Posted on by Fraser Cain

What About a Mission to Titan?

What About a Mission to Titan?
What About a Mission to Titan?


As you probably know, NASA recently announced plans to send a mission to Jupiter’s moon Europa. If all goes well, the Europa Clipper will blast off for the world in the 2020s, and orbit the icy moon to discover all its secrets.

And that’s great and all, I like Europa just fine. But you know where I’d really like us to go next? Titan.

Titan, as you probably know, is the largest moon orbiting Saturn. In fact, it’s the second largest moon in the Solar System after Jupiter’s Ganymede. It measures 5,190 kilometers across, almost half the diameter of the Earth. This place is big.

It orbits Saturn every 15 hours and 22 days, and like many large moons in the Solar System, it’s tidally locked to its planet, always showing Saturn one side.

Titan image taken by Cassini on Oct. 7, 2013 (Credit: NASA/JPL-Caltech/Space Science Institute)

Before NASA’s Voyager spacecraft arrived in 1980, astronomers actually thought that Titan was the biggest moon in the Solar System. But Voyager showed that it actually has a thick atmosphere, that extends well into space, making the true size of the moon hard to judge.

This atmosphere is one of the most interesting features of Titan. In fact, it’s the only moon in the entire Solar System with a significant atmosphere. If you could stand on the surface, you would experience about 1.45 times the atmospheric pressure on Earth. In other words, you wouldn’t need a pressure suit to wander around the surface of Titan.

You would, however, need a coat. Titan is incredibly cold, with an average temperature of almost -180 Celsius. For you Fahrenheit people that’s -292 F. The coldest ground temperature ever measured on Earth is almost -90 C, so way way colder.

You would also need some way to breathe, since Titan’s atmosphere is almost entirely nitrogen, with trace amounts of methane and hydrogen. It’s thick and poisonous, but not murderous, like Venus.

Titan has only been explored a couple of times, and we’ve actually only landed on it once.

The first spacecraft to visit Titan was NASA’s Pioneer 11, which flew past Saturn and its moons in 1979. This flyby was followed by NASA’s Voyager 1 in 1980 and then Voyager 2 in 1981. Voyager 1 was given a special trajectory that would take it as close as possible to Titan to give us a close up view of the world.

Saturn’s moon Titan lies under a thick blanket of orange haze in this Voyager 1 picture. Credit: NASA

Voyager was able to measure its atmosphere, and helped scientists calculate Titan’s size and mass. It also got a hint of darker regions which would later turn out to be oceans of liquid hydrocarbons.

The true age of Titan exploration began with NASA’s Cassini spacecraft, which arrived at Saturn on July 4, 2004. Cassini made its first flyby of Titan on October 26, 2004, getting to within 1,200 kilometers or 750 miles of the planet. But this was just the beginning. By the end of its mission later this year, Cassini will have made 125 flybys of Titan, mapping the world in incredible detail.

Cassini saw that Titan actually has a very complicated hydrological system, but instead of liquid water, it has weather of hydrocarbons. The skies are dotted with methane clouds, which can rain and fill oceans of nearly pure methane.

And we know all about this because of Cassini’s Huygen’s lander, which detached from the spacecraft and landed on the surface of Titan on January 14, 2005. Here’s an amazing timelapse that shows the view from Huygens as it passed down through the atmosphere of Titan, and landed on its surface.

Huygens landed on a flat plain, surrounded by “rocks”, frozen globules of water ice. This was lucky, but the probe was also built to float if it happened to land on liquid instead.

It lasted for about 90 minutes on the surface of Titan, sending data back to Earth before it went dark, wrapping up the most distant landing humanity has ever accomplished in the Solar System.

Although we know quite a bit about Titan, there are still so many mysteries. The first big one is the cycle of liquid. Across Titan there are these vast oceans of liquid methane, which evaporate to create methane clouds. These rain, creating mists and even rivers.

This false-color mosaic of Saturn’s largest moon Titan, obtained by Cassini’s visual and infrared mapping spectrometer, shows what scientists interpret as an icy volcano. Credit: NASA/JPL/University of Arizona

Is it volcanic? There are regions of Titan that definitely look like there have been volcanoes recently. Maybe they’re cryovolcanoes, where the tidal interactions with Saturn cause water to well up from beneath crust and erupt onto the surface.

Is there life there? This is perhaps the most intriguing possibility of all. The methane rich system has the precursor chemicals that life on Earth probably used to get started billions of years ago. There’s probably heated regions beneath the surface and liquid water which could sustain life. But there could also be life as we don’t understand it, using methane and ammonia as a solvent instead of water.

To get a better answer to these questions, we’ve got to return to Titan. We’ve got to land, rove around, sail the oceans and swim beneath their waves.

Now you know all about this history of the exploration of Titan. It’s time to look at serious ideas for returning to Titan and exploring it again, especially its oceans.

Planetary scientists have been excited about the exploration of Titan for a while now, and a few preliminary proposals have been suggested, to study the moon from the air, the land, and the seas.

The spacecraft, balloon, and lander of the Titan Saturn System Mission. Credit: NASA Jet Propulsion Laboratory

First up, there’s the Titan Saturn System Mission, a mission proposed in 2009, for a late 2020s arrival at Titan. This spacecraft would consist of a lander and a balloon that would float about in the atmosphere, and study the world from above. Over the course of its mission, the balloon would circumnavigate Titan once from an altitude of 10km, taking incredibly high resolution images. The lander would touch down in one of Titan’s oceans and float about on top of the liquid methane, sampling its chemicals.

As we stand right now, this mission is in the preliminary stages, and may never launch.

The Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR) concept for an aerial explorer for Titan. Credit: Mike Malaska

In 2012, Dr. Jason Barnes and his team from the University of Idaho proposed sending a robotic aircraft to Titan, which would fly around in the atmosphere photographing its surface. Titan is actually one of the best places in the entire Solar System to fly an airplane. It has a thicker atmosphere and lower gravity, and unlike the balloon concept, an airplane is free to go wherever it needs powered by a radioactive thermal generator.

Although the mission would only cost about $750 million or so, NASA hasn’t pushed it beyond the conceptual stage yet.

On the left is TALISE (Titan Lake In-situ Sampling Propelled Explorer), the ESA proposal. This would have it’s own propulsion, in the form of paddlewheels. Credit: bisbos.com

An even cooler plan would put a boat down in one of Titan’s oceans. In 2012, a team of Spanish engineers presented their idea for how a Titan boat would work, using propellers to put-put about across Titan’s seas. They called their mission the Titan Lake In-Situ Sampling Propelled Explorer, or TALISE.

Propellers are fine, but it turns out you could even have a sailboat on Titan. The methane seas have much less density and viscosity than water, which means that you’d only experience about 26% the friction of Earth. Cassini measured windspeeds of about 3.3 m/s across Titan, which half the average windspeed of Earth. But this would be plenty of wind to power a sail when you consider Titan’s thicker atmosphere.

And here’s my favorite idea. A submarine. This 6-meter vessel would float on Titan’s Kraken Mare sea, studying the chemistry of the oceans, measuring currents and tides, and mapping out the sea floor.

It would be capable of diving down beneath the waves for periods, studying interesting regions up close, and then returning to the surface to communicate its findings back to Earth. This mission is in the conceptual stage right now, but it was recently chosen by NASA’s Innovative Advanced Concepts Group for further study. If all goes well, the submarine would travel to Titan by 2038 when there’s a good planetary alignment.

Okay? Are you convinced? Let’s go back to Titan. Let’s explore it from the air, crawl around on the surface and dive beneath its waves. It’s one of the most interesting places in the entire Solar System, and we’ve only scratched the surface.

If I’ve done my job right, you’re as excited about a mission to Titan as I am. Let’s go back, let’s sail and submarine around that place. Let me know your thoughts in the comments.

Posted on by Fraser Cain

Why Doesn’t Earth Have Rings?

Why Doesn't Earth Have Rings?
Why Doesn't Earth Have Rings?

Before we really get started on today’s episode, I’d like to share a bunch of really cool pictures created by my friend Kevin Gill. Kevin’s a computer programmer, 3-D animator and works on climate science data for NASA.

And in his spare time, he uses his skills to help him imagine what the Universe could look like. For example, he’s mapped out what a future terraformed Mars might look like based on elevation maps, or rendered moons disturbing Saturn’s rings with their gravity.

Earth’s Rings over San Bernadino. Credit: Kevin Gill (CC BY-SA 2.0)

But one of my favorite sets of images that Kevin did were these. What would it look like if Earth had rings? Kevin and his wife went to a few cool locations, took some landscape pictures, and then Kevin did the calculations for what it would look like if Earth had a set of rings like Saturn.

And let me tell you, Earth would be so much better. At least you’d think so, but actually, it might also suck.

Last time I checked, we don’t have rings like this. In fact, we don’t have any rings at all.

Why not? Considering the fact that Saturn, Jupiter, Uranus and Neptune all have rings, don’t we deserve at least something?

Did we ever have rings in the past, or will we in the future? What’s it going to take for us to join the ring club? Short answer, an apocalypse.

Before we get into the inevitable discussion of death and devastation, let’s talk a bit about rings.

A lovely view of Saturn and its rings as seen by the Cassini spacecraft on Aug. 12, 2009. Credit: NASA/JPL-Caltech/Space Science Institute.

Saturn is the big showboat, with its fancy rings. They’re made of water ice, with chunks as big as a mountain, or as small as a piece of sand. Astronomers have been arguing about where they came from and how old they are, but the current consensus – sort of – is that the rings are almost as ancient as Saturn itself: billions of years old. And yet, some process is weathering the rings, grinding the particles so they appear much younger.

Jupiter’s rings. Image Credit: University of Maryland

Jupiter’s rings are much fainter, and we didn’t even know about them until 1979, when the Voyager spacecraft made their flybys. The rings seem to be created by dust blown off into space by impacts on the planet’s moons.

Hey, we’ve got a moon, that’s a sign.

Uranus imaged by Voyager 2 in 1986. Credit: NASA

The rings around Uranus are bigger and more complex than Jupiter’s rings, but not as substantial as Saturn’s. They’re much younger, perhaps only 600 million years old, and appear to have been caused by two moons crashing into each other, long ago.

Again, another sign. We still have the potential for stuff to crash around us.

The labeled ring arcs of Neptune as seen in newly processed data. The image spans 26 exposures combined into a equivalent 95 minute exposure, and the ring trace and an image of the occulted planet Neptune is added for reference. Credit: M. Showalter/SETI Institute

The rings around Neptune are far dustier than any of the other ring systems, and much younger than the Solar System. And like the rings around Uranus, they were probably formed when two or more of its moons collided together.

Now what about our own prospects for rings?

The problem with icy rings is that the Earth orbits too closely to the Sun. There’s a specific point in the Solar System known as the “frost line” or “snow line”. This is the point in the Solar System where deposits of ice could have survived for long periods of time. Any closer and the radiation from the Sun sublimates the ice away.

This point is actually located about 5 astronomical units away from the Sun, in the asteroid belt. Mars is much closer, so it’s very dry, while Jupiter is beyond the frost line, and its moons have plenty of water ice.

The Earth is a mere 1 AU from the Sun. That’s the very definition of an astronomical unit, which means it’s well within the frost line. The Earth itself can maintain water because the planet’s magnetosphere acts like a shield against the solar wind. But the Moon is bone dry (except for the permanently shadowed craters at its poles).

And if there was an icy ring system around the Earth, the solar wind would have blasted it away long ago.

Instead, let’s look at another kind of ring we can have. One made of rock and dust, containing death and sorrow, from a pulverized asteroid or moon. In fact, billions of years ago, we definitely had a ring when a Mars-sized planet crashed into the Earth and spewed out a massive ring of debris. This debris collected together into the Moon we know today. That impact turned the Earth’s surface inside out. It was all volcanoes, everywhere, all the time.

Credit: Kevin Gill (CC BY-SA 2.0)

It’s also possible we had a second moon in the ancient past, which collided with our current Moon. That would have generated an all new ring of material for millions of years until it was recaptured by the Moon, kicked out of orbit, or fell down onto the Earth.

It’s that “fell down onto Earth” part that’s apocalyptic. As mountains of ring material entered the Earth’s atmosphere, it would increase the temperature, baking and boiling away any life that couldn’t burrow deep underground.

It’s kind of like the book Seveneves, which you should totally read if you haven’t already. It talks about what we would see if the Moon broke apart into a ring, and the terrible terrible thing that happens next.

Earth’s Rings from New Hampshire. Credit: Kevin Gill (CC BY-SA 2.0)

If Earth did get a set of rings, they’d be pretty, but they’d also be a huge pain for astronomers. As you saw in Kevin’s original pictures, the rings take up a huge chunk of the sky for most observers. The farther north or south you go, the more dramatically the rings will ruin your view. Only if you were right at the equator, you’d have a thin line, which would be borderline acceptable.

Furthermore, the rings themselves would be incredibly reflective, and completely ruin the whole concept of dark skies. You know how the Moon sucks for astronomy? Rings would be way way worse.

Finally, rings would interfere with our ability to launch spacecraft and maintain satellites. It depends on how far they extend, but we wouldn’t be able to have any satellites in that region or cross the ring plane. Oh, and that fiery death apocalypse I mentioned earlier.

We know that the Moon is drifting away from the Earth right now thanks to the conservation of angular momentum. But in the distant future, billions of years from now, there might be a scenario that turns everything around.

The Sun’s habitable zone in its red giant phase. Credit: NASA/Goddard Space Flight Center Conceptual Image Lab

As you know, when it runs out of fuel in its core, the Sun is going to bloat up as a red giant, consuming Mercury and Venus. Scientists are on the fence about Earth. Some think that Earth will be fine. The Sun will blast off its outer layers, but not actually envelop Earth. Others think that at the Sun’s largest point, we’ll be orbiting within the outer atmosphere of the Sun. Ouch, that’s hot.

The orbiting Moon will experience drag as it goes around the Earth, slowing down its orbital velocity, and causing it to spiral inward. Once it reaches the Roche Limit of the Earth, about 9,500 km, our planet’s gravity will tear the Moon apart into a ring. The chunks in the ring will also experience drag in the solar atmosphere and continue to spiral inward until they crash into the planet.

The Moon tearing apart to become a ring around Earth. Credit: Universe Sandbox ²

That would be considered a very bad day, if it wasn’t for the fact that we were already living inside the atmosphere of the Sun. No amount of terraforming will fix that.

Sadly, the Earth doesn’t have rings like Saturn, and it probably never did. It might have had rings of rock and dust for periods, but they weren’t that majestic to look at. In fact, seeing rings around the planet would mean we’d lost a moon, and our planet was about go through a period of bombardment. I’ll pass.

Posted on by Fraser Cain

Weekly Space Hangout – Mar 17, 2017: Stuart McNeill of the Intrepid Sea, Air & Space Museum

Host: Fraser Cain (@fcain)

Special Guest:
Stuart McNeill is the the Community Engagement specialist in charge of Family Programs and Demonstrations at the Intrepid Sea, Air & Space Museum. Check out their membership site here.

Guests:
Kimberly Cartier ( KimberlyCartier.org / @AstroKimCartier )
Paul M. Sutter (pmsutter.com / @PaulMattSutter)

Their stories this week:

The original weird star: Przybylski’s Star may contain short-lived isotopes

Enceladus’ sub-surface ocean under thin(ner) ice

Star orbiting black hole at 1% c

We use a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!

If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!

If you’d like to join Fraser and Paul Matt Sutter on their tour to Iceland in February, 2018, you can find the information at astrotouring.com.

If you would like to sign up for the AstronomyCast Solar Eclipse Escape, where you can meet Fraser and Pamela, plus WSH Crew and other fans, visit our site here and sign up!

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Universe Today, or the Universe Today YouTube page

Posted on by Nancy Atkinson

Warm Poles Suggest Enceladus’ Liquid Water Near Surface

Saturn's moon Enceladus could harbor microbial life in the warm salty water thought to exist under its frozen surface. Respondents in the study seemed to like that possibility. Credits: NASA/JPL-Caltech/Space Science Institute

One of the biggest surprises from the Cassini mission to Saturn has been the discovery of active geysers at the south pole of the moon Enceladus. At only about 500 km (310 miles) in diameter, the bright and ice-covered moon should be too small and too far from the Sun to be active. Instead, this little moon is one of the most geothermally active places in the Solar System.

Now, a new study from Cassini data shows that the south polar region of Enceladus is even warmer than expected just a few feet below its icy surface. While previous studies have confirmed an ocean of liquid water inside Enceladus which fuels the geysers, this new study shows the ocean is likely closer to the surface than previously thought. Additionally – and most enticing – there has to be a source of heat inside the moon that is not completely understood.

“These observations provide a unique insight into what is going on beneath the surface,” said Alice Le Gall, who is part of the Cassini RADAR instrument team, from Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), and Université Versailles Saint-Quentin (UVSQ), France. “They show that the first few meters below the surface of the area that we investigated, although at a glacial 50-60 K, are much warmer than we had expected: likely up to 20 K warmer in some places. This cannot be explained only as a result of the Sun’s illumination and, to a lesser extent, Saturn’s heating so there must be an additional source of heat.”

Tiger stripes on the south pole of Enceladus. The region studied is indicated by the coloured band. NASA/JPL-Caltech/Space Science Institute; Acknowledgement: A. Lucas

Microwave data taken during a close flyby in 2011 shows there is excess heat at three fractures in the surface of Enceladus. While similar to the so-called “tiger-stripe” features on this moon that are actively venting ice and water molecules into space, these three fractures don’t appear to be active, at least not in 2011.

Scientists say the seemingly dormant fractures lying above the moon’s warm, underground sea point to the dynamic character of Enceladus’ geology, suggesting the moon might have experienced several episodes of activity, in different places on its surface.

The 2011 flyby provided the first – and unfortunately, the only — high-resolution observations of Enceladus’ south pole at microwave wavelengths.

It looked at a narrow, arc-shaped swathe of the southern polar region, about 25 km (15 miles) wide, and located just 30 km to 50 km (18-30 miles) north of the tiger-stripe fractures.

The heat that was detected appears to be lying under a much colder layer of frost.

Because of operational constraints of the 2011 flyby, it was not possible to obtain microwave observations of the active fractures themselves. But this allowed the scientists to observe that the thermally anomalous terrains of Enceladus extend well beyond the tiger stripes.

Cassini’s view down into a jetting “tiger stripe” in August 2010. Credit: NASA

Their findings show it is likely that the entire south pole region is warm underneath, meaning Enceladus’ ocean could be just 2 km under the moon’s icy surface in that area. The finding agrees with a 2016 study, led by another Cassini team member, Ondrej Cadek, which estimated the thickness of the crust on Enceladus’ south pole to be less than the rest of the moon. That study estimated the depth of the ice shell to be less than 5 km (1.2 miles) at the south pole, while average depth on other areas of Enceladus is between 18–22 km (11-13 miles).

What generates the internal heat at Enceladus? The main source of heat remains a mystery, but scientists think gravitational forces between Enceladus, Saturn, and another moon, Dione pull and flex Enceladus’ interior. Known as tidal forces, the tugging causes the moon’s interior to rub, creating friction and heat. It also creates stress compressions and deformations on the crust, leading to the formation of faults and fractures. This in turn creates more heat in the sub-surface layers. In this scenario, the thinner icy crust in the south pole region is subject to a larger tidal deformation that means more heat being created to help keep the underground water warm.

Dramatic plumes, both large and small, spray water ice out from many locations along the famed “tiger stripes” near the south pole of Saturn’s moon Enceladus. Credit: NASA/JPL/Space Science Institute

Since the geysers weren’t known until Cassini’s arrival at Saturn, the spacecraft didn’t have a specific payload to study them, but scientists used the instruments at their disposal to make the best observations they could, flying the spacecraft to within 49 km (30 miles) of the surface. To fully study the tidal heating — or to determine if there is another source of heat — scientists will continue to study the data already taken by various Cassini instruments. But since the mission will be ending in September 2017, it may require another mission to this intriguing moon to fully figure out this mystery.

“This discovery opens new perspectives to investigate the emergence of habitable conditions on the icy moons of the gas giant planets,” says Nicolas Altobelli, ESA’s Project Scientist for Cassini–Huygens. “If Enceladus’ underground sea is really as close to the surface as this study indicates, then a future mission to this moon carrying an ice-penetrating radar sounding instrument might be able to detect it.”

“Finding temperatures near these three inactive fractures that are unexpectedly higher than those outside them adds to the intrigue of Enceladus,” said Cassini Project Scientist Linda Spilker at the Jet Propulsion Laboratory. “What is the warm underground ocean really like and could life have evolved there? These questions remain to be answered by future missions to this ocean world.”

Feel free to submit your mission proposals in the comment section below…

An artist’s illustration of Cassini entering orbit around Saturn. Credit: NASA/JPL.

Sources: ESA
JPL
Paper: Thermally anomalous features in the subsurface of Enceladus’s south polar terrain” by A. Le Gall et al. (2017), published in Nature Astronomy

Posted on by Bob King

Fried Egg? Flying Saucer? Nope. Just Cool New Closeups of Saturn’s Moon Pan

Saturn's "UFO moon" Pan up close. Credit: NASA/JPL/Space Science Institute
This new view of Saturn’s moon Pan is the closest yet, snapped by Cassini from a distance of 15,268 miles (24,572 km) on March 7, 2017. Pan measures 22 miles wide by 14 miles across and displays a number of small craters along with parallel ridges and grooves. Its broad, thinner equatorial ridge displays fine, parallel striations. Credit: NASA/JPL/Space Science Institute

Besides Earth, Saturn may be the only other planet where you can order rings with a side of ravioli. Closeup photos taken by the Cassini probe of the the planet’s second-innermost moon, Pan, on March 7 reveal remarkable new details that have us grasping at food analogies in a feeble attempt to describe its unique appearance.

A side view of Pan better shows its thin and wavy ridge likely built up through the accumulation of particles grabbed from Saturn’s rings. The ridge is between 0.9 and 2.5 miles (1-4 km) thick. Credit: NASA/JPL/Space Science Institute

 

As Pan moves along the Encke Gap its gravity creates ripples in Saturn’s A-ring. Credit:
NASA/JPL/Space Science Institute

The two-part structure of the moon is immediately obvious: a core body with a thin, wavy ridge encircling its equator. How does such a bizarre object form in the first place? There’s good reason to believe that Pan was once part of a larger satellite that broke up near Saturn long ago. Much of the material flattened out to form Saturn’s rings while large shards like Pan and another ravioli lookalike, Atlas, orbited within or near the rings, sweeping up ring particles about their middles. Tellingly, the ridges are about as thick as the vertical distances each satellite travels in its orbit about the planet.

Pan casts its shadow on Saturn’s A-ring from within the 200-mile-wide (325 km) Encke Gap, which is maintained by the presence of the moon. Pan shares the gap with several diffuse ringlets from which it may still be gathering additional material around its equatorial ridge. Credit: NASA/JPL/Space Science Institute

Today, Pan orbits within and clears the narrow Encke Gap in Saturn’s outer A-ring of debris. It also helps create and shape the narrow ringlets that appear in the gap It’s lookalike cousin Atlas orbits just outside the A-ring.

Pan and Altas (25×22 miles) orbit within Saturn’s ring plane and may both be fragments from a larger moon breakup that created Saturn’s rings. Both have swept up material from the rings to form equatorial ridges. Credit: NASA/JPL/Space Science Institute

Moons embedded in rings can have profound effects on that material from clearing gaps to creating new temporary ringlets and raising vertical waves of material that rise above and below the ring plane. All these effects are produced by gravity, which gives even small objects like Pan dominion over surprisingly vast regions.

Enjoy this animated gif created from photos of the close flyby of Pan. Credit:
NASA/JPL/Space Science Institute

 

Posted on by Fraser Cain

What Did Cassini Teach Us?

What Did Cassini Teach Us?
What Did Cassini Teach Us?


Ask me my favorite object in the Solar System, especially to see through a telescope, and my answer is always the same: Saturn.

Saturn is this crazy, ringed world, different than any other place we’ve ever seen. And in a small telescope, you can really see the ball of the planet, you can see its rings. It’s one thing to see a world like this from afar, a tiny jumping image in a telescope. To really appreciate and understand a place like Saturn, you’ve got to visit.

And thanks to NASA’s Cassini spacecraft, that’s just what we’ve been doing for the last 13 years. Take a good close look at this amazing ringed planet and its moons, and studying it from every angle.

Space Probes
Cassini orbiting Saturn. Credit: NASA

Throughout this article, I’m going to regale you with the amazing discoveries made by Cassini at Saturn. What it taught us, and what new mysteries it uncovered.

NASA’s Cassini spacecraft was launched from Earth on October 15, 1997. Instead of taking the direct route, it made multiple flybys of Venus, a flyby of Earth and a flyby of Jupiter. Each one of these close encounters boosted Cassini’s velocity, allowing it to make the journey with less escape velocity from Earth.

It arrived at Saturn on July 1st, 2004 and began its science operations shortly after that. The primary mission lasted 4 years, and then NASA extended its mission two more times. The first ending in 2010, and the second due to end in 2017. But more on that later.

Before Cassini, we only had flybys of Saturn. NASA’s Pioneer 11, and Voyagers 1 and 2 both zipped past the planet and its moons, snapping pictures as they went.

But Cassini was here to stay. To orbit around and around the planet, taking photos, measuring magnetic fields, and studying chemicals.

For Saturn itself, Cassini was able to make regular observations of the planet as it passed through entire seasons. This allowed it to watch how the weather and atmospheric patterns changed over time. The spacecraft watched lightning storms dance through the cloudtops at night.

This series of images from NASA’s Cassini spacecraft shows the development of the largest storm seen on the planet since 1990. These true-color and composite near-true-color views chronicle the storm from its start in late 2010 through mid-2011, showing how the distinct head of the storm quickly grew large but eventually became engulfed by the storm’s tail. Credit: NASA/JPL-Caltech/Space Science Institute

Two highlights. In 2010, Cassini watched a huge storm erupt in the planet’s northern hemisphere. This storm dug deep into Saturn’s lower atmosphere, dredging up ice from a layer 160 kilometers below and mixing it onto the surface. This was the first time that astronomers were able to directly study this water ice on Saturn, which is normally in a layer hidden from view.

Natural color images taken by NASA’s Cassini wide-angle camera, showing the changing appearance of Saturn’s north polar region between 2012 and 2016.. Credit: NASA/JPL-Caltech/Space Science Institute/Hampton University

The second highlight, of course, is the massive hexagonal storm churning away in Saturn’s northern pole. This storm was originally seen by Voyager, but Cassini brought its infrared and visible wavelength instruments to bear.

Why a hexagon? That’s still a little unclear, but it seems like when you rotate fluids of different speeds, you get multi-sided structures like this.

Cassini showed how the hexagonal storm has changed in color as Saturn moved through its seasons.

This is one of my favorite images sent back by Cassini. It’s the polar vortex at the heart of the hexagon. Just look at those swirling clouds.

The polar vortex, in all its glory. Credit: NASA/JPL-Caltech/Space Science Institute

Now, images of Saturn itself are great and all, but there was so much else for Cassini to discover in the region.

Cassini studied Saturn’s rings in great detail, confirming that they’re made up of ice particles, ranging in size as small a piece of dust to as large as a mountain. But the rings themselves are actually quite thin. Just 10 meters thick in some places. Not 10 kilometers, not 10 million kilometers, 10 meters, 30 feet.

The spacecraft helped scientists uncover the source of Saturn’s E-ring, which is made up of fresh icy particles blasting out of its moon Enceladus. More on that in a second too.

Vertical structures, among the tallest seen in Saturn’s main rings, rise abruptly from the edge of Saturn’s B ring to cast long shadows on the ring in this image taken by NASA’s Cassini spacecraft two weeks before the planet’s August 2009 equinox. Credit: NASA/JPL/Space Science Institute

Here’s another one of my favorite images of the mission. You’re looking at strange structures in Saturn’s B-ring. Towering pillars of ring material that rise 3.5 kilometers above the surrounding area and cast long shadows. What is going on here?

They’re waves, generated in the rings and enhanced by nearby moons. They move and change over time in ways we’ve never been able to study anywhere else in the Solar System.

Daphnis, one of Saturn’s ring-embedded moons, is featured in this view, kicking up waves as it orbits within the Keeler gap. Credit: NASA/JPL-Caltech/Space Science Institute

Cassini has showed us that Saturn’s rings are a much more dynamic place than we ever thought. Some moons are creating rings, other moons are absorbing or distorting them. The rings generate bizarre spoke patterns larger than Earth that come and go because of electrostatic charges.

Speaking of moons, I’m getting to the best part. What did Cassini find at Saturn’s moons?

Let’s start with Titan, Saturn’s largest moon. Before Cassini, we only had a few low resolution images of this fascinating world. We knew Titan had a dense atmosphere, filled with nitrogen, but little else.

Cassini was carrying a special payload to assist with its exploration of Titan: the Huygens lander. This tiny probe detached from Cassini just before its arrival at Saturn, and parachuted through the cloudtops on January 14, 2005, analyzing all the way. Huygens returned images of its descent through the atmosphere, and even images of the freezing surface of Titan.

Huygen’s view of Titan. Credit: ESA/NASA/JPL/University of Arizona

But Cassini’s own observations of Titan took the story even further. Instead of a cold, dead world, Cassini showed that it has active weather, as well as lakes, oceans and rivers of hydrocarbons. It has shifting dunes of pulverized rock hard water ice.

If there’s one place that needs exploring even further, it’s Titan. We should return with sailboats, submarines and rovers to better explore this amazing place.

A view of Mimas from the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute

We learned, without a shadow of a doubt, that Mimas absolutely looks like the Death Star. No question. But instead of a megalaser, this moon has a crater a third of its own size.

Saturn’s moon Iapetus. Image credit: NASA/JPL/SSI

Cassini helped scientists understand why Saturn’s moon Iapetus has one light side and one dark side. The moon is tidally locked to Saturn, its dark side always leading the moon in orbit. It’s collecting debris from another Saturnian moon, Phoebe, like bugs hitting the windshield of a car.

Perhaps the most exciting discovery that Cassini made during its mission is the strange behavior of Saturn’s moon Enceladus. The spacecraft discovered that there are jets of water ice blasting out of the moon’s southern pole. An ocean of liquid water, heated up by tidal interactions with Saturn, is spewing out into space.

And as you know, wherever we find water on Earth, we find life. We thought that water in the icy outer Solar System would be hard to reach, but here it is, right at the surface, venting into space, and waiting for us to come back and investigate it further.

Icy water vapor geysers erupting from fissures on Enceladus. Credit: NASA/JPL

On September 15, 2017, the Cassini mission will end. How do we know it’s going to happen on this exact date? Because NASA is going to crash the spacecraft into Saturn, killing it dead.

That seems a little harsh, doesn’t it, especially for a spacecraft which has delivered so many amazing images to us over nearly two decades of space exploration? And as we’ve seen from NASA’s Opportunity rover, still going, 13 years longer than anticipated. Or the Voyagers, out in the depths of the void, helping us explore the boundary between the Solar System and interstellar space. These things are built to last.

The problem is that the Saturnian system contains some of the best environments for life in the Solar System. Saturn’s moon Enceladus, for example, has geysers of water blasting out into space.

Cassini spacecraft is covered in Earth-based bacteria and other microscopic organisms that hitched a ride to Saturn, and would be glad to take a nice hot Enceladian bath. All they need is liquid water and a few organic chemicals to get going, and Enceladus seems to have both.

NASA feels that it’s safer to end Cassini now, when they can still control it, than to wait until they lose communication or run out of propellant in the future. The chances that Cassini will actually crash into an icy moon and infect it with our Earth life are remote, but why take the risk?
For the last few months, Cassini has been taking a series of orbits to prepare itself for its final mission. Starting in April, it’ll actually cross inside the orbit of the rings, getting closer and closer to Saturn. And on September 15th, it’ll briefly become a meteor, flashing through the upper atmosphere of Saturn, gone forever.

This graphic illustrates the Cassini spacecraft’s trajectory, or flight path, during the final two phases of its mission. The view is toward Saturn as seen from Earth. The 20 ring-grazing orbits are shown in gray; the 22 grand finale orbits are shown in blue. The final partial orbit is colored orange. Image credit: NASA/JPL-Caltech/Space Science Institute

Even in its final moments, Cassini is going to be sciencing as hard as it can. We’ll learn more about the density of consistency of the rings close to the planet. We’ll learn more about the planet’s upper atmosphere, storms and clouds with the closest possible photographs you can take.

And then it’ll all be over. The perfect finale to one of the most successful space missions in human history. A mission that revealed as many new mysteries about Saturn as it helped us answer. A mission that showed us not only a distant alien world, but our own planet in perspective in this vast Solar System. I can’t wait to go back.

How have the photos from Cassini impacted your love of astronomy? Let me know your thoughts in the comments.

Posted on by Matt Williams

What is the Weather like on Saturn?

The Saturn hexagon as seen by Voyager 1 in 1980 (NASA)

Welcome back to our planetary weather series! Next up, we take a look at the ringed-beauty, Saturn!

Saturn is famous for many things. Aside from its ring system, which are the most visible and beautiful of any gas giant, it is also known for its extensive system of moons (the second largest in the Solar System behind Jupiter). And then there its banded appearance and gold color, which are the result of its peculiar composition and persistent weather patterns.

Much like Jupiter, Saturn’s weather systems are known for being particularly extreme, giving rise to features that can be seen from great distances. It’s high winds periodically create massive oval-shaped storms, jet streams, hurricanes, and hexagonal wave patterns that are visible in both the northern and southern polar regions.

Saturn’s Atmosphere:

The outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium by volume. The gas giant is also known to contain heavier elements, though the proportions of these relative to hydrogen and helium is not known. It is assumed that they would match the primordial abundance from the formation of the Solar System.

The huge storm churning through the atmosphere in Saturn’s northern hemisphere overtakes itself as it encircles the planet in this true-color view from NASA’s Cassini spacecraft. Credit: NASA/JPL-Caltech/SSI

Trace amounts of ammonia, acetylene, ethane, propane, phosphine and methane have been also detected in Saturn’s atmosphere. The upper clouds are composed of ammonia crystals, while the lower level clouds appear to consist of either ammonium hydrosulfide (NH4SH) or water. Ultraviolet radiation from the Sun causes methane photolysis in the upper atmosphere, leading to a series of hydrocarbon chemical reactions with the resulting products being carried downward by eddies and diffusion.

Saturn’s atmosphere exhibits a banded pattern similar to Jupiter’s, but Saturn’s bands are much fainter and wider near the equator. As with Jupiter’s cloud layers, they are divided into the upper and lower layers, which vary in composition based on depth and pressure. In the upper cloud layers, with temperatures in range of 100–160 K and pressures between 0.5–2 bar, the clouds consist of ammonia ice.

The presence of hydrogen gas results in clouds of deep red. However, these are obscured by clouds of ammonia, which are closer to the outer edge of the atmosphere and cover the entire planet. The exposure of this ammonia to the Sun’s ultraviolet radiation causes it to appear white. Combined with its deeper red clouds, this results in the planet having a pale gold color.

Water ice clouds begin at a level where the pressure is about 2.5 bar and extend down to 9.5 bar, where temperatures range from 185–270 K. Intermixed in this layer is a band of ammonium hydrosulfide ice, lying in the pressure range 3–6 bar with temperatures of 290–235 K. Finally, the lower layers, where pressures are between 10–20 bar and temperatures are 270–330 K, contains a region of water droplets with ammonia in an aqueous solution.

Great White Spot:

On occasion, Saturn’s atmosphere exhibits long-lived ovals, similar to what is commonly observed on Jupiter. Whereas Jupiter has the Great Red Spot, Saturn periodically has what’s known as the Great White Spot (aka. Great White Oval). This unique but short-lived phenomenon occurs once every Saturnian year, roughly every 30 Earth years, around the time of the northern hemisphere’s summer solstice.

These spots can be several thousands of kilometers wide, and have been observed in 1876, 1903, 1933, 1960, and 1990. Since 2010, a large band of white clouds called the Northern Electrostatic Disturbance have been observed enveloping Saturn, which was spotted by the Cassini space probe. If the periodic nature of these storms is maintained, another one will occur in about 2020.

Meteorological Phenomena:

The winds on Saturn are the second fastest among the Solar System’s planets, after Neptune’s. This is due in part to Saturn’s high rotational velocity – which is 9.87 km/s (6.13 mi/s), which works out to 35,500 km/h (22,058.7 mi/h). At this rate, it only takes the planet 10 hours 33 minutes to rotate once on its axis. However, due to it being a gas giant, there is a difference between the rotation of its atmosphere and its core.

Data obtained by the Voyager 1 and 2 missions indicated peak easterly winds of 500 m/s (1800 km/h). Saturn’s northern and southern poles have also shown evidence of stormy weather. At the north pole, this takes the form of a hexagonal wave pattern, whereas the south shows evidence of a massive jet stream.

Saturn makes a beautifully striped ornament in this natural-color image, showing its north polar hexagon and central vortex. Credit: NASA/JPL-Caltech/Space Science Institute

The persisting hexagonal wave pattern around the north pole was first noted in the Voyager images. The sides of the hexagon are each about 13,800 km (8,600 mi) long (which is longer than the diameter of the Earth) and the structure rotates with a period of 10h 39m 24s, which is assumed to be equal to the period of rotation of Saturn’s interior.

The south pole vortex, meanwhile, was first observed using the Hubble Space Telescope. These images indicated the presence of a jet stream, but not a hexagonal standing wave. These storms are estimated to be generating winds of 550 km/h, are comparable in size to Earth, and believed to have been going on for billions of years.

In 2006, the Cassini space probe observed a hurricane-like storm that had a clearly defined eye. Such storms had not been observed on any planet other than Earth – even on Jupiter. This storm appeared to be caused by heat that was generated in the depths of the warm interior of Saturn, which then escaped to the upper atmosphere and escaped the planet.

Saturn has also been noted for its “string of pearls” feature, which was captured by Cassini’s visual and infrared mapping spectrometer in 2006. This feature, which appeared in it’s northern latitudes (and has not been seen on any other gas giant) is a series of cloud clearings spaced at regular intervals that show how Saturn’s atmosphere is lit by its own internal, thermal glow.

So how is the weather on Saturn? Pretty violent and stormy! And not surprising given the planet’s mass, composition, powerful gravity, and rapid rotation. Makes you feel happy we live on Earth, where the Earth is (comparatively speaking) pretty calm and boring!

We have written many interesting articles about planetary weather here at Universe Today. Here’s What’s the Weather Like on Mercury?, What’s the Weather Like on Venus?, What’s the Weather Like on Mars?, What’s the Weather Like on Jupiter?, What is the Weather Like on Uranus? and What is the Weather Like on Neptune?

For more information, check out NASA’s Solar System Exploration – Saturn, and the facts about Saturn from Space Facts.

Astronomy Cast has recorded some interesting episode on the subject. Here’s Episode 59: Saturn, and Episode 61: Saturn’s Moons.

Sources:

Posted on by Evan Gough

Cassini Images Of Enceladus Highlight Possible Cradle For Life

Saturn's moon Enceladus, in all its glory. Captured by the Cassini probe. Image: NASA/JPL-Caltech/Space Science Institute

During its long mission to Saturn, the Cassini spacecraft has given us image after spectacular image of Saturn, its rings, and Saturn’s moons. The images of Saturn’s moon Enceladus are of particular interest when it comes to the search for life.

At first glance, Enceladus appears similar to other icy moons in our Solar System. But Cassini has shown us that Enceladus could be a cradle for extra-terrestrial life.

Our search for life in the Solar System is centred on the presence of liquid water. Maybe we don’t know for sure if liquid H2O is required for life. But the Solar System is huge, and the effort required to explore it is immense. So starting our search for life with the search for liquid water is wise. And in the search for liquid water, Enceladus is a tantalizing target.

Cassini captured this image of Enceladus with Saturn’s rings. The vapor plumes are slightly visible at the south polar region (bottom of image). Image: NASA/JPL/Space Science Institute

Though Enceladus looks every bit like a frozen, lifeless world on its surface, it’s what lies beneath its frigid crust that is exciting. Enceladus appears to have a subsurface ocean, at least in it’s south polar region. And that ocean may be up to 10 km. deep.

Before we dive into that, (sorry), here are a few basic facts about Enceladus:

  • Enceladus is Saturn’s sixth largest moon
  • Enceladus is about 500 km in diameter (Earth’s Moon is 3,474 km in diameter)
  • Enceladus was discovered in 1789 by William Herschel
  • Enceladus is one of the most reflective objects in our Solar System, due to its icy surface

In 2005, Cassini first spied plumes of frozen water vapor erupting from the southern polar region. Called cryovolcanoes, subsequent study of them determined that they are the likely source of Saturn’s E Ring. The existence of these plumes led scientists to suspect that their source was a sub-surface ocean under Enceladus’ ice crust.

This close up image of Enceladus clearly shows multiple plumes erupting into space. Image: NASA/JPL/Space Science Institute

Finding plumes of water erupting from a moon is one thing, but it’s not just water. It’s salt water. Further study showed that the plumes also contained simple organic compounds. This advanced the idea that Enceladus could harbor life.

This image of Enceladus shows the features known as “Tiger stripes”. They are the source of the vapor plumes that erupt from the surface. Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

The geysers aren’t the only evidence for a sub-surface ocean on Enceladus. The southern polar region has a smooth surface, unlike the rest of the moon which is marked with craters. Something must have smoothed that surface, since it is next to impossible that the south polar region would be free from impact craters.

In 2005, Cassini detected a warm region in the south, much warmer than could be caused by solar radiation. The only conclusion is that Enceladus has a source of internal heating. That internal heat would create enough geologic activity to erase impact craters.

So now, two conditions for the existence of life have been met: liquid water, and heat.

In 2005, data from Cassini showed that the so-called “Tiger Stripe” features on Enceladus’ south pole region are warm spots. Image:NASA/JPL/GSFC/SwRI/SSI

The source of the heat on Enceladus was the next question facing scientists. That question is far from settled, and there could be several sources of heat operating together. Among all the possible sources for the heat, two are most intriguing when it comes to the search for life: tidal heating, and radioactive heating.

Tidal heating is a result of rotational and orbital forces. In Enceladus’ case, these forces cause friction which is dissipated as heat. This heat keeps the sub-surface ocean in liquid form, but doesn’t prevent the surface from freezing solid.

Radioactive heating is caused by the decay of radioactive isotopes. If Enceladus started out as a rocky body, and if it contained enough short-lived isotopes, then an enormous amount of heat would be produced for several million years. That action would create a rocky core surrounded by ice.

Then, if enough long-lived radioactive isotopes were present, they would continue producing heat for a much longer period of time. However, radioactive heating isn’t enough on its own. There would have to be tidal heating also.

Gravity measurements by NASA’s Cassini spacecraft and Deep Space Network suggest that Saturn’s moon Enceladus, which has jets of water vapor and ice gushing from its south pole, also harbors a large interior ocean beneath an ice shell, as this illustration depicts.
Image Credit:
NASA/JPL-Caltech

More evidence for a large, sub-surface ocean came in 2014. Cassini and the Deep Space Network provided gravitometric measurements showing that the ocean is there. Those measurements showed that there is likely a regional, if not global, ocean some 10 km thick. Measurements also showed that the ocean is under an ice layer 30 to 40 km thick.

This close up image of Enceladus show the variability of its icy features. The dark spots were originally called “Dalmatian” terrain when first imaged in 2005. There exact nature remained a mystery until ten years later, when Cassini flybys showed that they are actually blocks of bedrock ice scattered along a ridge. The blocks range in size from tens to hundreds of meters. Image: NASA/JPL/Cal-Tech.

The discovery of a warm, salty ocean containing organic molecules is very intriguing, and has expanded our idea of what the habitable zone might be in our Solar System, and in others. Enceladus is much too distant from the Sun to rely on solar energy to sustain life. If moons can provide their own heat through tidal heating or radioactive heating, then the habitable zone in any solar system wouldn’t be determined by proximity to the star or stars at the centre.

Cassini’s mission is nearing its end, and it won’t fly by Enceladus again. It’s told us all it can about Enceladus. It’s up to future missions to expand our understanding of Enceladus.

Numerous missions have been talked about, including two that suggest flying through the plumes and sampling them. One proposal has a sample of the plumes being returned to Earth for study. Landing on Enceladus and somehow drilling through the ice remains a far-off idea better left to science fiction, at least for now.

Whether or not Enceladus can or does harbor life is a question that won’t be answered for a long time. In fact, not all scientists agree that there is a liquid ocean there at all. But whether it does or doesn’t harbor life, Cassini has allowed us to enjoy the tantalizing beauty of that distant object.

Enceladus. Cassini Imaging Team, SSI, JPL, ESA, NASA
Posted on by Nancy Atkinson

Unprecedented Views of Saturn’s Rings as Cassini Dances Death Spiral

This image shows a region in Saturn's outer B ring. NASA's Cassini spacecraft viewed this area at a level of detail twice as high as it had ever been observed before. And from this view, it is clear that there are still finer details to uncover. Credit: NASA/JPL-Caltech/Space Science Institute

As the Cassini spacecraft moves ever closer to Saturn, new images provide some of the most-detailed views yet of the planet’s spectacular rings. From its “Ring-Grazing” orbit phase, Cassini’s cameras are resolving details in the rings as small as 0.3 miles (550 meters), which is on the scale of Earth’s tallest buildings.

On Twitter, Cassini Imaging Team Lead Carolyn Porco called the images “outrageous, eye-popping” and the “finest Cassini images of Saturn’s rings.”

Project Scientist Linda Spilker said the ridges and furrows in the rings remind her of the grooves in a phonograph record.

These images are giving scientists the chance to see more details about ring features they saw earlier in the mission, such as waves, wakes, and things they call ‘propellers’ and ‘straw.’

This Cassini image features a density wave in Saturn’s A ring (at left) that lies around 134,500 km from Saturn. Density waves are accumulations of particles at certain distances from the planet. This feature is filled with clumpy perturbations, which researchers informally refer to as “straw.” Credit: NASA/JPL-Caltech/Space Science Institute

As of this writing, Cassini just started the 10th orbit of the 20-orbit ring-grazing phase, which has the spacecraft diving past the outer edge of the main ring system. The ring-grazing orbits began last November, and will continue until late April, when Cassini begins its grand finale. During the 22 finale orbits, Cassini will repeatedly plunge through the gap between the rings and Saturn. The first of these plunges is scheduled for April 26.

The spacecraft is actually close enough to the ‘F’ ring that occasionally tenuous particle strike Cassini, said project scientist Linda Spilker, during a Facebook Live event today.

“These are very small and tenuous, only a few microns in size,” Spilker said, “like dust particles you’d see in the sunlight. We can actually ‘hear’ them hitting the spacecraft in our data, but these particles are so small, they won’t hurt Cassini.”

I talked with Spilker about ring particles for my book “Incredible Stories From Space:”

Spilker has envisioned holding a ring particle in her hand. What would it look like?

“We have evidence of the particles that have an icy core covered with fluffy regolith material that is very porous,” she said, “and that means the particle can heat up and cool down very quickly compared to a solid ice cube.”

The straw features are caused by clumping ring particles and the propellers are caused by small, embedded moonlets that creates propeller shaped wakes in the rings.

The wavemaker moon, Daphnis, is featured in this view, taken as NASA’s Cassini spacecraft made one of its ring-grazing passes over the outer edges of Saturn’s rings on Jan. 16, 2017. This is the closest view of the small moon obtained yet. Daphnis is 5 miles or 8 kilometers across. Credit: NASA/JPL-Caltech/Space Science Institute

This stunning view of the moon Daphnis shows the moon interacting with the ring particles, creating waves in the rings around it.

A close-up of Saturn and its rings. Assembled using raw uncalibrated RGB filtered images taken by the Cassini spacecraft on January 18 2017. Credit:
NASA/JPL-Caltech/SSI/image editing by Kevin M. Gill

“These close views represent the opening of an entirely new window onto Saturn’s rings, and over the next few months we look forward to even more exciting data as we train our cameras on other parts of the rings closer to the planet,” said Matthew Tiscareno, a Cassini scientist who studies Saturn’s rings at the SETI Institute, Mountain View, California. Tiscareno planned the new images for the camera team.

Further reading: JPL, CICLOPS

Posted on by Nancy Atkinson

Land On Titan With Huygens in Beautiful New Video

The view of Titan from the descending Huygens spacecraft on January 14, 2005. Credit: ESA/NASA/JPL/University of Arizona.

On December 25, 2004, the piggybacking Huygens probe was released from the ‘mothership’ Cassini spacecraft and it arrived at Titan on January 14, 2005. The probe began transmitting data to Cassini four minutes into its descent through Titan’s murky atmosphere, snapping photos and taking data all the while. Then it touched down, the first time a probe had landed on an extraterrestrial world in the outer Solar System.

JPL has released a re-mix of the data and images gathered by Huygens 12 years ago in a beautiful new video. This is the last opportunity to celebrate the success of Huygens before Cassini ends its mission in September of 2017.

Watch as the incredible view of Titan’s surface comes into view, with mountains, a system of river channels and a possible lakebed.

After a two-and-a-half-hour descent, the metallic, saucer-shaped spacecraft came to rest with a thud on a dark floodplain covered in cobbles of water ice, in temperatures hundreds of degrees below freezing.

Huygens had to quickly collect and transmit all the images and data it could because shortly after landing, Cassini would drop below the local horizon, “cutting off its link to the home world and silencing its voice forever.”

How much of this video is actual images and data vs computer graphics?

Of course, the clips at the beginning and end of the video are obviously animations of the probe and orbiter. However, the slow descending 1st-person point-of-view video is made using actual images from Huygens. But Huygens did not take a continuous movie sequence, so a lot of work was done by the team that operated Huygens’ optical imager, the Descent Imager/Spectral Radiometer (DISR), to enhance, colorize, and re-project the images into a variety of formats.

The view of the cobblestones and the parachute shadow near the end of the video is also created from real landing data, but was made in a different way from the rest of the descent video, because Huygens’ cameras did not actually image the parachute shadow. However, the upward looking infrared spectrometer took a measurement of the sky every couple of seconds, recording a darkening and then brightening to the unobstructed sky. The DISR team calculated from this the accurate speed and direction of the parachute, and of its shadow to create a very realistic video based on the data.

If you’re a data geek, there are some great videos of Huygens’ data by the University of Arizona Lunar and Planetary Laboratory team, such as this one:

The movie shows the operation of the DISR camera during the descent onto Titan. The almost 4-hour long operation
of DISR is shown in less than five minutes in 40 times actual sped up to landing and 100 times actual speed thereafter.

Erich Karkoschka from the UA team explained what all the sounds in the video are. “All parts of DISR worked together as programmed, creating a harmony,” he said. Here’s the full explanation:

Sound was added to mark various events. The left speaker follows the motion of Huygens. The pitch of the tone indicates the rotational speed. Vibrato indicates vibration of the parachute. Little clicks indicate the clocking of the rotation counter. Noise corresponds to heating of the heat shield, to parachute deployments, to the heat shield release, to the jettison of the DISR cover, and to touch down.

The sound in the right speaker follows DISR data. The pitch of the continuous tone goes with the signal strength. The 13 different chime tones indicate activity of the 13 components of DISR. The counters at the top and bottom of the list get the high and low notes, respectively.

You can see more info and videos created from Huygens’ data here.

Read some reminiscences about Huygens from some of the Cassini team here.