Contact for the Study Group: Dirk Schulze-Makuch E-mail
website maintained by Anthonie Muller:
E-mail
last updated October 14, 2002; under permanent construction; part of the content is always draft
See also the earlier link
Titan Study Group
|
|
Contact for the Study Group: Dirk Schulze-Makuch E-mailwebsite maintained by Anthonie Muller:
E-mail
See also the earlier link
Titan Study Group
|
Dear Louis,
My comments on Venus life in "Planetary Dreams" (1999) did not originate there but were adapted in part from earlier ones in "Life Beyond Earth" (Feinberg and Shapiro, 1980). My late colleague, Gerald Feinberg, developed the idea, using Carl Sagan's airborne Jovian life as a source of inspiration. I have included a quote from pages 336-338 of that book below.
I think that you and Dirk have done the Astribiology community a service by pumping new life into the idea and developing the metabolic and strategic aspects of it. Keep up the good work.
Best Regards,
Bob Shapiro
From "Life Beyond Earth":
It is possible that conditions on Venus were different in the distant past. There may have been an ample supply of free energy available at the surface before the evolution of the present atmosphere. Paradoxically, the lack of a thick atmosphere would also have led to a lower surface temperature because there would be no greenhouse effect. In this case there may have been abundant chemical reactions, of the type assumed to occur in the early Earth, on early Venus as well. If so, there may have been life forms based on carbon chemistry. It is hard to believe that such life could survive the transition to present conditions on the Venerian surface, but this may have happened. Some conditions on Earth today are immensely different from the early Earth, but life has survived both by evolving and by being oblivious to the changes. If the conditions on Venus changed slowly enough, it could be that primitive life there could have evolved to survive and thrive even in the present conditions. Indeed, some of the organisms may have grown to like their present circumstances. After all, even hell is the beloved home for some orders of demons, and present-day Venus, with its heat, storms, and sulfurous clouds, is a fine approximation on of hell.
One possibility along these lines is that Venerian life became airborne and survives now in the upper atmosphere, where conditions are more like those of early Venus. The lack of a solid surface need not be a problem for such life any more than it is to the fish that live in our oceans. Achieving buoyancy in the thick atmosphere should not be difficult. This could be done if "airbags" containing gas from the thin upper atmosphere were included in the bodies of the living creatures. An alternate possibility is that the creatures of Venus float on permanent updrafts of wind that blow from the lower to the upper atmosphere. Such floating life forms were proposed by Harold Morowitz and Carl Sagan some years ago. It is unlikely that life could have evolved under these conditions because the density of matter is low, but migration of surface life to an atmospheric home is more plausible. Earthlife has migrated back and forth from water to land , and perhaps to air as well; so there is a precedent for such developments on Venus. Future explorations of the atmosphere of Venus should shed light on both of these possibilities.
I did not hear anyone opposed to the change in scope. Thus, let go and name ourselves "Life in the Solar System (Discussion) Group". I think given that all of us joint initially because of interest in Titan and the on-going Cassini mission, that discussion about Titan will automatically be a big part. Anthonie, if you please could make the changes on our website - thank you.
I like Louis' idea of bouncing ideas freely around and noone should feel offended in anyway in those kind of discussions. Contrary to Louis I have a difficult time of thinking of organisms floating from layer to layer in Jupiter's atmosphere, but certainly everything should be considered. Regarding Robert's comment that a solid surface does not have to be a requirement for the origin of life - I agree - it only appears to me that certain early cell functions would very much be assisted by a solid surface (I would have never thought that I find myself now on the conservative side arguing).. However, we should not assume anything a priori as a requirement for life. May be Gustaf or Jim, as resident experts on the origin of life on Earth, can let us know what they think on this issue.
Regarding Venus, I think that Louis' and my contribution were to come up with overall metabolic reactions for microbial life in the Venusian atmosphere and then find the chemical signatures that provide scientific support to these reactions as well as putting a comprehensive list together of arguments in favor - not evidence - but all items put together it would appear that microbes would be the most straightforward and easiest explanation (e.g. Orcam's Razor). However, Louis is correct that the talk at the conference in Austria was about different mission concepts for atmospheric sampling (the Astrobiology Journal article published about 1.5 month earlier was on the issue of microbial life), but I guess that is freedom of the press.
Anyway I enjoy the revived discussion. Please continue,
Dirk
Dear BeyondTitans:
I've been enjoying the revitalized discussions brought about by the
expansion of the purvue of our group, and support it generally. My only
suggestion is that we continue to give more that token attention to Titan,
because of the impending possibility that the Huygens probe will give us
more data from that distant body than we'll have on Europa, Venus, Io, or
any closer body that might appear to be a more likely candidate for life
vaguely like we know it. However, it does make sense that Jonathon's Titan
Focus Group is the best venue for attending to Titan specifically.
David, I side with your preference to keep our objective rather broad and
open-ended. Until our sample size for life exceeds 1, I believe it behooves
us to consider the broadest range of possibilities. The peer review process
keeps us disciplined and conservative, so let's enjoy one avenue where we
can be unabashedly speculative (with the understanding that truly silly
ideas will be shot down deservedly with no personal affront taken).
On the issue of atmospheric life, I side with those of you who see more
opportunities than problems, whether at Venus, Titan, or the Gas Giants.
Life is pervasive in the Earth's atmosphere, so we know that once started,
it can thrive there. Admittedly, there is a question about whether
air-borne organisms go through multiple life cycles without touching the
ground, but that they can survive for long periods in the breeze seems
clear.
I do side with Dirk on the importance of solid surfaces or contained volumes
for the origin of life, though this derives more from my observation as a
biologist that complexity inevitably arises more readily at interfaces than
in homogeneous media. Once begun and delivered, however, I can envision life
perpetual in the clouds, so have no problem with the possibility that all
the gas giants could be teeming with strata-specific biotas. I never
thought I would think that, but am beginning to do so. Someone may need to
"bring me back to earth", so to speak, on this issue.
Robert, I appreciated the quotes from your book. You have framed the
scenario for the possibility of life on Venus very well. You, Grinspoon, and
others have clearly foreseen the possibilities for life at Venus well before
Dirk and I turned our attention in that direction. The recent publicity
about our Venus Sample Return paper at the Graz meeting was, in that regard
misleading, in that the main focus of the paper was evaluation of sample
collection and return strategies rather than the notion of finding life
there in the first place, which obviously is not original with us.
Vladimir, thanks also to you for your provocative thoughts about hot origins
for planetary systems. Not being a planetary scientist, I don't know
whether such an idea is really that "mad", but would like to hear the
opinions of others. On a side note, I have never been happy with the
prevailaing theory about the moon's origin (biproduct of early catastrophic
collision), and wonder if your theory provides an alternative scenario for
the origin of the moon. An accretion mechanism has always seemed more
plausible to me. But again, I'm not a planetary scientist.
Thanks again to everyone for all the stimulating thoughts.
Regards, Louis
Dear Lifers (oh dear, "Titans" sounded much better!),
Having just a single point on our graph (i.e. Earth life) we can draw an
infinite number of curves in trying to extrapolate what life might be like
elsewhere. That is the great pleasure and the great problem of astrobiology
today. Given that almost anything remains a possibility at this stage, I'd
be interested to hear from group members if they feel that any particular
areas of focus are needed in our discussions. I'm rather for keeping things
pretty open at this stage because it may encourage new lines of thought. But
I'm curious if the new "Titan and Beyond Group" (if that is what it is to
become) sees itself as having any definite scientific goals, or evolving
instead into a kind of unfettered (though informed) think tank that simply
generates lots of ideas that may or may not be useful.
On the specific issue of atmospheric life that Dirk and Bob have been
discussing, I should point out (if we're simply brainstorming) that there
are ways in which, for example, life could exist in the atmospheres of gas
giants, but not have originated there. It could have been transferred by
asteroid/comet impact from a nearby (putative) life-bearing moon (e.g.
Europa to Jupiter). Or, if one gives credence to the notion that primitive
life might actually develop aboard periodic comets (complex i/s mols in ice
+ repeated solar heating) it could have been delivered directly by impacting
comets (such as Comet Shoemaker-Levy 9). Atmospheric life may or may not
exist. But if we find that it does, we can't immediately rule out the
possibility that life always requires some solid surface on which to
originate. In any event, I've very optimistic, given the tenacity and
adaptability of terrestrial microbes (remember the bugs on Surveyor 3 that
survived 18 months on the Moon!), that if life gets transferred abruptly
from one environment to another that it can, in some cases at least,
survive, adapt, and, ultimately, prosper.
Best wishes to all,
David Darling
Dear Dirk, and Life-in-the-Solar System group,
Thanks, Dirk, for your distinction between the possibility of
atmospheric life on Venus, in which the organisms fled to the atmosphere
after a conventional surface origin, and atmospheric life in the heavy
planets, which, if it exists, presumably originated in the atmosphere. With
regard to the latter, I would give Jovian atmosphere life a lower priority
in our searches than the exploration of Mars, Titan and Europa, because it
is easier to search for things that we are familiar with than things that
may be strange to us. However, I would choose to avoid unnecessary
pessimism in advance of any actual observational data. We had more than
enough gloom-and-doom back in the 1980's, when Prof. Norman Horowitz was
releasing comments such as: "The failure to find life on Mars was a
disappointment, but it was also a revelation. Since Mars offered by far the
most promising habitat for extraterrestrial life in the solar system, it is
now virtually certain that the earth is the only life-bearing planet in our
region of the galaxy."
With regard to your specific arguments, I can only quote my late
colleague Gerald Feinberg who concluded, after extensive analysis, in Life
Beyond Earth (p 212-213): "These arguments suggest that while the presence
of liquids as a medium for chemical reactions may be convenient, it does
not seem absolutely essential. A dense gas, especially at the high
temperatures which enhance reaction rates, could be an equally convenient
medium for chemical reactions, and one which is much more common in the
Universe than liquids."
Apart from the liquid vs. dense gas comparison, I am puzzled by
your specification that a solid interface is required for the origin of
life. Admittedly, an evolving system needs some sort of compartment or
enclosure to prevent its essential components from scattering (literally,
in the case of Jupiter) to the winds.
But this compartment could be made of a fluid membrane, as in Lancet and
Deamer's lipid world, by aerosol droplets, or of other non-solid materials.
Radiation could be destructive to certain chemical systems, but to
others it might provide a very tasty energy source.
Perhaps, in this group, we can move to a position of guarded
optimism, and leave the conservatism to the congressional appropriations
committees and NASA administrators.
Best wishes to all, and lets keep the discussion going.
Bob Shapiro
Dear All,
I strongly support the idea about re-orientation of our group. Athough
there actually exists a risk to loss focus, we feel that insufficient
database about Titan, at least this time, is an obstacle to further
development of our suppositions and hypotheses concerning life processes
on the planet. I will think over what can I add to our discussion.
Now I would like to inform you about my last work that concerns to
new suggested field of our team. My last broshure "Nonequilibrium State
of Stars and Dichotomous Formation of Planetary Systems" that was
distributed at ISSOL02 and Bioastronomy'02 Meetings, devoted to elaboration
of the hypothesis of hot origin of all bodies of our solar system, due
to chain division of initial hot protoplanetary mass ejected from early Sun.
The hypothesis can seems "mad" from the point of view of well-known theory
of origination of solar planets due to cold accretion. So, I do not call
to do it a background for comparison of the planets, but may be somebody
will like it (the abstract is given at the end of the message and the whole
broshure as attached file). Hot prehistory of all bodies of solar systems,
that suggested in the broshure, permits to consider and evaluate
systematically opportunities for life origination/existence on the planets,
satellites and asteroides, because from this point of view all main
conditions for life origin (liquid water, organic matter, source of energy
and added by me avaiability of strong fluctuations) could exists in
principle elsewhere.
So, it would be possible to distinguish some groups of bodies for comparison:
Earth; Earth-like planets (Mars, Venus); rest terrestrial planet (Mercury);
geologically-active satellites (Io. Europa, etc.?); geologically-passive
satellites (Moon, etc.); asteroides.
Best wishes,
Vladimir Kompanichenko
Kompanichenko V.N. Non-equilibrium State of Stars and Dichotomous
Formation of Planetary Systems. PGS Publisher, Khabarovsk, 2002.
The dichotomous conception of origin of planetary systems and stars’
associations is based in this brochure. The basic thesis of the conception
is that a star is able to eject a part of its mass at the earliest
stage of evolution (i.e. is able to divide under certain conditions),
due to contradictory interaction between the forces of gravitational
compression and heat expansion. Extremely non-equal division represents
in fact the ejection of initial protoplanetary mass. Further successive
dichotomous (i.e. on two components) division of the ejected mass leads
to formation of planets as well as smaller bodies. «Brown dwarf»
appears instead protoplanetary mass in case the difference between
masses of two divided components is smaller. More or less equal division
of the initial star often leads to formation of binary stellar systems.
Dear Robert and All
Thank you for your stimulating paragraphs on Venus. I was
not aware of your recent book, but am quite familiar with
Grinspoon's ideas and also your earlier book "Life beyond
Earth" (which by the way I believe is one of the best or
the best book that I encountered on this topic).
It may come to a surprise to you that I'm generally quite
skeptical of atmospheric based life. The reasons are
1. for any type of origin of life process, especially in
regard to information content, there appears to be a solid
interface required. There isn't much of that in an
atmosphere
2. life also appears to require a solvent for multiple
exchange processes, liquids are present in any atmosphere
but only at minor concentrations
3. the lower density of an atmosphere makes interaction of
molecules and thus life-supporting processes much more
difficult
4. much stronger radiation exposure in an atmosphere than
for life on the surface or in the subsurface of a planet
5. true, buoyancy can counteract fall to the surface or
hot interior by gravitational force, but it imposes another
serious contrain
Thus, I consider life on a surface or in the subsurface much
more likely than life in an atmosphere. I
think the chance is very low that there is life in Jupiter's
atmosphere even though it consists of many organic
molecules. Hardly any organic molecules were detected on Venus,
but I regard Venus as one of the famous exceptions.
Venus had an ocean very early on in the Solar System, thus life
could have developed in a similar setting to terrestrial
life with a solid interface (or it could have been transported
by meteorites from Earth - many of the early phototrophs and
chemotrophs on Earth were thermoacidophiles, which would
nicely fit in). If the environmental transformation on Venus
went not too rapid, microbial life would have had time to adapt
to life with minute amounts of water and more radiation in the
atmosphere. Buoyancy may not be a problem either for
possible Venusian microbes because the atmosphere is very
stable in a way that aerosols appear to stay suspended for months
(compared to days in Earth's atmosphere), thus microbes
could easily pro-create in that time span (before
sinking down and die) even though they may be heavier than the
surrounding atmosphere.
That way many of the severe constrains of atmospheric
life could have been resolved by selected adaptations.
Other lines of evidence for the possibility of life on
Venus are given in our hypothesis article in Astrobiology
Journal that I forwarded to you last time and will not repeat
here.
I generally agree with you absolutely that we have to make
us free from our human- and Earth-centered ideas. But by the
same token I think that life is more than established order
or even ordered structures induced into a chaotic system by
energy flow (minerals would have to be considered alive
then as well). Of course, my ideas above are somewhat
Earth-centered as well, and there may be for examples ways
for the origin of life without a solid interface, but
without any at least theoretical model, I guess, I would
tend to stay "conservative" in regard to this issue.
In regard to the expansion of our group to a "Life in
Solar Systems" or 'Life in the Solar System" group I
received so far only positive remarks either emailed to the
whole group or only to me, not a single negative one. Thus,
I would think to probably go with that if there are no
objections, but lets leave "the floor" still open for
comments on this for a week or so before making the change.
Cheers, Dirk
It is a good idea that makes a lot of sense. The risk might be a loss
of focus.
Cheers to all,
Remy Hennet
Dear Dirk,
Well done! I was delighted to see your speculations aired on CNN, BBC World
Service, etc -- excellent publicity for astrobiology. I've included an item,
together with another mention for the Titan Group, on my Astrobiology
Central website at http://www.daviddarling.info
I'm sure you'll all be aware of the new work by Christopher England (JPL)
suggesting possible oceans on Titan and other outer moons, besides Europa,
Ganymede, etc. If not, here is an overview:
http://news.bbc.co.uk/1/hi/sci/tech/2290005.stm
Perhaps we should expand the remit of the Group beyond Titan to include the
possibilities for life elsewhere in the Solar System. This might to lead to
some useful cross-fertilization of ideas.
Best wishes,
David
Dear group members,
I think that the expansion of our vision to encompass the entire
solar system should be fine, especially for the purpose of a discussion on
the nature of life in general and possible limits to life. On the other
hand, the funds available for the search for such life are quite likely to
be limited, so some painful setting of priorities will be needed, when we
consider which goals we should advocate. The possibility of Venus life was
one of the topics in my last book, "Planetary Dreams" and I have reproduced
a few paragraphs below for your consideration.
Regards,
Robert Shapiro
New York University
COMPLEXIFICATION ON VENUS?
We know life only as we have seen it on this planet. Our first
inclination when considering other worlds has been to extend our
experience. We saw Venus as hot, but habitable, with creatures that were
unpleasant but shared enough Earth biochemistry to digest us without
complaint. When these visions collapsed, astronomers rushed to firm
conclusions, for example: “extant life on Venus is out of the question” and
“it is unlikely that life ever arose on Venus”.
If we wish to search for a Life Principle, however, we cannot be
so abrupt. Water is not unique - other liquids can support chemistry.
Venus, alas, has no oceans of any type on its surface, except for possible
transient lava flows. A dense atmosphere with liquid droplets, however may
possibly support chemical cycles leading to self-organization. Energy poses
no problem: ultraviolet light, chemical sources, and other energy supplies
are available in abundant amounts. One planetologist, David Grinspoon of
the University of Colorado, has been willing to speculate along these lines.
He cites novel features on Venus which indicate that something
that we do not understand is going on. The clouds contain dark mobile
markings, visible in the ultraviolet, and unusual particles. The mountains
peaks are all “surprisingly shiny”. That glitter is not due to ice but to
some mineral substance such as pyrites or tellurium. Possibly, complex
cycles based on sulfur chemistry are at work, and some form of
complexification is taking place.
My late collaborator, Gerald Feinberg, had speculated earlier
about life in the clouds of Venus. For organisms adapted to the cloud
temperatures, descent to the furnace-like surface might be a disaster.
Survival for them would depend on buoyancy, and they would need to take
advantage of updrafts or use devices such as airbags filled with lighter
gases. Evolved creatures might have such resources, but it is hard to
visualize an extended series of earlier steps taking place in suspension
above the inferno. One other scenario remains possible, however.
The current surface of Venus appears to be only a few hundred
million years old. Some catastrophe involving massive lava flows may have
eradicated a different set of conditions that existed before that time. If
early Venus was more Earth-like in nature, then any creatures that evolved
in that era may have had a time to adapt and flee to the clouds, before
disaster caught up with them.
The extended series of assumptions and speculations needed to
imagine cloud life on Venus does not make it our best bet, and the
corrosive nature of the chemicals would hinder robotic exploration. Sooner
or later we should look there, but we will find better possibilities for
cloud life in the gas giants.
Dirk and everyone,
I definitely love the idea of a "Life on Planets" group. I find that I think best in "comparative planetology" mode. I've learned more about Earth from thinking about conditions for life on other planets than I ever would have by confining my thoughts to Earth.
We are seeing the beginnings of a science more general in scope and application than biology as confined to earth. Future applications of this science will include remote life detection telescopic missions like Terrestrial Planet Finder and the like as well as missions to our own solar system.
Cheers,
Penny
Dear All,
what do you think of David's idea to expand the group to
other planetary bodies in our Solar System with respect to
life or properties that could make life feasible ? I think
that may be a good idea, specially because (1) many of us do
not work only with Titan, and (2) there is now a NASA
Titan Focus Group led by Jonathan. In expanding our remit
we could nicely develop complimentary ideas and function as
a scientific Think Tank Group for bouncing of ideas for life
in the Solar System.
Please let us know what you think !
Cheers, Dirk
Dear All
Although this is the Titan Group and not a Venus Group I
thought I email you our original article (attached) that was
published in Astrobiology Journal in the current issue (vol 2,
no 2).
It went all over the media last week (something we
really did not expect since our presentation in Graz
[by Louis Irwin, Troy Irwin and myself] was more about mission
alternatives how to sample the Venusian atmosphere). Some of
the things came out not really correct (e.g. New Scientist
putting stuff together after interview with me where not
everything was reported quite how I said it; then CNN, BBC
etc getting it from New Scientist and so on, things taking
on there own "life".
Anyhow, I thought it would be a good idea if you have the
original article and would appreciate any input you have.
The approach, may in part, have some relevance to Titan as
well, although the atmosphere is of course very much
different.
Cheers, Dirk
For those of us not at Graz this week:
http://sci.esa.int/content/news/index.cfm?aid=12&cid=35&oid=30548
Best wishes,
David
Re: AGU session: Remote Detection of the Ingredients for Life Date:
Dear All:
Venkat Lakshmi and I have a proposal pending for convening a
Union Session at the next AGU FALL Meeting in San Francisco
(please see below). Would anyone of you, who is AGU (American
Geophysical Union) member (and best if affiliated with the
Biogeosciences section, or if not the Planetology section) be
interested to co-chair the proposed Union Session with us?
The Union Sessions are special sessions that are of general
interest and include at least 3 different areas (e.g. here: Hydrology,
Planetology and Biogeosciences).
Please let me know if you are interested. Any
suggestion to the title and description are welcome
as well.
Cheers,
Dirk
Title and short draft description of session:
Remote Detection of the Ingredients for Life
Liquid Water, polymeric chemistry and energy sources are the
ingredients of life as we know it. As in-situ exploration is
expensive and not feasible for many solar system bodies in
the near future, the primary insights will be obtained by
remote sensing using space probes or Earth as platform.
Thus, it is essential to know what indicators and
signatures of life we can detect, how well we can detect
them with which type of remote sensing techniques, and
to know the limits of their application. Examples of
relevant remote sensing applications include the detection
of volcanic activity beneath glaciers on Earth, observations
consistent with a liquid water ocean beneath Europa's icy
surface, the detection and quantification of polymeric
compounds on Saturn's moon Titan, and the screening for
present and past habitable environments on Mars.
Re: Titan and origin of life possibilities
Dear All:
Dirk, I agree with Remy Hennet "that the origin(s) of life on the early
Earth
was inescapable rather than an extremely unlikely event". My opinion that:
"The Living Object is the structural formation, which is limited in space
and time, informationaly sufficient for self-reproduction in an adequate
media and is inevitably generated in the specific time of Universe's
evolution"
(http://www.geocities.com/awjmuller/pdf_files/LivingUniverse.pdf). In the
second my article
(http://www.geocities.com/awjmuller/pdf_files/DropChemEvol.pdf) I formulated
conditions for origin of protocell with membrane outside and chiral
oligomeres inside of drop's water. According my calculations the all time of
the chemical evolution into the drop is about one second. This time is
negligible as compared with times of organic syntheses in gas atmosphere or
in water on Earth's surface under UV-light energy, cosmic rays, Earth's
radioactivity, discharging of atmosphere electricity and volcano's heart.
At last, always problem chicken-and-egg i.e. what was the first: DNA(RNA) or
peptides? And how was origin of genetic code? In my mind, the genetic code
is not due to chemical and prebiotic evolutions - chemical structure 4th
nucleotides and 20th canonic amino acids and it's mapping for each other are
determined by proper act of Origin of Universe. Another wordes, wherever and
whenever we will find living microorganism its genetic structure is the same
as the Earth's living systems
(http://www.geocities.com/awjmuller/pdf_files/LivingUniverse.pdf). So the
problem chicken-and-egg can be solved if we suggest that own chemical more
exactly biochemical pathway in a drop-protocell is the single that leading
to origin of self-reproduction system. How is the way to prove it?
Cheers to all!
Victor Gusev
Re: Gustaf Arrhenius: Titan and origin of life possibilities
Hi All,
I do not want push my personal origin of life model too often,
BUT if there has been an internal heat source on Titan
(radioactivity, tidal heat, heat by induction currents), then life could have started there according to my thermosynthesis model.
The combination of internal heat and a cold surface on a planet
or moon that contains a fluid at its surface must result in convection of that
fluid, which in turn could drive thermosynthesis in the organisms carried
along by the convection currents.
These conditions could apply to the early earth and
to Titan as well.
By the way, the thermosynthesis model is the only model
that explains so many parts of the origin of life.
For more details I refer to the thermosynthesis home page:
Regards,
Anthonie Muller
The Thermosynthesis Home Page
Re: Gustaf Arrhenius: Titan and origin of life possibilities
Please see below an email from Gustaf Arrhenius that he sent
me earlier this week as discussion contribution. His
comments are in UPPER CASE embedded in my previous email.
Cheers, Dirk
At 4/24/2002 you wrote:
= FROM GUSTAF ARRHENIUS
=
= = Dear All:
= =
= = I just like to run some thoughts by you. There always had
= = been some discussion whether Titan somewhat in a crude way
= = resembles conditions similar to early Earth. If so, the
= = question arises could life originate on Titan.
= =
= = That is difficult to answer because we don't even know how
= = life originated on Earth. As an outside observer, I would
= = think life originating on Earth would be an extremely
= = unlikely event. It seems to be incredibly complicated with
= = that interplay within a sea of polar and non-polar compounds
= = that somehow leads to something really complex.
=
= THE CRUCIAL PROBLEM IS
= TO FIND SPONTANEOUS NATURAL SYNTHESIS PATHS
= TO MOLECULES THAT CAN STORE
= AND TRANSFER INFORMATION (THE CRICK-ORGEL CENTRAL DOGMA). STEPS TOWARD
= SOLUTION OF THAT PROBLEM HAVE PROGRESSED REMARKABLY FAR , CONSIDERING THE
= 'PERCEIVED' COMPLEXITY OF RNA, p-RNA, TNA AND OTHER ANALOGS. SYNTHESIS
= IN THE INTERSTELLAR MEDIUM AND IN LAB. PLASMAS (W.LOEB) OF THE BASIC
= SUGAR BACKBONE COMPONENTS, GLYCOLALDEHYDE AND FORMALDEHYDE HAVE BEEN
= DEMONSTRATED. FACILE PHOSPHORYLATION MECHANISMS (ORGEL, KRISHNAMURTHY)
= AND HIGHLY EFFECTIVE, SELECTIVE MINERAL INDUCED NUCLEOSIDE PRODUCTION
= (PITSCH) HAS BEEN SHOWN, AS WLL AS MINERAL INDUCED OLIGOMERIZATION OF
= NUCLEOTIDES TO FORM NUCLEIC ACIDS (ORGEL, FERRIS). DEEP INSIGHTS INTO
= AUTOCATALYTIC, CHIRAL REPLICATION OF p-RNA AND TNA HAS BEEN GIVEN BY
= ESCHENMOSER AND HIS COLLABORATORS
=
= = If, for a moment, we don't see Earth as a model, how would
= = one rate the possibility of the origin of life in a sea
= = of near-pure hydrocarbons with very little polar and ionic
= = compounds around (such as Titan where essentially all the polar
= = compounds are solid ice). Would that possibly simplify our problem ?
=
= YES, WATER IS THE ENEMY OF SYNTHETIC ORGANIC CHEMISTS
= =
= = Or, seeing it from another standpoint, the most important
= = physical attributes to a cell (at least for me based on my
= = limited understanding) are metabolism,THE LEAST DIFFICULT a boundary (e.g.
= = cell membrane)
=
= OR EVEN MORE SIMLPE, EXPANDING DOUBLE LAYER MINERALS
= SUCH AS MIXED VALENCE METAL HYDROXIDES
=
= = and a replication mechanism.
= Again, in a crude
= = way, metabolism appears in principal easy: a chemical reaction
= = that releases energy. A boundary doesn't seem that difficult
= = either based on David Deamer's suggestions (e.g.
= = his presentation "Self-assembly of Organic Molecules and the
= = Origin of Cellular Life" at the Astrobiology Conference 2 weeks
= = ago).
=
= A LIPID BILAYER WOULD BE DIFFICULT TO CREATE AND MAINTAIN IN A
= SEA OF HYDROCARBONS - CELLULAR MINERALS OFER NO SUCH DIFFICULTY.
=
= =That
= leaves the replication mechanism. How DNA is replicated
= = appears to be very complicated to me
=
= WORKS SPONTANEOUSLY IN SURFACE
= CATALYZED REACTIONS IN THE LAB.
=
= = Isn't there any
= = simpler way to do that ?
=
= HARDLY
=
= = Would replication, just possibly,
= = be easier in an environment that has only organic compounds
= = around such as in some environments on Titan ?
=
= THE ONLY WAY TO ARRIVE
= AT CONSTRUCTIVE AND MEANINGFUL INSIGHTS IS BY EXPERIMENT. SO, BACK TO THE
= LAB, ALL.
= =
= = I gave that issue quite some thought, but appear to be
= = somewhat stuck. Any ideas, suggestions or comments ? Or am I
= = here totally off-course ?RIGHT ON!
= =
= = Cheers, Dirk
= =
Re: Titan and origin of life possibilities
Dear Dirk,
To engage your question in the broadest sense, I see three
possibilities through which we may learn about the origin of life (any
life) by studying Titan:
(1) Impacts or water volcanism may have created episodes of
aqueous chemistry in lakes on Titan’s surface, perhaps lasting thousands of
years before they froze over. Each such frozen lake represents a suspended
experiment in chemical self-organization awaiting our examination. Did some
energy-driven self-organization take place in the water? We need only to
perform an analysis to find out. See R.D. Lorenz, et al., Enantiomer 6, 83
(2001).
(2) Titan may contain an internal ammonia-water ocean (A.D.
Fortes, Icarus 146, 444 (2000)). If so, considerable evolution may have
taken place over billions of years, and the problem of life detection is
comparable to that faced in investigations of Europa. If we uncover another
example of evolved life, we may not learn about its origin, but another
huge question will have been answered; is Earth life the only possible
basis for life? (Evolution there would almost certainly produce another
system than evolution here).
(3) Evolution toward life may have taken place in the frigid
hydrocarbon seas of Titan. Self-organization under such circumstance would
probably involve very weak non-covalent forces, but provided an appropriate
energy source was available and sufficient time, nothing in the laws of
physics forbids it. The detection such organized systems would provide the
deepest insights of all, as it would demonstrate that the circumstances
under which life can develop are very broad indeed. To learn more, see
“Life Beyond Earth” by G. Feinberg and R. Shapiro (me), Morrow, New York
(1980).
In connection with your specific question, I would suggest that
DNA or RNA replication is a high-tech advanced product of evolution. In the
beginning, life probably made do with reproduction instead, which may have
involved as simple a mechanism as the division of a lipid compartment into
two smaller daughter compartments. See R. Shapiro, A Replicator Was Not
Involved in the Origin of Life, IUBMB Life 49, 173-176 (2000) and D. Segré
and D. Lancet, Composing Life. EMBO Reports 1, 217-222 (2001).
Best wishes,
Bob Shapiro
Re: Titan and origin of life possibilities Date: David Darling
Dear All,
Regarding the origin of life in general, it seems that the distinction
between Remy's and Dirk's viewpoints has to do with hindsight. Given that
life *did* appear on Earth under what seem (to us, as humans) remarkably
unclement conditions, it seems almost inevitable that it *would* appear. In
other words, rewind history by 4.5 billion years, and you would put money on
life arising again. But without that hindsight, which is what I took Dirk to
mean, we could not anticipate anything so complex as life emerging from an
unpromising stew of primitive organics and energy gradients. The whole thing
seems preposterous. In fact, there is still such a huge gap between the
simplest conceivable life-form and the type of organics we know exactly how
to manufacture that we have to admit that the origin of life remains, in
large part, a mystery.
Titan is such a vastly different place from Earth today that if life evolved
there under anything like the present conditions, it must surely be quite
different from the terrestrial variety. The question I would like to ask the
group is: Can we say much about what the physico-chemical conditions were
like on Titan in its early youth, say 4 billion years ago, when presumably
there was still a substantial amount of heat rising from the moon's core and
possibly other factors made for a more Earth-like abiogenic environment? My
point being that if life emerged at this early stage on Titan, when it was
more similar to the young Earth, at least in terms of subsurface
temperatures, it may gradually have adapted to survive under the present,
more hostile conditions -- for example, by evolving a long-term cryptobiotic
state from which it can emerge when temporarily favorable conditions allow
or other "tricks" that allow it get along with a fundamentally familiar
biological make-up in a very unfamiliar environment. Bottom-line: the
conditions under which life generally originates may be much narrower than
those to which it can eventually adapt.
All the best,
David
RE: Titan and origin of life possibilities Date:
Dirk -- I prefer to assume that the origin(s) of life on the early Earth
was inescapable rather than an extremely unlikely event as you
suggested. The problem remaining that we do not fully understand the
mechanisms as yet. Assuming that an extremely unlikely event explains
the unknown strikes me as a bad start.
If one approaches the problem at the scale of micro environments, the
existence of mixtures of polar and non-polar compounds on Earth is not
relevant. Polar and non-polar environments exist/existed on Earth and
it is likely that an important part of the physics and chemistry that
led to first life on Earth occurred at the interface of and within these
micro environments. Accepting the hypothesis that life somehow
originated on the early Earth leads to the likely conclusion that it
continues to do so since primordial micro environments continue to be
represented on Earth, albeit not to the same extent they have been. A
lot more experimental and theoretical work will have to be conducted
before breakthrough occurs to test this hypothesis; but the endeavor is
likely worthwhile.
As for Titan, we may not yet have the right picture as to the nature and
distribution of micro-environments. It can be argued that the
"freezing" out of polar compounds is either a boost or a detriment to
life. We just do not know. Once again, the sampling and
characterization of diverse environments on Titan would be quite
enlightening and so would the results of well-designed experiments.
Cheers to all!
Remy Hennet
Re: Titan and origin of life possibilities
Dear All:
I just like to run some thoughts by you. There always had
been some discussion whether Titan somewhat in a crude way
resembles conditions similar to early Earth. If so, the
question arises could life originate on Titan.
That is difficult to answer because we don't even know how
life originated on Earth. As an outside observer, I would
think life originating on Earth would be an extremely
unlikely event. It seems to be incredibly complicated with
that interplay within a sea of polar and non-polar compounds
that somehow leads to something really complex.
If, for a moment, we don't see Earth as a model, how would
one rate the possibility of the origin of life in a sea
of near-pure hydrocarbons with very little polar and ionic
compounds around (such as Titan where essentially all the polar
compounds are solid ice). Would that possibly simplify our problem ?
Or, seeing it from another standpoint, the most important
physical attributes to a cell (at least for me based on my
limited understanding) are metabolism, a boundary (e.g.
cell membrane) and a replication mechanism. Again, in a crude
way, metabolism appears in principal easy: a chemical reaction
that releases energy. A boundary doesn't seem that difficult
either based on David Deamer's suggestions (e.g.
his presentation "Self-assembly of Organic Molecules and the
Origin of Cellular Life" at the Astrobiology Conference 2 weeks
ago). That leaves the replication mechanism. How DNA is replicated
appears to be very complicated to me. Isn't there any
simpler way to do that ? Would replication, just possibly,
be easier in an environment that has only organic compounds
around such as in some environments on Titan ?
I gave that issue quite some thought, but appear to be
somewhat stuck. Any ideas, suggestions or comments ? Or am I
here totally off-course ?
I am pleased to announce that the NASA Astrobiology Institute will initiate a Focus Group on the Astrobiology of Titan beginning in November of 2002. I will chair the group. To give you a sense of what the Focus Group will deal with and on what schedule, I append both a prospectus and a strawman timeline of activities.
Most of the work will be by e-mail with some telecons and meetings coordinated with the NAI annual meeting. A pre-start meeting will occur next mont at the NASA Astrobiology conference in Ames. If any of you are planning to be at that conference, please let me know.
I hope that, as part of Dr. Schulze-Makuch's superb e-mail group on Titan, you will participate as well. Suggestions, ideas, innovations are welcome.
With kindest regards,
Jonathan Lunine
Announcement April 7-11, 2002, Astrobiology Science Conference 2002
agenda
Speakers present from this club:
L. Irwin, D. Schulze-Makuch: Alternative Trajectories for Life on Other Worlds: Lessons from the Evolution of Life on Earth
Jonathan Lunine: Tales from the Outer Limits of Astrobiology: Titan and Giant Planets (Near and Far)
Titan Study Group Website
Bill Arnett on Titan: basic data. With links to discussion of other moons of Saturn. Bill Arnett
Bill Arnett by UCSB: another route Bill Arnett by UCSB
Calvin Hamilton on Titan: Calvin Hamilton Site contains some slowly popping-up advertising.
J.D. Knight on Titan: J.D. Knight
Louis Pinto on Titan: Louis Pinto
David Darling: (member of the Study Group!) Astrobiology Central: The Quest for Extraterrestrial Life
On-line Astrobiology articles and links:
The Astrobiology Index (articles from various science journals): The Astrobiology Index
Space.com Astrobiology site Space.com Astrobiology site
Astrobiology 2001 conference Astrobiology 2001 conference
Year 2000 abstracts, AbSciCon 2000 AbSciCon 2000
NASA site on Cassini-Huygens mission to Saturn and Titan. NASA on Cassini-huygens
Subpage on Titan: Subpage on Titan
Another NASA page on Titan Another NASA page on Titan
JPL pages on Titan JPL 2001 Conference Papers
Voyager-2 picture of Titan Voyager-2 picture
Hubble Space Telescope pictures Hubble Space Telescope
French research French research group
SETI site SETI
Life in the Universe site: Life in the Universe
Lunar and Planetary Institute: Lunar and Planetary Institute
Discovery Channel Discovery Channel
CNN: CNN on Titan
PBS: PBS on Titan
Thesis by Andrew Dominic Fortes, student at University of London college; 1997-1999. Lots of material. Andrew Fortes
Thinkquest: prepared by students. Thinkquest
| Name | Institute | Interests | E-mail address | E-mail link |
| Gustav Arrhenius | Scripps Institute of Oceanography/NASA | origin of life, organic chemistry | arrhenius@ucsd.edu | |
| John Bang | University of Texas at El Paso | medical sciences, biochemistry | jjbang@utep.edu | |
| Penny Boston | University of New Mexico | subsurface microbiology, geochemistry | pboston@complex.org | |
| David Darling | Science Writer/Minnesota | astrobiology, planetary science | darling@uslink.net | |
| Christian De Duve | C. de Duve Inst. of Cellular Pathology, Belgium | origin of life, medical sciences | vandemaele@icp.ucl.ac.be | |
| Jim Ferris | Rensselaer Polytechnic Institute, New York | origin of life, planetary atmospheres | ferrij@rpi.edu | |
| Huade Guan | New Mexico Institute of Mining and Technology | geochemistry, microbial transport | hdguan@nmt.edu | |
| Victor Gusev | Russian Academy of Sciences | biophysics, astro- and nuclear physics | vgus@math.nsc.ru | |
| Bob Hazen | Carnegie Institution of Washington | organic chemistry, origin of life | hazen@gl.ciw.edu | |
| Remy Hennet | SSP&A, Maryland, USA | geochemistry (inorganic and organic) | rhennet@sspa.com | |
| Jimmy Hincapie | University of Texas at El Paso | geophysics, remote sensing | jimmyh63@yahoo.com | |
| Louis Irwin | University of Texas at El Paso | astrobiology, neurobiology | lirwin@miners.utep.edu | |
| Tom Kieft | New Mexico Institute of Mining and Technology | subsurface microbiology, extreme environments | tkieft@nmt.edu | |
| Vladimir Kompanichenko | Russian Academy of Sciences | non-linear dynamics, origin of life | vkomp@as.khb.ru | |
| Antonio Lazcano | University National Autonoma Mexico | origin of life, biochemistry | halar@hp.fciencias.unam.mx | |
| Jonathan I. Lunine | LPL/ University of Arizona | planetary physics, atmospherics | jlunine@lpl.arizona.edu | |
| Anthonie Muller | post-doc | origin and evolution of biological energy conversion |
AnthonieMuller@aol.com | |
| Matthew Pruis | NorthWest Research Associates | microbiology, sample retrieval technologies | matt@nwra.com | |
| Francois Raulin | LISA, University of Paris, France | atmospherics, origin of life | raulin@lisa.univ-paris12.fr | |
| Bartlomiej Rzonca | Cracow Technical University, Poland | hydrological sciences, modeling | br@uci.agh.edu.pl | |
| Dirk Schulze-Makuch | University of Texas at El Paso | astrobiology, hydrological sciences | dirksm@geo.utep.edu | |
| Robert Shapiro | Department of Chemistry, New York University | organic chemistry, particular DNA, computer modeling of DNA, origins of life | rs2@nyu.edu |
working method
As general guideline, please feel free to bounce off ideas that you may feel to be ridiculous to some. We want to keep as open minded and less earth-centric as possible. However, we also want to be backed up by science as much as possible and particularly come up with predictions for the Huygens probe (which will measure (1) atmospheric chemisty, (2) wind direction and velocity (thus energy indirectly), (3) surface topology/imagery, (4) surface chemistry, and (5) temperature gradients).
Hopefully, an expressed statement from everyone to this set of questions will start a lifely discussion via email (again, please address to everyone on the list).We will stop when it looks like that we have accomplished a task (e.g. this time a thorough characterization of Titan as a possible life environment - generally, on a planetary scale) When the input/discussion slows down or latest after a set time period (2-3 weeks?) we will move on to a new set of questions.
After being done with a set of questions, I will summarize on what we agreed and where there may be still dissent.If you have any suggestions for questions to be incorporated into the emailed set of question at any time, please let me know and I will try to incorporate them. Hopefully, that way we can steer the discussion into a fruitful direction. Any critique at any time is welcome.
The latest set of questions will also be posted on the GBiG research web site under Titan Study Group: link.
I believe we have a somewhat final group together with a total of 18 members (please see below). Because all our time is very valuable, we not just want to chat, but also achieve constructive results. I believe we have a great breath of expertise and I hope that this group fulfils the expectations you have. Please feel free to comment or make suggestion on how to proceed (this is a new type of project for me also).
There is quite a variety of background about Titan among group participants, from near-zero to some of you who wrote an article or a book about Titan. I thought we start our discussion with a cartoon depicting major factors controlling the environment on Titan and characterizing it in a broad outline (please see attached file).
Lets address in the first round the following set of questions:
Q 1. Can you identify/add other important physical or chemical parameters that are not depicted on the figure - that are relevant to the atmosphere, surface, subsurface or other environment on Titan ?
Q 2. What type of organic chemical reactions do you know or would expect to occur in any of the types of environments on Titan (please feel free to speculate as we need to link those reactions or possible reactions at some later time to possible biochemical reactions).
Q 3. What would you believe would be the most likely environment for life on Titan (if it exists) ? - or in other words on what type of environment should we focus, or do you feel that we should not focus at that time but first describe each environment thoroughly ?
Everyone please send an email to everyone else on the list with your assessment. If you feel you can't address every question, that's fine, please still forward a statement to at least one of the questions (e.g. for Q 3 everyone should be able to come up with an opinion).
Summary to Set I Questions and Discussion
Life on Titan is envisioned by us as a possibility, by some of us seen as unlikely while others take a more optimistic viewpoint. If it exists, it would most likely be associated with subsurface geothermal regions although other possibilities should not be dismissed. Even if life is confined to the subsurface, ejecta from volcanic activity may spread evidence of life into the atmosphere. If life does not exist on Titan, Titan would still be a useful sampling point for prebiotic, cosmic organic molecules. There is also the possibility that life may have existed at some point on Titan (closer to the formation of the moon when it was warmer), but not anymore.
Pathways to life that were pointed out were supercritical phases that have the capability to concentrate organic chemicals (one of my Ph.D. students currently looks into that) and also cloud droplets as possible protocells. We discussed the minimal conditions for life, which can probably be summarized by the presence of a liquid, an energy source, polymeric chemistry and some kind of protection from hostile space (e.g. atmosphere, ice shield).
It was pointed out that amino acids are not evidence for life (which is also supported by the recent discovery of amino acids in space). Life without information content is unthinkable. Thus, more suitable molecules that can be suggested to be screened for are phosphorylated aldoses, nitrogen bases and cyano compounds. A conclusive proof for life is difficult to make and Carl Sagan's saying "Extraordinary claims warrant extraordinary evidence" is certainly making the point. The ringing question appears to be "Can we do better than chirality, …etc". The second set of questions will further explore that problem.
Other not answered questions from set 1 remaining are : Is there dynamic activity and disequilibrium in Titan's atmosphere ? How do we explain the high nitrogen content of Titan's atmosphere ? These questions address atmospheric issues, an expertise in which we are a bit underrepresented. Thus, if anyone still knows an atmospheric scientist to join us, please contact that person or let me know.
P.S. I did some slight revision to the figure of Titan's Environment also (please see attached). I believe Louis is correct with pointing out the low density of Titan making solid substrate near the surface probably quite rare. Certainly we would not expect any mountain ranges as indicated in the first version of the figure.
Here are the questions for Set II: - please feel free to address part of the question set only
1. What do we consider evidence for life, or as Remy phrased it "Can we do better than chirality ………..etc [it would be great if we could put together a comprehensive list here] ?
2. Are there any physical features or fossilized physical features of life we can use as evidence for current or past life (e.g. minerals., reef/stromatolite like assemblages) ? What evidence for life can we gather by using remote sensing ? Would that be enough to make a conclusive case ? Given the Huygens probe measurements (which will measure (1) atmospheric chemisty, (2) wind direction and velocity (thus energy indirectly), (3) surface topology/imagery, (4) surface chemistry, and (5) temperature gradients), what type of measurements would support the notion that life is present ?
3. Is the atmosphere a possible environment for life ? What are the characteristic and organically important processes in the atmosphere of Titan ?
Summary of Set II:
We agree that a general encompassing definition of life would be extremely useful. However, even in its absence, we can point to certain properties of life that are measurable and useful parameters for a positive identification of life systems (some more direct, some more indirect):
(1) polymeric compounds of high molecular weight of 1,000 or higher
(2) homochirality
(3) isotopic fractionation toward the light biogenic elements (particularly C12/C13 in methane to indicate whether the methane on Titan is likely to be biogenic)
(4) cellular compartmentalization
(5) microgeomorphological and mineralogical evidence consistent with life
(6) oxygenated compounds in significant quantity in Titan's reducing atmosphere (and probably surface) as evidence of life-sustaining redox reactions
(7) detection of some kind of reasonable metabolic by-product
(8) detection of chemical(s)that could be the building block of a genetic code
(9) detection of high polymeric (organic) compounds at disequibrium boundary zones
Not a single property of those listed above is evidence for life but the presence of a majority of those listed would certainly point toward this direction.The more exotic (in the sense different from us), the more difficult it would be to arrive at a positive proof (e.g. if life for example would not be based on redox-reactions).
What can the Huygens probe do ?(1) (3-? anybody knows for sure?) (6) (7) (8) (9, if lucky)
What does the next generation probe have to do ?(2) (3) (4) (5) (9) and others with a higher sensitivity
Opinions varied greatly on the chemical make-up of life on Titan, if present.
Opinions ranged from a make-up basically identical to Earth' life to the theoretical possibility of silicon-based life (which can be dismissed if Huygen's does not detect any Si- or Si-C polymers and possible by-products such as silanes).Given Titan's exotic environment, if life is present and detected, it would allow an intriguing test how different life can be from that observed on Earth.
In a paper by Jonathan crater impact zones and zones associated with cryovolcanisms were pointed out as possible environment of life, but also photosynthesis and an acetylene-powered chemistry was pointed out as possible options. We will look into these issues somewhat closer in the next question set, because as pointed out by John: without growth medium (suitable environment for fitting reactions) there is no growth of cells.
1. The first question refers to the summary of Question Set
II.Anyone knows whether the Huygens probe can detect isotopic fractionation ?For indicators (7), (8) and (9) some specific chemicals were mentioned here and then. Can we add to this ? Can we come up with certain indicator chemicals for which to screen ?
Also, any other comments and suggestions on the summary set are (still) welcome.
2. In the cold environment of Titan, life, if it exist, may be kinetically (metabolically) slow, life cycles may be very long compared to life times on Earth, and population densities very low.How do we deal with this problem ? As Remy already mentioned, how intense and extensive would life activity have to be on Titan to register a signal at detectable levels, especially if we sample in the atmosphere only ?
3. Given you have only one try, where on the surface of Titan would you sample for life ?Why ?Are there other energy sources that life on Titan could make a living on? Particularly, is photosynthesis an option as suggested on theoretical reasons by Jonathan (in one of the Enantiomer papers) ?
2.2.4 Set IV
1. Please check out the graphs for the atmosphere and
interior of Titan at http://www.seds.org/~rme/titan.htm.
What kind of thermodynamically favorable reactions can you
envision that could serve as a primary metabolic pathway for
life if it exists (such as CO2 + 4 H2 to CH4 + 2H2O on
Earth) ? Is there any photosynthetic reaction you believe
would constitute a reasonable possibility ?
2. In the interior model of Titan the possibility of a NH3-H2O ocean is pointed out. Is this an analog to the likely ocean within Europa ? Would the possibility of life with NH3 in the water be enhanced or reduced ?
3. Does anyone know of some direct evidence of volcanic activity on Titan ? Volcanic activity is usually inferred by Titan's size but do we have any (even indirect) evidence of volcanic activity ?
4. Given you have only one try, where on the surface of Titan would you sample for life ? Why ?
Reactions
03/13/02 Jaime Hincapie
Hello, Titan Fans
I’m kind of left behind, but catching up fast... at least trying.
First of all, Huade’s idea about a web page is wonderful. Since all of us are busy, I’m sure someone has some time off (and I’m sure that at this point Dirk is thinking “So, Jimmy, you seem to have some free time, why don’t you work on the Titan Group web page?”), so in order to come back to active duty, I volunteer to work on the web page. Of course, if everyone agrees, and if I get ideas and pictures from everyone. I’ll work on some schematics and sketches and as input comes in I’ll improve and submit the results to the group.
Regarding the questions, here are some thoughts:
I find the web site quite interesting. Huade and I made a comparison chart with info from several sources. The initial idea was to look for similarities among Solar System bodies. Unfortunately we couldn’t get to something really solid to show, so we left it aside. I think that it could be a good starting point to tackle these questions since the web site provides physical and chemical data that should be contrasted against the other bodies’ data. Here I provide attachments with the charts and other information that could be useful.
Now, coming back to the web site, several things intrigue me. First of all, under the physical conditions of gravity pull and temperature, is it possible to have a shallow ethane-methane sea?, this is, a LIQUID shallow sea? If it is, then we might have some conditions set to provide a partial answer to question 1, since a solvent is already present to host the potential constituents for life. This could also applicable to question 2. Huade’s comment about having an ocean “sandwiched” between a couple of ice shells is very in order to me. My initial suggestion would be that heavy elements are still dissolved in that layer as they find their way to the interior of Titan (due to their high specific gravity), and the radioactive decay prevents this layer to freeze.
Regarding question 3, it would be AWESOME if we had ANY evidence or at least any INDICATION of volcanic activity. This would provide at least one comparison point with life on Earth, since volcanic activity could be a very important energy source. In any case, I believe that making comparisons between bodies and look to their initial similarities (or differences) would point out their differences (or similarities), as we gain more information about them.
About question 4, if I had only one chance to sample Titan’s surface for life, I’d try the equator. The reason is that it seems that along the equatorial line any celestial body gets the most radiation from its star. In this case, UV light, IR, protons, and all the cosmic goodies would strike the surface with greater frequency, enhancing the possibilities for any well adapted organisms to harvest energy.
03/12/02 Robert Hazen
I've enjoyed reading the exchanges during the past couple of months. This is my first comment.
At the Carnegie Institution we have quite a lot of new data on hydrothermal synthesis and stability of ammonia in aqueous media (+/- transition metal oxides and sulfides), as well as hydrothermal amino acid stability and AA synthesis from ammonia + carboxylic acids. We are well set up to perform additional hydrothermal synthesis experiments and have been exploring some of the well articulated theoretical ideas (e.g., Shock, Wachtershauser, Morowitz). We'd be happy to conduct runs to document organic synthesis reactions under possible Titan ocean conditions.
We'd need to have suggestions for experimental ranges of T, P, composition and other parameters, but we can certainly test experimentally any promising ideas. Any thoughts? Recent experiments here and elsewhere lead to an interesting conclusion.
Organic synthesis appears to be facile under almost any environment with simple carbon molecules and appropriate energy (dense interstellar molecular clouds, Miller-Urey, hydrothermal, impacts, etc.). Life as we know it will consume much of that prebiotic organic inventory. Therefore, certain suites of energy-rich molecules (e.g. food), if present in abundance on another body, may represent "abiomarkers" -- i.e., clear evidence that life has not been present. In thinking about the search for life on Titan and elsewhere we should be aware that recognition of such abiomarkers would be an important, if less newsworthy, discovery.
3/12/02 Remy Hennet
Of primary importance in understanding pre-biotic or biotic chemistry in Titan's ammonia-water ocean is to establish a range of prevalent conditions in that ocean (including bottom sediments and ocean-sediment interface). Conditions such as pH, Eh, mineral buffers, temperature, pressure and partial pressures, etc. drive and limit the types of chemical reactions or syntheses that can take place. Give those conditions to geochemical modelers (for example Schock or Helgeson types) and they can calculate chemical activities resulting from the synthesis of many organic molecules of interest (amino acids, sugars, or anything for that matter). These types of calculation can serve to guide the understanding process and design experiments or sampling activities. All of that has to be done prior to going to Titan to sample. This group could be a good place to start.
Geochemical modeling could also help narrow down sampling locations where most interesting organic chemistry might take place on Titan. For example, is it enough to sample the bulk of the ammonia-water ocean or is it more important to sample the sediment, or is it necessary to locate hydrothermal activity within that ocean to have a good probability to find something diagnostic of life or no life?
I think it would be useful to bring aboard a couple of geochemical or chemical modelers to help us progress in that area.
03/11/02 Huade Guan
I checked the interesting titan website. It is good. I think it is a good idea for us to build a webpage, in which we can put together some facts on Titan, and some idea contributed by us on it. This way, everybody knows what we have done so far, and what the common points we have. From here, then we can go further. I know it is time consuming to put together all the information. But we can divide it into details, and everybody interested do one of them. And then put together. For example, regarding the volcano on Titan (if it is critical for life), we need to show the basic conditions for a volcano on planet or a moon, then compare the conditions of Titan with those with volcanoes, for example IO. Since members of this group come from all different background, I think it would benefit all of us if we have such integrated basic information.
The following is some of my thought on the questions (2 and 3):
#2. In the interior model of Titan the possibility of a NH3-H2O ocean is pointed out. Is this an analog to the likely ocean within Europa ? Would the possibility of life with NH3 in the water be enhanced or reduced ?
I think the Titan ocean here is a little different from that of Europa. Europa's ocean is under the solid ice layer, however, Titan's ocean is over the solid H2O and NH3. If this model is the case, we should assume the heat causing the liquid ocean is not (or not significantly) attributed to the radioactive decay occurring in the solid rock, or the heat is mainly caused by the tidal forces. Is there any other possible energy contributing to the liquid ocean?
Regarding the possibility of life in a ocean with NH3, I tend to think it is enhanced. The reasons are 1. NH3 + H2O does not decrease the solubility of solutes which are needed for life. I guess, so I need help here 2. Life needs NH3.
#3. Does anyone know of some direct evidence of volcanic activity on Titan ? Volcanic activity is usually inferred by Titan's size but do we have any (even indirect) evidence of volcanic activity ?
Are there any direct evidence that volcano occurs on Europa? Since a lot surveys have been done on Europa, it is a good thing for us to compare Europa and Titan. If we don't find volcano on Europa, then probably no volcano on Titan based on the conceptual model.
03/11/02 Dirk Schulze-Makuch
Questions Set 4
We appear to be stuck on the question set III. Anthony mentioned an interesting website about Titan http://www.seds.org/~rme/titan.htm. Please check it out. They have interesting models about the interior and atmosphere of Titan. May be we can use these figures to refresh our discussion. Thus, please see below Question Set IV. But feel free to discuss any previous issue we haven't covered fully, especially set III (because of that reason I will hold off with a summary at this time).
2/11/02 Dirk Schulze-Makuch
I thought Louis' contribution was intriguing and I agree that if life is possible in the cold, near-surface environment of Titan it would likely have a slow metabolism and long life spans very different from what we are used to (I guess that is what fascinates me about Titan - the bizarre possibilities).
Also, I agree that we certainly could use some more insight about "cold, hydrophobic solvents" and possibilities that arise in such an environment. And, as Anthonie pointed out, with convection cells we have the first type of order in chaos.
Let me here no address some thoughts I had about some aspects of question 3 of the last set in regard to other type of energy sources that could be used by life on Titan (if it exists) aside from chemical and light energy. In theory that could be pressure gradients, thermal gradients, convection cells, electromagnetic energy and gravitational energy.
Electromagnetic energy is provided by Saturn's magnetic field but due to Titan's thick atmosphere (which is a bad conducter), that possibility is likely only theoretical. The same holds for gravitational energy. Louis and I made some calculations for grav. energy on Europa (for our latest Astrobiology Paper, in press) and that did not work. Titan is not that much bigger, so I don't believe that would work here either.
Pressure gradients, either osmotic or otherwise, could be envisioned to power a microbial organism (there are actually mechanical devices that can transform pressure gradients into free energy). Pressure gradients could theoretically be harvested in the atmosphere. On the surface or below surface osmotic gradients would be more applicable, however, given possibly ethane lakes and organic-rich compounds on the surface, I'm not sure whether that would inhibit large salinity gradients. Anyone has some insight on that ?
Convection cells would be another energy source that could be theoretically harvested. Although, to my knowledge no-one detected yet a convection cell on Titan it just makes sense that they would exist in the atmosphere and probably also in the subsurface (hydrothermal or better "liquid-thermal?")
Thermal energy could be harvested, also. Heat pumps are a mechanical example how to extract energy from temperature gradients. However, they are very inefficient and the excess unusable energy (according to the 2nd Law of Thermodynamics) would have to be transported away to not degrade the thermal gradient (may be by convection cells?). Nevertheless, a lot of energy could be harvested (even in a cold environment or otherwise in the subsurface). The question however remains, if thermal energy is so favorable, why did it not develop on Earth ? Anthonie's hypothesis is that thermosynthesis may be the precursor of photosynthesis (he may want to elaborate on that, I won't go into details), so the Earth's version of a thermotroph may have been just out-competed by phototrophs ?
23/01/02 Louis Irwin
With regard to the point about life histories at extremely low temperatures, I concur with those who argue that this is not a significant impediment. As long as energy transformations (?metabolism? in living organisms) can proceed at all, once life evolves, it can be sustained.
Of greater concern to me on Titan would be the nature of cellular boundaries in a non-aqueous medium. The life forms we know of exist in an aqueous medium, where the hydrophobic properties of lipids can form boundaries (membrane cores) that separate the living components from their non-living environments. If the medium is much more hydrophobic, as liquid on or near the surface of Titan seems likely to be, what kind of chemical constituents could create boundary conditions?
That question in turn leads me to wonder if the miniaturization of cellular life in water on Earth may be a misleading model for life in a non-aqueous environment. In an extremely cold, hydrophobic (but liquid) environment, surface/volume ratio considerations may be less constraining than at higher temperatures in polar solvents. Could life on Titan involve huge (by Earth standards), very slowly metabolizing cells bounded by layers of exotic chemical constituents? I would really like to see chemists model such a boundary layer for a cold hydrophobic solvent (if they have not already done so).
"Living Universe"
Unpublished document (2002?) on !!please give a short, one-sentence description!! : As acrobat file (PDF) (10 pages)
Published in Fundamental of Life. Elsevier, Paris. 2001. Chap-IV-06, p. 41.
