Is Astrobiology a Legitimate Scientific Field?

[Lacy33]

Thank you for the continued interest in this thread. I am not qualified to contribute but so enjoy learning as it goes on.

 

[Widdekind]

I'll follow the link after I get through the forums today. However, it sounds as though we're counting on gravitational pressure to generate heat and core of the comet. Is that the model used in that article? I was assuming an external heat source, like the sun (or other star, in the case of solar comets).

I understand, that Prof. Wickramasinghe considers Nuclear Fission, from the heavy elements w/in the rocky parts of the comet, as the primary heat source in the comet's core.

 

[Chronos]

I seriously doubt there is enough fissile material in your typical comet to be of any consequence.

 

[Widdekind]

I seriously doubt there is enough fissile material in your typical comet to be of any consequence.

Prof. Wickramasinghe et al (cited above) conclude an ~8 km comet can keep its core warm "for millions of years", which they say is sufficient for Life to have developed amidst the organic-rich goo in that comet core.

That primordial microbes were comet-carried Chemosynthesizers, adapted to the dark, is consistent with claims that Earth's earliest Lifeforms were Thermophiles found around volcanic vents. Indeed, all Earth Lifeforms can be depicted on "the universal tree of life based on ribosomal RNA data". This Phylogenetic Tree groups Earth Life into three (3) clusters: Bacteria, Archaea, and Eukarya. And:

The organisms closest to the center of the tree, those that populate the deepest & shortest branches, are the Thermophiles & Hyperthermophiles. These are heat loving microscopic organisms found near hot springs and deep-sea hydrothermal vents... One interpretation of the ribosomal RNA tree is that the course of evolution has generally moved from high to low temperatures.

Another important feature of the ribosomal RNA tree is that the majority of the deepest branching organisms do not use light as an energy source. This suggests that Photosynthesis may be a later development than processes utilizing geochemical energy sources... The phylogenetic tree seems to be telling us that our Last Common Ancestor may have been similar to heat-loving Chemosynthetic organisms that populate hydrothermal vents today*.​

Microbes buried in comets' cores could, also, be most likely to survive impacts. Perhaps comets gave the early Earth heat-loving microbes, which first flourished around volcanic vents, which were (somewhat) similar to the hot hearts of their parent comets.

* Iain Gilmore & Mark A. Sephton. An Introduction to Astrobiology, pg. 39.​

 

[Widdekind]

Pity the thread got hijacked.

Lurch, you're right. Gravity is not the only way to create that pressure. In fact, comets are too small to be held together by gravity; it's largely chemical bonds that keep them together.

Also, the calculation done by Mr. Widdekind uses his own...um...highly speculative model for densities. Observations, such as those made on 19P/Borrelly, 9P/Tempel 1 and Shoemaker-Levy 9 indicate that the densities of these comets are lower than Mr. Widdekind predicts, by possibly an order of magnitude or more.

They have Specific Gravities of 16 or more ? That's denser than Lead & Mercury. Even Osmium & Iridium only have densities of ~22 g cm³.

Carroll & Ostlie (Intro. to Mod. Astrophys., pp. A3-A4) cite densities, for Icy Bodies, of ~2 g cm³. And, Prof. Wickramasinghe et al corroborate, that comets must indeed be about 2+ km across.

 

[Vanadium 50]

Life, while common across our galaxy, is apparently absent from others

There is no evidence for either half of that statement.

 

[Vanadium 50]

Observations, such as those made on 19P/Borrelly, 9P/Tempel 1 and Shoemaker-Levy 9 indicate that the densities of these comets are lower than Mr. Widdekind predicts, by possibly an order of magnitude or more.

They have Specific Gravities of 16 or more ? That's denser than Lead & Mercury. Even Osmium & Iridium only have densities of ~22 g cm³.

Lower densities mean that the real densities are less than your prediction. That's what the word "lower" means.

 

[granpa]

why would life in space require water?

 

[Lacy33]

why would life in space require water?

Thank you for bringing this up. I am NOT a scientist, but I would like to ask if life as to be considered only within the biological framework that we observe life on this planet?
I have always thought with fancy about existence in or partially constructed out of dimensions that we have not currently defined in science. This I know is speculative and possibly entirely unacceptable here on this forum, if I am cranking, BOP me.

 

[Widdekind]

I understand, that water is a necessary (liquid) Solvent for all the Biochemical Reactions which power bacteria. It would seem hard to sustain such reaction rates in solids or gaseous phases.

Moreover, all Earth Life seems to need water (yes?). Assuming Panspermia, so did our archaic astral ancestors.

 

[Widdekind]

Lower densities mean that the real densities are less than your prediction. That's what the word "lower" means.

Comet Tempel 1 has a mean density of ~0.62*. It is described as a "rubble pile", implying that it was shattered in an ancient impact**.

* http://en.wikipedia.org/wiki/Comet_Tempel_1
** http://en.wikipedia.org/wiki/Rubble_pile​

CONCLUSION: This suggests that Biogenesis probably began in un-shattered, "monolithic" comets. Prof. Wickramasinghe focuses on comets at least 8 km across, (somewhat) more massive than Tempel 1. Perhaps such comets can withstand impacts. Otherwise, this could provide an extra constraint on (minimum) habitable comet masses.

 

[Vanadium 50]

Lower densities mean that the real densities are less than your prediction. That's what the word "lower" means.

Comet Tempel 1 has a mean density of ~0.62*.

Which is a factor of ~3 less than your theory predicts.

Not only is your theory overly speculative (and I now see the mods locked the thread where you originally tried to push it), it simply doesn't agree with the data. In science, that means its wrong.

It is described as a "rubble pile", implying that it was shattered in an ancient impact**.

Which has nothing to do with astrobiology. Your thread hijacking is now complete.

This suggests that Biogenesis probably began in un-shattered, "monolithic" comets.

Where is the evidence? You keep saying this over and over again. You haven't provided any evidence for this speculation.

 

[sas3]

I have been running S.E.T.I. on computers since 1999, if that is not "Real Science" then I have wasted a lot of processor power and so have a lot of other people.
http://www.boincstats.com/signature/user_127693.gif"

At this time I think S.E.T.I.@Home is one of the best chances we have of finding life, that's why I run it.
Plus I get to receive and process data from the Arecibo Observatory, How cool is that?

 

[LURCH]

I understand, that Prof. Wickramasinghe considers Nuclear Fission, from the heavy elements w/in the rocky parts of the comet, as the primary heat source in the comet's core.

Oh my! Well, I now see that the "link" that I promised to check out earlier is not in fact a link at all, but merely the title of a source (properly underlined as per MLA referencing). However, given the position stated above, I would have to question the legitimacy of this source. What is the energy source that initiated this "fission"? How is it sustained over millions of years? Why is the comet not blown apart by the fission reaction?

Why would the author take this position, when life on Earth does not derive its energy from any similar source? For example; comets orbit the sun, just like the planets do. Why wouldn't the sun be the source of energy? Or, given their highly elliptical orbits, why not tidal flexion, like on Io?

The BS alarm on my bunk-o-meter just get triggered.

 

[jmason52]

Evidence of life on exoplanets is not as difficult to find as it might appear. Detection of significant amounts of oxygen in the atmosphere of an exoplanet would be a compelling indicator.

I too am a real noob at this, but have a question. Why do we assume that unless an exoplanet has either liquid water or oxygen, there is little liklihood of life being available there? Is it going into the realm of science fiction to think that maybe life can form in other types of atmospheres?

I just think that by projecting what we know, which granted is all we have to go by, we limit the possibilities.

I'm certainly open to flame here, but would like to hear some opinions.

Cheers!

 

[granpa]

I'm always wondering what it would be like to live on a world with a liquid hydrogen atmosphere (not cold hydrogen but just compressed to the point that it has the same density as liquid hydrogen)

the density of liquid hydrogen is 1/15th that of water so you couldn't swim in it but wings would work pretty well. it would also provide considerable protection from meteorites. the big question is how much light could make it through to the surface.

I wonder if the hydrogen and helium would separate? (shrug) who knows.

 

[jmason52]

Exactly! I guess what prompts my thoughts on this are the extreme biologies we find here on earth. One that comes to mind are the marine creatures that live in the strongly sulpheric atmosphere of volcano vents. Yes, the are in an ocean of liquid water, but if an organic being here can live in that sulpheric "cosmos" diluted by water, why couldn't one have grown in a purely acidic environment.

 

[LURCH]

I too am a real noob at this, but have a question. Why do we assume that unless an exoplanet has either liquid water or oxygen, there is little liklihood of life being available there? Is it going into the realm of science fiction to think that maybe life can form in other types of atmospheres?

I just think that by projecting what we know, which granted is all we have to go by, we limit the possibilities.

I'm certainly open to flame here, but would like to hear some opinions.

Cheers!

The key to this question, is to understand that we are looking for life " as we know it." Of course there could be some world that possesses shallow seas in which (as one PFer once suggested) quartz crystals grown in latticework formations resembling sea fans make a living off of the energy generated by piezoelectric affect caused by wave motion. Or maybe there are living clouds that use the temperature differential in the atmosphere through some form of "thermosynthesis."

But what, then, would we look for? Planets that have any form of liquid and any form of crystal? Planets that have clouds and an atmosphere with a non uniform temperature?

The only kind of life which we have even a remote chance of locating is the kind of life we have observed already. Those are the only forms of life which we know for certain to exist. Other kinds of life may exist, or they may not. But if there's life out there that does not resemble Earth life, we would have to ask ourselves the question, " then, what does it look like?" Unfortunately, the answer is that it could look like anything; we simply have no clue what to look for. Heck, life forms that exotic could exist right here on earth, and we would never see them.

 

[Arch2008]

Here’s a very good treatment of why our favorite molecules are the ones that won the “biology lottery” and some insight into the wanta be’s:
http://books.nap.edu/catalog.php?record_id=11919#toc

Also, this is a link to an article in Astronomy magazine that describes how none of the believed chemical precursors to life seem to exist around red dwarf stars (M-dwarf stars):
http://www.astronomy.com/asy/default.aspx?c=a&id=8093
If the star has no chemical precursors to life in its planetary disk, then planets around these stars may have no life (no chickens if no eggs). These “cooler” M-dwarfs apparently don’t get the necessary chemistry going to create hydrogen cyanide, perhaps because of less UV radiation. So an ocean on an Earth sized planet in the habitable zone around such a star with no hydrogen cyanide molecules might be a lifeless pool. As 70% of the stars in the Milky Way are M-dwarfs, this is probably not good news for SETI, unless life on such a planet is radically different from what we know works.

 

[Chronos]

I don't think the host star is necessarily the source of precursor molecules. A stellar 'birth' cloud is usually an admixture of molecules furnished by nearby firecrackers. The difference between a G and M star is mainly one of mass. Non-detection of cyanide molecules is, IMO, more an issue of instrument sensitivity.

 

[Widdekind]

Oh my! Well, I now see that the "link" that I promised to check out earlier is not in fact a link at all, but merely the title of a source (properly underlined as per MLA referencing). However, given the position stated above, I would have to question the legitimacy of this source. What is the energy source that initiated this "fission"? How is it sustained over millions of years? Why is the comet not blown apart by the fission reaction?

Fission reactions — aka "Radioactive Decay" — in the interiors of Comets is essentially the same as that which occurs in the Cores of larger, planetary bodies. Lord Kelvin famously showed, that the Earth should have radiated its heat from formation (~ G M² / R) in roughly 50-100 million years... but the Earth's interior has remained molten for 4-5 billion years (up to 100x longer than expected). This is the result of Fission reactions (Radioactive Decay) in the Earth's interior. These reactions are not explosive, like a run-away chain reaction in a bomb. Rather, they are slow and steady, much like a heat-generating Nuclear Reactor.

Thus, even as the Earth is not "blown apart by the fission reaction", neither would Comets explode either. And, just as on Earth, where all the heat pouring out of the Core (from these Fission reactions) ultimately provides the energy source for Chemosynthetic Life to thrive upon — eg. at Black Smokers & Geothermal Vent systems along spreading Mid-Ocean Ridges, whose Plate Tectonics are powered by the motions of the Mantle, whose Convection cells are driven by the heat pouring out of the Earth's radioactive Core — so, too, the same might be said for Comets.

I may have missed, or mis-understood, some things, but I think the argument is something like this:

Radioactive Decay --> Heat --> Comet Core becomes a "gooey" mess of Organic Compounds --> Primordial "soup" of first Life​

 

[Chronos]

Water is a natural search target. It is the only substance necessary for life as we know it. There may be other options that work, but, we do not know of any at present. So, it makes perfect sense to look for water as an indicator of life elsewhere in the universe. We also have reason to believe water is abundant in the universe. I'm still not buying the radioactive comet thing, Why would such heavy elements exist in abundance in the Oort cloud? It makes much more sense for them to be concentrated near the sun.

 

[Widdekind]

Why would such heavy elements exist in abundance in the Oort cloud? It makes much more sense for them to be concentrated near the sun.

Wouldn't the "collapsing cloud" of the proto-Solar Nebula be chemically well-mixed ? Couldn't a clump create a comet, containing many 'metals', even far from the proto-core of the collapsing cloud ?

Are you saying, that proto-stellar nebulae undergo Gravitational Differentiation, as in planetesimals, where all the heavy metals migrate to the center of mass ?

 

[Widdekind]

According to Wikipedia, the Oxygen-binding organo-chemicals, in the "blood" of both Arthropods (Hemocyanin) and Mammals (Hemoglobin), have closely comparable coefficients (Hill Coefficients) for binding Oxygen:

In some hemocyanins of horseshoe crabs and some other species of arthropods, cooperative binding is observed, with Hill Coefficients of 1.6 - 3.0. Hill constants vary depending on species and laboratory measurement settings. Hemoglobin, for comparison, has a Hill Coefficient of usually 2.8 - 3.0.​

Thus, the best binders of Oxygen, anywhere in the Animal kingdom, appear to asymptote towards a Hill Coefficient of ~3. Applying this (cautiously, of course) to the Cosmos, might this mean, that (Oxygen metabolizing) Exo-fauna might "max out" at comparable coefficients ?

 

[Widdekind]

Would (Oxygen-metabolizing) Exo-fauna have blue "blood" ??

Arthropods' "blood" contains Hemocyanin, to transport Oxygen. And, "Oxygenation causes a color change between the colorless Cu(I) deoxygenated form and the blue Cu(II) oxygenated form".

Likewise, it is well-known, that Oxygenated Hemoglobin is blue.

And, it is well-known, that the sky appears blue, b/c atmospheric Oxygen (& Nitrogen) preferentially scatter shorter (bluer) wavelengths of light.

QUESTION: Does all this imply, that "Oxygen is just plain blue" in appearance (since it scatters shorter wavelength light) ??

And, if so, would that mean, that any hypothetical Oxygen-binding compound, appearing in the "blood" (equivalent) of Exofauna, be likely to be blue in appearance (when Oxygenated) ??

 

[Chronos]

Uniformly mix heavy and light elemenst in solution. Add a central 'attractor to draw them in, then 'shock' the media [like a star igniting]. Do the heavy elements tend to collect nearer or more distant to the star?

 

[Widdekind]

I don't know how to answer that. Don't pre-Main Sequence, proto-stellar nebulae, take many millions of years to form ? That might make plenty of time for gravitational differentiation, or it might mean that the cloud's collapse is so slow, and quasi-static, such that such differentiation doesn't proceed apace.

What about stars forming in clusters, and nearby Supernova explosions "polluting" proto-stellar collapsing clouds w/ more metals -- such a process would preferentially populate the periphery of the collapsing cloud w/ the most metals.

According to the PBS documentary Exploring Space -- The Quest for Life (DVD), "comet & asteroid" impacts, upon this planet, have produced copious quantities of heavy metals mostly found only in Earth's core. For one example, the Vredefort Crater in S.Africa has produced fully 40% of all Earth's mined gold, and the narrator listed a long list of other craters, yielding copper, coal, and hydrocarbons. This strongly suggests, that "comets & asteroids" contain copious quantities of many metals -- but, perhaps, all the coal comes from carbonaceous comets, and all the metals from meteorites (?).

 

[LURCH]

Are you saying, that proto-stellar nebulae undergo Gravitational Differentiation, as in planetesimals, where all the heavy metals migrate to the center of mass ?

That is one model (one to which I happen to subscribe). It is based on the composition of planets in our own solar system, with rocky planets near the center, and the gas giants toward the outside. Of course, this model has problems, not the slightest of which is the overwhelming central mass of the sun, which is almost entirely hydrogen and helium.

Likewise, it is well-known, that Oxygenated Hemoglobin is blue.

I thought hemoglobin was only blue when it is depleted of oxygen. Oxygenated hemoglobin is red, is it not?

 

[qraal]

Comets and asteroids in the protoplanetary nebula would have been efficiently heated by Aluminium-26 decay.

 

[Vanadium 50]

Likewise, it is well-known, that Oxygenated Hemoglobin is blue.

No, it's not. It's red.