Anyone believe in Aliens?

[PatTheRat]

I remember reading somewhere that our telescopes have identified around 8 planets that could potentially support life outside our solar system. Any movement on this?

An also, if these planets could support life, what are the chances they could support human life? What are the chances that oxygen, carbon dioxide, water etc have formed identically in another world?

[Clanad]

Page 5

D. Vokrouhlicky and P. Farinella, �Efficient Delivery of Meteorites to the Earth from a Wide Range of Asteroid Parent Bodies,� Nature, 407 (2000), pp. 606-608.
Yumiko Watanabe, Jacques E. J. Matini, and Hiroshi Ohmoto, �Geo-chemical Evidence for Terrestrial Ecosystems 2.6 Billion Years Ago,� Nature, 408 (2000), pp. 574-578.
Hugh Ross, �Bacteria Help Prepare Earth for Life,� Connections, v. 3, n. 1 (2001), p. 4.
Crisogono Vasconcelos and Judith A. McKenzie, �Sulfate Reduc-ers�Dominant Players in a Low-Oxygen World?� Science, 290 (2000), pp. 1711-1712.
Matthias Labrenz, et al, �Formation of Sphalerite (ZnS) Deposits in Natural Biofilms of Sulfate-Reducing Bacteria,� Science, 290 (2000), pp. 1744-1747.
Jochen Erbacher, Brian T. Huber, Richard D. Morris, and Molly Markey, �Increased Thermohaline Stratification as a Possible Cause for an Ocean Anoxic Event in the Cretaceous Period,� Nature, 409 (2001), pp. 325-327.
M. M. M. Kuypers, R. D. Pancost, J. S. A. Sinninghe Damst�, �A Large and Abrupt Fall in Atmospheric CO2 Concentrations During Cretaceous Times, Nature, 399 (1999), pp.342-345.
Subir K. Banerjee, �When the Compass Stopped Reversing Its Poles,� Science, 291 (2001), pp. 1714-1715.
Fred C. Adams and Gregory Laughlin, �Constraints on the Birth Aggregate of the Solar System,� arXiv:astro-ph/0011326 (Nov. 16, 2000).
Ian A. Bonnell, Kester W. Smith, Melvyn B. Davies, and Keith Horne, �Planetary Dynamics in Stellar Clusters,� Monthly Notices of the Royal Astronomical Society (2001), in press.

[newtron]

I asked for references, so the last three pages of citations is all I wanted.  Thanks.  I found a similar reference list on the web.  Lots to read, but it will be interesting.

[Clanad]

Sooo, that's 57 of 96 citations.  If you have an interest in the rest, I'll be happy to provide them...BTW, the list has now expanded to 258 characteristics. 

And, finally to address slimfandango's question, I'll quote this source:

One other possibility must still be addressed, a question that often hampers progress toward a realistic assessment of the chance for life elsewhere: To what degree might extraterrestrial life differ from �life as we know it�? At one time biologists speculated that extraterrestrial life might be based on exotic chemistry, something other than carbon.

So, biochemists went to work on the problem. Their research showed that only silicon and boron, besides carbon, can serve as the basis for adequately complex molecules�molecules capable of sustaining basic life functions, such as self-replication, metabolism, and information storage. This finding presents some significant problems, however. First, silicon can hold together a string of no more than a hundred amino acids�far too short a string to accommodate any conceivable life systems and processes. Second, throughout the universe boron is less abundant than carbon; so carbon always supersedes it. Third, concentrated boron is toxic to certain life-critical reactions.

The conclusion, published as early as 1961, still stands. Physicist Robert Dicke deduced at that time that if anyone wants physicists (or any other physical life forms, for that matter), carbon-based biochemistry is a must.40 The key word, here, is physical. What about life that is not physical?

[newtron]

After looking through the citation list, I found that I have read a few, but it has been a while.  Clannad, have you read all these references?  For future reference, when I ask for references, I am interested in the source(s) that you got the information from not the reference lists that were included in those sources.  I can read the citation lists from those sources just as you did.  Thank you for all your effort though.   

[slimfandango]

good effort clanad, thanks.

[newtron]

PatTheRat, despite the small chance of life being elsewhere, scientists are looking for life on other planets, especially Mars.  I know a person who studies microorganisms in extreme environments such as deep caves, subsurface sediments, and black smokers, etc. and believes that that these type of environments are the best place to start the search for extraterrestrial life.  In fact most scientists I have talked to think that if there is liquid water, there is probably life.

[landie]

Yes, I do, they must exist.

I've seen a special walkway for them at the airport.

[Clanad]

newtron, I've read many of them.  A lot of the 200 some odd characteristics I've listed are from various sources.  As you can see from the citation list, Dr. Hugh Ross, an astrophysicist (Phd. Astronomy, University of Toronto, 1973) is an active contributor, and I've read many compilations of his work...

No excuses, but the list of charctersistics, being as long as it is, was cited from many works. Thanks for the interest.  You have a background in geology, do you not?

[newtron]

Yes, I have a bachelor of Science in geology.

[jake-the-peg]

Hmmm have we stumbled onto a hobby horse Clannad?

I'm a little concerned about the logic here in a number of areas.

Firstly Universal constant values such as the decay rates of particles are the same for everybody so if they are OK for life for us they should be OK for life elsewhere and thus should be discounted.

I'm not sure that all of your parameters are truely independant of each other - if the chances of blond hair are 1 in 10 and the chances of blue eyes are 1 in 5, the chances of blond hair AND blue eyes are not 1 in 50.

Thirdly I'm not entirely convinced that all of these are actually necessary factors in the development of life - I cannot see how galaxy size can be so critical that only 1 in 10 galaxies could support life. 

It does strike me that if we take a figure for stars in the universe of something like 10 to the 25 then your figure makes our own existance so improbable as to almost be a proof of God.

You don't have a hidden agenda here do you? 

Incidently Newtron can we have the link you found on the web

[newtron]

http://www.reasons.org/resources/fff/2002issue08/index.shtml

Here you go.  As you can see jake-the-peg, this website is all about proving the existance of god as you have mentioned.  Dr. Hugh Ross is at the center of it.  I agree that some of the characterisitcs seem strange.  For example, what does the position and mass of Jupiter relative to earth have to do with the existence of life on earth?    

[jake-the-peg]

Thanks

Ah, I can answer that one about Jupiter, it acts as a giant gravitational hoover without it earth would be hit by a lot more meteoritic impacts - however that's not to say that life on earch could not exist without Jupiter put it might have started a lot later.

Incidently I do have to agree with Clannad about Carbon based life forms - while I can't say it's impossible I think it's actually pretty unlikely that you could have non-carbon based lifeforms.

OK you could get around the chain length problem by imagining genetic information being passed via three dimentional crystals but Silicon has a much higher affinity for Oxygen which means you'd have to have another gaseous fuel and it all becomes very messy  

[jake-the-peg]

Oh dear Oh dear we seem to have a bit of manipuation going on here.

Dr Ross Says:

FACTS for FAITH contributing author and astronomer Guillermo Gonzalez, determined that the abundance of uranium and thorium relative to iron in the interstellar medium has been declining for the past 4.5 billion years.1 This suggests that only a planet formed 4.5 billion years ago could possibly possess enough uranium and thorium to sustain plate tectonics and volcanism long enough for advanced life to be possible. 2

What the paper actually says is The evolving
concentration of the geophysically important radioisotopes in the ISM establishes a window
of time (albeit with fuzzy boundaries) in the history of the Milky Way during which
terrestrial habitable planets with long-lasting geological activity can exist. That window is slowly closing with a timescale of billions of years.

It's here if you want to read the full thing

http://arxiv.org/abs/astro-ph/0103165

I don't think I'll waste too much more time with Dr Ross

[Clanad]

Well, jake, it's probably best just to leave it there... I do think your bias is showing, however. 

But just to clarify: what Ross actually says, in full, is "Uranium and thorium play a vital role in the plate tectonics and volcanism of planets. Consequently, the amount of these two metallic elements influences the ability of any planet to support advanced life." He then continues with your quote, then adds..."The star of such a planet would need to have been formed more recently than five billion years ago. Therefore, the number of stars that might be candidates to possess a planet with the capacity to support advanced life is just a tiny percentage of the total stars in existence. Stars that formed significantly earlier than about five billion years ago or later than about 4.5 billion years ago would not be candidate".
This, then, compared to Gonzalez, (page 38) who states ..."Therefore, in order to calculate the radiogeneic heating in the interior of an Earth-like terrestrial planet, we must scale the stellar K/Fe, Th/ Fe, and U/Fe abundance ratios in Fig.5 using bulk Earth -to-Cl- chondrite ratios given above. We show the results of such calculations in Fig.7. They indicate that a terrestrial planet with the same formation time and age as the Earth produces only 36% as much radiogeneic heat, and one forming today will, in 4.5Gyr, produce only 21%as much. This is due to the smaller value of 40K/Fe predicted by our Galactic chemical evolution calculations�an Earth-twin formed today will, in 4.5 Gyr, have 60% of the present Earth�s heat production."

Where's the disagreement or manipulation?

Contd.

 

[Clanad]

Page 2,

Finally, Gonzalez in his summary does state..."�Given the lack of suitable alternative geothermal energy source, radiogenic heating is a necessary requirement for the long term maintenance of a terrestrial planet�s habitability via climate stability provided by the carbon cycle�.
Your quote comes from pages 37 and 38... � The evolving concentration of the geophysical important radioisotopes in the ISM establishes a window of time (albeit with fuzzy boundaries) in the history of the Milky Way during which terrestrial habitable planets with long-lasting geological activity can exist. That window is slowly closing with a timescale of billions of years�.
This, very obviously, refers to the length of time that such planets can exist (my emphasis), not form. The full context of the text clearly deals with the placement within the Glactic disk of the Earth-like planets with the best chance of providing habitability.

A full reading of the document indicates no disagreement between Ross and Gonzales... In my opinion...

[jake-the-peg]

The "diagreement" is that Ross makes the leap that planets with a lower abundance of Uranium and Thorium would be unable to support life, and has placed narrow time limits not implicit in the original without considering the degree of variation in the data.

Even with a lower abundance of these isotopes a slightly larger earth type planet would produce significant Vulcanism.

But that's not the main problem, Ross draws firm conclusions from considered scientific papers, discarding all the provisos and allowances for error in the original (rather like a politician with statistics)

Gonzalez et al. note amoungst other things that this relates to earth-like aerobic life only they also note that the requirements for plate tectonics are not well known They also note that since observations can only
give us the present values of the Galactic abundance gradients, estimates of their evolution are rather model dependent.

Indeed the charts themselves have estimted errors in the order of 50% - This sort of error is not unusual in astronomy and error bars can sometimes exceed 100%.

The point is that you just cannot draw the sort of conclusions from this work that Ross does. It's not a disagreement he just plays fast and loose with the data to support his perspective.

Although even if he were right and there were less than a million habitable planets in our galaxy there are millions upon millions of galaxies just like ours.

Personally if I wanted to argue for the uniqueness of human life I would concentrate on the remarkable presence of mitochondria in the cell - now that's hard to explain.

 

[pprules]

Of course there is. Mars so every possible sign of life. There has to be.