While or­bit­ing Saturn nearly 300 times, Cassini made ma­jor dis­cov­er­ies, such as the liq­uid methane seas of the planet's gi­ant moon Ti­tan and the sprawl­ing sub­sur­face ocean of Ence­ladus, a small Saturn moon

Financial Chronicle - - MISCELLANY -

NASA'S Cassini probe is count­ing its fi­nal hours be­fore one last plunge into Saturn on Fri­day that will cap a fruit­ful 13-year mis­sion that greatly ex­panded knowl­edge about the gas gi­ant. While or­bit­ing Saturn nearly 300 times, Cassini made dis­cov­er­ies like the liq­uid methane seas of the planet's gi­ant moon Ti­tan and the sub­sur­face ocean of Ence­ladus, a Saturn moon.

"Cassini-Huy­gens is an ex­tra­or­di­nary mis­sion of discovery that has rev­o­lu­tion­ized our un­der­stand­ing of the outer so­lar sys­tem," said Alexan­der Hayes, as­sis­tant pro­fes­sor of astronomy at Cor­nell Univer­sity.

Data col­lected by Cassini's spec­trom­e­ter while pass­ing through a va­por plume at Ence­ladus's south pole showed hy­dro­gen shoot­ing up through cracks in its ice layer.

The gas was a sign of hy­dro­ther­mal ac­tiv­ity fa­vor­able to life, sci­en­tists said in April when they un­veiled the find­ing. Launched in 1997 and equipped with a dozen sci­en­tific in­stru­ments, the 2.5-tonne probe en­tered Saturn's or­bit in 2004, land­ing on Ti­tan in De­cem­ber of that year.

On April 22, it be­gan the ma­neu­vers for its fi­nal jour­ney. Mov­ing closer to Ti­tan, the space­craft took ad­van­tage of the mas­sive moon's grav­i­ta­tional push to make the first of 22 weekly dives be­tween Saturn and its rings -- ven­tur­ing for the first time into the un­charted 2,700-kilo­me­tre space.

Cassini's last 5 or­bits will take it through Saturn's up­per­most at­mos­phere, be­fore a fi­nal plunge di­rectly into the planet on Septem­ber 15. Cassini flew by Ti­tan one last time on Tues­day be­fore trans­mit­ting im­ages and sci­en­tific data from the flight.

Mis­sion en­gi­neers will use the in­for­ma­tion gath­ered from the en­counter they dubbed "the good­bye kiss" to make sure the ves­sel is fol­low­ing the right path to plunge into the gas gi­ant's at­mos­phere.

"The Cassini mis­sion has been packed full of 4 firsts, and our unique plan­e­tary rev­e­la­tions will con­tinue to the very end of the mis­sion as Cassini be­comes Saturn's first plan­e­tary probe, sam­pling Saturn's at­mos­phere up un­til the last sec­ond," said Linda Spilker, Cassini project sci­en­tist at Nasa's Jet Propul­sion Lab­o­ra­tory in Pasadena, Cal­i­for­nia.

"We'll be send­ing data in near real time as we rush head­long into the at­mos­phere -- it's truly a first-ofits-kind event at Saturn."

Cassini is ex­pected to lose com­mu­ni­ca­tions with Earth one or two min­utes into its fi­nal dive, but 10 of its 12 sci­en­tific in­stru­ments will be work­ing right up un­til the last mo­ment to anal­yse the at­mos­phere's com­po­si­tion. That data could help un­der­stand how the planet formed and evolved.

On the eve of its fi­nal de­scent, other in­stru­ments will make ob­ser­va­tions of Saturn's aurora bo­re­alis, tem­per­a­tures and po­lar storms. Cassini's fi­nal ma­neu­vers be­gin at 0714 GMT on Fri­day. At 1031 GMT, the space­craft is due to en­ter Saturn's at­mos­phere. Just a minute later, at some 940 miles (1,510 kilo­me­ters) above Saturn's clouds, the probe's com­mu­ni­ca­tions will stop be­fore Cassini be­gins to dis­in­te­grate mo­ments later, Nasa pre­dicts. "The Grand Fi­nale rep­re­sents the cul­mi­na­tion of a seven-year plan to use the space­craft's re­main­ing re­sources,” said Earl Maize, Cassini project man­ager at the Jet Propul­sion Lab­o­ra­tory. "By safely dis­pos­ing of the space­craft in Saturn's at­mos­phere, we avoid any pos­si­bil­ity Cassini could im­pact one of Saturn's moons, keep­ing them pris­tine for fu­ture ex­plo­ration."

The Cassini-Huy­gens mis­sion's to­tal cost is about $3.26 bil­lion, in­clud­ing $1.4 bil­lion for pre-launch de­vel­op­ment, $704 mil­lion for mis­sion op­er­a­tions, $54 mil­lion for track­ing and $422 mil­lion for the launch ve­hi­cle. The US paid $2.6 bil­lion to the project, the Euro­pean Space Agency $500 mil­lion and the Ital­ian Space Agency $160 mil­lion.

Ital­ian as­tronomer Gio­vanni Cassini dis­cov­ered four of Saturn moons in the 17th cen­tury, although sci­en­tists have since iden­ti­fied more than 60. Dur­ing the same era, Dutch math­e­ma­ti­cian Chris­ti­aan Huy­gens found that Saturn had rings. He also was the first per­son to ob­serve Ti­tan.

On April 22, it be­gan the ma­neu­vers for its fi­nal jour­ney by us­ing Ti­tan's grav­i­ta­tional push

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