Space-geek Satur­na­lia

As the Cassini mis­sion to Saturn ends, its lead imag­ing sci­en­tist re­calls her fa­vorite pho­to­graphs and mo­ments

Newsweek International - - NEWS - BY STAV ZIV @stavziv

A SPECTACULAR SPACE ex­plo­ration mis­sion will con­clude with a dra­matic death. The Cassini space­craft will self-de­struct by plung­ing into Saturn’s at­mos­phere, ul­ti­mately burn­ing up and dis­in­te­grat­ing. The planned mid-septem­ber dive will be the nal farewell for a nearly three­decade-long col­lab­o­ra­tion be­tween NASA, the Euro­pean Space Agency and the Ital­ian Space Agency. It’s been good while it lasted, Saturn.

The Cassini space­craft launched aboard a Ti­tan Ivb/cen­taur rocket from Cape Canaveral in Florida on Oc­to­ber 15, 1997, and spent seven years en route to its tar­get, Saturn. It en­tered or­bit around the ringed planet in 2004 for what was in­tended as a four-year mis­sion, but was twice ex­tended for a to­tal run of 13 years, or nearly 20 if you count the jour­ney there.

Cassini com­pleted the rst in-depth re­con­nais­sance of Saturn, its moons and its rings. When the mis­sion dropped the Huy­gens probe on Ti­tan, it was the rst to land on the moon of a planet other than Earth. There it dis­cov­ered rain, rivers, lakes and seas. Cassini also found the rst ev­i­dence of ex­trater­res­trial hy­dro­ther­mal ac­tiv­ity on the moon Ence­ladus, where it also ob­served erupt­ing gey­sers. Its de­tailed ob­ser­va­tions of Saturn’s rings could help sci­en­tists un­der­stand how the plan­ets in our so­lar sys­tem formed.

On the eve of the mis­sion’s ex­pi­ra­tion, Newsweek spoke with Carolyn Porco—the leader of the imag­ing sci­ence team on the Cassini mis­sion, who worked as an imag­ing sci­en­tist on the Voy­ager mis­sions in the 1980s—about the stun­ning rev­e­la­tions and vis­ual record of the his­toric ight.

What was it like when you were pre­par­ing for the Cassini mis­sion?

I was just com­ing o the Voy­ager project, which was the best mis­sion that’s ever been con­ducted. It had been such a rush to be part of such a his­toric voy­age, like we were all just plan­e­tary ex­plor­ers on Mag­el­lan’s ship. Then it came to an end, and we just wanted to do it again.

How did Cassini build on Voy­ager?

I was hop­ing we would an­swer many of the ques­tions that we were left with after the Voy­ager en­coun­ters with Saturn. Voy­ager at each planet [it vis­ited Jupiter, Saturn, Uranus and Nep­tune] was just a breath­less rush, just a eet­ing glimpse, maybe a week or two of high-res­o­lu­tion views of what was in the plan­e­tary sys­tem. There were so many things we just got a few looks at, and we won­dered, “What does that mean?”

There were some struc­tures in the rings that hadn’t been pre­dicted be­fore Voy­ager got there, and they were spectacular to see. We spent the in­ter­ven­ing 23 years try­ing to make sense of it on a the­o­ret­i­cal ba­sis. But re­ally we knew [we needed] a closer look and more time there. Then there was Ti­tan—voy­ager never got to see down to the sur­face of Ti­tan be­cause the ca­pa­bil­i­ties of the cam­era, the imag­ing sys­tem, were ex­actly mis­matched to the spec­tral ab­sorb­ing char­ac­ter­is­tics of the at­mos­phere. We were an­tic­i­pat­ing

nally be­ing able to ex­plore the sur­face of Ti­tan with Cassini. We knew how to al­ter our ob­serv­ing strate­gies so that we’d be able to see down to the sur­face.

What were your hopes for the Cassini mis­sion? I was look­ing for­ward to the spectacular stu I knew we were go­ing to get, be­cause I knew what the ca­pa­bil­i­ties of our cam­era sys­tem were com­pared to what we had car­ried on Voy­ager. I was ex­pect­ing that we would come away with a far richer story about what the Saturn sys­tem was all about. My uno cial hope was that we would blow peo­ple away with the vis­ual record of our trav­els around the Saturn sys­tem, like the ul­ti­mate in­ter­plan­e­tary trav­el­ogue. I wanted to give peo­ple a sense of rid­ing along with us. No one


re­ally had ever done this. In the Voy­ager days, no one spent any time try­ing to gure out how to make the im­ages art­ful or beau­ti­ful.

We also took se­quences of mov­ing phe­nom­ena so that we could, in a sense, turn our cam­eras into a video cam­era. We took im­ages of the rings chang­ing per­spec­tive when we were in or­bit around Saturn. We made movies of the moons go­ing around the planet, moons oc­cult­ing other moons, shad­ows of the moons mov­ing across the rings, chang­ing cloud pat­terns, light­ning strikes. We just turned it into a doc­u­men­tary. I think peo­ple re­ally felt a sense of be­ing there. It’s been a feast, an in­tel­lec­tual and vis­ual feast.

What did the Cassini mis­sion see in the rings of Saturn?

In the case of the moon Pan, we got to see that there were scal­lops on the edges of the Encke Gap. We didn’t ex­pect that any dis­tur­bance cre­ated by a moon like Pan would go all the way— 360 de­grees—around the ring. We thought it was just lo­cal­ized to the moon, and it turns out we were wrong.

Where the ring par­ti­cles are shoved to­gether be­cause of per­tur­ba­tions by moons, the par­ti­cles

+ Left, from top: NASA sci­en­tists, in­clud­ing Carl Sa­gan, dis­cuss im­ages from the Voy­ager 2 probe; prep­ping the Cassini space­craft at Kennedy Space Cen­ter in 1997; Porco dur­ing a press tour in 2017.

+ After its launch at Cape Canaveral, Florida, in Oc­to­ber 1997, Cassini trav­eled 2.2 bil­lion miles to reach Saturn in June 2004.

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