Extraterrestrial Niches for Thermosynthesizers

Astronomy Headlines from SPACE.com

General info on exobiology:
Astrobiology Index

: The Electronic Astrobiology Newsletter

University course on astrobiology: Origin and evolution of habitable worlds
Harold Geller and G. Taylor astrobiology web site at George Mason University

Extensive web site on Astrobiology by the author of 'Life everywhere' and 'The extraterrestrial encyclopedia'
David Darling astrobiology web site

Extraterrestrial niches for thermosynthesizers

Bill Arnett's overview of the Solar System

A few centuries ago people found it easy to imagine that life could occur in the rest of the Solar System. Michael Crowe in his book The Extraterrestrial Life Debate. 1750-1900 [Crow86, p. 35]:

John Peter Biester, in his Enquiry into the Probabilty of the Planets Being Inhabited, advocates life on all planets, but not on their satellites. . . . having Mercurians populate their planet's pole

Until a few years ago, almost all of the Solar System was considered to be inhabitable. Possible niches for thermosynthesizers can however be pointed out everywhere in the Solar System. Meteorites can transport organisms between these niches: ejecta from impact by one meteorite on a body of the Solar system can turn into a second meteorite that impacts on another body.
In this regard the martian meteorite ALH84001, discovered at Alan Hills on the ice in Antarctica in 1984, is the most famous.

Many bodies of the Solar System have an ice cover. The ice may contain old meteorites with the remnants of the very first organisms of the Solar System and may therefore contain fossils of thermosynthesizers.

Mercury

Bill Arnett on Mercury thinkquest links to data on Mercury
Due to its short distance to the Sun, the surface of Mercury is very hot. At the poles, the crater interiors are however shielded from the sun and are in eternal shadow. Such craters constitute cold traps, where water and other volatile substances condense. Radar has demonstrated the presence of ice [Slad95, Harm94]. As this ice may be heated from below by volcanism, the presence of convecting water is plausible under this ice, a possible niche for thermosynthesizers.
NASA on ice on Mercury

Venus

Bill Arnett, on Venus
David Grinspoon, author of "Venus revealed"David Grinspoon
The ocean that Venus may have had has now boiled away. Until it evaporated, this strongly convecting ocean could have carried thermosynthesizers.

Carl Sagan has proposed life in the clouds of Venus that makes use of cyclic wetting and drying, a mechanism resembling thermosynthesis.
Life in convecting clouds has been considered [Dimm77, Dobs00]
CO² has a low critical temperature and pressure. Much of the CO² may therefore behave like a fluid, rather than as a gas or liquid. Supercritical CO² is a good solvent for small biomolecules, and the possibility of life in this semi-ocean should not be excluded.

The Moon

Bill Arnett, on The Moon
Ice has been observed in shaded lunar craters on the Moon, both by radar[ Noze96] and by neutron fluxes [Feld98]. Just as for Mercury, these craters constitute possible niches for thermosynthesizers. NASA on ice on the moon
Astronomy Now on ice on the moon

Mars

Bill Arnett, on Mars
At the moment on writing (March 2005) new evidence relevant to the possibility of life on Mars is coming in daily. It is hard to keep track. There may be liquid water just under the surface. In volcanic areas the surface ice may have melted, and convection is plausible. Subsurface aquifers may also contain convecting liquid water.

In the past Mars had an ocean, which may have convected. Under its surface, hydrogen, probably due to water, has been detected: NASA Odyssey mission, Lunar and Planetary Lab, University of Arizona

The Big Outer Planets

Bill Arnett, on the Outer planets: Jupiter
Saturn
Uranus
Neptune

The surfaces of the outer planets are at present too hot to permit life. Microorganisms might be carried along by the cooler clouds, though; thermosynthesis is a plausible energy source for such organisms.

In the future these planets may cool sufficiently to permit an ocean; here organisms could live on thermosynthesis.

The moons of the Outer Planets

Bill Arnett on the Moons of the Outer planets and Pluto: Io
Europa
Ganymede
Triton
Titan
Callisto
Pluto

Many moons of the big outer planets are covered with ice. Liquid water underneath this ice would constitute an environment that could permit thermosynthesis.

A prime candidate niche for thermosynthesizers is the Jovian moon Europa, which contains an ice-covered ocean that is intensely heated by tidal friction.

INDICATE SOURCE IMAGE
Schulze-Makuch and Irwin have considered energy sources for organisms in this ocean [Schu01]. Respiration and photosynthesis are considered to be unlikely, but they do consider heat, in general terms, as a possible energy source:

Thermotrophic life forms may be conceivable that use thermal gradients . . .

and:

A plausible energy-harvesting mechanism would be the presence of membrane macromolecules that catalyze high-energy metabolites through temperature-dependent conformational changes.

Convection is considered as a distinct energy source as well [Schu01]:

Directly harvesting the kinetic energy of convection cells or tidal currents on Europa's ocean floor or ice ceiling would be another way to sustain life in the absence of light and oxygen.

A complex mechanism for the formation of high-energy phosphate bonds using convection is proposed but no combined use of heat and convection as in thermosynthesis.
Obviously, organisms using PTS and MTS would have the described functionality.

For Saturn's moon Titan the presence of a deep ocean has been proposed:

The presence of geysers on Neptune's Triton shows that aquifers within this moon can also be subject to intense convection. [Shoc93, Duxb97, Grun00].

Asteroids, Meteorites, Comets and Kuiper Belt Objects

Bill Arnet, on Small Bodies Asteroids
Meteorites
Comets

These small bodies typically rotate in the sunlight. Their surface will therefore be thermally cycled. At a distance larger than about 3-4 astronomical units ice is stable against evaporation into space. Organism just under the surface of this ice could therefore live on thermosynthesis.
Fred Hoyle was a well known proponent for life on/in comets. The following site gives many references of Hoyle - and others - on the possibility of life on comets. references on life on comets

The Sun !?!

Bill Arnett on the Sun
Michael Crowe [Crow86, p. 67].

. . . an event reported in the Gentleman's Magazine for 1787. A certain Dr. Eliot brought to trial in London for having set fire to a lady's cloak by firing a pair of pistols near it. Insanity was the plea made of Elliot's bizarre behavior, especially his having prepared a paper for submission to the Royal Society in which he maintained the sun to be inhabited.

Obviously the present Sun is far too hot to permit any stable molecule, and life is therefore out of the question there. In the far future the Sun will cool, however. The possibility of 'Carnot creatures' in convection cells on the cooled sun has independently of the author been proposed by Daedalus [Jone97]. See also on Carnot creatures
Before the Sun cools, it will become much hotter first, and will expand so much that it will engulf the Earth. The atoms of our own body may therefore very well end up in such Solar thermosynthesizers. I leave the question to the reader to decide whether this end compares better with ending up in hell or ending up in heaven!.

The following picture shows the many possible thermosynthesis niches in the Solar System.

Because of the possibility of thermosynthesis life is present in almost the entire Solar System. Similarly, the habitable zones around all stars [Huan59], 60, Kast93] can drastically be increased, which increases the chance on extraterrestrial life in the Universe outside the Solar System as well.

The next page constitutes the last page of the Thermosynthesis Home Page: Conclusion.