Cassini space­craft bids farewell

Edmonton Journal - - FRONT PAGE - Colby Cosh

Af­ter 18 years of ob­serv­ing the so­lar sys­tem, NASA’s Cassini probe has been plunged sui­ci­dally into the gassy depths of Saturn. This led to a sur­pris­ing out­pour­ing of emo­tion among nerds who fol­low space ex­plo­ration. Many peo­ple have spo­ken of be­ing moved to tears by Cassini’s un­usual fate.

Cassini fol­lowed a com­plex path through the Satur­nine neigh­bour­hood, pho­tograph­ing satel­lites long­known and just-dis­cov­ered. The low-machismo, 21stcen­tury NASA rec­og­nizes a re­mote pos­si­bil­ity of space probes be­com­ing “con­tam­i­nated” by mi­cro-or­gan­isms dur­ing fly­bys of bod­ies that might be bi­o­log­i­cally vi­able. Ba­si­cally, the agency did not want to leave any risk of giv­ing Ence­ladus her­pes from Ti­tan, or vice versa, or what have you.

This led to a de­ci­sion to steer Cassini de­lib­er­ately into the face of Saturn, whose great mass will en­sure that the com­po­nents of the probe — which in­clude about 30 kilo­grams of plu­to­nium — are in­cin­er­ated, evap­o­rated, and im­mersed in the planet’s core like a drop in the ocean. Cassini was not launched with enough fuel to leave the grav­i­ta­tional neigh­bour­hood of Saturn when it was fin­ished with its work. Send­ing it into a so­lar or­bit — like Snoopy, the as­cent stage of the Apollo 10 lu­nar mod­ule, which am­a­teur as­tronomers are hunt­ing for al­most 50 years af­ter it was aban­doned — was not an op­tion.

Psy­chol­o­gists know that if you show hu­mans a short film of coloured geo­met­ric shapes mov­ing about ran­domly, they will nat­u­rally in­vent a story about it. “Oh, the tri­an­gle is in love with the square, and the hexagon is jeal­ous.” Our ten­dency to an­thro­po­mor­phize is nat­u­rally much stronger — and is ar­guably ap­pro­pri­ate! — when the ob­ject is an ac­tual ex­ten­sion of mankind, tak­ing sci­en­tific mea­sure­ments. We are pretty sure that a ma­chine doesn’t have feel­ings about reach­ing a state of ex­haus­tion, af­ter ful­fill­ing its pur­pose loy­ally, and col­lid­ing with a planet. But the ma­chine is a rep­re­sen­ta­tion of us.

It is, among other things, a piece of art. Any­one who bought the Lego Saturn V kit this sum­mer knows that. If hu­man­ity de­stroys it­self, and its space­far­ing ob­jects (per­haps even Snoopy) are found by ex­trater­res­trial cul­tures, they will be able to in­fer an in­cred­i­ble amount about us — and not just be­cause some of those probes were ex­plic­itly de­signed to com­mu­ni­cate facts about hu­man­ity. Hu­mans ad­dress the very far fu­ture in a col­lec­tive way, largely through engi­neer­ing and de­sign: lan­guage can only reach so far.

So we mourn, as we would mourn if it were an­nounced that Géri­cault’s Raft of the Me­dusa, or the Apollo Belvedere, were to be cer­e­mo­ni­ally de­stroyed on a par­tic­u­lar date. But in the case of Cassini there is also the pro­longed mis­sion, the one-way na­ture of its trip, and the novel cir­cum­stances. Other NASA “flag­ship” craft were dis­abled quickly and mer­ci­fully by hos­tile plan­e­tary en­vi­ron­ments — like the Vik­ing landers of the '70s — or are leav­ing the so­lar sys­tem with a de­cent chance of out­last­ing the hu­man species — like Voy­ager 1 and 2. Cassini was sac­ri­ficed, asked to die if you like, for an eth­i­cal prin­ci­ple. Nay, an en­vi­ron­men­tal one. What could be more 2017 than that?

To have died pho­tograph­ing Saturn — un­cov­er­ing bizarre mys­ter­ies about its sur­face, its or­bital com­pan­ions, and its rings — is a noble demise in­deed. Saturn has a spe­cial place in our species’ his­tory, and not just be­cause its satel­lites seem, by some chance, to be more in­ter­est­ing and weird over­all than those of Jupiter and other giants.

It’s the rings. We take them for granted so much that if you ask a child to draw a planet he will prob­a­bly pro­duce a ringed, Saturn-like ob­ject. But the rings were un­known to an­tiq­uity, and their dis­cern­ment in the early era of tele­scopes was among the key events that made sci­en­tific dis­cov­ery an in­tel­lec­tu­ally at­trac­tive fron­tier. Tele­scopes re­vealed the heav­ens to be full of un­sus­pected phe­nom­ena, but most of them could be un­der­stood with ref­er­ence to Earth or to astro­nom­i­cal chron­i­cles. When Galileo found moun­tain-like struc­tures on the Moon, the im­pli­ca­tions for tra­di­tional phi­los­o­phy were dread­ful. But in the end, moun­tains are not fun­da­men­tally dif­fi­cult for the mind to ab­sorb, given time.

But there was no nat­u­ral ana­logue or fa­mil­iar way for in­ter­pret­ing the rings of Saturn: as tele­scopes be­came more pow­er­ful they only be­came more un­fath­omable and beau­ti­ful. Why flat rings, with the in­ner edge fac­ing the planet? Why the ap­par­ent gaps be­tween rings?

It re­quired James Clerk Maxwell — who ap­peared more than 250 years af­ter Galileo, and who had the kind of mind that shows up about that of­ten — to work out the­o­ret­i­cally that the rings could not be con­tin­u­ous solid struc­tures. “When we con­tem­plate the Rings from a purely sci­en­tific point of view, they be­come the most re­mark­able bod­ies in the heav­ens,” Maxwell wrote in 1859. “When we have ac­tu­ally seen that great arch swung over the equa­tor of the planet with­out any vis­i­ble con­nec­tion, we can­not bring our minds to rest.” Surely th­ese last six words still ap­ply, de­spite Maxwell’s own work of math­e­mat­i­cal de­mythol­o­giza­tion: per­haps Cassini should have been named for him in­stead?


Cassini Space­craft Op­er­a­tions Team Man­ager Julie Web­ster re­acts af­ter con­fir­ma­tion of Cassini’s demise.

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