orbits the gas giant within the outer rings of the planet (although I guess really the famous rings themselves are composed of innumerable “moonlets”). Daphnis, which has the irregular shape of a potato, orbits Saturn in a 42-kilometer (26 mile) wide belt in the rings—the Keeler Gap. The moon is responsible for clearing this narrow track, and it is felt that by studying this interaction we may learn about accretion and the enigmatic happenings of the early solar system (when more things looked like Saturn). Here is a picture from NASA’s Cassini probe which was released yesterday which shows little Daphnis producing waves in the Keeler belt. What a remarkable image! I need to post more Cassini pictures here. They fill the heart with wonder and give us a chance to get off-planet for a little breather.
Artist’s conception of MESSENGER above Mercury (NASA)
On Thursday, humankind is deliberately crashing a spaceship into another planet! We could easily be the evil aliens in someone else’s space drama. Well, at least we could be, if there were any remote chance that Mercury, the intended target of our bombardment, were a possible haven for life. And bombardment is not really the right word: what is actually scheduled is the seemly & rational conclusion to NASA’s MESSENGER mission, a highly successful exploration of the solar system’s mysterious innermost world. The mission has been ongoing for more than a decade (a decade of our Earth time—or nearly 40 Mercury years).
A portrait of Mercury from MESSENGER
The 485-kilogram (1,069 pound) MESSENGER spacecraft was launched from Cape Canaveral in August 2004. The space probe has an awkward and contrived government acronym, which is why I keep talking about it in all caps—I’m not shouting (although planetary exploration does make me very excited). The craft took some amazing pictures of Venus (a planet which always calls to me) on its way to Mercury. Then MESSENGER flew by the small planet multiple times before entering orbit on March 18, 2011 (the first human spacecraft to do so). Since then MESSENGER has extensively scanned and mapped the surface of Mercury—a planet which is surprisingly elusive to astronomers because of its proximity to the sun. The mission revealed some surprising results which are leading to big new questions.
False Color Maps of Mercury (NASA)
Mercury has a small diameter—it is actually smaller in area than some of the moons of Saturn and Jupiter—but it has substantial mass because much of it is made of heavy metals. The face of the small world is thought to be ancient: scientists speculated that its bland pitted face might date back to the formation of the solar system, but it seems that Mercury does harbor secrets.
The mission featured a big surprise. Messenger found surface water in the form of ice frozen inside the polar craters of Mercury. This was not really a shock—astronomers have suspected that ice was present due to radio-telescope readings. What was surprising was that the ice was coated with tarlike black goo. My poor roommate (who is always wandering the house pointing at films, stains, and accretions in horror) would not be surprised by a black coating on anything, however scientists were taken aback because Mercury was not thought to have any “volatile” compounds. According to the current models of planetary formation, elements like chlorine, sulfur, potassium and sodium should have boiled away during the cataclysmic high-temperature formation of Mercury…yet there they are, like the scum in my kitchen. The scientific data from MESSENGER is likely to force a rethink of planetary formation (although frankly, considering all of the weird exoplanets that are being discovered, scientists probably need to refine their theories about planetary accretion anyway). The mission also measured subtle planetary flux which should give us a better sense of Mercury’s composition and internal workings.
The yellow patches show areas where water ice is believed to exist. (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
All good things must end, however, and MESSENGER has run out of fuel for maneuvering. Mission controllers have opted for an operatic exit and they are smashing the craft into the planet’s surface at 8,750 miles per hour (nearly four kilometers per second). This should create an 18 meter (50 foot) wide crater. Future scientists will have a known fresh disturbance to use as a benchmark for assessing the ancient craters of Mercury. Perhaps the plume will reveal some interesting secrets as well.
MESSENGER Crashes into Mercury (Wayne Ferrebee, 2015, ink and colored pencil)
Unfortunately, it will be a while before we see the results of our destructive acts. The site of impact is hidden from Earth, and we have no other spacecraft in any proximity to Mercury. A European and Japanese collaboration called BepiColombo is scheduled to launch from Earth in 2017 and arrive at Mercury in 2024. Perhaps we will have new questions for whatever answers MESSENGER is about to divulge in its unseen but spectacular final act!
Update: Through some grotesque oversight, NASA failed to portray MESSENGER’s final moments through the magic of art. I took the liberty of providing my own interpretation above. NASA did not return my questions about whether the spacecraft will wail in a plaintive manner as it impacts the surface–so I am forced to assume that it will. Did I mention that Mercury has no atmosphere? You should probably ignore that…
A Satellite Photo of Modern Gotland (reference needed)
Tonight we travel once again to the ancient and mysterious island of Gotland, the largest island in the Baltic Sea. Ferrebeekeeper has already visited Gotland as the (possible) land of origin of the enigmatic Goths and as a place which is absolutely covered in beautiful medieval churches, but in this post we push further back in Gotland’s mysterious past to contemplate an ancient sculpture. The Smiss stone (Smisstenen) also known as the Ormhäxan (which means snake-witch stone) is a carved picture stone shaped like a huge piece of toast which shows three zoomorphic serpent creatures entwined in a sort of triskelion pattern. Beneath the creatures, an apparently female human figure with legs spread holds aloft two writing serpents.
The Snake Witch Stone (unknown sculptor, ca. 400-600 AD)
As you can see, the actual stone is even more amazing than the already astonishing description (I get the sense that the red paint was added by a later hand, but, alas, I am unable to find an explanation for the brightness of the color). The stone was discovered in an ancient cemetery in Smiss in the När parish. Scholars and archaeologists have dated the stone’s construction back to 400–600 AD, the late Vendel era when great migrations changed the Germanic world–but all of the experts disagree concerning the stone’s meaning and purpose.
The “Hall of Picture Stones” at the Gotland Museum in Visby
Some historians (the reputable ones) believe the stone shows a pagan goddess or sorceress…perhaps Hyrrokkin (a snake wielding giantess) or maybe some unknown deity left out of the Eddas. Other thinkers have speculated that the stone depicts a Minoan snake goddess (although who knows how she got to Gotland from Crete), Odin making love (?), or Daniel in the lion’s den (???). I am usually good at determining how people perceive visual art, but I confess to being perplexed by these latter interpretations. The lovely knots and sinuous serpentine animals look very much like Celtic, Pictish, and Mercian designs to me–which would comfortably place the stone’s figures within the cryptic North Sea pantheon of late antiquity. Unfortunately, there is little and less which is certain about the faith and folktales of that time. We are left with a haunting beautiful sacred stone, but like so many of the most compelling statues from humanity’s history, the real meaning slips from our grasp and we are left with haunting conjecture.
The Snake-Witch Stone surrounded by other ancient picture stones from Gotland
ferrebeekeeper 