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Titan Saturn System Mission Backgrounder
Color image showing Saturn, its rings, Titan and several tiny moons.
Four moons, including giant Titan, huddle near Saturn's multi-hued disk.

Background/Significance: Earth-like atmosphere and geology. Titan is the only known moon with a fully developed earth-like atmosphere that consists of more than just trace gases. The atmosphere is 98.4 percent nitrogen - the only dense, nitrogen-rich atmosphere in the solar system aside from the Earth's - with the remaining 1.6 percent composed of methane and trace amounts of other gases such as hydrocarbons. The atmospheric pressure near the surface is about 1.6 bars, 60 percent greater than Earth's. Evidence gathered by Cassini and the Huygens probe suggests that the geology of Titan may be a close match to Earth - before life appeared on our home planet. Titan's surface temperature is about 94 K (-179 degrees Celsius, or -290 degrees Fahrenheit). The Titan Saturn System Mission (TSSM) would study Titan's Earth-like system, examine the moon's organics, examine its interior and explore Saturn's magnetosphere and its connection to Titan and Enceladus in order to gain a better understanding of Titan's origin and evolution.

Color image showing rocks on the surface of Titan.
This is the first color image returned from the surface of Titan by the European Space Agency's Huygens probe.

About Titan: Since its discovery in 1655 by the Dutch astronomer Christiaan Huygens, the surface of Titan has remained largely a mystery. A thick, cloudy atmosphere, largely impenetrable by telescopes and cameras, envelops Saturn's largest moon.

In December 2004, the robotic Huygens probe detached from the Cassini spacecraft and descended into Titan's thick, hazy atmosphere in January of 2005. Lasting a mere 3 hours in the cold atmosphere and on the surface of Titan (about minus 178 degrees Celsius, or minus 289 degrees Fahrenheit), the probe revealed a thick atmosphere, land masses with signs of erosion, and seas of methane on the surface. The Huygens probe came to rest on what appeared to be a floodplain, surrounded by rounded cobbles of water ice.

About 100 kilometers smaller in diameter than Jupiter's moon Ganymede, Titan is the second largest moon in our solar system. With an equatorial radius of 2,575 kilometers (1,600 miles), Titan is larger than both the Earth's moon and the planet Mercury.

Titan orbits Saturn at a distance of about 1.2 million kilometers (745,000 miles), taking almost 16 days to complete a full orbit.

Titan is of great interest to scientists because it is the only moon in the solar system known to have clouds, a mysterious, thick, planet-like atmosphere and surface lakes.

Color image showing lakes on Titan.
Cassini radar images confirmed the existence of liquid methane lakes on Titan.

History of exploration of Titan: Saturn's largest moon Titan has been an enigma at every stage of its exploration. Discoveries by Voyager I in the 1980's and Hubble Space Telescope observations in the 1990's provided valuable insight into the secrets of this unique world from a distance but did not reveal the complexity of the surface that Cassini-Huygens would uncover beginning in 2004. These recent discoveries leave us with many questions that require a future mission to answer.While the Huygens probe mission is complete, Cassini is still making flybys of Titan as it orbits Saturn on its Equinox mission.

During Cassini's primary mission, the spacecraft studied Titan's thick, smoggy nitrogen based hydrocarbon rich atmosphere in order to understand its structure and organic chemistry. Cassini- Huygens studied the frigid, alien surface of Titan and found vast methane lakes and large areas of wind-driven hydrocarbon sand dunes. Back on Earth, Cassini scientists concluded that Titan is likely hiding an internal, liquid water-ammonia ocean underneath its surface.

Color image showing Saturn and the limb of Titan.
Enshrouded in a thick, cloudy atmosphere, frigid Titan approaches the brilliant limb of Saturn.

At Titan researchers hope to catch the moon in the act of evolving, sending a future spacecraft would study the moon for signs of climate changes (storms, flooding, changes in lake levels) and will also search for further evidence of volcanic activity, subsurface ocean and evolutionary processes.

Comparison of Titan and Earth: Titan is a better chemical match to early Earth than to Venus, Mars, or even to current Earth. The nitrogen atmosphere is a thick haze filled with organic-rich chemistry, which resembles a frozen version of pre-biotic Earth - before organic life began pumping oxygen into the atmosphere. This makes it ideal for trying to understand the early formation of the Earth. (Titan/Saturn comparison chart.)

However, Titan is much colder than Earth ever was at about minus 178 degrees Celsius, or minus 289 degrees Fahrenheit), making liquid water and life as we know it not a distinct possibility but an environment under which methane and ethane exist in liquid form.

Cutaway image showing layers of Titan.
Titan animation.

Exploring Titan with Cassini Equinox: As the Cassini Equinox mission continues, the probe will study Titan's atmosphere and surface for evidence of seasonal changes. Cassini will continue to peer through Titan's thick haze to create high-resolution radar maps and images of the moon's surface features, lakes, mountains, and possible cryo-volcanoes. Over time, Cassini may be able to confirm the theory that a liquid ocean may exist underneath the surface of Titan.

Future exploration of Titan -- Titan Saturn System Mission (TSSM): With an estimated NASA cost of $2.5 Billion (FY07), the proposed Titan Saturn System Mission (TSSM) would launch in 2020, get gravity assists from Earth and Venus, and arrive at the Saturn system in 2029. The 4-year prime mission would include a two-year Saturn tour, a 2-month Titan aero-sampling phase, and a 20-month Titan orbit phase.

TSSM consists of three elements -- the NASA Orbiter, and European Space Agency (ESA) in situ elements, lake lander and montgolfiere. In addition to providing the launch vehicle, NASA would build the orbiter, which will be powered by a Radioisotope Power System, as well as a Solar Electric Propulsion (SEP) stage. ESA would provide the Montgolfiere hot-air balloonand Lake Lander. The montgolfiere would be released just following Saturn orbit insertion on the first Titan flyby, and the Lake Lander on the second Titan flyby.

Artist's elements showing orbiter, balloon and lander at Titan.
The three elements of TSSM: An orbiter, a balloon and a lake lander.

What do we want to know about Titan and what will we study when we return to the moon via the Titan Saturn System Mission (TSSM)? In concert with ESA, NASA's Titan Saturn System Mission (TSSM) Orbiter would explore Titan's Earth-like system, examine the moon's organics, and explore the magnetosphere of Saturn and its connection to Titan and Enceladus in order to gain a better understanding of Titan's origin and evolution. On its way to Titan, the orbiter would fly through the plumes of Enceladus to analyze plume samples and image the subsurface features of the tiger stripes in the south polar region.

The study of Titan may help us to understand how our own planet Earth formed and will evolve. Because Titan is a complex world, it appears to be more like the Earth than any other body in our solar system. Information from the Titan Saturn system Mission (TSSM) orbiter would clarify how The Titan system (geology, hydrology, meteorology, physice, climatology and atmospherics) is both similar and different from the Earth and other solar system bodies.

Questions that seek to be answered with TSSM include: How does Titan function as a system? How are the similarities and differences with Earth, and other solar system bodies, a result of the interplay of the geology, hydrology, meteorology, and aeronomy present in the Titan system?

Biochemistry on Titan: Scientists have many questions and theories about the complexity of organic chemistry in the atmosphere, lakes, on the surface, and within Titan's theorized subsurface ocean. Among other investigations, the proposed TSSM would measure the amount of pre-biotic molecules.

Grid and map showing hot spots on Titan.
The two regions on this map are hypothesized by some to be areas of cryovolcanic activity on Titan.

New Evidence Shows Cryovolcanic Activity on Titan: Data gathered from several Cassini flybys of Titan has already revealed evidence for cryovolcanic activity. Images include a puzzling haze floating over flow-like surface features. Unlike Earth volcanoes, which erupt with liquid rock, Titan's suspected volcanoes are believed to spew super-chilled water, methane, and ammonia into the moon's atmosphere.

Some Cassini scientists indicate that such volcanism could release methane from the interior, which explains Titan's seemingly continuous supply of fresh methane. Without replenishment, scientists say, Titan's original atmospheric methane should have been exhausted long ago.

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Last Updated: 2 February 2011

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Last Updated: 2 Feb 2011