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The Cassini-Huygens Mission: Lifting the Veil of Secrecy
(Released October 2004)

 
  by Salvatore Vittorio  

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It is difficult to say what is impossible, for the dream of yesterday is the hope of today and reality of tomorrow. - Robert Goddard

Introduction

On July 1st, 2004, the international Cassini-Huygens Mission spacecraft entered into orbit around the planet Saturn. The Cassini spacecraft will remain in Saturn's orbit for four years to probe its rings, its atmosphere, and its moons, among other things. On Christmas 2004, the Huygens probe, attached to the Cassini spacecraft, will disengage from Cassini and is scheduled to land on or about January 14, 2005, on Saturn's largest moon, Titan. If successful, this would mark one of mankind's greatest achievements. Titan, the second largest moon in the solar system, is of great interest to scientists because it is the only moon known to have clouds and a mysterious planet-like atmosphere. Titan's atmosphere appears as an opaque orange haze, obscuring its surface from view, and veiling its secrets. The Cassini-Huygens Mission seeks to lift that veil of secrecy during its four-year tour of Saturn, its moons, and its magnetosphere. Scientists hope to gain a better understanding of Titan's surface, atmosphere, and chemical composition, to perhaps shed some light about what primordial Earth might have been like billions of years ago.1

I. The Planet Saturn and its Natural Satellites

In Roman mythology, Saturn is the god of agriculture. The associated Greek god, Cronus, was the son of Uranus and Gaia and the father of Zeus (Jupiter). Saturn is the root of the English word "Saturday" (i.e., Saturn's day).

The planet Saturn has been known since prehistoric times. The Italian astronomer, physicist and mathematician Galileo Galilei (1564-1642) was the first to observe it with a telescope in 1610; he noted its odd appearance but was confused by it. This confusion continued through early observations of Saturn, which were complicated by the fact that the Earth passes through the plane of Saturn's rings every few years as Saturn moves in its orbit. A low resolution image of Saturn therefore changes drastically. It was not until 1659 that the Dutch astronomer Christiaan Huygens (1629-1695) correctly inferred the geometry of the rings. Saturn's rings remained unique in the known solar system until 1977 when very faint rings were discovered around the planet Uranus (and shortly thereafter around the planets Jupiter and Neptune).

Saturn is the sixth planet from the Sun and is the second largest in the solar system, with an equatorial diameter of 119,300 kilometers (74,130 miles). Saturn was first visited by the Pioneer 11 spacecraft in 1979; much of what is known about the planet is due to the Voyager 1 and Voyager 2 spacecraft explorations in 1980-81. Visibly flattened at the poles as result of the very fast rotation on its axis, Saturn has a day 10 hours, 39 minutes long, and the planet takes 29.5 Earth years to revolve about the Sun. The atmosphere is primarily composed of hydrogen (about 97 percent) with small amounts of helium (about 3 percent) and methane. Because Saturn is the only planet less dense than water (about 30 percent less), if a large enough body of water could be found, Saturn would float in it. The planet's hazy yellow hue is marked by broad atmospheric banding similar to, but fainter than, that found on Jupiter.

The wind blows at high speeds on Saturn, mostly in an easterly direction. Near the equator, it reaches velocities of 500 meters per second (1100 miles an hour). The strongest winds are found near the equator, and the velocity falls off uniformly at higher latitudes. At latitudes greater than 35 degrees, winds alternate east and west as latitude increases.

Saturn's ring system makes the planet one of the most beautiful objects in the solar system. The rings are divided into seven major divisions with alphabetic designators in the order of discovery. From the innermost ring to the outermost ring the designators are D, C, B, A, F, G and E. Each major division is further subdivided into thousands of individual ringlets. The F and G rings are very thin and difficult to see while the A, B, and C rings are broad and quite visible. The ring system has various gaps, the most notable of which is the Cassini Division, which separates the A and B rings. The French-Italian astronomer Jean Dominique (Giovanni Domenico) Cassini (1625-1712) discovered this division in 1675. Between the A and F rings lies the Keeler (Encke) gap, which includes the bright A and B rings and a fainter C ring. The Encke (pronounced EN-kee) Division, which splits the A Ring, is named after Johann Encke, who is credited with discovering it in 1837, but most likely never saw it. The Voyager pictures show the four D, E, F, and G faint rings. Space probes have shown that the main rings are really made up of a large number of narrow ringlets. The origin of the rings is obscure; it is thought that they may have been formed from larger moons that were shattered by impacts of comets, and meteoroids. The ring composition is not definitively known, but the rings do show a significant amount of water. They may be composed of icebergs and/or snowballs whose sizes may range from a few centimeters to a few meters. Much of the elaborate structure of some of the rings is due to the gravitational effects of nearby natural satellites (moons).

Radial spoke-like features in the broad B-ring were also found by the Voyager spacecraft. The features are believed to be composed of fine dust-size particles. The spokes were observed to form and dissipate in the time-lapse images taken by the Voyagers. While electrostatic charging may create spokes by levitating dust particles above the ring, the exact cause of the formation of the spokes is not well understood.2

To an earthling, Saturn's physical characteristics are mind-bogglingly large. Saturns mean distance from the Sun is 1,429,400,000 km or 9.54 Astronomical Units (AU) (An AU is the mean distance from the Earth to the Sun). Saturn's diameter is 120,536 km at its equator and its mass is 5.68 x 1026 kg, or 9.5181 Earth masses. As of now, Saturn has a total of 31 named moons (or natural satellites). The 31st and latest named moon (S/2003 S1) was found on February 5, 2003; previously, two as yet unnamed moons were discovered in 2004. Saturn's density is 0.69 grams per cubic centimeter, and its mean orbital velocity (the mean speed with which it travels around the Sun) is 9.67 kilometers per second (9.67 km/s), which is around 6 miles/s. The tilt angle of Saturn's axis of rotation is 25.33 deg. Saturn's atmospheric pressure is 1.4 bars; its mean cloud temperature is -125 degrees C (-125 C). Its largest moon Titan, with a radius of 2575.5 +/- 2 km, was discovered by Christiaan Huygens in 1655. Its four next largest moons, in descending order, are Rhea (764 +/- 4 km radius), Iapetus (730 km radius) Dione (559 +/- 5 km radius), and Tethys (529.9 +/- 1.5 km radius). All four of those moons were discovered by Giovanni Cassini in 1672 (Rhea), 1671 (Iapetus), and in 1684 (Dione and Tethys).3

II. Overview of the Cassini-Huygens Mission to Saturn and Titan

The Cassini spacecraft and Huygens probe
The Cassini spacecraft and Huygens probe begin their seven-year journey to the ringed planet
Source: NASA/JPL

Introduction

The Cassini-Huygens Mission to Saturn and its largest moon, Titan, is a $3.2-billion NASA/European Space Agency (ESA)/Italian Space Agency cooperative project that consists of the Cassini Saturn orbiter spacecraft coupled with the Huygens Titan atmosphere probe. Seventeen nations contributed to building the spacecraft. The Huygens-Cassini Mission was launched successfully on October 15, 1997, and is managed by the Jet Propulsion Laboratory (JPL) in Pasadena, California. After an almost seven-year journey in the solar system, the pair of spacecraft entered Saturn's orbit 1.6 billion km from Earth on July 1, 2004. The Cassini-Huygens spacecraft and probe are to examine the Saturnian system in unprecedented detail. Huygens will separate from Cassini during its third Saturn orbit on December 24th or 25th, 2004, and parachute through Titan's atmosphere on January 14, 2005. Cassini will continue to orbit Saturn, investigating the system for at least four years, from a wide range of orbital inclinations. The orbiter carries detectors capable of registering nearly every phenomenon, including infrared, visible, and ultraviolet light; radio, magnetic, and electric fields; plasma, dust, and elementary particles of all energies. The Huygens probe is equipped to sample and report on every facet of Titan's atmosphere, its aerosols and dynamics, and Titan's surface characteristics.4

Scientific Objectives

The Cassini-Huygens Mission is intended to provide a better understanding of the planet Saturn, its famous rings, its magnetosphere, its principal moon Titan, and its other moons or "icy satellites." Along with extensive preparation, planning and tracking throughout the mission, science objectives are divided into two parts: the goals en route to the ringed planet, and then those occuring after the spacecraft arrives.

To ensure all instruments on board the spacecraft are working properly for the upcoming tour of Saturn, checks were performed via remote control at launch time as well as after 14 months in space. This includes routine instrument maintenance, Gravitational Wave Experiments, instrument calibrations, and conjunction experiments for a time period of at least 30 days.

The 12 instruments on board the Cassini Spacecraft orbiter and 6 instruments on board the Huygens Probe are designed to perform in-situ (on-site) studies of elements of Saturn, its atmosphere, moons, rings, and magnetosphere. The instruments will study temperatures in various locations, plasma levels, neutral and charged particles, compositions of surfaces, atmospheres and rings, solar wind, and even dust grains in the Saturn system. Other instruments will perform spectral mapping for high-quality images of the planet, its moons and rings.5

The science objectives for Saturn's rings are (1) to study their configuration and the dynamic processes responsible for the ring structure, (2) to map the composition and size distribution of the ring material, (3) to investigate the interrelation of Saturn's rings and moons, including moons imbedded within the rings, (4) to determine the distribution of dust and meteoroid distribution in the vicinity of the rings, and (5) to study the interactions between the rings and Saturn's magnetosphere, ionosphere, and atmosphere. ionosphere and the planet's magnetic field; (5) to determine the composition, heat flux, and radiation environment present during Saturn's formation and evolution; and (6) to investigate the sources and nature of Saturn's lightning.7

Titan: Probing the Mystery

Saturns moon, Titan
Saturn's moon, Titan
Source: NASA/JPL

Titan is a time vault insofar as its unique environment and thick atmosphere may resemble that of Earth some several billion years ago, before life as we know it began pumping oxygen into our atmosphere.

Titan's atmosphere is made up primarily of nitrogen, which appears as an opaque orange haze, obscuring its surface from view. Titan is the second largest moon in the solar system, after Jupiter's moon Ganymede. At 5150 km (3200 miles, compared to 2160 miles for Earth's moon) in diameter, Titan is larger than each of the planets Mercury and Pluto. Titan orbits Saturn at a distance from the planet of 1,222,000 km (759,478 miles), taking 15.9 days to complete one revolution. Its mass is 1.34 x 10²³ kg; its average density is 1.88 g/cubic cm, and its surface temperature is 95 K (i.e., -178 C or -288 F).8

Through ongoing observations from Earth as well as data collected by the Pioneer and Voyager spacecraft, scientists now know that Titan's atmosphere is over 95 percent nitrogen, while only 5 percent is composed of methane, cyanide, and other hydrocarbons.

Titan is the only known moon in the solar system with a thick atmosphere, 10 times thicker than Earth's. Except for some clouds, Earth's surface is visible from space. But on Titan, a thick haze at 200 km (120 miles) above the surface obscures the entire moon from view. The atmosphere is thick enough so that a person standing on Titan's surface in the daytime would experience a level of daylight equivalent to 1/1000th the daylight on Earth's surface. This comparison not only takes into account the atmosphere's thickness, but also Titan's greater distance from the Sun. Nonetheless, light levels on Titan's surface are 350 times brighter than moonlight on Earth under a full moon.9

Titan's surface is shrouded from view, and so conditions on the surface are not well understood. Our knowledge comes from recent images using the Hubble Space Telescope. Brightness variations are evident in Hubble data, including a large continent-sized region on Titan's surface. Scientists believe this brightness difference is partly due to different chemical compositions on its surface, which could mean that Titan houses oceans of liquid hydrocarbons.

By combining results from the Cassini-Huygens Mission with Earth-based astronomical observation, Hubble data, laboratory experiments and computer models, scientists hope to answer basic questions regarding the origin and evolution of this intriguing satellite, such as why it developed an atmosphere similar to that of Earths, whereas the other moons didn't, and whether Titan evolved on its own or was ejected from Saturn itself.10

For the Cassini-Huygens Mission the scientific objectives for Titan are (1) to determine the most abundant elements, and most likely scenarios for the formation and evolution of Titan and its atmosphere; (2) to determine the relative amounts of different components of the atmosphere; (3) to observe vertical and horizontal distributions of trace gases, search for complex molecules, investigate energy sources for atmospheric chemistry, determine the effects of sunlight on chemicals in the stratosphere, and study the formation and composition of aerosols; (4) to measure winds and global temperatures; investigate cloud physics, general circulation and seasonal effects in Titan's atmosphere; search for lightning; (5) to determine the physical state, topography and composition of Titan's surface and characterize its internal structure; (6) to investigate Titan's upper atmosphere, its ionization and its role as a source of neutral and ionized material for the magnetosphere of Saturn; and (7) to determine whether Titan's surface is liquid or solid, and analyze the evidence of a bright continent as indicated in Hubble images taken in 1994.11

Huygens probe separating
Artists Concept: Huygens probe entering Titan's atmosphere
Source: NASA/JPL

The atmospheric descent of the Huygens probe through Titan's atmosphere, scheduled to take place on January 14, 2005, will last between two and two and a half hours. During its descent, Huygens' camera will capture more than 1100 images, while the Probe's five other instruments will sample Titan's atmosphere and determine its composition. Data from Huygens will be relayed to the Cassini Orbiter passing overhead and stored onboard Cassini's Solid State recorders (SSR) for playback to Earth.12

Cassini and Phoebe

Discovered more than 100 years ago by American astronomer William Pickering, Phoebe, one of Saturn's tiniest named moons, is a source of extensive scientific interest. Roughly spherical and with a diameter of 220 km (about 136.7 miles), which is equal to about one-fifteenth of the diameter of Earth's moon, Phoebe rotates on its axis every nine hours and completes a full orbit around Saturn in about 18 months. Its irregular elliptical orbit is inclined approximately 30 degrees toward Saturn's equator. Phoebe's orbit is also retrograde, which means it goes around Saturn in the opposite direction of most other moons, as well as of most other objects in the solar system. Its average distance from the ringed planet is 13 million km (about 8 million miles), which is almost four times farther away from Saturn than its nearest neighbor, the moon Iapetus. Phoebe and Iapetus are the only major moons in the Saturn region that do not orbit close to the plane of Saturn's equator.

On June 11, 2004, a few weeks before entering the orbit of Saturn, the Cassini spacecraft flew by Phoebe and began its landmark scientific mission. The distance from which images of Phoebe were taken is radically different from the early 1980s, when Voyager 2 embarked on its legendary tour of the solar system. Then, Voyager 2's cameras snapped images of Phoebe from about 2.2 million km (about 1.4 million miles) away. Cassini, on the other hand, snapped images from a mere 2000 km (about 1240 miles) from the moon's surface. In addition, thanks to significant technological improvements throughout the past 20 years, Cassini's cameras are not only far smaller than, but also far superior in image quality to, their earlier counterparts. Unlike most major moons orbiting Saturn, Phoebe is very dark and reflects only 6 percent of the sunlight it receives. Its darkness and irregular, retrograde orbit suggest that Phoebe is most likely a captured object, which is defined as a celestial body that is trapped by the gravitational pull of a much bigger body, generally a planet. Phoebe's darkness in particular suggests that the small moon comes from the outer solar system, a region known as the Kuiper Belt, where many celestial bodies contain dark material.

Some scientists think Phoebe could be a captured Centaur, a Kuiper Belt object that migrated into the inner solar system. Centaurs are found between the asteroid belt and the Kuiper Belt, and are considered to be intermediate bodies. If Phoebe is indeed a Centaur, images and scientific data taken by the Cassini spacecraft will give scientists the first intensive opportunity to study a Kuiper Belt object.

Kuiper Belt objects are of extreme interest to scientists because they are believed to be primordial; that is, they appear to date back to the formation of the solar system. Known as the "building blocks" of the solar system, Kuiper Belt objects exist as fragments that were never drawn together by gravity into a planet.

Because of its small size and poor reflective properties, Phoebe might not have generated enough heat since its formation to alter its original chemical composition. This is another major factor that increases the scientific value of the study of this mysterious moon.13

Summary of Key Dates and Highlights of the Cassini-Huygens Saturn Tour:

Key dates of the Saturn Tour include:

June 11, 2004 (19:32 UTC): Flyby of the furthest moon orbiting Saturn, Phoebe, at an altitude of 2000 km (1243 miles). July 1, 2004: Crossing of Saturn's Ring Plane during the spacecraft's critical Saturn Orbit Insertion sequence. December 25, 2004 (02:00 UTC) Huygens probe separates from the Cassini orbiter and begins its 21-day journey to Titan. December 25 counts as day one and January 14 is day 21. January 14, 2005: Huygens begins its descent through Titan's cloudy atmosphere, where it lands on the surface about two and one-half hours later. The probe is scheduled to encounter the upper fringes of Titan's atmosphere at 09:00 UTC.14

Highlights of the Saturn Tour include: 74 orbits of Saturn; 45 close flybys of Titan; eight close "targeted" flybys of other satellites: three of Enceladus, and one each of Phoebe, Hyperion, Dione, Rhea, and Iapetus; 30 additional satellite flybys at distances less than 100,000 km (about 62,100 miles); many Saturn and ring occultation opportunities; and one "Titan 180-degree" orbit transfer.15

III. The Story So Far Away

Phoebe

NASA's Cassini spacecraft successfully completed its first close flyby of a moon of Saturn on Friday, June 11, 2004, when the spacecraft captured images of the moon Phoebe. Detailed images revealed a heavily cratered surface that has astronomers debating the satellite's origins. The most detailed image released so far shows a tiny world riddled with ancient pockmarks, but with great variations of surface brightness. Phoebe in general is very dark, but close inspection revealed areas so bright that they were washed out in the picture. The sharp clear images showed many geological features. Though it is too early to say, researchers believe closer inspection of the pictures of Phoebe could reveal it to be indeed a Kuiper Belt object.

The highest resolution image so far released shows a crater near the right hand edge with bright rays that extend from its center. This suggests that dark material coats the outside of what may be a predominantly icy body. Kuiper Belt objects, more so than asteroids, are thought to consist largely of ice. The large craters have also led to speculation that Phoebe, the largest of Saturn's outer moons, might be the parent of the other, much smaller backward-orbiting outer moons of Saturn. "Looking at those big 50-km (31-mile) craters, one has to wonder whether their impact ejecta might be the other tiny moons that orbit Saturn on paths much like Phoebe's," said Joseph Burns, an imaging team member and professor at Cornell University.16

First images from the Cassini flyby of Phoebe reveal a scarred, cratered outpost with an ancient and mysterious past, and huge variation in surface brightness
Source: NASA/JPL/Space Science Institute

Saturn's Shadow and Titan's Glow

The Cassini spacecraft has detected lightning and a new radiation belt at Saturn, and a glow around the planet's largest moon, Titan. The spacecraft's radio and plasma wave science instrument detected radio waves generated by lightning. The crackling and popping sounds detected are the same as one hears when listening to an AM radio broadcast during a thunderstorm, according to Dr. Bill Kurth, deputy principal investigator on the radio and plasma wave instrument, University of Iowa, Iowa City. Dr. Kurth also says that, "These storms are dramatically different than those observed 20 years ago."

Cassini finds radio bursts from this lightning are highly episodic. There are large variations in the occurrence of lightning from day to day, sometimes with little or no lightning, suggesting a number of different, possibly short-lived storms, at mid- to high latitudes. Voyager observed lightning from an extended storm system at low latitudes, which lasted for months and appeared highly regular from one day to the next. The difference in storm characteristics may be related to very different shadowing conditions in the 1980s than currently. During the Voyager time period when lightning was first observed, the rings cast a very deep shadow near Saturn's equator. As a result, the atmosphere in a narrow band was permanently in shadow, making it cold, by contrast with the adjacent hottest band in Saturn's atmosphere. Turbulence between the hot and cold regions could have led to long-lived storms. However, during Cassini's approach and entry into Saturn's orbit, it was summer in the southern hemisphere and the ring shadow was distributed widely over a large portion of the northern hemisphere. This causes the hottest and coldest regions to be far apart.

A major finding of the magnetospheric imaging instrument is the discovery of a new radiation belt just above Saturn's cloud tops, up to the inner edge of the D-ring. This is the first time that a new Saturnian radiation belt has been discovered with remote sensing. This new radiation belt extends around the planet. It was detected by the emission of fast neutral atoms created as its magnetically trapped ions interact with gas clouds located planetward of the D-ring. With this discovery, the radiation belts are shown to extend far closer to the planet than previously known.

"This new radiation belt had eluded detection by previous visits to Saturn," according to Dr. Donald G. Mitchell, instrument scientist for the magnetospheric imaging instrument at the Johns Hopkins University Applied Physics Laboratory, Laurel, MD. "With its discovery we have seen something that we did not expect, that radiation belt particles can 'hop' over obstructions like Saturn's rings, without being absorbed by the rings in the process."

As for Titan, Cassini's visual and infrared mapping spectrometer captured it glowing both day and night, powered by emissions from methane and carbon monoxide gases in the moon's extensive, thick atmosphere. "Not only is Titan putting on a great light show but it is also teaching us more about its dense atmosphere," says Dr. Kevin Baines, science team member for the visual and infrared mapping spectrometer at JPL. "What is amazing is that the size of this glow or emission of gases is a sixth the diameter of the planet," he adds.

The Sun-illuminated fluorescent glow of methane throughout Titan's upper atmosphere, revealing the atmosphere's immense thickness and extending more than 700 km (435 miles) above the surface, was expected. However, the nighttime glow, persistently shining over the night side of Titan, initially surprised scientists. Titan glows throughout the near-infrared spectrum.17

Titan
Titan
Source: NASA/JPL/Space Science Institute

Two New Moons

The Cassini spacecraft has uncovered two moons, which may be the smallest bodies so far seen around Saturn: approximately 3 km (2 miles) and 4 km (2.5 miles) across. The moons, located 194,000 km (120,000 miles) and 211,000 km (131,000 miles) from the planet's center, are between the orbits of two other Saturnian moons, Mimas and Enceladus. They are provisionally named S/2004 S1 and S/2004 S2. The first may be an object spotted in a single image taken by NASA's Voyager spacecraft 23 years ago, called at that time S/1981 S14.

The moons were first seen by Dr. Sebastien Charnoz, a planetary dynamicist working with Dr. Andre Brahic, imaging team member at the University of Paris. The smallest previously known moons around Saturn are about 20 km (12 miles) across. Scientists expected that moons as small as S/2004 S1 and S/2004 S2 might be found within gaps in the rings and perhaps near the F ring, so they were surprised to discover these small bodies between two major moons. Small comets careening around the outer solar system would be expected to collide with small moons and break them to bits. The fact that these moons exist where they do might provide limits on the number of small comets in the outer solar system, a quantity essential for understanding the Kuiper Belt of comets beyond Neptune, and the cratering histories of the moons of the giant planets.18

More Rings and More Objects

Scientists examining Saturn's contorted F ring, which has baffled them since its discovery, have found one small body, possibly two, orbiting in the region, and a ring of material associated with Saturn's moon Atlas. A small object was discovered moving near the outside edge of the F ring, interior to the orbit of Saturn's moon Pandora, in images taken on June 21, 2004, just days before Cassini arrived at Saturn. Dr. Carl Murray, imaging team member at Queen Mary, University of London, states that, "I noticed this barely detectable object skirting the outer part of the F ring." Murray's group at Queen Mary then calculated an orbit for the object.

Scientists cannot yet definitively say if the object is a moon or a temporary clump, i.e., a relatively short-lived conglomeration of matter such as rocks or dust that is swept together by gravity or by rotational forces and which may give the appearance of a moon-like body. If it is a moon, its diameter is estimated at 4-5 km (2-3 miles), and it is located 1000 km (620 miles) from the F ring, Saturn's outermost ring. It is at a distance of approximately 141,000 km (about 86,000 miles) from the center of Saturn and within 300 km (190 miles) of the orbit of the moon Pandora. The object has been provisionally named S/2004 S3.

Scientists are not sure if the object is alone. This is because of results from a search through other images that might capture the object to pin down its orbit. The search by Dr. Joseph Spitale, a planetary scientist working with team leader Dr. Carolyn Porco at the Space Science Institute in Boulder, CO, revealed something strange. Spitale says, "When I went to look for additional images of this object to refine its orbit, I found that about five hours after first being sighted, it seemed to be orbiting interior to the F ring. . . . If this is the same object then it has an orbit that crosses the F ring, which makes it a strange object." Because of the puzzling dynamical implications of having a body that crosses the ring, the inner object sighted by Spitale is presently considered a separate object with the temporary designation S/2004 S4. S4 is roughly the same size as S3. In the process of examining the F ring region, Murray also detected a previously unknown ring, S/2004 1R, associated with Saturn's moon, Atlas. It is known from Voyager that the region between the main rings and the F ring is dusty, but the role of the moons in this region was a mystery," Murray explains. "It was while studying the F ring in these images that the faint ring of material was discovered. After some calculation Atlas was identified as the prime suspect."

With a width estimated at 300 km (190 miles), the ring is located 138,000 km (about 86,000 miles) from the center of Saturn in the orbit of the moon Atlas, between the A ring and the F ring. The ring was first spotted in images taken after Cassini-Huygens orbit insertion on July 1, 2004. There is no way of knowing yet if it extends all the way around the planet. Searches will continue for further detections of the newfound body or bodies seen in association with the F ring. If the two objects indeed turn out to be a single moon, it will bring the Saturn moon count to 34. The newfound ring adds to the growing number of narrow ringlets around Saturn.19

To Be Continued. . .

In the period from December 25th, 2004, to January 14, 2005, the scheduled descent of the Huygens probe through Titan's thick atmosphere will take place, culminating in the actual landing of the probe on Titan's surface. If all goes well, Titan will be the farthest planetary body that any man-made spacecraft has landed on so far. As Huygens penetrates Titan's hazy atmosphere during its descent and landing, more and more of the mysteries surrounding this most intriguing of all the solar system satellites will be unveiled. Stay tuned!

This Hot Topic will be updated periodically to reflect all significant events and findings of the mission.

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