Earth

Sky at Night Magazine - - ADVERTISEM­ENT FEATURE -

PLANET TYPE: Rocky

Our home planet is unique in the So­lar Sys­tem: liq­uid wa­ter cov­ers 70 per cent of its sur­face. Its pres­ence means Earth has ac­cess to a huge ar­ray of pro­cesses that can’t hap­pen on other plan­ets. Ge­o­log­i­cally, wa­ter acts as a lu­bri­cant be­tween Earth’s tec­tonic plates, keep­ing them mov­ing; as well as al­low­ing the for­ma­tion of min­er­als that oth­er­wise might not ex­ist such as hematite.

Most im­por­tantly, wa­ter is vi­tal for life. As we search for life through­out the So­lar Sys­tem and be­yond, the mantra is al­ways ‘fol­low the wa­ter’.

We still don't know, how­ever, why Earth has so much wa­ter: cur­rent the­o­ries of planet for­ma­tion sug­gest early Earth should have been so hot that all its wa­ter boiled away. The lead­ing ex­pla­na­tions are that Earth man­aged to re­tain wa­ter in its core, that later bub­bled to the sur­face, or that wa­ter was brought back to Earth af­ter it had formed, pos­si­bly by asteroids im­pact­ing the sur­face. EX­PLORED BY: Sput­nik 1 (1957); Ex­plorer 1 (1958); Land­sat pro­gramme (1972–2013); Eu­ro­pean Re­mote-Sens­ing Satel­lite (1991–2011); TERRA (1999); En­visat (2002) NUM­BER OF SPACE­CRAFT: 600+ (cur­rently)

One the­ory for Earth’s high wa­ter vol­ume is the un­lock­ing of un­der­ground re­serves by as­ter­oid im­pacts early in the planet’s life cy­cle

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