Posted on by Ian O'Neill

President Sarkozy and the French (Space) Revolution (Updated)

France hosts Europe's spaceport at Kourou, French Guiana (ESA)

It seems to be the week for big politics and space exploration. Yesterday, the Universe Today reported that Buzz Aldrin was worried about the future of the politically-driven US space policy; he is currently lobbying US President hopefuls Barack Obama and John McCain to increase NASA funding. On the other side of the pond, French President Nicolas Sarkozy also wants NASA’s European counterpart, ESA, to do better. However, Sarkozy wants to change the face of the ESA into the NASA model by making it politically driven, rather than leaving European bureaucrats to decide ESA priorities. ESA has operated independently from political pressures that often weigh down on space agencies, but Sarkozy is a huge advocate of the US system and believes space exploration should be politically motivated. This is bound to raise a few eyebrows, as the very agency he is promoting is facing some serious political uncertainty…

Update: Thanks to a couple of our readers from France, it has been pointed out that French astronauts are known as spationautes by the nation’s Centre National d’Études Spatiales (the French space agency). I have corrected the mini-discussion at the bottom of this article, reflecting this fact. Thank you Julien and Alexis!

In the 1960’s NASA’s motivation to land a man on the Moon was politically motivated, but in 1986, the UK Prime Minister Margaret Thatcher’s decision to pull Britain out of Europe’s manned space program was also politically motivated. Politics and space exploration can go hand-in-hand, but it can also hinder a nation’s development as space policy can be overturned depending who is in office. Worries to one side, President Nicolas Sarkozy believes that France may begin a revolution in the ESA’s outlook for the future. Amidst concerns aired by established space agencies that new space-faring nations like Japan, China and India may overtake Europe’s space agency, Sarkozy has announced radical plans for an accelerated effort for a politically driven push to send man back to the Moon and then to Mars.

Until now, ESA has maintained a more scientific approach to space exploration, but Sarkozy believes this approach has caused ESA to miss opportunities, possibly making Europe redundant in the future of space travel:

President Nicolas Sarkozy has huge aspirations for space (www.flickr.com/photos/besoindair/)

“The United States, Russia, China and Japan would not do what they do in space without a political motivation; Europe has only had a scientific motivation until now. So what we are saying is, let’s get the same chances as the others. Beside the scientific pilot, let us have a political pilot, too, which will be the EU, because there is only the EU that can speak at that level.” – President Sarkozy.

Although this is a bold statement, critics of Sarkozy’s stance point out that the comparison between NASA and ESA is not realistic. After all, NASA spends eight times more on space development than ESA, so Europe would need to allocate huge resources if there were to be a new political direction in ESA science. The 33-year old space agency is run by 17 member-states within the European Union (plus Switzerland, Norway and Canada) so Sarkozy’s aspirations may face setbacks, but the fact remains that France spearheads much of ESA’s operations so the French President’s views will not be ignored.

This is reflected in documents reviewed by the BBC that the French plans for an ESA overhaul are at an advanced stage. Key members of ESA have said that to become a space exploration powerhouse, they need to develop their own means to get European astronauts into space (a task that ESA have had to depend on the US and Russia till now). ESA have developed their own launch site in French Guiana (a major access to space for commercial satellites), have been heavily involved with the International Space Station, developed some of the most advanced robotics to be sent into space (i.e. the Automated Transfer Vehicle) and is currently developing the controversial European global positioning satellite system, Galileo. All is needed is an increase in funding so ESA can push toward manned missions to the Moon and Mars. Perhaps in this case, a politically orientated space agency may be a step in the right direction… until President Sarkozy’s term ends in any case…

Aside: A cosmonaut is a Russian astronaut, a taikonaut is a Chinese astronaut, but what is a French astronaut called? Well, the prefixes “astro-“, “cosmo-” and “taiko-” are pretty much equivolent. So what’s the French for “astro”? Well, “astro” actually… so a French astronaut is called an astronaut (or astronaute). I’m glad I cleared that up…

Update (July 3rd): Actually, the official designated name for a French astronaut is spationaute (according to the Centre National d’Études Spatiales). Thank you to our eagle-eyed French readers for sending me the tip! Now we have astronaut (US), cosmonaut (Russia), taikonaut (China) and spationaute (France). You learn something new every day!

Source: BBC

Posted on by Nancy Atkinson

Hubble Does Independence Day With Stars and Stripe

Back in 1006 A.D, observers from Africa to Europe to the Far East witnessed and recorded the arrival of light from what is now called SN 1006, a tremendous supernova explosion caused by the final death throes of a white dwarf star nearly 7,000 light-years away. One Egyptian astronomer recorded the object was 2 – 3 times as large as the disc of Venus and about one quarter the brightness of the moon. The supernova was probably the brightest star ever seen by humans, visible even during the day for weeks, and it remained visible to the naked eye for at least two and a half years before fading away. Remnants of this supernova are still visible to telescopes, and the Hubble Space Telescope captured this close-up a filament of the shock wave of the explosion, still reverberating through space, seen here against the grid of background stars. The full image of SN 1006 is pretty impressive, too…

SN 1006 has a diameter of nearly 60 light-years, and it is still expanding at roughly 6 million miles per hour. Even at this tremendous speed, however, it takes observations typically separated by years to see significant outward motion of the shock wave against the grid of background stars. In the Hubble image shown here, the supernova would have occurred far off the lower right corner of the image, and the motion would be toward the upper left.

It wasn’t until the mid-1960s that radio astronomers first detected a nearly circular ring of material at the recorded position of the supernova. The ring was almost 30 arcminutes across, the same angular diameter as the full moon. The size of the remnant implied that the blast wave from the supernova had expanded at nearly 20 million miles per hour over the nearly 1,000 years since the explosion occurred.

In 1976, the first detection of exceedingly faint optical emission of the supernova remnant was reported, but only for a filament located on the northwest edge of the radio ring. A tiny portion of this filament is revealed in detail by the Hubble observation. The twisting ribbon of light seen by Hubble corresponds to locations where the expanding blast wave from the supernova is now sweeping into very tenuous surrounding gas.

The hydrogen gas heated by this fast shock wave emits radiation in visible light. Hence, the optical emission provides astronomers with a detailed “snapshot” of the actual position and geometry of the shock front at any given time. Bright edges within the ribbon correspond to places where the shock wave is seen exactly edge on to our line of sight.

Original News Source: HubbleSite

Posted on by Ian O'Neill

Aldrin Warns that NASA will fall Behind Russia and China in Space Exploration

Buzz Aldrin and the US flag during NASAs biggest achievement - man on the Moon (NASA)

The world knows the huge potential China and Russia have for space exploration. Russia is maintaining a strong presence in space with their sturdy Soyuz program and China has set its sights on having their very first “taikonaut” EVA at the end of this year. But where does this leave NASA? The US space agency has spearheaded the exploration of space for the last 50 years, but amongst all the talk about NASA setbacks, overspending and delays, could the glory days be coming to an abrupt end? In May, the legendary astronaut John Glenn spoke out against Shuttle decommissioning and last week, US Senator Bill Nelson called a meeting at Cape Canaveral to raise concerns about announced job cuts in 2010. Now, the most famous NASA ex-employee and second man on the Moon, Buzz Aldrin has voiced warnings that the US could lose its grip on space and begin to be left behind by Russia and China…

On July 20th, 1969, the Apollo 11 Lunar Module Pilot waited for Neil Armstrong to make the first footprint in the lunar dust. Soon after, Buzz Aldrin joined Armstrong on this momentous step and making world history, setting the world alight with optimism that man was just about to embark on the next phase of evolution: leaving Earth and exploring the stars. Unfortunately this dream was only realised for three years (until 1972) after six successful lunar landings (Apollo 11, 12, 14, 15, 16 and 17), and to this day the Apollo 17 mission touch-down (December 15th, 1972) remains the last time we landed on the Moon.

Although we may not have revisited our natural satellite for the best part of four decades, we have been busy with our focus on the robotic exploration of the Solar System. But work has started on the Shuttle replacement, the Constellation Program, with the promise of sending man back to the Moon by 2020 and then Mars soon after, can we begin to get excited that NASA is gaining momentum for the next “giant leap for mankind?”

Many prominent figures are now worried that the light is beginning to dim for the future of NASA. NASA prides itself on developing new technologies, spearheading the push into space, but what happens when the funding dries up and other nations pick up where they left off? One voice that cannot be ignored is that of Buzz Aldrin who has voiced his grave concern that NASA, and indeed the USA, risks falling behind China and Russia in the “space race” if efforts were not redoubled by future US governments. With the US presidential elections looming, Aldrin has vowed to lobby both Barack Obama and John McCain to “retain the vision for space exploration,” not only to maintain, but increase NASA funding.

Buzz Aldrin on June 11th 2008

During an interview with the UK’s Sunday Telegraph newspaper he said, “If we turn our backs on the vision again, we’re going to have to live in a secondary position in human space flight for the rest of the century.” And he is not alone with this concern. Both fellow retired astronaut John Glenn and US Senator Bill Nelson have recently spoken out about their concerns for NASA’s future, ensuring the space exploration debate will remain alive over the coming months.

Although Russia has a long and proud history in human space flight, the Chinese are showing their thirst for a big push into space, with a manned mission to the Moon on the cards. “All the Chinese have to do is fly around the Moon and back, and they’ll appear to have won the return to the Moon with humans. They could put one person on the surface of the Moon for one day and he’d be a national hero,” Aldrin added. Plus, Russia’s Soyuz program could be extended for manned missions beyond Earth orbit he pointed out.

There is a real worry in NASA that the US could lose its foothold in the leadership of space exploration, so it is hoped big voices within the ranks of legendary astronauts might begin to get the future government thinking about how important space exploration is to the US.

Source: Telegraph.co.uk

Posted on by Nancy Atkinson

Solar Sail To Launch This Summer

NanoSail D. Image credit NASA

NASA’s Marshall and Ames Research Centers will team up with the commercial space company SpaceX to launch and deploy a solar sail this summer. A bread-box sized payload called NanoSail-D will travel to space onboard a SpaceX Falcon 1 Rocket and if all goes well, it will be the first fully deployed solar sail in space, and the first spacecraft to use a solar sail as a primary means of orbital maneuvering. The first launch window is from July 29th to August 6th, with a back-up window extending from August 29th to September 5th. Weighing less than 4.5 kilograms (10 pounds) the aluminum and plastic sail has about 9.3 m² (100 square feet) of light-catching surface which researchers hope will successfully propel the spacecraft.

Solar sails have been the stuff of dreams for years. Because there’s no friction in space, once a solar sail starts moving, it can go on forever. While rockets would run out of gas and begin to coast, a spaceship powered by solar sails would continue accelerating as long as there is a solar wind, reaching faster speeds and covering distances far greater than any rocket. No rocket has been invented that could carry enough fuel to reach the outer solar system in as short a time. And like a marine sail, a solar sail could also bring you home. You could use the solar sail to travel “against the wind,” back to Earth.

“It’s not so much about how far a sail will go compared to a rocket; the key is how fast,” says Edward “Sandy” Montgomery of NASA’s Marshall Space Flight Center. “The Voyagers have escaped the solar system, and they were sent by rockets, but it’s taken more than three decades to do it. A sail launched today would probably catch up with them in a single decade. Sails are slower to get started though. So, for example, between the Earth and the moon, rockets might be preferred for missions with a short timeline. It’s a trip of days for rockets, but months for a solar sail. The rule of thumb, therefore, would be to use rockets for short hops and solar sails for the long hauls.”

Previous attempts to launch and deploy a solar sail in space have met limited success. In 2004 Japan launched prototype solar sails that deployed, but they weren’t used for propulsion. The Planetary Society attempted a solar sail launch in 2005, called Cosmos 1, but the Russian launch vehicle failed to reach orbit. NASA did successfully deploy a solar sail in a vacuum chamber in 2004, but of course, its propulsive capability wasn’t able to be tested.

Montgomery believes a successful mission would be huge for the future of spaceflight. If successful, solar sails could potentially help with a growing problem of space debris.

“Currently, micro-satellites in orbit above a few hundred kilometers can stay in orbit for decades after completing their mission,” Montgomery said. “This creates an orbital debris collision risk for other spacecraft. NanoSail-D will demonstrate the feasibility of using a drag sail to decrease the time satellites clutter up Earth’s orbit. Although our sail looks like a kite, it will act like a parachute (or like a drag sail) in the very thin upper atmosphere around Earth. It will slow the spacecraft and make it lose altitude, re-enter the Earth’s atmosphere and burn off in a relatively short period of time. A drag sail is a lighter alternative to carrying a propulsion system to de-orbit a satellite.”

Movie of how NanoSail D will unfurl.

Original News Source: Science at NASA

Posted on by Ian O'Neill

Forget Neutron Stars, Quark Stars Might be the Densest Bodies in the Universe

The difference between a neutron star and a quark star (Chandra)

So neutron stars may not be the densest exotic objects in the cosmos after all. Recent observations of ultra-luminous supernovae suggest that these explosions may create an even more exotic remnant. Neutron stars can form after a star ends its life; measuring only 16 km across, these small but massive objects (one and a half times the mass of the Sun) may become too big for the structure of neutrons to hold it together. What happens if the structures of the neutrons inside a neutron star collapse? Quark stars (a.k.a. “Strange” stars) may be the result, smaller and denser than neutron stars, possibly explaining some abnormally bright supernovae observed recently…

Three very luminous supernovae have been observed and Canadian researchers are hot on the trail as to what may have caused them. These huge explosions occur at the point when a massive star dies, leaving a neutron star or black hole in their wake. Neutron stars are composed of neutron-degenerate matter and will often be observed as rapidly spinning pulsars emitting radio waves and X-rays. If the star was massive enough, a black hole might be formed after the detonation, but is there a phase between the mass of a neutron star and a black hole?

It appears there might be a smaller, more massive star on the block, a star composed not of hadrons (i.e. neutrons), but of the stuff that makes up hadrons: quarks. They are thought to be one step up the star-mass ladder, the point at which the mass of the supernova remnant is slightly too big to be a neutron star, but too small to form a black hole. They are composed of ultra-dense quark matter, and as neutrons break down it is thought some of their “up” and “down” quarks are converted into “strange” quarks, forming a state known as “strange matter.” It is for this reason that these compact objects are also known as strange stars.

Quark stars may be hypothetical objects, but the evidence is stacking up for their existence. For example, supernovae SN2005gj, SN2006gy and SN2005ap are all approximately 100 times brighter than the “standard model” for supernova explosions, leading the Canadian team to model what would happen if a heavy neutron star were to become unstable, crushing the neutrons into a soup of strange matter. Although these supernovae may have formed neutron stars, they became unstable and collapsed again, releasing vast amounts of energy from the hadron bonds creating a “Quark-Nova”, converting the oversized neutron star into a quark star.

If quark stars are behind these ultra-luminous supernovae, they may be viewed as super-sized hadrons, not held together by the nuclear strong force, but by gravity. Now there’s a thought!

Source: NSF

Posted on by Fraser Cain

What is the Closest Planet to Saturn?

What is the closest planet to Saturn? That depends on where Saturn is in its orbit, and the position of the other planets.

But for the majority of its orbit, the closest planet to Saturn is Jupiter. When the two planets are lined up perfectly, so that it goes: Sun, Jupiter, Saturn, the two planets are separated by only 655 million km.

Of course, when the planets are on opposite sides of the Sun (Jupiter – Sun – Saturn), they’re separated by 2.21 billion km, and all of the inner planets are closer to Saturn than Jupiter.

In fact, Uranus sometimes gets closer to Saturn than Jupiter. At their closest, Uranus and Saturn can be 1.43 billion km apart.

In case you were wondering, the closest planet to Jupiter is Mars, and the closest planet to Mars is Earth.

Here’s Hubblesite’s News Releases about Saturn, and NASA’s Solar System Exploration guide.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.

Posted on by Fraser Cain

Gravity on Saturn

Saturn doesn’t have a solid surface, so it’s impossible to actually walk on the surface and feel the gravity of Saturn. But let’s pretend that you could. What kind of force would you feel if you could actually stand on the surface of Saturn and walk around.

Even though Saturn has much more mass than Earth, second in the Solar System only to Jupiter, it also has the lowest density of all the planets in the Solar System. When you spread that mass across the entire volume of Saturn, the actual gravity pulling at any spot on the surface is only 91% of Earth’s gravity. In other words, if your bathroom scale said 100 kg on Earth, it would say 92 kg on the “surface” of Saturn.

Just for comparison, if you wanted to walk on the “surface” of Jupiter, you would experience 2.5 times the gravity of Earth. And if you walked on the surface of Mars, you would experience about 1/3rd the gravity of Earth. You would have 1/6th your weight on the Moon.

What contributes to all this Saturn gravity? Saturn is largely comprised of hydrogen and helium, which came together at the beginning of the Solar System, gathered by their mutual mass. It’s the same composition as Jupiter and the Sun. These primordial elements were formed at the beginning of the Universe in the Big Bang.

Here’s more information about the gravity of Jupiter, and the gravity on Mars.

This page will help you calculate the gravity on Saturn, and this cool site lets you calculate gravity on all the planets.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.

Posted on by Fraser Cain

Density of Saturn

Saturn has the lowest density of all the planets in the Solar System. The actual number is 0.687 grams per cubic centimeter. This is actually less dense than water; if you had a large enough pool of water, Saturn would float.

You can also check out these cool telescopes that will help you see the beauty of planet Saturn.

Just for comparison, Jupiter has an average density of 1.33 grams per cubic centimeter. So it wouldn’t float on water. And Earth, the densest planet in the Solar System, measures 5.51 grams/cubic centimeter.

If you’d like to calculate the density of Saturn for yourself, grab a calculator, and then divide the mass of Saturn (5.6846×1026 kg) by its volume (8.2713×1014 cubic kilometers. This gives you a final number of 0.687 g/cubic centimeter.

Here’s an article about a fluffy extrasolar planet, even less dense than Saturn, and more information about the density of Jupiter.

Here’s a textbook that helps you make the density calculations for yourself, and more information here.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.

Posted on by Tammy Plotner

Cosmic Mystery: NGC 7008 by Dietmar Hager

NGC 7008 by Dietmar Hager

Over the weeks we’ve taken a look at some very curious objects which have often raised some wonderful questions. One such question dealt with what could be observed should a supernova event involve a planetary system. In this case, it’s not quite the explosive mass destruction scenario – but a planetary nebula that consumed its planets…

Veteran sky observers have long been aware of the unique structure of planetary nebula NGC 7008. Located about 2800 light years distant in the constellation of Cygnus, report after report shows even amateur telescopes easily resolve out the central star and unusual bright areas in the outer shell. We might wonder about it when we see it, but what lay within is quite unique.

Because the central star of NGC 7008 is so prominent, the original lines of thinking on this nebula’s formation focused around the central star itself. Says Francesco Pala: “Much of the recent attention on primordial stars has focused on the properties of massive objects, considered the natural outcome of first structure formation. While there are reasons to believe that massive stars were common, but not unique, in the early universe, the question of their actual formation is still not adequately understood…. how unique must have been the physical conditions in primordial clouds to yield such an unusual distribution of stellar mass.”

In 1995, the Hubble Telescope was pointed towards NGC 7008. The primary aim of the survey was to find close, resolved main-sequence companions of the central stars, which through main-sequence fitting would provide excellent distance estimates for the nebulae. What they found was only the beginning of the end.

Scientist Mario Perniotto studies planetary nebulae and their gas dynamics. “I first recall the history of PNe which are generated from low and intermediate mass stars through successive mass loss processes starting in the Red Giant phase of evolution and continuing also after the termination of the pulsed AGB phase, where most of the nebular mass is believed to be ejected. The corresponding stellar winds are the ingredients of the nebula. Their initial properties and subsequent mutual interactions, under the action of the evolving stellar radiation field, are responsible for the properties of the nebula.” Through studies with the Hubble, the kinetic structure of NGC 7008 has been observed to have another unusual feature – Fast Low Ionization Emitting Regions.

Says Perinotto: “Attention is focused on FLIERs and on the proposed mechanisms to interpret them. Recent observations with the Hubble Space Telescope have provided us with a wealth of detailed (subarcsec) information on the nebular structures. The inner structure of FLIERs is here illustrated to consist of substructures of various shapes with an high degree of individually from object to object, also within the same planetary nebula. These new data call for deeper theoretical efforts to solve the problems of cosmic gas dynamics, posed by their observed properties.”

But the motions of the gas aren’t all that’s being observed – the dust itself plays an important role. According to studies done by Klaas and Walker, some of NGC 7008’s dynamic structure comes from dual layers of radically different dust which originated from two different sources. Could this be the result of a binary star taking its last twin breath? First the older star… And then the younger? Says Tylenda and Gorny: “Therefore we can conclude that the H-poor layers in these stars have been exposed shortly after the PN formation at the tip of AGB. This excludes, from our considerations, scenaria like that of a final helium shell flash which produced a H-poor, He-burning nucleus surrounded by an old, large nebula.”

But astronomer Noam Soker wasn’t taking that for an answer. “For NGC 7008, a deviation from symmetry is expected and indeed a departure is observed, but the main signature is on the outskirts of the nebula, and hence an interaction with the ISM (interstellar medium) is possible. If the companion is associated with the PN central star, as claimed… I put a question mark, since it is not clear if the morphology is compatible with the claimed companion or is solely due to an interaction with the ISM.”

Close-up on NGC 7008 - Dietmar Hager

Enter the Instituto de Astronomía in México. “We suggest that some of the structures observed in the envelopes of planetary nebulae are caused by the interaction of central star wind and radiation with preplanetary nebula debris: planets, moons, minor objects and ring and ring arcs. Recently considerable amount of planetary material has been reported to exist around solar type stars, this debris could be evaporated during the envelope ejection and alter the chemical abundance and produce some of the envelope inhomogeneities. If there are massive enough rings of material surrounding the progenitor and planets in their vicinity, arc rings could be formed. If the rings are viewed pole on when the envelope is detached from the central star, it will interact with the arc ring material and produce ansae and pedal and garden-hose-shape structures observed in some planetaries.”

Next time you visit NGC 7008 – take a closer look like Dr. Dietmar Hager did. There’s something more to this story than just another pretty cosmic face. Something he recognized and asked me to investigate. Not only does his image reveal the presence of FLIERS and the well resolved central region, but a structure that’s made scientists look again and again over the years. Of all the explanations and science that I’ve researched, I like Noam Soaker’s answer best:

“I propose that the destruction of brown dwarfs and massive planets inside the envelopes of asymptotic giant branch stars can lead to the formations of jets and ansae in elliptical planetary nebulae. Thick disks with jets on their two sides are the plausible outcome of this process. The process is likely to occur at late states of the AGB, and the jets push their way out of the envelopes in the course of a number of year. The Roche lobe overflow continues for several hundred years and destroys the secondaries. This scenario predicts that the same material will be contaminated by two sources. Once source is the AGB cores, from which material can be mixed into the jets and the other consists of the destroyed secondaries.”

Always look twice and think about what you’re observing… Because there is so much more there than what meets the eye!

These awesome images were done by Avanced Optical/ Radio Astronomers and International Associates member Dr. Dietmar Hager from StarGazer Observatory. Many thanks for the investigative challenge!

Posted on by Fraser Cain

Discovery of Saturn

Saturn is one of the 5 planets visible with the unaided eye. In fact, it often appears as one of the brightest stars in the sky, and so ancient people have known about Saturn for thousands of years. In fact, it’s impossible to know who made the Saturn discovery.

The Romans named Saturn after their god of the harvest and time, the same entity as the Greek God Chronos.

The first observation of Saturn through a telescope was made by Galileo Galilei in 1610. His first telescope was so crude that he wasn’t able to distinguish the planet’s rings; instead he thought the planet might have ears or two large moons on either side of it. When he looked at Saturn a few years later, the moons had disappeared, but this was just because the angle of Saturn had changed, and the rings were being seen edge on.

The Dutch astronomer Christiaan Huygens observed Saturn in 1659, and solved the mystery, realizing that the “arms” around Saturn were really a system of rings. He also was the first to observe Saturn’s moon Titan.

Better and better telescopes helped reveal that the rings were really a system of particles, and Jean-Dominique Cassini discovered 4 other major moons of Saturn: Iapetus, Rhea, Tethys and Dione.

The first close up observations of Saturn were made by NASA’s Pioneer 11 spacecraft, which made a flyby of the planet on September 1, 1979 at a distance of only 21,000 km above the planet’s cloud tops. It send back the first close-up images of Saturn.

Other spacecraft have visited Saturn, including NASA’s Voyager probes. And the Cassini has been orbiting Saturn since its arrival in July 2006.

Here’s an article about what Galileo might have seen, and an article about Cassini’s observations of Saturn.

Here’s a great history of Saturn from NASA, and more information from NASA’s JPL.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.