An Extraterrestrial Ocean Unearthed (or Unsaturned)

Ever since the Cassini spacecraft uncovered water plumes venting from its south poles, Enceladus has always been the subject of intriguing speculation concerning life in the solar system. Now, NASA scientists have presented remarkable evidence that this Saturnine wonder hides a global liquid ocean encircling it, between its rocky core and icy crust.

enceladus2
Enceladus: Artist’s impression. Credit: NASA

The Subsurface Ocean: A Possibility That Has Long Lingered 

The Cassini spacecraft, currently in orbit around Saturn, first flew by Cassini, back in 2005. Pictures taken revealed icy geysers erupting 500 kilometres into space from cracks in its southern polar regions, in a remarkable cosmic process, known as cryovolcanism. The best possible explanation for such a process had thus far been pressurized water underneath getting heated by Enceladus’ core and being forced to rise to the surface, as a result. These vast eruptions also spout ice crystals and condense them into orbit  (as a result of Enceladus’ low gravity) which then become part of the majestic rings of Saturn. The Cassini spacecraft also revealed that geysers spouted outwards contained active ingredients for life (CO2, H2O, methane, and nitrogen). Images also showed remarkable tiger stripe features cascading throughout, and they were warmer than the rest of the icy surface. Data indicated that these features were indeed the source of the erupting plumes. Such amazing findings quite wonderfully etched into our minds an image of a geologically active world and further hinted at the possibility of subsurface ocean abode, capable of supporting extraterrestrial life.

Enceladus Ice Geysers Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA
Enceladus Ice Geysers; Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

The Wobble of Enceladus 

New data from the Cassini spacecraft has now finally yielded the best evidence so far of a global subsurface ocean. NASA scientists relied on measurements of Enceladus’ wobble (oscillating motion) as it orbits Saturn. The wobble was found to be large enough such that there must exist a global encircling ocean between the core and the surface. Such unstable wobbly motion is most likely due to the result of water splashing around inside Enceladus and would not be possible if the core and the surface were connected together with solely ice. This finding was accomplished using more than 7 years’ worth of data, where the researchers mapped the positions of craters on Enceladus and the discrepancies in their positions at different points in time so as to analyze changes in rotation.

A conundrum persists however with respect to what could have possibly prevented such an ocean from freezing. It is quite possible indeed that there is a heat source due to Saturn’s gravity. As Enceladus orbits Saturn, Saturn’s gravity pulls on it. The mechanical energy generated applies immense strain on Enceladus (it is squeezed and stretched) and quite possibly, this mechanical energy is then converted into interior heat. Radioactive decay of rocky elements (separation of the ice and rocky core and then the radioactive decay of the rocky core warming the ice) might have equally played a role as well. Still another possibility might lie in Enceladus’ eccentric elliptical orbit. Enceladus orbits Saturn in resonance with Dione, another Saturnine moon. Enceladus and Dione both exert gravitational influence upon each other and the ratio of their orbital periods is 1:2. That means that each time Dione orbits Saturn once, Enceladus orbits Saturn twice. So, Enceladus is periodically stretched by Dione’s gravity. This leads to tidal friction, which could possibly power such activities exhibited by Enceladus.

Illustration of Enceladus global ocean Credit: NASA/JPL-Caltech
Illustration of Enceladus global ocean; Credit: NASA/JPL-Caltech

Our Solar System is just an obscure corner in the outer spiral arm of a revolving disc of stars. But, one cannot deny that it is quite an intriguing place, full of vast wonders and unexplained mysteries. But, to understand all this and reflect upon it is quite an incredible thing and it makes me feel that we are really not that inconsequential. Indeed, such curiosities must always continue to persist. We ought to understand our place in the cosmos.

Featured image courtesy of: NASA/JPL

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