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Cassini has Observed the Evidence of Existence of an Underground Ocean of Water and Amonia on Saturn's Mon Titan

Cassini has discovered evidence that points to the existence of an underground ocean of water and ammonia on Saturn's moon Titan. The findings were made using radar measurements of Titan's rotation.

"With its organic dunes, lakes, channels and mountains, Titan has one of the most varied, active and Earth-like surfaces in the solar system," said Ralph Lorenz, lead author of the paper and Cassini radar scientist at the Johns Hopkins Applied Physics Laboratory in Maryland, USA. "Now we see changes in the way Titan rotates, giving us a window into Titan's interior beneath the surface."

Members of the mission's science team used Cassini's Synthetic Aperture Radar to collect imaging data during 19 separate passes over Titan between October 2005 and May 2007. The radar can see through Titan's dense, methane-rich atmospheric haze, detailing never-before-seen surface features and establishing their locations on the moon's surface.

Using data from the radar's early observations, the scientists and radar engineers established the locations of 50 unique landmarks on Titan's surface. They then searched for these same lakes, canyons and mountains in the reams of data returned by Cassini in its later flybys of Titan.

They found that prominent surface features had shifted from their expected positions by up to 30 km. A systematic displacement of surface features would be difficult to explain unless the moon's icy crust was decoupled from its core by an internal ocean, making it easier for the crust to move.

"We believe that about 100 km beneath the ice and organic-rich surface is an internal ocean of liquid water mixed with ammonia," said Bryan Stiles of NASA's Jet Propulsion Laboratory, California, USA. Stiles is a contributing author to the paper reporting the findings.

The study of Titan is a major goal of the Cassini-Huygens mission because it may preserve, in deep-freeze, many of the chemical compounds that preceded life on Earth. Titan is the only moon in the solar system that possesses a dense atmosphere. The moon's atmosphere is 1.5 times denser than Earth's. It is also the largest of Saturn's moons, bigger than the planet Mercury.

"The combination of an organic-rich environment and liquid water is very appealing to astrobiologists," Lorenz said. "Further study of Titan's rotation will let us understand the watery interior better, and because the spin of the crust and the winds in the atmosphere are linked, we might see seasonal variation in the spin in the next few years."

Cassini scientists will not have long to wait before another go at Titan. On March 25, just prior to its closest approach at an altitude of 1000 km, Cassini will employ its Ion and Neutral Mass Spectrometer to examine Titan's upper atmosphere. Immediately after closest approach, the spacecraft's Visual and Infrared Mapping Spectrometer will capture high-resolution images of Titan's southeast quadrant.

About Cassini–Huygens
Cassini–Huygens is a joint NASA/ESA/ASI robotic spacecraft mission currently studying the planet Saturn and its moons. The spacecraft consists of two main elements: the NASA Cassini orbiter, named after the Italian-French astronomer Giovanni Domenico Cassini, and the ESA Huygens probe, named after the Dutch astronomer, mathematician and physicist Christiaan Huygens. It was launched on October 15, 1997 and entered into orbit around Saturn on July 1, 2004. On December 25, 2004 the Huygens probe separated from the orbiter at approximately 02:00 UTC, as confirmed by the Jet Propulsion Laboratory. It reached Saturn's moon Titan on January 14, 2005, where it made an atmospheric descent to the surface and relayed scientific information. Cassini is the first spacecraft to orbit Saturn and the fourth to visit Saturn.

Cassini has seven primary objectives:
Determine the three-dimensional structure and dynamic behavior of the rings of Saturn
Determine the composition of the satellite surfaces and the geological history of each object
Determine the nature and origin of the dark material on Iapetus's leading hemisphere
Measure the three-dimensional structure and dynamic behavior of the magnetosphere
Study the dynamic behavior of Saturn's atmosphere at cloud level
Study the time variability of Titan's clouds and hazes
Characterize Titan's surface on a regional scale
The Cassini–Huygens spacecraft was launched on October 15, 1997 from Cape Canaveral Air Force Station's Launch Complex 40 using a US Air Force Titan IVB/Centaur launch vehicle. The launch vehicle was made up of a two-stage Titan IV booster rocket, two strap-on solid rocket motors, the Centaur upper stage, and a payload enclosure, or fairing. The complete Cassini flight system was composed of the launch vehicle and the spacecraft.

The spacecraft is composed of the Cassini orbiter and the Huygens probe. The orbiter was designed to orbit Saturn and its moons for four years. The probe was to dive into the atmosphere of Titan and land on its surface, which it did early in the mission. Seventeen nations contributed to building the spacecraft. The Cassini orbiter was built and managed by NASA/Caltech's Jet Propulsion Laboratory. The Huygens probe was built by the European Space Agency (ESA). The Italian Space Agency (ASI) provided Cassini's high-gain communication antenna, and a revolutionary compact and light-weight multimode radar (synthetic aperture radar, radar altimeter, radiometer).

The total cost of the mission is about US$3.26 billion, including $1.4 billion for pre-launch development, $704 million for mission operations, $54 million for tracking and $422 million for the launch vehicle. The US contributed $2.6 billion, ESA $500 million and ASI $160 million.

The nominal end of the mission is in 2008; an extension to the mission is being planned which will end in 2010, although this has yet to be formally announced. It is possible that funding will be granted for additional extensions.

About Synthetic Aperture Radar
Synthetic aperture radar (SAR) is a form of radar in which sophisticated post-processing of radar data is used to produce a very narrow effective beam. It can only be used by moving instruments over relatively immobile targets, but it has seen wide applications in remote sensing and mapping.

In a typical SAR application, a single radar antenna will be attached to the side of an aircraft. A single pulse from the antenna will be rather broad (several degrees) because diffraction requires a large antenna to produce a narrow beam. The pulse will also be broad in the vertical direction; often it will illuminate the terrain from directly beneath the aircraft out to the horizon. However, if the terrain is approximately flat, the time at which echoes return allows points at different distances from the flight track to be distinguished. Distinguishing points along the track of the aircraft is difficult with a small antenna. However, if the amplitude and phase of the signal returning from a given piece of ground are recorded, and if the aircraft emits a series of pulses as it travels, then the results from these pulses can be combined. Effectively, the series of observations can be combined just as if they had all been made simultaneously from a very large antenna; this process creates a synthetic aperture much larger than the length of the antenna (and in fact much longer than the aircraft itself).

Combining the series of observations requires significant computational resources. It is normally done at a ground station after the observation is complete, using Fourier transform techniques. The result is a map of radar reflectivity (including both amplitude and phase). The phase information is, in the simplest applications, discarded. The amplitude information, however, contains information about ground cover, in much the same way that a black-and-white picture does. Interpretation is not simple, but a large body of experimental results has been accumulated by flying test flights over known terrain.

Before rapid computers were available, the processing stage was done using holographic techniques. This was one of the first effective analogue optical computer systems. A scale hologram interference pattern was produced directly from the analogue radar data (for example 1:1,000,000 for 0.6 meters radar). Then laser light with the same scale (in the example 0.6 micrometers) passing through the hologram would produce a terrain projection. This works because SAR is fundamentally very similar to holography with microwaves instead of light.

About Jet Propulsion Laboratory
Jet Propulsion Laboratory (JPL) is a NASA research center located in the cities of Pasadena and La Cañada Flintridge, near Los Angeles, California, USA. Managed by the California Institute of Technology (Caltech), it builds and operates unmanned spacecraft for the National Aeronautics and Space Administration (NASA). Among its current projects are the Cassini-Huygens mission to Saturn, the Mars Reconnaissance Orbiter, and the Spitzer Space Telescope.

JPL's Space Flight Operations Facility and Twenty-five-foot Space Simulator are designated National Historic Landmarks.

JPL dates back to the 1930s, when Caltech professor Theodore von Kármán began running rocket propulsion experiments at the Guggenheim Aeronautical Laboratory on the site. JPL was co-founded in 1944 with rocket scientists Tsien Hsue-shen and Jack Parsons, which has led some to affectionately refer to it as the Jack Parsons Lab. Despite its name, JPL has always been focused on developing and building rocket engines, not turbojets or other air-breathing jet engines; rockets were often called "jets" or "ramjets" before the mid-1940s. During World War II, the United States Army Air Forces asked JPL to analyze the V2 rockets that were developed by Nazi Germany, as well as work on other projects for the war effort.

Almost all of the 177 acres (72 ha) of the U.S. federal government/NASA owned property that makes up the JPL campus is actually located in the city of La Cañada Flintridge, California, but the JPL main gate and several buildings are in Pasadena, so it maintains a Pasadena address (4800 Oak Grove Drive, Pasadena, CA 91109). There has been periodic conflict between the two cities over the issue of which should be mentioned in the media as the home of the laboratory.

In figure, Possible liquid ocean beneath Titan's surface