redeye wrote:I've long considered Titan to be the best candidate for life in our Solar System (probably cos I read it somewhere).
There is also speculation as to the presence of liquids on it's surface which could provide an emulsion which is considered necessary for life.
It's quite speculative but I've been waiting ten years for news like this.
HelloNiceToMeetYou wrote:Thats what they said about arsenic. Now look whos laughing
I'm no ethnobiologist and a lousy chemist, but how do you conduct redox reactions for energy where the elements being considered are all what we consider "fuels"? Is acetylene an oxidizer? In our metabolism, energy comes from oxidizing reactions with our carbon-based food and cell contents. We breathe in our "oxidizer" - literally, oxygen molecules in air - but what would a Titan resident breathe or aspirate or absorb to do the same? Not the hydrogen, which is an electron donor, not an electron "receiver" like fluorine or oxygen, etc. This will be interesting to follow and see if it gets any traction.
Phosphorus is the ninth most abundant element in living organisms. Its compounds are found in teeth, bones, cell membranes, and a host of important biomolecules, including cells' main source of chemical fuel, adenosine triphosphate. Phosphate groups also hold together the nucleotides in RNA and DNA.
Because arsenic belongs to the same group in the periodic table as phosphorus, it can readily replace phosphorus in biomolecules. But the arsenated compounds don't work—hence the element's toxicity. The newly discovered bacteria are remarkable in that they apparently possess a chemical means of mitigating the toxicity.
But before you start scanning the skies for arsenic-laced M-class planets, keep in mind that arsenic is cosmically rarer than its group V neighbor phosphorus. In Earth's crust arsenic occurs at a concentration of about 1.5 parts per million. Phosphorus is 1000 times more abundant.
Life as we know it on Earth originated just once, a reflection of its low probability of getting started. I'm therefore skeptical that life forms based on a rare element such as arsenic evolved elsewhere.
I can't resist ending this blog entry by pointing out another scientific substitution of arsenic for phosphorus. Three years ago in his quest to find semiconductors with interesting magnetic properties, Hideo Hosono and his team from the Tokyo Institute of Technology synthesized a compound with the chemical formula LaOFeP.
The material becomes superconducting at the unremarkably low temperature of 4 K. But the arsenic-substituted compound, when doped with fluorine, superconducts at 26 K, which is uncomfortably high for a normal superconductor. Hosono had discovered a new and exciting class of superconductor.
Despite spawning thousands of papers from excited physicists and chemists around the world, Hosono's discovery barely registered in the mainstream media.
... [S]and on (Saturn's moon) Titan is not made of silicates as on Earth, but of solid hydrocarbons that precipitate out of the atmosphere. These then aggregate into millimetre-sized grains by a still unknown process.
... Though similar in shape to the linear dunes found on Earth in Namibia or the Arabian Peninsula, Titan's dunes are gigantic by our standards. They are on average 0.6 to 1.2 miles (1 to 2 kilometers) wide, hundreds of miles (kilometers) long and around 300 feet (100 meters) high. However, their size and spacing vary across the surface, betraying the environment in which they have formed and evolved.
Radar images from NASA's Cassini spacecraft reveal some new curiosities on the surface of Saturn's mysterious moon Titan, including a nearly circular feature that resembles a giant hot cross bun and shorelines of ancient seas...
..."The 'hot cross bun' is a type of feature we have not seen before on Titan, showing that Titan keeps surprising us even after eight years of observations from Cassini," said Rosaly Lopes, a Cassini radar team scientist based at NASA's Jet Propulsion Laboratory, Pasadena, Calif...
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