Cassini, NASA's 13-year Saturn mis­sion, has ended

Sunday Times (Sri Lanka) - - INTERNATIONAL - By Ash­ley Strickland

Con­tact has been lost with the Cassini space­craft af­ter it com­pleted a "death dive" into the up­per at­mo­sphere of Saturn and trans­mit­ted its fi­nal sig­nal, ac­cord­ing to NASA.

The space­craft de­lib­er­ately sank into Saturn's up­per at­mo­sphere at a high speed and plunged it­self into the planet just af­ter 6:30 a.m. ET Friday. Given the amount of time it takes sig­nals to reach Earth, the fi­nal sig­nal and last bits of data reached the Deep Space Net­work's Can­berra Sta­tion in Aus­tralia about an hour and a half later.

NASA con­firmed the space­craft's demise at 7:55 a.m. ET, as pre­dicted.

For about a minute, Cassini was able to trans­mit new data about the planet's com­po­si­tion as long as its an­tenna re­mained pointed to­ward Earth, with the as­sist from small thrusters. Then, the space­craft burned and dis­in­te­grated due to the heat and high pres­sure of the hos­tile at­mo­sphere. It be­came part of the planet it set out to ex­plore.

No space­craft has ever been so close to Saturn.

"You can think of Cassini as the first Saturn probe," said Linda Spilker, Cassini project sci­en­tist.

On Thurs­day, Cassini took its last im­ages and trans­mit­ted all the data on its recorder to pre­pare for the fi­nal plunge.

For the team be­hind the mis­sion, los­ing their space­craft is bit­ter­sweet: Many are sad that the mis­sion is over but ex­cited to see the ground­break­ing sci­ence pro­vided by un­prece­dented prox­im­ity to Saturn dur­ing the fi­nal dive.

Af­ter launch­ing in 1997, trav­el­ing nearly a mil­lion miles and reach­ing the Saturn sys­tem in 2004, Cassini spent 13 years ex­plor- ing the planet and its moons. The data and im­ages led to numer­ous dis­cov­er­ies that changed how sci­en­tists think about our so­lar sys­tem.

Why the dra­matic end­ing?

Cassini had its clos­est ap­proach with Saturn's moon Ti­tan on Monday, dubbed a "good­bye kiss" by the mis­sion's en­gi­neers be­cause it pro­vided the grav­ity as­sist that sent the space­craft on its fi­nal en­counter with Saturn.

Mis­sion sci­en­tists and op­er­a­tors gave Cassini this fiery send-off on pur­pose. Al­though many other op­tions were con­sid­ered -- such as "park­ing" the space­craft in or­bit -- they didn't want to risk Cassini col­lid­ing with any of Saturn's moons.

Cassini data and ob­ser­va­tions re­vealed that while seem­ingly in­hos­pitable to us, the moons Ence­ladus and Ti­tan could be hab­it­able for some form of life. And NASA didn't want to risk con­tam­i­nat­ing the moons or any fu­ture stud­ies of them with Earth par­ti­cles. Al­though Cassini has been in space for 20 years, mi­crobes from Earth could still ex­ist on the space­craft with­out air, wa­ter or pro­tec­tion from ra­di­a­tion.

Al­though the mis­sion it­self has ended, the data and ob­ser­va­tions pro­vided by Cassini will pro­vide new de­tails about the planet, its unique rings and its moons for decades to come.

Dur­ing the fi­nal plunge, the Ion and Neu­tral Mass Spec­trom­e­ter acted as the "nose" of the space­craft, di­rectly sam­pling the com­po­si­tion and struc­ture of the at­mo­sphere -- some­thing that can't be done from or­bit, said Hunter Waite, team lead for the spec­trom­e­ter.

This was in the hopes of in­ves­ti­gat­ing the "ring rain" phe­nom­e­non dis­cov­ered by NASA's Voy­ager mis­sion in the early 1980s, in which it ap­peared that the rings were rain­ing down ma­te­rial on the planet and caus­ing changes in the at­mo­sphere. The spec­trom­e­ter could de­ter­mine what ma­te­rial is from the rings and what ma­te­rial is part of the at­mo­sphere.

Cassini's grand fi­nale ac­tu­ally be­gan in April, with a series of dives be­tween Saturn's rings, close to the planet and its moons, pro­vid­ing un­prece­dented in­sight. This is an­other rea­son the mis­sion sci­en­tists de­cided on Cassini's par­tic­u­lar endgame: The fi­nal dive was a dra­matic con­clu­sion to this long and sci­en­tif­i­cally valu­able good­bye.

What Cassini taught us and what's next

In­spired to learn more af­ter fly­bys of Saturn by NASA's Voy­ager mis­sions, the Cassini mis­sion was de­signed to be an in­ter­na­tional ef­fort that united NASA, the European Space Agency and the Ital­ian Space Agency.

It is known as the CassiniHuy­gens mis­sion be­cause it de­liv­ered the European agency's Huy­gens probe to Ti­tan, the "first de­scent and land­ing on a world in the outer so­lar sys­tem," ac­cord­ing to NASA.

The Cassini mis­sion has been ex­tended twice and fi­nally used up the last of its rocket pro­pel­lant this week.

In the end, Cassini wit­nessed about half of a Saturn year. When the craft ar­rived, Saturn's north­ern hemi­sphere was emerg­ing from win­ter. As sea­sons on Saturn last about seven Earth years each, Cassini was just able to wit­ness sum­mer in the north­ern hemi­sphere be­fore the mis­sion ended.

Over the years, Cassini has re­vealed in­sights about Saturn, its rings and how they op­er­ate, the com­plex­i­ties of its moons, the his­tory of the so­lar sys­tem and planet for­ma­tion and even the other places in our so­lar sys­tem where life might ex­ist: ocean worlds. Cassini has col­lected more than 450,000 im­ages us­ing a vis­i­ble light cam­era.

It has trav­eled nearly five bil­lion miles, ex­e­cuted 2.5 mil­lion com­mands, con­ducted 162 tar­geted fly­bys of Saturn's moons, com­pleted 294 or­bits and its col­lected data has led to the pub­li­ca­tion of nearly 4,000 re­search pa­pers.

When Cassini ar­rived, it wit­nessed a gi­ant storm cir­cling the planet for nine months. We learned that there are 3-D struc­tures in the rings. Serendip­i­tous ob­ser­va­tions showed that icy jets erupt from Ence­ladus. And Ti­tan not only has seas and lakes of liq­uid eth­ane and meth­ane, it has an at­mo­sphere of chem­i­cals that rain down, form­ing a unique chem­istry that could lead to life.

"Cassini has trans­formed our think­ing in so many ways but es­pe­cially with re­gard to sur­pris­ing places in the so­lar sys­tem where life could po­ten­tially gain a foothold," said Thomas Zur­buchen, as­so­ciate ad­min­is­tra­tor for NASA's Sci­ence Mis­sion Di­rec­torate, in a state­ment.

And the space­craft it­self, as well as its in­stru­ments, are in­form­ing fu­ture mis­sions like NASA's Europa Clip­per mis­sion to ex­plore Jupiter's icy moon, launch­ing in the 2020s.

"Cassini has en­abled those fu­ture mis­sions to be pos­si­ble," said Jim Green, NASA's di­rec­tor of plan­e­tary sci­ence.

In­trigued by Cassini's dis­cov­er­ies, sci­en­tists have sub­mit­ted con­cepts for fu­ture "space­craft to drift on the meth­ane seas of Ti­tan and fly through the Ence­ladus plume to col­lect and an­a­lyze sam­ples for signs of bi­ol­ogy" that are un­der con­sid­er­a­tion, ac­cord­ing to NASA.

Courtesy: CNN

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