Titan (moon)

Titan is the largest moon of Saturn and the second-largest natural satellite in the Solar System. It is the only moon known to have a dense atmosphere, and the only known moon or planet other than Earth on which clear evidence of stable bodies of surface liquid has been found.[15]

Titan
Pictured in 2012 in natural color. The thick atmosphere is orange due to a dense organonitrogen haze.
Discovery
Discovered byChristiaan Huygens
Discovery dateMarch 25, 1655
Designations
Designation
Saturn VI
Pronunciation/ˈttən/ (listen)[1]
Named after
Τῑτάν Tītan
AdjectivesTitanian[2] or Titanean[3] (both /tˈtniən/)[4][5]
Orbital characteristics[6]
Periapsis1186680 km
Apoapsis1257060 km
1221870 km
Eccentricity0.0288
15.945 d
5.57 km/s (calculated)
Inclination0.34854° (to Saturn's equator)
Satellite ofSaturn
Physical characteristics
Mean radius
2574.73±0.09 km (0.404 Earths)[7] (1.480 Moons)
8.3×107 km2 (0.163 Earths) (2.188 Moons)
Volume7.16×1010 km3 (0.066 Earths) (3.3 Moons)
Mass(1.3452±0.0002)×1023 kg
(0.0225 Earths)[8] (1.829 Moons)
Mean density
1.8798±0.0044 g/cm3[8]
1.352 m/s2 (0.138 g) (0.835 Moons)
0.3414±0.0005[9] (estimate)
2.639 km/s (0.236 Earths) (1.11 Moons)
Synchronous
Zero
Albedo0.22[10]
Temperature93.7 K (−179.5 °C)[11]
8.2[12] to 9.0
Atmosphere
Surface pressure
146.7 kPa (1.45 atm)
Composition by volumeVariable

Stratosphere:
98.4% nitrogen (N
2
),
1.4% methane (CH
4
),
0.2% hydrogen (H
2
);

Lower troposphere:
95.0% N
2
, 4.9% CH
4
;[13]
97% N
2
,
2.7±0.1% CH
4
,
0.1–0.2% H
2
[14]

    Titan is one of seven gravitationally rounded moons in orbit around Saturn, and the second most distant from Saturn of those seven. Frequently described as a planet-like moon, Titan is 50% larger (in diameter) than Earth's Moon and 80% more massive. It is the second-largest moon in the Solar System after Jupiter's moon Ganymede, and is larger than the planet Mercury, but only 40% as massive.

    Discovered in 1655 by the Dutch astronomer Christiaan Huygens, Titan was the first known moon of Saturn, and the sixth known planetary satellite (after Earth's moon and the four Galilean moons of Jupiter). Titan orbits Saturn at 20 Saturn radii. From Titan's surface, Saturn subtends an arc of 5.09 degrees and, were it visible through the moon's thick atmosphere, would appear 11.4 times larger in the sky than the Moon from Earth.

    Titan is primarily composed of ice and rocky material, which is likely differentiated into a rocky core surrounded by various layers of ice, including a crust of ice Ih and a subsurface layer of ammonia-rich liquid water.[16] Much as with Venus before the Space Age, the dense opaque atmosphere prevented understanding of Titan's surface until the Cassini–Huygens mission in 2004 provided new information, including the discovery of liquid hydrocarbon lakes in Titan's polar regions. The geologically young surface is generally smooth, with few impact craters, although mountains and several possible cryovolcanoes have been found.

    The atmosphere of Titan is largely nitrogen; minor components lead to the formation of methane and ethane clouds and heavy organonitrogen haze. The climate—including wind and rain—creates surface features similar to those of Earth, such as dunes, rivers, lakes, seas (probably of liquid methane and ethane), and deltas, and is dominated by seasonal weather patterns as on Earth. With its liquids (both surface and subsurface) and robust nitrogen atmosphere, Titan's methane cycle bears a striking similarity to Earth's water cycle, albeit at the much lower temperature of about 94 K (−179.2 °C; −290.5 °F).