The following diary was based on this article published in SciTechDaily.
Planetary scientists have considered Jupiter’s moon Europa (one of the four Galilean moons) as a good candidate where life might be found. While its icy surface is far colder than any temperature naturally occurring on Earth, an ocean of liquid water lies below that surface. How is it possible for this ocean to exist? Europa’s orbit around Jupiter is quite elliptical, resulting in significant distance difference between closest and furthest distance. Thus the strength of the gravity exerted by Jupiter varies significantly When Europa is close to Jupiter, its normal spherical shape is slightly distorted, while when it is further away this distortion is much smaller. As when you bend a piece of wire back and forth, the alternation in level of distortion causes the planet to heat up, and so there is enough heat to melt water below Europa’s icy surface.
Life on Earth is dependent on liquid water, so the presence of liquid water is a good sign that life is possible on Europa. Yet, just the presence of liquid water is not enough. There also has to be an energy source that can drive the processes of life. On Earth, solar energy is harvested by plants to make food for itself as well as for nearly all other living things on the planet. However, processes such as photosynthesis are not likely to take place in Europa’s ocean because very little sunlight will make it through the ice layer above it. This raises a question: What other kind of energy sources, besides sunlight, would be able to drive life processes?
[Of course, early life on Earth, and its archaic bacterial descendants flourished near deep-sea hydrothermal vents, but Europa lacks the geological processes that cause such hydrothermal vents.]
Scientists at the University of Sao Paulo in Brazil discovered an organism in a South African mine living in lightless conditions similar to what one might expect on Europa. What powers its life processes? Would you believe radioactivity? The organism, a bacterium, is called Candidatus Desulforudis audaxviator, and it was discovered in the Mponeng gold mine near Johannesburg. Deep in the mine, there are traces of uranium, which naturally decays, producing radioactivity. The radioactivity breaks up water molecules, producing radicals (hydrogen atoms, H, and hydroxyl radical, OH). Among the surrounding rocks, there’s pyrite, FeS2 (also called fool's gold). The radicals react with the pyrite to produce sulfate, and the bacteria can then use this sulfate to drive its life processes.
The discovery of Candidatus Desulforudis audaxviator and how it lives proves that life can survive in the dark, run by radioactive processes. As radioactive isotopes are as common on Europa as they are on Earth, it is possible that life processes can take place in Europa’s ocean, even though it lies in darkness. There is a probe planned to visit Europa with the mission of attempting to determine if there’s life there, but it’s not expected to get there until 2030.
On to the comments, which you’ll find below the fold. But first, a word from our sponsor:
Here at Top Comments we strive to nourish community by rounding up some of the site's best, funniest, most mojo'd & most informative commentary, and we depend on your help!! If you see a comment by another Kossack that deserves wider recognition, please send it either to topcomments at gmail or to the Top Comments group mailbox by 9:30pm Eastern. Please please please include a few words about why you sent it in as well as your user name (even if you think we know it already :-)), so we can credit you with the find!
Top Comments (July 21, 2018):
From John M Webb:
From Youffraita:
A truly terrific comment by Bo Realis, in jamess's diary.
Top Mojo (July 20, 2018):
Top Mojo is courtesy of mik! Click here for more on how Top Mojo works.
Top Photos (July 20, 2018):