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Triton's surface is considered relatively young, not more than 10 million years by uniformitarian models.<ref name=Schenk>Schenk, Paul M., and Zahnle, Kevin. "[http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4PFW6FV-2&_user=10&_coverDate=12%2F01%2F2007&_rdoc=10&_fmt=summary&_orig=browse&_srch=doc-info(%23toc%236821%232007%23998079998%23674080%23FLA%23display%23Volume)&_cdi=6821&_sort=d&_docanchor=&_ct=19&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=cea35d4a7d94052a325123729f8dfcf0 On the Negligible Surface Age of Triton]." ''Icarus'', 192(1):135-149, December 1, 2007. <doi:10.1016/j.icarus.2007.07.004 > Accessed May 9, 2008.</ref> Geologists count 100 impact craters on the leading hemisphere (the one facing in the direction of its motion around Neptune) and suspect that debris from collisions involving the inner or outer moons of Neptune have struck Triton on this leading surface.
Triton's surface is considered relatively young, not more than 10 million years by uniformitarian models.<ref name=Schenk>Schenk, Paul M., and Zahnle, Kevin. "[http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4PFW6FV-2&_user=10&_coverDate=12%2F01%2F2007&_rdoc=10&_fmt=summary&_orig=browse&_srch=doc-info(%23toc%236821%232007%23998079998%23674080%23FLA%23display%23Volume)&_cdi=6821&_sort=d&_docanchor=&_ct=19&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=cea35d4a7d94052a325123729f8dfcf0 On the Negligible Surface Age of Triton]." ''Icarus'', 192(1):135-149, December 1, 2007. <doi:10.1016/j.icarus.2007.07.004 > Accessed May 9, 2008.</ref> Geologists count 100 impact craters on the leading hemisphere (the one facing in the direction of its motion around Neptune) and suspect that debris from collisions involving the inner or outer moons of Neptune have struck Triton on this leading surface.
Triton has many deep chasms on its surface. In addition, [[Voyager 2]] recorded multiple [[geyser]]-like eruptions of [[nitrogen]] gas and dust from beneath the surface. This gas has created a very low-pressure "[[atmosphere]]" that is the only atmosphere-like feature of any solar system body other than earth to have nitrogen as its principle component.<ref name=Hamilton/>
The trailing hemisphere of Triton has a puckered surface with few, widely-spaced ridges and valleys and far fewer impact craters. This "cantaloupe terrain" has not been observed on any other celestial body.<ref name=ps>"[http://www.planetary.org/explore/topics/neptune/triton.html Neptune's Moon Triton]." ''The Planetary Society''. Accessed May 10, 2008.</ref>
== Theories of origin ==
Triton's retrograde orbit continues to puzzle secular astronomers. Virtually none of them believe that Triton formed at the same time as did Neptune; the [[nebula hypothesis]] simply would not allow that. The general consensus, therefore, is that Triton is a captured [[Trans-Neptunian Objects|trans-Neptunian object]] and possibly a [[Kuiper belt]] object.<ref name=Hamilton/><ref name=Arnett/><ref name=Goudarzi>Goudarzi, Sara. "[http://www.space.com/scienceastronomy/060510_triton_origin.html Neptune Might Have Captured Triton]." ''<http://www.space.com/>'', May 10, 2006. Accessed May 10, 2008.</ref> Some authorities suggest that the capture and its aftermath might have melted Titan's interior and caused it to differentiate.<ref name=Hamilton/><ref name=Arnett/><ref name=darling>"[http://www.daviddarling.info/encyclopedia/T/Triton.html Entry for Triton]." ''The Internet Encyclopedia of Science''. Accessed May 10, 2008.</ref>
But ''how'' that capture might have occurred remains an open question. The two favorite theories are:
# Triton collided with another object, the remains of which persist today as part of Neptune's ring system.<ref name=Arnett/> The primary difficulty with that theory, as opposed to any other capture theory, is the question of what exactly became of the remains of any object large enough to slow Triton down to enable Neptune to capture it. Neptune's ring system would not appear to have nearly enough matter to account for the destruction of such an object.
# Triton was originally part of a binary or near-binary system, similar to the system of [[Pluto]] and [[Charon]], and Neptune separated Triton from its former companion as it passed.<ref name=Goudarzi/><ref name=Clark>Clark, Stuart. "[http://space.newscientist.com/article/mg19025514.200-how-neptune-snagged-a-passing-moon.html How Neptune snagged a passing moon]." ''New Scientist'', 2551:8, May 10, 2006. Accessed May 10, 2008.</ref><ref name=Stephens>Stephens, Tim. "[http://currents.ucsc.edu/05-06/05-15/triton.asp New capture scenario explains origin of Neptune's oddball moon Triton]." ''UC Santa Cruz Currents'', May 15, 2006. Accessed May 10, 2008.</ref><ref name=Agnor>Agnor, Craig B., and Hamilton, Douglas. "[http://www.nature.com/nature/journal/v441/n7090/abs/nature04792.html;jsessionid=96C8003B3E24E3AEA9816D7B1225884F Neptune's capture of its moon Triton in a binary–planet gravitational encounter]." ''Nature'', 441:192-194, May 11, 2006. <doi:10.1038/nature04792> Accessed: May 10, 2008.</ref> However, Agnor and Hamilton, the proponents of this three-body capture model, make no attempt to identify Triton's former companion, if it had one. As a further complication, Triton itself is larger than any other Kuiper belt object except the [[dwarf planet]] [[Pluto]]. Pluto's orbit is, of course, so eccentric that its periapsis is less than Neptune's apoapsis, so that occasionally Pluto's orbit carries it closer to the Sun than is Neptune. But as one commentator observed,{{cquote|The unusual nature of Triton's orbit, the similarity of bulk properties between Pluto and Triton, and the highly eccentric, Neptune-crossing nature of Pluto's orbit suggest some historical connection between them. Exactly what this might be is purely conjecture at this time however.<ref name=Arnett/>}}
A further problem for ''any'' capture theory is that Triton's orbit, though retrograde, is almost perfectly circular. Immediately following capture, Triton's orbit would necessarily have been highly eccentric. Ćuk and Gladman admit that tidal deceleration alone would have taken longer than the supposed age of the solar system (i.e. longer than 4.5 billion years) for the orbit to become so circular. Therefore some other mechanisms must have acted to produce the observed outcome. Ćuk and Gladman propose repeated collisions with other satellites and the absorption of the resulting debris by Triton.<ref name=Gladman>Ćuk, Matija, and Gladman, Brett. J. "[http://adsabs.harvard.edu/abs/2005ApJ...626L.113C Constraints on the Orbital Evolution of Triton]." ''Astrophys. J.'' 626(2):L113-L116, June 2005. Accessed May 10, 2008.</ref>
Triton's retrograde orbit does suggest a theoretical "doom" for Triton. With every orbit, tidal forces slow Triton by a tiny amount. At the present rate, secular astronomers estimate that in 1.4 or 3.6 billion years, Triton will pass within Neptune's [[Roche limit]] and disintegrate.<ref name=Chyba>Chyba, C. F.; Jankowski, D. G.; Nicholson, P. D. "[http://adsabs.harvard.edu/abs/1989A&A...219L..23C Tidal evolution in the Neptune-Triton system]." ''Astronomy and Astrophysics'', 219(1-2):L23-L26, July 1989. Accessed May 10, 2008.</ref>
== Gallery ==
== Gallery ==