Huygens Spacecraft

The Huygens probe was carried to the Saturn system by the Cassini orbiter spacecraft. Bolted to the Cassini mother spacecraft and fed electrical power through an umbilical cable, Huygens rode along during the nearly seven-year journey largely in a sleep mode. However, mission controllers did awaken the robot probe about every six months for three-hour-duration instrument and engineering checkups. Huygens is sponsored by the European Space Agency and named after the Dutch physicist and astronomer Christiaan Huygens (1629-95), who first described the nature of Saturn's rings and discovered its major moon, Titan, in 1655.

The Cassini spacecraft's second Titan flyby on December 13, 2004, left the spacecraft (which was still carrying the hitchhiking Huy-gens probe) on a trajectory that, if uncorrected, would lead to a subsequent flyby of Titan at an altitude of about 2,860 miles (4,600 km). To get the Huygens probe traveling into Titan's atmosphere at just the right angle, the Cassini mother spacecraft performed a targeting maneuver before it released its hitchhiking robot companion. On December 17, the Cassini spacecraft completed a precise targeting maneuver that shaped its course and pointed the cojoined robot spacecraft team on a direct impact trajectory to Titan.

On December 25, 2005 (at 02:00 universal time coordinated), the spin/eject device separated Huygens from Cassini with a relative speed of 1.1 feet per second (0.35 m/s) and a spin rate of 7.5 revolutions per minute. As a result of these successful maneuvers and actions, the spin-stabilized atmospheric probe was targeted for a southern-latitude landing site on the dayside of Titan. To support a variety of mission needs and parameters, the probe entry angle into Titan's atmosphere was set at a relatively steep 65 degrees. ESA mission controllers selected this entry angle to give the probe the best opportunity to reach the surface of Titan. Following probe separation, the Cassini orbiter performed some final maneuvers to avoid crashing into Titan and to position itself to collect data from Huygens as it descended into Titan's opaque, nitrogen-rich atmosphere.

On January 14, 2005, after coasting for 20 days, the Huygens probe reached the desired entry altitude of 790 miles (1,270 km) above Titan and started its parachute-assisted descent into the moon's atmosphere. Within five minutes, the probe began to transmit its science data to the Cassini orbiter as it floated down through Titan's atmosphere.

During the first part of the probe's atmospheric plunge, instruments on board Huygens were controlled by a timer. For the final 6 to 12 miles (10 to 20 km) of descent, a radar altimeter on board the probe controlled its scientific instruments on the basis of altitude. About 138 minutes after starting its plunge into Titan's upper atmosphere, the Huygens probe came to rest on the moon's surface. Images of the site were collected just before landing. The probe survived impact on a squishy surface that was neither liquid nor frozen solid—the two candidate surface conditions most frequently postulated by planetary scientists for this cloud-enshrouded moon. As the Cassini orbiter disappeared over the horizon, the mother spacecraft stopped collecting data from its hardworking robot companion. The probe had been continuously transmitting data for about four and one-half hours.

magnetosphere also consists of the electrically charged and neutral particles within this magnetic bubble. Scientific investigation of Saturn's magnetosphere includes: its current configuration; particle composition, sources and sinks; dynamic processes; its interaction with the solar wind, satellites, and rings; and Titan's interaction with both the magnetosphere and the solar wind.

During the orbit tour phase of the mission (from July 1, 2004, to June 30, 2008), the Cassini orbiter spacecraft will perform many fyby encounters of all the known icy moons of Saturn. As a result of these numerous satellite flybys, the spacecraft's instruments will investigate: the characteristics and geologic histories of the icy satellites; the mechanisms for surface modification; surface composition and distribution; bulk composition and internal structure; and interaction of the satellites with Saturn's magnetosphere.

The moons of Saturn are diverse—ranging from the planetlike Titan to tiny, irregular objects only tens of miles (km) in diameter. Scientists currently believe that all of these bodies (except for perhaps Phoebe) hold not only water ice but also other chemical components, such as methane, ammonia, and carbon dioxide. Before the advent of robotic spacecraft in space exploration, scientists believed that the moons of the outer planets were relatively uninteresting and geologically dead. They assumed that (planetary) heat sources were not sufficient to have melted the mantles of these moons enough to provide a source of liquid, or even semiliquid, ice, or silicate slurries.

As if Titan was not providing scientists with enough surprises, in March 2006, the Cassini spacecraft appears to have found evidence of liquid-water reservoirs that erupt in Yellowstone Park-like geysers on Saturn's moon Enceladus. The rare occurrence of liquid water so near the surface raises many new scientific questions about this mysterious moon of Saturn. One current speculation is that the jets of water being ejected from Enceladus might be erupting from near-surface pockets of liquid water above 32°F (0°C) like cold versions of Yellowstone Park's Old Faithful geyser on Earth. This discovery placed Enceladus in an exclusive solar-system club—that of planetary bodies where active volcanism exists. Jupiter's moon Io, Earth, and possibly Neptune's moon Triton are the other currently known members of that exclusive group. The presence of liquid water, perhaps just 100 feet (30 m) or less below the moon's icy crust now makes Enceladus one of the most exciting places in the solar system.

Scientists are quick to point out that this recent discovery has given the search for liquid water beyond Earth a dramatic new turn. The type of evidence for liquid water on Enceladus is very different from what scientists have seen at Jupiter's moon Europa. On Europa, the evidence from surface geological features suggests an internal liquid-water ocean. On Enceladus,

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  • Sami
    Which moon did the huygens spacecraft land on?
    1 year ago

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