Just a question.

Life-forms may be silicon based...I imagine that they would exist in very cold conditions because silicon polymers forms fragile strings...Is this true?
Has anybody got any insights into this?.

silicon lif forms exist in warm fake breasts
if u freez them, they mutate in2 real breast but turn fake again wen u warm them up

The problem with silicon is that it has a tendencies to be too stable as a oxidized polymer. This would mean that to over come this you would need very high temperatures! Lets say silicon life could exist on Venus. If it did the next problem would be what is its transporting fluid? All life needs as fluid medium to carry out reactions and transport products. If silicon life were to exist at 400C it would need lead or aluminum as a working fluid! Also these critters would weigh much MUCH more then carbon base life… mainly from being made of silicon and having a liquid metal for cytoplasmic fluid and all. At such high temperatures weird things will happen with chemical reaction: most reactions that we use to live would not be stabile enough to exist here. Most likely silicon life would need D orbital reactions and would need heavy elements that are rare here in this section of the galaxy.

Silicon life might be possible but considering the conditions it needs to occur I doubt it is very common.

http://nai.arc.nasa.gov/astrobio/feat_questions/silicon_life.cfm

How about inside rocky planets? or a planet that orbits very near to its sun...?

sounds good to me... we have not found anything yet that is a problem: so it remains just a hypothesis.

are there any other contenders?

The only other contenders can think of are really just the carbon based life form that are found deep 20-100(?)km down in the earths crust. They use hydrogen sulfide(?) as `food`... perhaps there is as much biomass inside the earth an on top...

How plausible are gaseous creatures that live in interstellar space (still carbon based)?

There was a hypothesis that life could live using Methane or ammonia as a working fluid. this would allow life to live on a moon like Titan. the problem is at such low temps (Below 100K) chemical reactions are so very sloooooooooooow, these reactions also demand a lot of energy beacuse of the lack of any thermal energy in this situation. So deep cold life would live grow and evolve very VERY SLOWLY. In fact if we go to Titan I will bet all we will find is nothing more complex then prebotic molecules like RNA.

so far what seems to define life is water and temps and pressures at which water can exist. So no life floating in outer space (unless this life is hibernating).

Yeah, but finding that soup will be in some ways better than finding something alive. Might give some insight as to what can happen between the phases of dead organics and life. Just wish we had some nuclear engines on Cassini so it was there already and could work longer.

2006 just three more year!

Less than that...

The 318-kilogram (701-pound) Huygens probe will separate from the Cassini orbiter in December of 2004, and will begin a 22-day coast phase toward Titan. Remaining on the Cassini orbiter will be the probe support equipment (PSE), which includes the electronics necessary to track the probe and to recover the data gathered during its descent. Then, in January of 2005, at just 45 minutes before the spacecraft reaches the atmosphere of Titan, timers will wake up the Huygens probe.

That soup may be found between the stars...?
It takes a long time for life to evolve in a cool environment? Yes probably...but there has been over 4 billion years of time to do it...And it may have been evolving long before that in deep space.

i think i mentioned in another thread that all DNA lifeforms (on earth) have right handed helixes...why?
i also remember that organic(?) sugars can be left-handed or right-handed but only one form is utilised by life-forms...why?

Perhaps ONE ancestral life-form pre-seeded the early earth...

(digressing from silicon)

i think Deep space 1 is nuclear powered...

I have nothing against the seeding theory

Right and left hand DNA,RNA, peptieds are not compatable with each other. As a result both forms had to compete and it was a random flip of the coin which one won.

Not directly, it's powering an ion engine.

In Niven's The Mote In God's Eye, he used the right vs left handed molecules idea, where the alien life could not break down our version, so they could eat it, but it passed through without being digested at all. Led to an accidental strawberry infestation...

Is this plausible, that the two types are incompatible, even in terms of diseases? Or do we even a have a clue yet?

As for silicon, it's not impossible, but I think conditions are going to have to be even more perfect than for carbon to exist, due to silicon not being as good at bonding as carbon is. Carbon rules. :)

Carbon exhibits a handedness...yes?
Silicon doesn`t, but it doesn`t matter, does it?

i`m not sure about carbon being that much better to silicon in forming long chains.

http://www.physics.hku.hk/~tboyce/sfseti/21strange.html

Silicon has two problems...weaker bonds, and an affinity for oxygen.

Silicon has two problems...weaker bonds, and an affinity for oxygen.
So would they use something else for respiration?

HeHe, we may as well say Carbon has two problems...stronger bonds, and an affinity for oxygen,

CO2?

As for `breathing` i don`t know, how about sulphur?
what about metals?

Sulphur is fairly abundant in the universe.

Sulfur “breathing” life exists here on Earth in volcanic water… usually hot. Nothing seems to prevent a whole plant from living off sulfur instead of oxygen. The sulfur would need to be very plentiful though. Think of the planet like the moon IO but with a very thick atmosphere of Sulfides and temps supporting liquid water: very good chance we would see some evolved creatures breathing this stuff. Though sulfur is not as efficient in the electron ladder as oxygen so the chemistry of bio-sulfurics would be very different to be competitive with the easy of use of oxygen. Halogens would be even better oxidizers (taking away electrons) then oxygen but there is no real viable situation for planets with atmospheres and oceans contains large amounts of halogens. As of yet there is no life on earth that oxidizes using halogens as a primary source of non-aerobic metabolism. Life could also live by reducing (giving electrons) organics. Such life would breath Hydrogen (or very unlikely considering its nature: alkaloid metals) Life like this does exist on earth, in fact farting is a good example of such life forms byproducts. Unfortunately hydrogen does not seem very productive metabolically and my not support the evolution of higher life forms. Hydrogen breathing life would live on planets with a Hydrogen atmosphere like Jupiter. Only problem with living on a planet that has no surface is that there would need to be a very long retention time in the atmosphere so that life forms would not have to worry about getting sucked down to their horrible deaths near such planets cores.

interesting points made, and noted...

But i was really referring to silicon lifeforms that live inside planets (or on i suppose?)...

The crystalline structure of silicon (cubic?) is similar to the structure of sulfer...were as carbon is hexagonal...it would perhaps be Better at forming `life-form` reactions...

no silicon and carbon are similar (+-4 charge) Sulfur is similar to oxygen (-2 charge) the problem with silicon is that it is filling its second P orbital and the electron affinity is lower. This results in weaker bond strengths and easier reaction that are of determent such as oxidation.

HEhe , you must be a biochemist!

sry, I meant the crystalline form...
Does nitrogen form a hexagon?

(MY thinking is that early `life` on the earth may have used crystals to form the building blocks that lead to cells, etc .)

I thought that silicon life forms had been found on earth, in very hot conditions. in volcanic vents on the ocean floor and whatnot.

Originally posted by blobrana
HEhe , you must be a biochemist!

sry, I meant the crystalline form...
Does nitrogen form a hexagon?

(MY thinking is that early `life` on the earth may have used crystals to form the building blocks that lead to cells, etc .)

Yes the idea of crystal structures in sand or ferrites helping to from pre-biotic molecules is common. I don't know what you mean by crystalline structure, any molecule that you purify and enters into a solid state will naturally crystallize.

Computers though are not alive because they cannot (yet) reproduce and computer advancement also does not follow the laws of Darwinian evolution.

No now life on earth uses silicon-baring substitutes for there DNA,RNA, Proteins so forth. There are some creature that use silicon though. Pollen is made of a good percentage of silicon. There are insects that have silicon polymers to strengthen their exoskeletons… you know the ones :D : those cockroaches you need to hit with a @#$%ing sledgehammer just to knock unconscious!

those cockroaches you need to hit with a @#$%ing sledgehammer just to knock unconscious!

I thought that was to get their attention... :D

Are you serious about roaches having silicon polymers to strengthen their "shells"? Have a link on that?

i just had a quick checkup on the abundance of the `building blocks` for life in the interstellar dust clouds...

looks like there are loads of carbon based compounds, but really only silane for the silicon based lifeforms...

This fact alone probably means that there isn`t any silicon life-forms...but, it doen`t rule out the possibility that it could be created artificially...