Editing Deuterium (section)

=== Abundance ===
[[File:Standard Model Deuterium.svg|thumb|right|Simplified chart of particle content]]Deuterium occurs in trace amounts naturally as deuterium [[gas]] ({{sup|2}}H{{sub|2}} or D{{sub|2}}), but most deuterium in the [[Universe]] is bonded with {{sup|1}}H to form a gas called [[hydrogen deuteride]] (HD or {{sup|1}}H{{sup|2}}H).<ref>{{cite journal |author=IUPAC Commission on Nomenclature of Inorganic Chemistry |title=Names for muonium and hydrogen atoms and their ions |journal=[[Pure and Applied Chemistry]] |year=2001 |volume=73 |issue=2 |pages=377–380 |doi=10.1351/pac200173020377 |s2cid=97138983 |url=http://www.iupac.org/publications/pac/2001/pdf/7302x0377.pdf |url-status=live |archive-url=https://web.archive.org/web/20030425124156/http://www.iupac.org/publications/pac/2001/pdf/7302x0377.pdf |archive-date=2003-04-25}}</ref> Similarly, natural water contains deuterated molecules, almost all as [[semiheavy water]] HDO with only one deuterium.

The existence of deuterium on Earth, elsewhere in the [[Solar System]] (as confirmed by planetary probes), and in the spectra of [[star]]s, is also an important datum in [[physical cosmology|cosmology]]. Gamma radiation from ordinary nuclear fusion dissociates deuterium into protons and neutrons, and there is no known natural process other than [[Big Bang nucleosynthesis]] that might have produced deuterium at anything close to its observed natural abundance. Deuterium is produced by the rare [[cluster decay]], and occasional absorption of naturally occurring neutrons by light hydrogen, but these are trivial sources. There is thought to be little deuterium in the interior of the Sun and other stars, as at these temperatures the [[nuclear fusion reaction]]s that consume deuterium happen much faster than the [[proton–proton reaction]] that creates deuterium. However, deuterium persists in the outer solar atmosphere at roughly the same concentration as in Jupiter, and this has probably been unchanged since the origin of the Solar System. The natural abundance of {{sup|2}}H seems to be a very similar fraction of hydrogen, wherever hydrogen is found, unless there are obvious processes at work that concentrate it.

The existence of deuterium at a low but constant primordial fraction in all hydrogen is another one of the arguments in favor of the [[Big Bang]] over the [[Steady State theory]] of the Universe. The observed ratios of hydrogen to helium to deuterium in the universe are difficult to explain except with a Big Bang model. It is estimated that the abundances of deuterium have not evolved significantly since their production about 13.8 billion years ago.<ref>{{cite web |title=Cosmic Detectives |url=http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives |publisher=The European Space Agency (ESA) |date=2 April 2013 |access-date=2013-04-15}}</ref> Measurements of [[Milky Way]] galactic deuterium from ultraviolet spectral analysis show a ratio of as much as 23 atoms of deuterium per million hydrogen atoms in undisturbed gas clouds, which is only 15% below the [[WMAP]] estimated primordial ratio of about 27 atoms per million from the Big Bang. This has been interpreted to mean that less deuterium has been destroyed in star formation in the Milky Way galaxy than expected, or perhaps deuterium has been replenished by a large in-fall of primordial hydrogen from outside the galaxy.<ref>{{cite press release |title=FUSE Satellite solves the case of the missing deuterium |publisher=[[NASA]] |url=http://www.nasa.gov/vision/universe/starsgalaxies/fuse_stars.html |access-date=12 September 2013 |archive-date=14 August 2020 |archive-url=https://web.archive.org/web/20200814054630/https://www.nasa.gov/vision/universe/starsgalaxies/fuse_stars.html |url-status=dead }}</ref> In space a few hundred light years from the Sun, deuterium abundance is only 15 atoms per million, but this value is presumably influenced by differential adsorption of deuterium onto carbon dust grains in interstellar space.<ref>{{cite web |title=Graph of deuterium with distance in our galactic neighborhood |series=FUSE Satellite project |publisher=[[Johns Hopkins University]] |place=Baltimore, MD |url=http://fuse.pha.jhu.edu/wpb/sci_d2h_solved.html |archive-url=https://web.archive.org/web/20131205014518/http://fuse.pha.jhu.edu/wpb/sci_d2h_solved.html |archive-date=5 December 2013 }}
: See also
{{cite journal | vauthors =Linsky JL, Draine BT, Moos HW, Jenkins EB, Wood BE, Oliveira C, Blair WP, Friedman SD, Gry C, Knauth D, Kruk JW | display-authors = 6 |year=2006 |title=What is the Total Deuterium Abundance in the Local Galactic Disk? |journal=The Astrophysical Journal |volume=647 |issue=2 |pages=1106–1124 |doi=10.1086/505556 |bibcode=2006ApJ...647.1106L |arxiv=astro-ph/0608308| s2cid = 14461382 }}</ref>

The abundance of deuterium in [[Jupiter]]'s atmosphere has been directly measured by the [[Galileo space probe|''Galileo'' space probe]] as 26 atoms per million hydrogen atoms. ISO-SWS observations find 22 atoms per million hydrogen atoms in Jupiter.<ref>{{Cite journal | vauthors = Lellouch E, Bézard B, Fouchet T, Feuchtgruber H, [[Thérèse Encrenaz|Encrenaz T]], de Graauw T |year=2001 |title=The deuterium abundance in Jupiter and Saturn from ISO-SWS observations |journal=[[Astronomy & Astrophysics]] |volume=670 |issue=2 |pages=610–622 |doi=10.1051/0004-6361:20010259 |doi-access=free |bibcode=2001A&A...370..610L |url=http://www.aanda.org/articles/aa/pdf/2001/17/aa10609.pdf}}</ref> and this abundance is thought to represent close to the primordial Solar System ratio.<ref name="Hersant" /> This is about 17% of the terrestrial ratio of 156 deuterium atoms per million hydrogen atoms.<!--News reports of Hubble measurements of "6 atoms of 2H per 10,000" in Jupiter are wrong; the correct figure is 6 parts 2H per 100,000 by weight, which is 30 parts per million atom-fraction, close to the Galileo result of 26 parts per million, atom-fraction-->

Comets such as [[Comet Hale-Bopp]] and [[Halley's Comet]] have been measured to contain more deuterium (about 200 atoms per million hydrogens), ratios which are enriched with respect to the presumed protosolar nebula ratio, probably due to heating, and which are similar to the ratios found in Earth seawater. The recent measurement of deuterium amounts of 161 atoms per million hydrogen in Comet [[103P/Hartley]] (a former [[Kuiper belt]] object), a ratio almost exactly that in Earth's oceans (155.76 ± 0.1, but in fact from 153 to 156 ppm), emphasizes the theory that Earth's surface water may be largely from comets.<ref name="nature2"/><ref name="Hersant"/> Most recently the {{sup|2}}H{{sup|1}}HR of [[67P/Churyumov–Gerasimenko]] as measured by ''Rosetta'' is about three times that of Earth water.<ref name="sciencemag.org"/> This has caused renewed interest in suggestions that Earth's water may be partly of asteroidal origin.

Deuterium has also been observed to be concentrated over the mean solar abundance in other terrestrial planets, in particular Mars and Venus.<ref>{{Cite journal |last=Hunten |first=Donald M. |name-list-style=vanc |year=1993 |title=Atmospheric evolution of the terrestrial planets |journal=[[Science (journal)|Science]] |volume=259 |issue=5097 |pages=915–920 |doi=10.1126/science.259.5097.915 |jstor=2880608 |bibcode=1993Sci...259..915H |s2cid=178360068 |issn=0036-8075}}</ref>