OT: Extrasolar planets discovered directly

[Hunpecked]

Strategia and Renegade make the point that "life" in our galaxy need not be of a sort familiar to us, i.e. carbon-based. This is certainly valid (within the limits of our knowledge), and makes irrelevant any probability calculations requiring Earth-like conditions. Of course it's only natural to look for more-or-less familiar life forms first: we already have one example of a carbon-based ecosystem, but exactly zero examples of any other type.

What forms could "unconventional" life take? I vaguely recall a juvenile science fiction novel which featured Mercurian creatures that resembled ball lightning. Arthur C. Clarke wrote a short story ("Out of the Sun" ???) in which an electromagnetic entity of some sort was ejected from the sun in a solar flare. Silicon seems to be a popular basis for sci fi life forms, probably because of its position just below carbon in the Periodic Table. If I recall correctly the "Horta" of Star Trek fame (episode "Devil in the Dark") was silicon-based.

Nevertheless, silicon is not carbon. As I recall from my prehistoric chemistry classes, silicon's 4 valence electrons are one electron shell "out" from carbon's, giving the elements roughly similar but far from identical chemical properties. For example, silicon does form polymer chains (as the bosoms of countless Hollywood starlets attest), but I've read (I'm no chemist) that these chains don't approach the length and complexity of carbon polymers (DNA, anyone?). Recall also that silicon dioxide is a solid at temperatures that vaporize carbon dioxide. Now some earth organisms (e.g. diatoms, sponges) take advantage of that and use silicon dioxide STRUCTURALLY, but on Earth at least evolution has favored carbon chemistry for life's vital functions, despite the greater abundance of silicon.

Incidentally, as a naive layman I wonder if a detailed study of the ways these creatures build their silica frameworks might suggest how a hypothetical silicon-based life form could "work".

A couple of places on the web with some tidbits about silicon:

http://en.wikipedia.org/wiki/Silicon_dioxide

http://www.webelements.com/index.html (click on the elements)

[Fyron]

There are silicon-based lifeforms on the Earth right now... They are all monerans, nothing complex, but they are out there.

[Hunpecked]

Interesting. I wasn't aware that any Monerans formed silicaceous structures. Protistans, yes. Any references on the web?

[Fyron]

Dunno. It was in a scientific journal of some sort I read several years ago. A quick google turned up this mention to an upcoming book. No idea if this is a reputable site or not, but there it is:

http://www.gsreport.com/articles/art000035.html

[Hunpecked]

Fyron,

Thanks for the link. I thought your post was about silica structures secreted by certain prokaryote cells, but I see that the link actually refers to Dr. Tom Gold's (so far unconfirmed) speculations on the existence of true silicon-based organisms on Earth. Dr. Gold's book was indeed published in 1999; I found a review here:

http://www.findarticles.com/p/articl...80/ai_56022636

Unfortunately, none of the reviews I read mentions any discussion of silicon-based life. The focus of the book is Dr. Gold's theory of a deep underground biosphere supported by an abundance of hydrocarbons (oil and gas) left over from the formation of the Earth (i.e. of non-biological origin). Of relevance to our forum discussion is his suggestion to look for extraterrestrial life BELOW the surface of such bodies as the moon, Mars, and Saturn's moon Titan.

[Baron Munchausen]

Whoa... Using silicon in part of their metabolism does not make them 'silicon based' life. Don't monerans have ordinary DNA like every other form of life on earth? Something analagous to DNA but using silicon that forms the core of their entire suite of biochemical processes would be 'silicon based' life. I don't think there is any such thing known.