Water is indeed the central ingredient for the sustenance of life; wherever there is water there will be life, though the nature of the living organism varies depending on the status of the water. Earth is the only planet in our solar system to have two thirds of her surface covered with liquid ocean water which is believed to be the key factor that triggered the flourishing of lives here on this planet in the first place. But lately, based upon stern scientific observations, it is slowly becoming apparent that oceans and waters are also quite common within our very solar system and in other extra-solar planets as well and the possibilities of extra-terrestrial life-forms in those vicinities are evident than ever before.
Within our solar system the most prominent candidate harbouring oceans and extra-terrestrial life-forms is Europa, the sixth moon of Jupiter. The Galileo Spacecraft mission of NASA that orbited Jupiter for eight years beginning in 1995 provided vital information on this significant satellite of hers which revealed that the underneath the icy crust of Europa lies salty ocean which is kept warm by tidally generated heat and volcanic activities. Aided by the “thick ice” model, astronomers argue that the largest of Europa's craters are surrounded by concentric rings and likely to be filled with ice and it is believed that this outer crust of ice is approximately 100km thick only the top 10km are frozen solid which plants the possibility of the existence of a global ocean in a liquid form and at least 62 miles deep beneath these icy crust. Naturally, the hopes of possible life on Europa's ocean skyrocketed with such critical discoveries it has been scientifically suggested that life is very likely to exist in Europa's ocean. Some say such celestial beings could be microbial while others say there might be ones like that of the movie “Cloverfield”, the gargantuan monster that went on rampaging NYC! Only the findings from the future Europa bound missions could tell what lies beneath this planet, probably the one NASA is planning to launch in 2020, the “Europa Jupiter System Mission” armed with objectives ranging from examining Europa's chemical composition to search extensively for extra-terrestrial life in her sub-surface ocean. Two other moons of Jupiter, Ganymede, the largest moon in the Solar system is thought to have a saltwater ocean nearly 200km deep below her surface and Callisto, which the spacecraft Galileo has also revealed to have a subsurface ocean more than 100km deep.
Enceladus, the sixth largest moon of Saturn is also another planet within our solar neighbourhood that is likely to host liquid water. In 2005, NASA's Cassini spacecraft provided strong evidence on the possibility of liquid salty ocean beneath the frozen surface of this planet. During the flyby mission, the spacecraft detected jets containing water vapour, gas and tiny grains of ice and dust that shoot off hundreds of kilometres into the space from Enceladus's South Pole. This lead to the belief amongst the astronomical community that this enigmatic moon of Saturn, has a vast water reservoir hidden deep beneath the moon's icy interior and this global ocean of hers is in contact with the planet's rocky core which is why the eruption of water vapour and ice particles occurs. The possibility of a sub-surface ocean in Enceladus leads to the speculation that this planet, just like Europa, is very likely harbouring extra-terrestrial life-form. Another moon of Saturn, Titan, is also subjected to a great astronomical interest because apart from the possibilities of Sub-surface Ocean it is the only planet in the solar system, besides Earth, to have stable bodies of surface liquids. But her surface liquids are mostly composed of methane, ethane and dissolved nitrogen.
|Enceladus is a planet that is most likely to host liquid water.
But the data from the same Cassini mission indicated along with the observational findings on the seasonal variations of the rotation rate of the planet, that this largest moon of Saturn houses a reservoir of liquids, an ammonia-water solution at least 200 km deep, beneath her thick icy surface and a possible host for marine microbial extra-terrestrial life. More interestingly, with Titan's liquid both on surface and subsurface and a energetic nitrogen atmosphere, she has been viewed as analogous to the early earth and it has been also suggested that enough organic materials exists on Titan to commence a chemical evolution exactly like the one that is thought to have started life here on Earth.
One planet in the extra-solar region certainly requires a great deal of consideration concerning the presence of liquid water. And that is Gliese 581 d which is orbiting the star Gliese 581 and the most crucial aspect regarding this planet is her location in the Habitable Zone of space which is astronomically defined as the region in space where stellar conditions are favourable for life as it is found on Earth. This planet is classified as a Super-Earth due to her mass, which is nearly 8 times that of Earth, and because of this vastness of hers it is also believed that Gliese 581 d is too massive to be made of only stony materials. Further studies have lead to the strong speculations that her atmospheric and temperature conditions are suitable enough for Gliese 581 d to even have a liquid ocean on her surface and thus very much capable of supporting extra-terrestrial life.
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