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To celebrate the season, here is a special Christmastime Sunday space post! Discovered in 1948 Comet 46P/Wirtanen orbits the sun every 5.4 Earth years.   The comet’s apoapsis (the point of its orbit farthest from the Sun) is out in the vicinity of Jupiter’s orbit, but the closest point in its orbit brings it to Earth’s orbit.  Unfortunately, because of the dance of the planets it only in relative proximity to Earth every 11 years, and even then, it is generally barely visible except to hardened astronomers.  The comet is also known as the Christmas comet because its periapsis (when it is closest to the sun—and thus, sometimes to Earth) is in December and because the comet has a distinct viridian tinge!

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This year, 46P/Wirtanen’s periapsis is unusually close to Earth.  Tonight, the comet will be a mere 11.4 million kilometers (7.1 million miles) from Earth.  That sounds like a fairly large distance but it is quite close, astronomically speaking:  only 10 comets have come in such near proximity to our home planet in the past 70 years!  Filled with excitement, I glanced out my window only to see that it is raining in Brooklyn and the sky is filled with clouds.  But don’t worry, the comet will nearly as visible for another week.   If you have an internet connection (and if you don’t, how are you reading this?) you can go to this link and find the comet in the sky from your location (that link is an amazing resource, so maybe hold onto it).

 

So why is this comet such a delightful color?  Comet 46P/Wirtanen is mostly melted—it consists of a solid kernel approximately a kilometer in diameter trailing a cloud of gases hundreds of thousands of kilometers long.  The majority of these gases reflect light in green wavelengths. Additionally, the comet is hyperactive—which, in this case, does not mean that overpaid physicians will prescribe it unnecessary medications so it can learn rote facts. In an astronomical context, hyperactive bodies are emitting more water than expected.

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Unless you are avidly examining the comet with a gas spectrograph, its color is likely to be a source of awe and reflection. Does the comet’s color reflect the seasonal green of Yuletide or is it an ironic reprimand for the envy and jealously which grip all of human society?  Is it the eye of a great sky panther or a kindly celestial sea turtle (hint: actually more of a ball of gas with an icy nucleus).  Whatever your conclusions, I hope you enjoy this close-up view of “the Christmas Comet” before it zips back towards Jupiter’s orbit. Season’s greetings to all of my readers.  I will try to find some special posts for this solstice week, before we all take a much-needed Christmas break.

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Ferrebeekeeper has a great love of space-themed art. Yet the beginnings of western art as we know it today were not about space, but instead about religion. Christian iconography dominated: the heavens were not the literal heavens but instead the supernatural …uh…actually, never mind.  This is a fresco by Giotto from the Arena Chapel.  Giotto single-handedly reshaped the classical and medieval precepts of art (and remade our notion of visual culture).  The Arena Chapel is his masterwork–a project where Byzantine opulence, Christian devotion, linear perspective, and new Italian realism converged to give birth to the European artistic tradition (although, to be sure, Western art had many grandparents…and lots of weird uncles that were an influence before–and after–Giotto).

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Here is the birth of art…showing the birth of Christ, and there, proudly in the center of the composition, right above Jesus and the adoring Magi, is a comet which would not look out of place in nineteen-sixties space art.  The flying ball of fire points directly into the manger where the astonished kings (and their even more astonished camels pay homage to the new-born savior who has appeared as a refugee child).  It is a beautiful picture–and an unexpected appearance of outer space imagery right at the dawn of the 14th century as art began to manifest itself in familiar fashion.

 

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Last week I meant to include an elegiac post to Rosetta, an astonishing space mission, which stretched out over a dozen years and logged 4.9 billion miles of travel.  Rosetta was launched way back in 2004.  It was originally supposed to rendezvous with comet 46P/Wirtanen in 2011, but problems with the launch in Guyana caused the probe to miss the launch window for the primary mission.  The ESA changed the mission parameters so that the spacecraft ended up exploring Comet 67P/Churyumov–Gerasimenko instead (this second comet was functionally the same as the first—except for a much more difficult-to-say name). During its journey to the comet, Rosetta also flew by Mars and two asteroids.  After flying by Mars in February of 2007, the craft flew by Earth in November of 2007.  It caused a miniature panic when astronomers of the Catalina sky survey spotted it and misidentified it as a 20 meter near-Earth asteroid on a possible collision path with Earth!

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The spacecraft arrived at  Comet 67P/Churyumov–Gerasimenko in August of 2014 and the most famous…and infamous…part of the mission took place in November of that same year, when Rosetta launched the Philae lander to harpoon itself to the comet.  Although Philae (which was named after a Rosetta-like obelisk with the same text in Greek and Egyptian) succeeded in landing and not bouncing off into the void, sadly the little lander came down in a miserable crevasse.  Scientists intimately studied pictures of the comet (from Rosetta) until they found the lander in the icy chaos.  It was a pretty ghastly scene which reminded me of my sock drawer (if it were dropped from space onto Tungnafellsjökull glacier).

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(See it there at bottom right?)

Rosetta’s long and mostly successful mission came to an end last Friday in a truly operatic fashion. Mission controllers chose to use the last vestiges of power to smash the orbiter into the comet! Well, although I am saying “smashed” what actually happened was more like a grandmother walking into a snowbank.  The lander was lowered onto the comet at about one mile per hour. Except, despite the fact that Rosetta traveled more than 5 billion miles (“uphill both ways”) it was not designed for landing and its last communication was a photo just above the comet surface.  RIP Rosetta, you were one good probe!

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Congratulations to the European Space Agency for successfully landing the robot probe “Philae” on comet 67P!  The lander, which is about the size of a washing machine, made a soft touch-down on the comet at 3:30 a.m. Brooklyn time. The comet itself has a diameter of four kilometers (2.5 miles) meaning it is approximately as wide as the Verrazano Bridge is long.  To bring such objects together as they hurtle at ridiculous speeds through the vast darkness of space is a tremendous feat of engineering.  Ferrebeekeeper described the long and complex journey of Philae’s mothership, Rosetta, in this previous post.

An artist's mock-up of how the probe might look on the comet's surface (the underdressed astrophysicist is added for scale and is presumably not there)

An artist’s mock-up of how the probe might look on the comet’s surface (the underdressed astrophysicist is added for scale and is presumably not there)

Philae is equipped with space harpoons which are designed to fire into the comet’s surface–thus securing the craft to the flying iceball with lamprey-like tenacity. Actually, a lamprey might be the wrong comparison: the lander looks astonishingly like a bacteriophage (a fact which I think is exceedingly strange and funny). At any rate, it is presently unclear whether the landing harpoons correctly deployed into the comet’s surface.  We’ll know more in coming days.

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Indeed, in coming days we should be finding out lots of things regarding the comet.  The lander has a small drill which is meant to mine 20 cm (8 inches) into the icy substrate.  The sophisticated machine is also equipped with devices to analyze the core sample, gas analyzers to identify any complex organic compounds, and instruments to measure the comet’s magnetic field.   Scientists will be keeping a close eye on the comet to see what effect the solar wind has on it as 67P sweeps in close to the sun in coming months.

ayiomamitis_mcnaught2009r1November 13th UPDATE:  It seems the plucky lander had a more adventuresome landing than yesterday’s rosy headlines may have indicated.  Apparently Philae landed not once, but multiple times as it bounced down a cliff and fetched up (on two of three legs) in a shadow.  Mission controllers are contemplating whether to fire the landing harpoons, but are concerned that the resultant explosion could send Philae careening off the comet into the outer dark.  Anyone who has thrown a washing machine down an ice cliff in low gravity will surely sympathize with their predicament…

Artist's Impression of the Rosetta Mission

Artist’s Impression of the Rosetta Mission

Devoted readers have most likely been fretting and worrying about what happened to the ESA spacecraft Rosetta which Ferrebeekeeper wrote about back in January. In that article, I wrote that the spacecraft was meant to rendezvous with comet 67P/Churyumov-Gerasimenko in May—but that never happened. What’s the story? Did something go wrong?

Fortunately today’s space news is good: after a ten-year chase which has spanned back and forth across the solar system, the little spacecraft finally entered orbit around comet 67P/Churyumov-Gerasimenko. The comet and the spacecraft are currently about 405 million kilometers from Earth (which puts them between the orbits of Mars and Jupiter). It turns out that May was actually the date that pre-orbit maneuvers were first commenced—it has taken three months to bring the spacecraft into proper position for orbital insertion. I’m sorry I got your hopes up prematurely, but this is a good illustration of how delicately operations must be conducted when dealing with objects going 55,000 kilometers per hour (34,000 miles per hour).

 

 An August 3 photograph of Comet 67P/Churyumov-Gerasimenko taken by space probe Rosettas OSIRIS from a distance of 285 km (Photo: ESA/Rosetta)


An August 3 photograph of Comet 67P/Churyumov-Gerasimenko taken by space probe Rosettas OSIRIS from a distance of 285 km (Photo: ESA/Rosetta)

The probe has already taken some amazing pictures of the comet which has two distinct masses joined together by a narrow neck—rather like a rubber duck. We can expect even more stunning pictures of the weird icy surface of the comet as the probe edges nearer to the big dirty snowball over the next few months. The real excitement will(probably) take place in November which is when the probe Philae is tentatively scheduled to launch. Philae is a comet lander which looks curiously like a bacteriophage. It will shoot harpoons into the comet and then fasten down onto the surface to study the origins of the solar system! Get ready for a thrilling fall!

Artist's impression of the Philae landing craft, anchored by harpoons and drills to the comet's surface

Artist’s impression of the Philae landing craft, anchored by harpoons and drills to the comet’s surface

An Artist's Rendering of Rosetta Approaching the Comet (ESA)

An Artist’s Rendering of Rosetta Approaching the Comet (ESA)

Today a winter snow storm has transformed Brooklyn into a huge ice ball–at least metaphorically speaking–but the weather will surely improve.  Home will not be a ball of ice forever.  The same cannot be said for the Philae robotic lander which is currently aboard the European Space Agency’s Rosetta spacecraft (which, in turn, is currently in outer space returning to the inner solar system after 31 months in the dark cold outer solar system).  If all goes according to plan, the Rosetta spacecraft will enter a slow orbit around comet 67P/Churyumov–Gerasimenko in May of 2014.  Once the space probe is in orbit around the comet, it will (eventually) fire the Philae probe onto the comet itself.  Philae is equipped with space harpoons to latch on to the comet’s surface and cling to the hurtling slushball.  Once there, the little robot lander will assay the comet with its drill and ten onboard sensors in order to learn more about the birth of the solar system–when the comet (probably) came into existence.

An artist's rendering of Philae Making a Soft Landing on the Comet this coming November (ESA)

An artist’s rendering of Philae Making a Soft Landing on the Comet this coming November (ESA)

There are many remarkable aspects to this astonishing mission (which launched a decade ago), but one of the most harrowing periods just ended.  Because the spacecraft is powered by solar panels, it did not receive sufficient energy to operate during its long sojourn through the outer solar system.  For two-and-a-half years, the mission controllers in Darmstadt, Germany have been in suspense waiting to see if Rosetta had survived being all but shut down (because of a last-minute mission rewrite, the craft was not designed for any such suspended animation).  Yesterday the spaceship woke up and radioed back to Earth!  The mission is on!  I can hardly wait for May (for multiple reasons).

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Lake Lonar

Approximately 650,000 years ago, an outer space object–either a comet or a meteor– struck the Deccan plateau (an immense basaltic flow on the Indian subcontinent dating back to the twilight of the dinosaurs).   The resultant crater in Maharashtra is now the sight of a very interesting saltwater lake, Lake Lonar.  The geology of this region has been intensely studied because the great basaltic mass of the Deccan traps is thought to mirror the igneous geology of Mars and the moon.

Lake Lonar proper is nearly circular with a diameter of 1.2 kilometers.  The greater meteor crater rim is about 1.8 kilometers and the crater measures 500 feet deep in the deepest part of the lake.  In addition to the obvious features of an extraterrestrial impact (um, a large round hole), the region features many other unique geological signs of such an event. Maskelynite, a material only naturally known from meteorites and meteorite impact areas, is found around Lake Lonar, as are silicate minerals with planar deformation features (distinctive high-stress crystalline irregularities which have only been found in silicates from meteorites, craters, and nuclear test areas).  The deeper geology of the lake region displays shatter cones in the bedrock, and extreme deformation of the basalt layers. Finally the surrounding region has been spattered with a non-volcanic ejecta blanket. 

Lake Lonar: pink-beige indicates bare ground, blue and off-white indicate human-made structures, dark blue indicates water, green indicates vegetation, and dull purple indicates fallow fields (NASA: Terra Satellite)

By measuring the accumulated radiation in certain crystals (aka thermoluminescence) scientists had assigned an approximate age of 50,000 years to the crater. However a 2010 study of isotopic Argon in Lonar impact melt rock estimated the true time of impact to be 650,000 years ago (give or take 80,000 years).  The compelling 2010 study drily notes “The discrepancy between the thermoluminescence age and the new isotopic 40/Ar/39Ar age is flagrant.”

Daitya Sudan, a temple to Vishnu

Several abandoned temples and archaeological sights are also located around the lake.  For example, the beautiful Daitya Sudan Temple to Vishnu was built by the Chalukya Dynasty which ruled of Maharashtra from the 6th and 12th centuries.  The local town, Lonar, still has an active temple to Vishnu, the great protector of the universe who features prominently in local legend.  According to the Skanda Purana (a canon of Hindu scripture universally cited when a story is doubtful or can not be found elsewhere) a great underworld demon, Lonasur, lived where Lake Lonar is today.  From time to time the demon would venture from his subterranean abode to torment the countryside and challenge the gods. Assuming the form of an extremely beautiful young man, Vishnu…somehow convinced the demon’s sisters to divulge where the monster could be found.  The god then lifted up the countryside like a great lid and found the demon hiding in his huge circular lair. After Vishnu slew the demon, the demon’s dwelling place filled up with water made salty by the fiend’s blood.    

Although threatened by India’s ever growing sprawl, Lonar Lake is a rich wetland with abundant wildlife—particularly birds.  The jungles, fields, and lake are a birder’s paradise featuring flamingos, grebes, black-winged stilts, dabchicks, ducks, shell-ducks, shovellers, teals, herons, rollers, parakeets, hoopoes, weavers, larks, tailorbirds, magpies, robins, swallows, peacocks, coots, white-necked storks, lapwings, grey wagtails, black droungos, green bee-eaters, and tailorbirds (to name just some).

The Jungle around Lake Lonar

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