astronomy Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...

, a thalassogen denotes a substance capable of forming a planetary

ocean The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...

.Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm Thalassogens are not necessarily life sustaining, although most interest has been in the context of

extraterrestrial life Extraterrestrial life, or alien life (colloquially, aliens), is life that originates from another world rather than on Earth. No extraterrestrial life has yet been scientifically conclusively detected. Such life might range from simple forms ...

.Committee on the Limits of Organic Life in Planetary Systems, Committee on the Origins and Evolution of Life, National Research Council. The Limits of Organic Life in Planetary Systems. National Academies Press (2007) The term was coined by

Isaac Asimov Isaac Asimov ( ; – April 6, 1992) was an Russian-born American writer and professor of biochemistry at Boston University. During his lifetime, Asimov was considered one of the "Big Three" science fiction writers, along with Robert A. H ...

in his essay "The Thalassogens", later published in his 1972 collection ''

The Left Hand of the Electron ''The'' is a grammatical article in English, denoting nouns that are already or about to be mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The ...

''. Said term was coined via the Ancient Greek prefix thalasso- ("sea") and the suffix -gen ("producer"). Elements making up thalassogens have to be relatively abundant, the substance must be chemically stable in its environment, and must remain liquid under the conditions found on some planets. Freitas gives the following table, noting that the liquid range typically increases with increasing pressure: The critical temperature and pressure represents the point where the distinction between gas and liquid vanishes, a possible upper limit for life (though life in

supercritical fluid A supercritical fluid (SCF) is a substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid. It can effuse through porous sol ...

s has been discussed both in science and fiction, such as in '' Close to Critical'' by

Hal Clement Harry Clement Stubbs (May 30, 1922 – October 29, 2003), better known by the pen name Hal Clement, was an American people, American science fiction writer and a leader of the hard science fiction subgenre. He also painted astronomically oriented ...

). Later authors have also suggested

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

ethane Ethane ( , ) is a naturally occurring Organic compound, organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is List of purification methods ...

, and water/ammonia mixtures as possible thalassogens. The discovery of possible subsurface oceans on moons such as

Europa Europa may refer to: Places * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Cliffs, Alexan ...

(and, less obviously, Ganymede and

Callisto CALLISTO (''Cooperative Action Leading to Launcher Innovation in Stage Toss-back Operations'') is a reusable VTVL Prototype, demonstrator propelled by a small 40 kN Japanese LOX-LH2 rocket engine. It is being developed jointly by the CNES, French ...

) also extends the range of possible environments.

References

{{reflist Astrobiology Astronomical hypotheses Planetary science

See also

References