Cassini-Huygens Mission
Cassini-Huygens is a unmanned space mission intended to study Saturn and its moons. Cassini is now in orbit around Saturn and sending back data.
The Cassini-Huygens mission is a joint NASA/ESA/ASI unmanned space mission intended to study 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 Christiaan Huygens. Cassisi is the largest interplanetary craft built so far, at two stories tall and thirteen feet wide.
The Cassini spacecraft was launched on October 15th, 1997 from Cape Canaveral, Florida. Cassini flew by Venus and Earth before heading for its close flyby of Jupiter on December 30, 2000, where it performed many scientific measurements. About 26 thousand images were taken of Jupiter during the course of the month-long flyby, producing the most detailed global colour portrait of Jupiter. Cassini was then slingshot on its 4 year voyage towards Saturn.
It arrived at Saturn on 1 July 2004 to begin a four-year exploration of the ringed planet and its moons.
Cassini is now in orbit around Saturn and sending back data. The Huygens probe successfully landed on Saturns moon Titan on the 14th January 2005, sending back amazing views of the moons surface.
Cassini-Huygens probe (artist impression).
Picture Credit: NASA.
Plutonium power source and controversy
Because of Saturns distance from the Sun, solar arrays were not feasible power sources for the spacecraft. To generate enough power, such arrays would have been too large and heavy. Thus, the Cassini orbiter gets its power from three radioisotope thermoelectric generators or RTGs, which use heat from the natural decay of plutonium (in the form of plutonium dioxide) to generate direct current electricity. These RTGs are of the same design as those which flew on the Galileo and Ulysses spacecraft and are designed to have a long operational lifetime. At the end of the 11-year Cassini mission, they will still be capable of producing at least 628 watts of power.
Test of Einsteins theory of general relativity
On October 10, 2003, the Cassini science team announced the results of a test of Einstein's theory of general relativity, using radio signals from the Cassini probe. The researchers observed a frequency shift in the radio waves to and from the spacecraft, as those signals travelled close to the Sun. According to the theory of general relativity, a massive object like the Sun causes space-time to curve, and a beam of radio waves (or light) that passes by the Sun has to travel further because of the curvature. The extra distance that the radio waves travel from Cassini past the Sun to the Earth delays their arrival; the amount of the delay provides a sensitive test of the predictions of Einstein's theory. Although deviations from general relativity are expected in some cosmological models, none were found in this experiment. Past tests were in agreement with the theoretical predictions with an accuracy of one part in one thousand. The Cassini experiment improved this to about 20 parts in a million, with the data still supporting Einstein's theory.
Lakes found on Titan
Lakes found on Titan.
Picture Credit: NASA.
Using a complex radar system, Cassini has discovered very strong evidence of liquid hydrocarbon lakes on Saturns moon, Titan.
Scientists have speculated that liquid methane or ethane might form lakes on Titan, particularly near the somewhat colder polar regions. In the images, a variety of dark patches, some with channels leading in or out of them, appear. The channels have a shape that strongly implies they were carved by liquid. Some of the dark patches and connecting channels are completely black, that is, they reflect back essentially no radar signal, and hence must be extremely smooth. In some cases rims can be seen around the dark patches, suggesting deposits that might form as liquid evaporates. The abundant methane in Titan's atmosphere is stable as a liquid under Titan conditions, as is its abundant chemical product, ethane, but liquid water is not. For all these reasons, scientists interpret the dark areas as lakes of liquid methane or ethane, making Titan the only body in the solar system besides Earth known to possess lakes. Because such lakes may wax and wane over time, and winds may alter the roughness of their surfaces. Repeat coverage of these areas should test whether indeed these are bodies of liquid.
New moons of Saturn
Daphnis is a recently discovered moon of Saturn.
Picture Credit: NASA
Using images taken by Cassini, two new moons of Saturn were discovered in June, 2004. They are both very small and were given the provisional names S/2004 S 1 and S/2004 S 2 before being named Methone and Pallene at the end of 2004.
On May 1, 2005, a new moon was discovered by Cassini in the Keeler gap. It was given the designation S/2005 S 1 before being named Daphnis. The only other moon inside Saturn's ring system is Pan.
Spoke phenomenon Verified
The spokes phenonomon seen on Saturns rings.
Picture Credit: NASA.
In images captured 5 September 2005, Cassini finally detected spokes in Saturn's rings, hitherto seen only by the Voyager spacecraft in the early 1980s. The exact cause of the spokes is not yet understood; but some believe it to be the way light reflects from the small particles in the rings. These spokes manifest themselves as bright streaks across the rings.
Radio occultations of Saturns rings
In May, 2005, Cassini began a series of occultation experiments, designed to measure the size-distribution of particles in Saturn's rings, and to measure the atmosphere of Saturn itself. For over 4 months, Cassini will complete orbits specifically designed for this purpose. During these occultation experiments, Cassini will fly behind the ring plane of Saturn, as seen from Earth, and transmit radio waves through the particles. The radio signals are received on Earth, where the frequency, phase, and power of the signal is analysed to help determine the structure of the rings.
The Huygens probe
Artist impression of Huygens Probe.
Picture Credit: NASA.
The Huygens probe, supplied by the ESA is named after the 17th century Dutch astronomer Christiaan Huygens. Its mission was to analyse the clouds, atmosphere, and surface of Saturn's moon Titan, in its descent on 15 January 2005. It was designed to enter and brake in Titans atmosphere and parachute a fully instrumented robotic laboratory down to the surface. The Huygens probe system consisted of the probe itself, which descended to Titan, and the probe support equipment (PSE) on Cassini, which remained attached to the orbiting spacecraft. The PSE includes the electronics necessary to track the probe, to recover the data gathered during its descent, and to process and deliver the data to the orbiter, from which it was transmitted to Earth.
The main mission phase was a parachute descent through Titans atmosphere. The batteries and all other resources were sized for a Huygens mission duration of 153 minutes, corresponding to a maximum descent time of 2.5 hours plus at least 3 additional minutes (and possibly a half hour or more) on Titans surface. The probes radio link was activated early in the descent phase, and the orbiter "listened" to the probe for the next 3 hours, including the descent phase, and the first thirty minutes after touchdown. Not long after the end of this three-hour communication window, Cassini's high-gain antenna (HGA) was turned away from Titan and toward Earth.
Findings
Saturns Moon: Titan.
Picture Credit: NASA
The preliminary findings confirm that the targeted landing site was near the shoreline of a liquid ocean. The photos indicate the existence of drainage channels near the mainland and what appears to be a methane sea complete with islands and a mist-shrouded coastline. There are indications of chunks of water ice scattered over an orange surface, the majority of which is covered by a thin haze of methane. The instruments revealed "a dense cloud or thick haze approximately 18-20 kilometres (11-12 miles) from the surface which is likely the reservoir of methane on the surface. The surface itself appears to be clay-like material which might have a thin crust followed by a region of relative uniform consistency.
Measurements of wind speed started at 150 kilometres above Titans surface, where Huygens was blown eastwards at more than 400 kilometres per hour, agreeing with earlier measurements of the winds at 200 kilometres altitude, made over the past few years using telescopes. Between 60 and 80 kilometres, Huygens was buffeted by rapidly fluctuating winds, which are thought to be vertical wind shear. At ground level, the Earth-based Doppler shift and VLBI measurements show gentle winds of a few metres per second, roughly in line with expectations.
References
- NASA copyright policy states that "NASA material is not protected by Copyright unless noted".
- Cassini-Huygens Homepage
- The Nine Planets
- Wikipedia
- Wikipedia Cassini Huygens
