Everything You Need to Know About Cassini’s Final Enceladus Flyby

An authoritative chapter in our exploration of the solar system concludes tomorrow , when NASA ’s Cassini probe have its final close flyby ofEnceladus , an frigid synodic month orbiting Saturn with aglobal oceanbeneath its surface . Cassini has alreadycollected samplesto determine if Enceladus ’ brine might be inhabitable — but we still have some unfinished commercial enterprise with this petite Saturnian artificial satellite .

On December 19th at 9:49 a.m. PST ( 12:49 p.m. EST ) , Cassini will zip within 3,106 nautical mile ( 4,999 klick ) of Enceladus ’ south polar terrain , wherecurtains of ocean spraysurge into space at a rip - roaring 800 miles per hour , feeding Saturn ’s atomic number 99 - hoop . It ’ll be the 22nd time Cassini has flown by Enceladus since entering Saturn ’s orbit in 2004 . While it is n’t our closest bye by a long - blastoff — we sailed within 16 international mile of the moon ’s surface in 2008 , and tookanother cryptical divethorough its south diametric plume this past October — tomorrow ’s flyby distance was cautiously select to do a vital enquiry : how much heat is emanate from Enceladus ’ ocean ?

“ valuate the warmth from the south perch is a very important restraint on how much high temperature there is in the inside , ” Linda Spilker , Cassini task scientist at NASA ’s Jet Propulsion Laboratory , distinguish Gizmodo in a earpiece interview . And fix how hot the synodic month ’s core is will aid astrobiologists figure out whether Enceladus really can support sprightliness .

A mere 301 statute mile ( 484 km ) in diam , Enceladus is a complex , geologically dynamic moon with thick outer Methedrine case and a jolting core kept warm through the gravitational tug of Saturn and another moon , Dione . sandwich between frosty crust and jolting Interior Department is a world - spanning ocean that ’s become one of the most interesting places to trace for lifespan beyond Earth .

Best of all , cracks in the moonshine ’s south pole shabu mainsheet are shoot jets of frozen saltwater into blank space — innocent samples for any curious outer space probes who befall to be in the region . In October , Cassini train a deep dip through that south pole plume , passing within 30 miles ( 48 km ) of Enceladus ’ surface to collect a droplet of alien ocean weewee .

Scientists are hard at work analyzing the October sample ’s chemical science , and desire to foretell their findings within the coming months . “ We ’re really look forward to completing the aggregated spec analysis of molecular hydrogen , ” Spilker enounce . Molecular hydrogen , or H2 , is a simple push source that feed microbial communities living in cryptic ocean vents on Earth today , and if we feel it on Enceladus , that ’d be a big deal .

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Conceptual model of Enceladus ’ south rod . A hot , rocky heart maintains a liquid sea level beneath the moon ’s thick outer ice sheet . Cracks in that ice-skating rink tabloid sacking pressurized material from the inside . range of a function Credit : NASA / JPL - Caltech

Tomorrow ’s flyby will add another piece to the habitability puzzle . Life does n’t just need a chemic energy source , it needs heat . “ We now have evidence of nanosilica grain that could only be generated in very blistering H2O , leading us to discuss hydrothermal vent , ” Spilker say .

And of all the piazza to wait for hydrothermal natural action , the south pole is most promising . For one , it ’s currently in the darkness of a years - long Saturnian wintertime . Without the Sun ’s ray striking Enceladus ’ control surface , scientist will have an easier clock time detect heat energy from the Department of the Interior . What ’s more , late modeling piece of work indicate that the encrustation over the south pole is peculiarly thin . “ possibly that thin crust means we have a warmer region in the Dixie , ” Spilker said .

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By angling its Composite Infrared Spectrometer ( CIRS ) instrument at the south perch during tomorrow ’s flyby , Cassini should be able to fabricate a good pictorial matter of heat flow rate across the moon ’s splintered surface . “ The length of this flyby is in the sweet spot for us to map out the heat coming from within Enceladus — not too close , and not too far away , ” said Mike Flasar , CIRS squad lead at NASA ’s Goddard Space Flight Center in astatement . “ It allows us to map a dear portion of the challenging south polar region at good resolving . ”

With the data point Cassini collects tomorrow , and all the other skill it ’s accomplished this retiring year , we can wait to have a much better image of Enceladus ’ habitableness aspect in the near hereafter . One way or another , our find about this little frappe moon have been an incredible , and unexpected , outcome of Cassini ’s decade - long exploration of Saturn ’s band .

Plume jet plane rise from Enceladus ’ south pole in this Cassini double taken in 2014 . In the foreground , you could see the textured , volcanic crater - free terrain that ’s characteristic of the south polar region . simulacrum Credit : Cassini Imaging Team / SSL / JPL / NASA / ESA

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“ What ’s amazing is when we first planned our commission , we had three flybys of Enceladus , ” Spilker said . “ After the first , when we detected the plume , we basically reshaped the mission around getting as many as we could . ”

“ I remember over the course of the Cassini commission , we ’ve really changed our paradigm of where we might look for life , ” she continue . “ It ’s not just about finding that zone for fluent weewee on its surface — but determine the correct weather for a liquid ocean , a source of free energy , middleman with a rocky core . ”

Who know — peradventure first contact wo n’t involve an rocky planet in the habitable zone of a sun - like star , but a eldritch , foreign moon , nuzzle in the shadows of a monstrous gas giant in the frozen reaches of space .

Photo: Jae C. Hong