Exploring the atmosphere

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Titan’s Methane Cycle


Voyager 1 and 2 twin spacecraft was launched by NASA in separate months in the summer of 1977 from Cape Canaveral, Florida. The primary mission was the exploration of Jupiter and Saturn, Saturn's rings, and the larger moons of the two planets. As the mission went on, and with the successful achievement of all its objectives, their five-year lifetimes stretched to 12 and is now near thirty years, with the additional flybys of the two outermost giant planets, Uranus and Neptune. The flyby of each planet bends the spacecraft's flight path and increases its velocity enough to deliver it to the next destination, which is known by ’gravity assistance’ technique. Voyager 1 was brought to Saturn on November 12, 1980, followed by Voyager 2 to Saturn on August 25, 1981. 

Detecting Titan’s atmosphere

Space crafts flying by Titan, probes sent to Titan’s surface, telescope observing the giant satellite from the Earth, people are observing Titan’s atmosphere via a wide varieties of methods.

These images show two views of Titan's planet-wide stratospheric haze just before (left) and after (right) Cassini's first close encounter with the shrouded moon. The image on the left was taken on Oct. 25, 2004, through an ultraviolet filter, which is sensitive to scattering of sunlight by small haze particles. It shows the high-altitude haze at the north pole (top) illuminated above a surface blanketed in darkness during this winter season. Numerous striations are visible in the haze, indicating either waves passing through the layer or the presence of multiple layers. The pixel scale of this image is 2.8 kilometers (1.7 miles).

The image on the right was taken on Oct. 26, 2004, and shows Titan's night-side backlit by the Sun after Cassini's closest approach to the moon. The haze layer ringing the planet is illuminated because the small particles scatter significant sunlight in the forward direction. Variations in haze concentration and thickness around the globe are also evident and seem to be symmetric around the north pole (upper left). The pixel scale of this image is 6.6 kilometers (4.1 miles).

Titan's surface cannot be seen in any Voyager photos; it is hidden by a dense, photochemical haze whose main layer is about 300 kilometers (200 miles) above Titan's surface. Several distinct, detached haze layers can be seen above the opaque haze layer. The haze layers merge with the main layer over the north pole of Titan, forming what scientists first thought was a dark hood. The hood was found, under the better viewing conditions of Voyager 2, to be a dark ring around the pole. The haze layer is thought to be made of organic compounds of the photolysis product. 

Left: Voyager false-color view of Titan’s Haze layer, shot in Nov 12, 1980. The detached layers of haze hundreds of kilometers above the surface.


The Huygens Probe, supplied by the European Space Agency, is advanced spacecraft system that is a crucial part of the overall Cassini mission. Two elements comprise the spacecraft: The Cassini orbiter and the Huygens probe. In 2004, Cassini-Huygens reached Saturn and its moons.  In December 25, 2004, Cassini ejected the Huygens probe. After its 20-day coast, the cone-shaped probe descended into Titan's cloudy atmosphere. Three sets of parachutes deployed to slow the probe and to provide a stable platform for scientific measurements. Two hours twenty-seven minutes after entering Titan's atmosphere, the probe landed near the moon's equator. Huygens is now the furthest human-made object ever to land on a celestial body.

The Huygens probe payload also consisted of a complement of six scientific instruments, which were each designed to perform a different function as the probe descended into Titan's murky atmosphere. The six instruments were:

Huygens Atmospheric Structure Instrument (HASI)  contained a suite of sensors that measured the physical and electrical properties of Titan's atmosphere.

Doppler Wind Experiment (DWE) was to measure the wind speed during Huygens' descent through Titan's atmosphere by observing changes in the carrier frequency of the probe due to the Doppler effect.

Descent Imager/Spectral Radiometer (DISR) made a range of imaging and spectral observations using several sensors and fields of view.

Gas Chromatograph Mass Spectrometer (GCMS) This instrument was a versatile gas chemical analyzer that identified and measured chemicals in Titan's atmosphere.

Aerosol Collector and Pyrolyser (ACP) drew in aerosol particles from the atmosphere through filters, then heated the trapped samples in ovens (the process of pyrolysis) to vaporize volatiles and decompose the complex organic materials. The products were then flushed along a pipe to the GCMS instrument for analysis. Two filters were provided to collect samples at different altitudes.

Acknowledgement: Contents and pictures are referred to the NASA websites for Voyager and Cassini.


This probe system consisted of the probe itself, which reached Titan in January 2005, and the probe support equipment (PSE), which remained attached to the orbiting spacecraft. The PSE included the electronics necessary to track the probe, recover the data gathered during its descent, and process and deliver the data to the orbiter. The data was then transmitted or "downlinked" from the orbiter to the ground.


Cassini-Huygens Mission "Petal Plot"  with aerial view.

Voyager tour of the four planets using the ‘gravity assistance ‘ technique. (click to enlarge)