The Sky at Night pre­sen­ter re­caps her Cassini high­lights as the probe be­gins its Grand Fi­nale

Sky at Night Magazine - - A PASSION FOR SPACE - with Mag­gie Aderin-Po­cock Mag­gie Aderin-Po­cock co-presents The Sky at Night and CBee­bies Stargaz­ing

The Cassini space­craft is on a mis­sion that keeps giv­ing. Orig­i­nally it was due to be op­er­a­tional for just four years, but it gath­ered so much data dur­ing that short time that it was ex­tended to a whop­ping 13 years. All good things must come to an end, how­ever, and on 15 Septem­ber 2017 Cassini will be crashed into the planet it has been ob­serv­ing for so long. Its seems a fit­ting end: even in its death throes the space­craft will be col­lect­ing in­for­ma­tion about the amaz­ing Saturn sys­tem.

The Cassini-Huy­gens space probe was launched in 1997 and made a jour­ney of 3.5 bil­lion km to ren­dezvous with Saturn. The com­bined space­craft went into or­bit around the planet in July 2004. In De­cem­ber that year the Huy­gens lan­der, made by ESA, was re­leased and touched down on the sur­face of Saturn’s largest moon Ti­tan. This set the record for the farthest land­ing from Earth that a space­craft has ever made.

Since then our knowl­edge of Saturn and its moons has been trans­formed. My top five high­lights of the mis­sion so far are:

When Cassini launched from Cape Canaveral in 1997, we were aware of 18 moons in or­bit around Saturn. Now, with ob­ser­va­tions from Earth and anal­y­sis by Cassini, many more have been found – per­haps as many as 62, rang­ing in size from larger than planet Mer­cury to about the size of a foot­ball sta­dium.

2) Ti­tan has lakes and seas of liq­uid meth­ane, re­plen­ished by rain from hy­dro­car­bon clouds. The mis­sion also pro­vided ev­i­dence that Ti­tan is hid­ing an in­ter­nal, liq­uid ocean be­neath its sur­face, likely com­posed of wa­ter and am­mo­nia.

3) The par­ti­cles that make up Saturn’s rings range in size from smaller than a grain of sand to as large as moun­tains. Cassini found that wa­ter jets from the moon Enceladus pro­vide some of the ma­te­rial in Saturn’s E ring, a dif­fuse ring sit­u­ated out­side the main, bright rings.

4) Saturn’s moon Enceladus is a small, icy body, but Cassini re­vealed that a liq­uid ocean ex­ists un­der its crust. Geyser-like jets spew­ing wa­ter vapour and ice par­ti­cles from its un­der­ground ocean were also de­tected. Anal­y­sis of this wa­ter re­vealed the pres­ence of or­ganic ma­te­rial, molec­u­lar hy­dro­gen. With its global ocean, unique chem­istry and in­ter­nal heat, Enceladus is now thought one of the So­lar Sys­tem’s most sci­en­tif­i­cally in­ter­est­ing des­ti­na­tions.

5) Anal­y­sis of Saturn’s poles re­vealed gi­ant hur­ri­cane sys­tems. At the north pole the sys­tem is hexag­o­nal in shape. Enor­mous planet-en­gulf­ing thun­der­storms some­times erupt from Saturn’s at­mos­phere, af­fect­ing the cli­mate of the planet for many years.

As the mis­sion en­ters its Grand Fi­nale, ma­noeu­vres are be­com­ing more dar­ing and risky, with or­bits tak­ing the space­craft to within 300km of the in­ner edge of the rings and through un­known re­gions that could bom­bard its in­stru­ments with dust. Even with just a few months left, Cassini still has the op­por­tu­nity to trans­form our un­der­stand­ing and I for one can’t wait to see what it will re­veal.

The gi­ant hexag­o­nal storm on Saturn’s pole is now one of the planet’s most fa­mous fea­tures

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