Titan (moon)

[[File:Two_Titans_(PIA21624).jpeg|thumb|right|Two views of Titan by the ''Cassini'' spacecraft. Note the polar seas, clouds, and the equatorial dunefields on the right image.]]{{Astronomy}}
'''Titan''' is the largest moon of [[Saturn]] and the second largest natural satellite of the Solar System after [[Jupiter]]'s moon Ganymede, with a diameter of 5,150 kilometers. Despite this, it's too faint to be seen with the naked eye, and binoculars or a small telescope are needed to observe it.

==Discovery==
Titan was discovered in 1655 by the Dutch astronomer Christiaan Huygens, who simply named it ''Saturni Luna'' ([[Latin]] for "Saturn's moon"). It was not until 1847 that the British astronomer John Herschel baptized it as "Titan", brothers and sisters of Cronus (Saturn for the [[Roman]]s) in the [[Greece|Greek]] mythology.

==Study and exploration==
For many years, very little of Titan was known besides its orbit around Saturn. Things began to change in 1907 when the [[Spain|Spanish]] astronomer Josep Comas i Solà observed how Titan's limb was darker than its center ("limb darkening"), evidence of the presence of an atmosphere surrounding it. However it was not until 1944 that it was confirmed it had an atmosphere composed of [[methane]] by the American astronomer Gerard P. Kuiper, making it the only moon of the Solar System with a (dense) atmosphere. Again, years would pass before it was possible to learn more about that distant moon &mdash; and this time ''in situ'', with spacecraft.

While the first spacecraft to study Titan was ''Pioneer 11'', ''Voyager 1'' and ''Voyager 2'' were able to obtain much more scientific data as well as better images of it. Sadly, these probes found that Titan's surface is hidden from view by an orange haze of organic compounds and while they returned a wealth of information they also opened many new mysteries. A new mission was needed to unlock the mysteries of Saturn's largest moon, and that mission &mdash; ''Cassini-Huygens'', a joint project of [[NASA]], the [[ESA]], and the Italian Space Agency &mdash; after being launched in 1997 and a seven-year journey and several fly-bys of [[Venus]], [[Earth]], and Jupiter, finally arrived at the Saturnian system with that purpose. Most of what we know today about Titan comes courtesy of the ''Cassini'' probe, that danced around Saturn from 2004 to 2017 and which included a lander &mdash; ''Huygens'' &mdash; that landed on Titan in 2005.

Future mission proposals include most notably the ''{{wpl|Dragonfly (spacecraft)|Dragonfly}}'', a [[Nuclear energy|nuclear]]-powered [[drone]] part of [[NASA]]'s "{{wpl|New Frontiers program|New Frontiers Program}} that after having been greenlighted would be launched around 2025.

==Hitchhiker's guide to Titan==
Titan is a cold and dark world with a surface temperature of -180°C and whose dense atmosphere, which gives it an atmospheric pressure almost 1.5 times the density of Earth's and it's almost entirely composed of nitrogen with a small number of organic compounds, primarily methane, causes its surface to receive around 1/1,000th or even less of the [[Sun]]'s light that Earth receives (surface light levels at day have been compared to those on our planet during twilight<ref>[https://en.wikipedia.org/wiki/Extraterrestrial_skies#The_sky_of_Titan The sky of Titan]</ref>). It's so cold (even [[Finland]] is hot in comparison) that [[water]] is granite-solid ice (and liquid water is the Titanian equivalent of magma and lava) and liquid methane replaces Earth's rock and water respectively, with a methane cycle that is analogous to Earth's water cycle. Results from NASA's ''Cassini'' spacecraft also suggest the existence of a subsurface ocean of (salty) water mixed with ammonia.

Because of its large amount of organic compounds (it has ''a whole lot more'' than [[Earth]]<ref>[https://www.nasa.gov/mission_pages/cassini/media/cassini-20080213.html Titan's Surface Organics Surpass Oil Reserves on Earth]</ref>), Titan has been compared to a frozen analog of our planet and this analogy goes even farther when one considers that the interplay between methane, its dense atmosphere, and ice has produced equivalents of Earth's surface features as hydrocarbon lakes, some sea-sized and quite deep, &mdash; in the poles &mdash; complete with rivers and canyons, large dunefields of organic compounds covering its equator, and hydrocarbon snow covering icy mountains (with names taken from Tolkien's ''The Lord of the Rings'', no less<ref>[https://planetarynames.wr.usgs.gov/Page/TITAN/target Planetary Names: Titan]. There's even a Doom Mons!</ref>). Surface craters caused by the impacts of asteroids and comets, so abundant in other Solar System bodies, are relatively rare on Titan, suggesting that geological activity and/or weather erodes or covers them. Nonetheless there are a few surface features that are indicative of ''cryo''volcanism (as at those gelid temperatures liquid water mixed with ammonia and some methane would replace molten rock).

It's also believed some hundreds of millions of years ago Titan's crust was much thinner, which meant a much more geologically active world than today, with such activity erasing both impact craters and past surface features, and that all those methane was expelled to the atmosphere by then covering Tiran in haze, and that once subsurface methane runs out in a few hundreds of millions of years at worst the atmosphere would clear out of haze as such gas disappears leaving a very different Titan behind.<ref>C.A. Wood, [https://www.hou.usra.edu/meetings/lpsc2019/pdf/3032.pdf Titan's Global Crustal Thickening]. Universities Space Research Association, 50th Lunar and Planetary Science Conference 2019.</ref>

==Life on Titan==
Being so abundant in organic compounds, Titan has been a prime target for searches for extraterrestrial life, and continues being so. However conditions on this moon appear unfavorable to the development of life as we know it: at the temperatures present on Titan, chemical reactions needed for life take place at a very slow rate, and there's no liquid water at the surface, at least permanently. However astronomers have attempted to circumvent those issues by suggesting that after the impact of a meteor a patch of liquid water could exist for some time, allowing abiogenesis to happen. Another possibility comes from the existence of the aforementioned mantle of liquid water mixed with ammonia under Titan's crust, which, while admittedly very salty, could support simple life.

Another more speculative theory is to set water aside and use instead hydrocarbons such as methane or ethane (liquid in Titan's conditions) as a water-equivalent. While some research suggests that life based on liquid methane could be possible,<ref>[http://advances.sciencemag.org/content/1/1/e1400067.full Membrane alternatives in worlds without oxygen: Creation of an azotosome]</ref> and some observations of the distribution of hydrogen and acetylene on Titan's atmosphere even seem to be caused by that kind of biochemistry, there's actually very little—if any—evidence that supports the existence of life on Titan, be it water- or hydrocarbon-based.

It has finally been suggested that once the [[Sun]] goes red giant, Titan's ices could melt and this moon would become more supportive of the development of life for a few hundred million years.<ref>[https://en.wikipedia.org/wiki/Titan_(moon)#Future_conditions The other Wiki]</ref>

==Woo==
Of course, as everything related to space exploration, Titan has received its share of woo with examples including the identification of "alien bases" on pictures by the method of overblowing images until you pretty much see whatever you want on the individual pixels,<ref>[http://istrangehuman.blogspot.com.es/2014/05/photos-of-two-et-bases-on-titan-where.html Photos of ET bases on Titan, where Huygens landed]</ref> and ignoring scale issues and the like.

==That other wiki==
*{{wpl|Titan (moon)}} The Titan article on Wikipedia, (deeper information, more references, and many cool pictures.)

*{{wpl|Life on Titan}} Wikipedia article about the possibility of life on Titan, also with more references.

==References==
{{reflist|2|80%}}

[[Category:Astronomy]]
[[Category:Moon]]
[[Category:Science]]

Categories: Astronomy, Moon, Science