Perpetual cycle of melting and refreezing may explain Saturn moon's odd activity

Published: Saturday, May 30, 2009, 12:16 [IST]

London, May 30 (ANI): In a new research, a scientist has suggested that a perpetual cycle of melting and refreezing may offer the best explanation for why Saturn's moon Enceladus seems so active today.

According to a report in New Scientist, the scientist in question is Norman Sleep of Stanford University, US.

In Sleep's scenario, Enceladus is now heading back into a long cold phase after a comparatively brief warm spell.

For any potential life on Enceladus, "it's boom and bust", said Sleep.

Sleep raised the idea after researchers learned that Enceladus is pouring out 15 gigawatts of heat - more than double earlier estimates.

The new number makes matters worse for scientists trying to explain where all the heat comes from.

It far exceeds what can be accounted for by the decay of radioactive elements and tidal stress - strains induced by Saturn's pull on the moon.

The effects of the heat are dramatic: Enceladus is one of the most active bodies in the solar system, with vast plumes of water molecules streaming from cracks in its icy crust.

There are also hints of a subsurface ocean below.

While this has raised excitement over Enceladus as a potential place to search for life, it is becoming clear that something is awry.

Enceladus cannot have been as it is now throughout its whole existence. It would have lost 20 percent of its mass via its geysers if that had been the case.

Sleep proposes a scenario in which Enceladus is frozen most of the time but thaws repeatedly.

Over hundreds of millions of years, an existing gravitational interaction with the moon Dione causes the orbit of Enceladus to grow increasingly more elongated, or eccentric.

This produces much more tidal stress than Enceladus experiences today and eventually causes wide-scale fracturing and friction within its icy crust.

The friction leads to runaway melting and produces an ocean and eruptions of water on the surface.

The trick is that in its fluid state, Enceladus can more easily dissipate energy, which weakens the effect that drove up its eccentricity to begin with.

The eccentricity returns to normal and then Enceladus refreezes, starting the cycle anew.

"This has probably happened a few times before," said Sleep.

"What strikes me about it is that you can start with Enceladus cold and re-melt it," said John Spencer of the Southwest Research Institute.

As to whether life can survive on such a schizophrenic moon, Sleep said it depends on whether Enceladus freezes completely during the cold spells or retains a few watery pockets where microbes can eke out an existence in the lean times. (ANI)

 

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