Posted on by Michael Habib

Let’s Put a Sailboat on Titan

An illustration showing how a sailboat mission to Titan might land and become operational. Copyright: Estevan Guzman for Universe Today.

The large moons orbiting the gas giants in our solar system have been getting increasing attention in recent years. Titan, Saturn’s largest moon, is the only natural satellite known to house a thick atmosphere. It’s surface, revealed in part by the Cassini probe, is sculpted by lakes and rivers. There is interest in exploring Titan further, but this is tricky from orbit because seeing through the thick atmosphere is difficult. Flying on Titan has been discussed around the web (sometimes glibly), and this was even one of the subjects treated by the immensely popular comic, XKCD.

However, there remains the problem of powering propulsion. The power requirements for flight are quite minimal on Titan, so solar wings might work. But Titan also presents an alternative: sailing.

Images from the Cassini mission show river networks draining into lakes in Titans north polar region. Credit: NASA/JPL/USGS.
Images from the Cassini mission show river networks draining into lakes in Titans north polar region. Credit: NASA/JPL/USGS.

With all those lakes and rivers, exploring Titan with a surface ship might be a great way to see much of the moon. The vehicle wouldn’t be sailing on water, though. The lakes on Titan are composed of liquid methane. The challenge is therefore making the vessel buoyant: liquid methane is only 45% as dense as liquid water. This means we would need a lot of displacement. A deep, hollow hull could do this, however, and it turns out that the liquid methane has an advantage that helps make up for the low density: it is much less viscous than water.

Reynolds number is proportional to the ratio of density to viscosity, and it turns out that friction drag on a hull is inversely proportional to Re. While Titan’s seas and lakes have only 45% the density of water, they also have only 8% of the viscosity. This means that the Titan sailing vessel would only experience about 26% of the friction drag as its Earth equivalent. [Yacht designers have found that the friction drag is about equal to 0.075/(log(Re)-2)^2)]. That leaves us room to make the hull deeper (important to compensate for the density as above), and longer (if we want a longer waterline, which will make the bow waves longer and improve maximum speed).

The sail itself would get less wind, on average, on Titan than Earth. Average wind speeds on Titan seem to be about 3 meters/s, according to Cassini, though it might be higher over the lakes. Average wind speed over Earth oceans is closer to 6.6 meters/s. But, the Titan atmosphere is also about 4x denser than Earth’s, and both lift and drag are proportional to fluid density. All told, this means that the total fluid force on the sail will be about 83% of what you’d get on Earth, all else being equal, which could be sufficient. There would be a premium on sail efficiency and size, and so we might have to take advantage of the low-friction hull to examine shapes with more stability that can house a larger, taller (and presumably high aspect ratio) sail.

This is all quite speculative, of course, but it provides a fun exercise and perhaps provides inspiration as we imagine tall-sailed robotic vessels silently cruising the lakes of Titan.

Titan Mare Explorer. Image credit: NASA/JPL
Titan Mare Explorer. Image credit: NASA/JPL

One concept for a boat on Titan has already been proposed: the Titan Mare Explorer (TiME) would send a floating high-tech buoy to land in a methane sea on this moon of Saturn to study its composition and its interaction with the atmosphere. But this Discovery-class mission concept was nixed in favor of sending the InSight lander to Mars.

But with all the recent discoveries on Titan by the Cassini spacecraft — things like lakes, seas, rivers and weather and climate patterns that create both fog and rain — a mission like this will be given more consideration in the future.

Posted on by Jason Major

Cassini Sees a “Zen Garden” on Titan

Radar image of rows of dunes on Titan. Credit: NASA/JPL-Caltech

Looking like the flowing designs carved by a Zen gardener’s rake, long parallel dunes of hydrocarbon sand stretch across the surface of Saturn’s moon Titan. The image above, acquired by Cassini in July 2013, reveals these intriguing and remarkably Earthlike landforms in unprecedented detail via radar, which can easily pierce through Titan’s thick clouds.

I’m feeling a little more enlightened already.

Although it piles into dunes like sand does here, Titan’s sand is not the same as what you’d find on a beach here on Earth. According to an ESA “Space in Images” article:

While our sand is composed of silicates, the ‘sand’ of these alien dunes is formed from grains of organic materials about the same size as particles of our beach sand. The small size and smoothness of these grains means that the flowing lines carved into the dunes show up as dark to the human eye.

Titan's surface is almost completely hidden from view by its thick orange "smog" (NASA/JPL-Caltech/SSI. Composite by J. Major)
Titan’s surface is almost completely hidden from view by its thick orange “smog” (NASA/JPL-Caltech/SSI. Composite by J. Major)

Radar imaging, although capable of seeing through Titan’s opaque orange atmosphere, doesn’t capture visible-light images. Instead it’s sensitive to the varying textures of a landscape as they reflect microwaves; the smoother an object or an area is the darker it appears to radar, while irregular, rugged terrain shows up radar-bright.

The pixelated “seam” cutting horizontally across the center is the result of image artifacting.

Learn more about Cassini’s RADAR instrument here, and read more about this image on the ESA site here.

Posted on by Jason Major

Surf’s Up on Titan! Cassini May Have Spotted Waves in Titan’s Seas

Cassini VIMS image of specular reflections in one of Titan's lakes from a flyby on July 24, 2012 (NASA/JPL-Caltech/SSI/Jason W. Barnes et al.)

It’s no surprise that Titan’s north polar region is covered with vast lakes and seas of liquid methane — these have been imaged many times by Cassini during its ten years in orbit around Saturn. What is surprising though is just how incredibly smooth the surfaces of these lakes have been found to be.

One would think that such large expanses of surface liquid — some of Titan’s seas are as big the Great Lakes — would exhibit at least a little surface action on a world with an atmosphere as dense as Titan’s. But repeated radar imaging has shown their surfaces to be “as smooth as the paint on a car.” Over the past several years scientists have puzzled over this anomaly but now they may have truly seen the light — that is, reflected light from what could actually be waves on Titan!

Seasonal winds may be finally kicking up waves in Titan's lakes. (Illustration © Ron Miller.)
Seasonal winds may be finally kicking up waves in Titan’s lakes. (Illustration © Ron Miller.)

Using data acquired during flybys of Titan in 2012 and 2013, planetary scientist Jason Barnes from the University of Idaho and a team of researchers from several other institutions including JPL, Cornell, and MIT, have identified what might be waves in the surface of Punga Mare, one of Titan’s biggest lakes.

For a sense of scale, Lake Victoria, the largest lake in Africa, could fit lengthwise across Titan’s 380-km (236-mile) -wide Punga Mare.

Read more: Titan’s North Pole is Loaded with Lakes

Variations in specular highlights in four pixels observed in the surface of Punga Mare by Cassini’s VIMS (Visible and Infrared Mapping Spectrometer) have been interpreted by the team as being the result of waves — or, perhaps more accurately, ripples, seeing as that they are estimated to be a mere 2 centimeters in height.

Still, based on what’s been observed thus far on Titan, that’s downright choppy.

If the Cassini observations interpreted by Barnes et al. are indicative of waves in Punga Mare, they could also explain previous specular variations seen in other bodies of liquid, like the smaller Kivu Lacus (top image).

Map of Titan's northern "Land o' Lakes" made from Cassini radar imaging passes (NASA/JPL/USGS)
Map of Titan’s northern “Land o’ Lakes” made from Cassini high-resolution radar imaging (NASA/JPL/USGS)

“If correct this discovery represents the first sea-surface waves known outside of Earth.”

– Jason W. Barnes et al.

Then again, wave action isn’t the only possible answer. Similar varied specular highlights could also be caused by a wet surface — like a methane mud flat. Further observations will be needed to rule out other possibilities and obtain a more accurate “surf forecast” for Titan.

The findings were presented by Jason Barnes at the 45th Lunar and Planetary Science Conference in Houston on March 17, 2014. Read the team’s abstract here, and read more in this article by Alexandra Witze on Nature News.

Posted on by Elizabeth Howell

Rocket Fail Video Shows Human And Technological Risk With Each Launch

The Challenger space shuttle a few moments after the rupture took place in the booster. Credit: NASA

What you see above is 32 minutes of something going wrong during each launch. While humanity has been launching things into space since the 1950s, you can see just how hard it is — over and over again. And when humans are riding aboard the rockets, the toll becomes more tragic.

According to the YouTube author of the video above, the vehicles shown include “V2, Vanguard TV3, Explorer S-1, Redstone 1, Titan I, Titan II, Titan IV, Atlas, Atlas-Centaur, N1, Delta, Delta III, Foton, Soyuz, Long March, Zenith, Space Shuttle Challenger, and more.”

Naturally, with each failure the engineers examine the systems and work to fix things for next time. A famous example is the Challenger shuttle explosion, which you can see about halfway through the video. There were multiple causes for the failure (human and technical), but one of them was an O-ring that failed in cold weather before the launch. NASA revised the launch rules and with contractors, made some changes to the booster rocket design, as a 2010 Air and Space Smithsonian article points out:

Freezing temperatures weakened an O-ring seal in a joint between two segments of the right booster. The weakness allowed hot gases to burn through the casing, causing the shuttle to break apart on ascent, which killed the seven-member crew. Two joints were redesigned with interlocking walls that had new bolts, pins, sensors, seals, and a third O-ring.

Still, launching is a risky business. That’s why it’s so important that engineers try to catch problems before they happen, and that as soon as a problem is seen, it’s fixed.

Posted on by Fraser Cain

What Are Cassini’s Most Interesting Discoveries?

What Are Cassini's Most Interesting Discoveries?

We recently interviewed Dr. Kevin Grazier, on of the scientist who has worked extensively on the Cassini mission. Here’s what he had to tell us about that mission’s discoveries.

“My name is Kevin Grazier. I am a planetary scientist, and for my research I do long-term integrations or simulations of early solar system evolution. I’m a former scientist on the Cassini mission and a consultant to several TV series such as Defiance, Falling Skies, the movie Gravity, and formerly, Battlestar Galactica.”

What are Cassini’s most amazing discoveries?
“Cassini has essentially rewritten the book on the Saturn system. I was on the spacecraft team for 15 years. I worked as a science planner and as the Investigation Scientist on the ISS instrument. (That’s Imaging Science Subsystem, not International Space Station.) And of the discoveries we found, I’m trying to think of what I’d call or classify as the most exciting.”

“One was predicted – the fact that it was believed that there could be ice volcanoes on Enceladus. And as a matter of fact, there are volcanoes on Enceladus, or active venting, however you want to look at that. Those vents create the “E” ring, so we have a ring created by material vented off Enceladus. That’s pretty exciting, because we see an active object venting material, and there aren’t a lot of active objects in the solar system.”

This mosaic of Titan was created from the first flyby of the moon by Cassini in 2004. Credit: NASA/JPL/SS
This mosaic of Titan was created from the first flyby of the moon by Cassini in 2004. Credit: NASA/JPL/SS

“The surface of Titan is really fantastic. We have open oceans or seas of hydrcarbons on Titan. We have the possibility of an open ocean underneath the crust, just like we believe is under the surface of Europa. We have one image which seems to capture what might be a volcanic eruption. That’s important, because in the outer solar system, planetary science considers ice a rock. What a rock is defined as depends on where you are in the solar system. So in the outer solar system, ice is a rock. All of the moons in the outer solar system except Io have icy crusts. Now, if you have a volcanic eruption on Titan, we have an eruption of magma, and if ice is a rock, that eruption is water. So we have evidence of magma chambers which could be cauldrons of life-giving water.”

“How cool is that? How counter-intuitive is that? How science-fiction-y is that? That one of the most interesting places to look for is a lava chamber or magma chamber that could be suitable for sustaining life. I think that’s really exciting.”

You can follow Dr. Kevin on Twitter

Posted on by Jason Major

Happy Holidays from Cassini!

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)

Cassini couldn’t make it to the mall this year to do any Christmas shopping but that’s ok: we’re all getting something even better in our stockings than anything store-bought! To celebrate the holiday season the Cassini team has shared some truly incredible images of Saturn and some of its many moons for the world to “ooh” and “ahh” over. So stoke the fire, pour yourself a glass of egg nog, sit back and marvel at some sights from a wintry wonderland 900 million miles away…

Thanks, Cassini… these are just what I’ve always wanted! (How’d you know?)

Saturn’s southern hemisphere is growing more and more blue as winter approaches there — a coloration similar to what was once seen in the north when Cassini first arrived in 2004:

Saturn's southern hemisphere images from a million miles away (Credit: NASA/JPL-Caltech/Space Science Institute)
Saturn’s southern hemisphere images from a million miles away (Credit: NASA/JPL-Caltech/Space Science Institute)

(The small dark spot near the center right of the image above is the shadow of the shepherd moon Prometheus.)

Titan and Rhea, Saturn’s two largest moons, pose for Cassini:

Rhea (front) and Titan, images by Cassini in June 2011 (Credit: NASA/JPL-Caltech/Space Science Institute)
Rhea (front) and Titan, images by Cassini in June 2011 (Credit: NASA/JPL-Caltech/Space Science Institute)

The two moons may look like they’re almost touching but in reality they were nearly half a million miles apart!

Titan’s northern “land of lakes” is visible in this image, captured by Cassini with a special spectral filter able to pierce through the moon’s thick haze:

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

Read more: Titan’s North Pole is Loaded with Lakes

The frozen, snowball-like surface of the 313-mile-wide moon Enceladus:

Enceladus: a "snowball in space" (Credit: NASA/JPL-Caltech/Space Science Institute)
Enceladus: a highly-reflective and icy “snowball in space” (Credit: NASA/JPL-Caltech/Space Science Institute)

(Even though Enceladus is most famous for its icy geysers, first observed by Cassini in 2005, in these images they are not visible due to the lighting situations.)

Seen in a different illumination angle and in filters sensitive to UV, visible, and infrared light the many fractures and folds of Enceladus’ frozen surface become apparent:

View of the trailing face of Enceladus (Credit: NASA/JPL-Caltech/Space Science Institute)
View of the trailing face of Enceladus (Credit: NASA/JPL-Caltech/Space Science Institute)

Because of Cassini’s long-duration, multi-season stay in orbit around Saturn, researchers have been able to learn more about the ringed planet and its fascinating family of moons than ever before possible. Cassini is now going into its tenth year at Saturn and with much more research planned, we can only imagine what discoveries (and images!) are yet to come in the new year(s) ahead.

“Until Cassini arrived at Saturn, we didn’t know about the hydrocarbon lakes of Titan, the active drama of Enceladus’ jets, and the intricate patterns at Saturn’s poles,” said Linda Spilker, the Cassini project scientist at NASA’s Jet Propulsion Laboratory. “Spectacular images like these highlight that Cassini has given us the gift of knowledge, which we have been so excited to share with everyone.”

Read more about the images above and see even more on the CICLOPS  Imaging Team website, and see the NASA press release here.

Thanks to Carolyn Porco, Cassini Imaging Team Leader, for the heads-up on these gifs — er, gifts!

Posted on by Nancy Atkinson

New Flyover Video Takes You on a Tour of Titan’s Lake Region

This colorized mosaic from NASA's Cassini mission shows the most complete view yet of Titan's northern land of lakes and seas. Saturn's moon Titan is the only world in our solar system other than Earth that has stable liquid on its surface. The liquid in Titan's lakes and seas is mostly methane and ethane. Image credit: NASA/JPL-Caltech/ASI/USGS

Saturn’s moon Titan has the only known liquid lakes beyond planet Earth, and new data from the Cassini spacecraft’s radar instrument provides an intriguing 3-D flyover of these hydrocarbon lakes and seas at the north pole region. Steve Wall, Cassini acting radar team lead, provided a guided tour as he presented the video at the American Geophysical Union conference in San Francisco, noting that the vertical heights are exaggerated tenfold and the data has been colorized, both for visual effect.

The video starts by zooming into the southern end of Kraken Mare, the largest of Titan’s seas, and as you fly a little farther, Wall said the things that look like little islands are just noise in the radar data. Next, comes Ligea Mare, with its rugged coastline, and you’ll see that the liquid flow into the surrounding terrain, which appear like river valleys.

The “smooth” area that stretches farther from Ligea Mare is actualy not so smooth, but is just an area when the science team doesn’t have topographical data yet.

The video then continues to other smaller lakes that are nestled into valleys and rugged terrain.

“Learning about surface features like lakes and seas helps us to understand how Titan’s liquids, solids and gases interact to make it so Earth-like,” said Wall. “While these two worlds aren’t exactly the same, it shows us more and more Earth-like processes as we get new views.”

The new data is not only visually stunning, but provides previously unknown details about these lakes and the region. For example, Kraken Mare is more extensive and complex than previously thought. They also show nearly all of the lakes on Titan fall into an area covering about 600 miles by 1,100 miles (900 kilometers by 1,800 kilometers). Only 3 percent of the liquid at Titan falls outside of this area.

“Scientists have been wondering why Titan’s lakes are where they are. These images show us that the bedrock and geology must be creating a particularly inviting environment for lakes in this box,” said Randolph Kirk, a Cassini radar team member at the U.S. Geological Survey in Flagstaff, Ariz. “We think it may be something like the formation of the prehistoric lake called Lake Lahontan near Lake Tahoe in Nevada and California, where deformation of the crust created fissures that could be filled up with liquid.”

Additionally, scientists now know that Ligeia Mare is about 560 feet (170 meters) deep. This is the first time scientists have been able to plumb the bottom of a lake or sea on Titan. This was possible partly because the liquid turned out to be very pure, allowing the radar signal to pass through it easily. The liquid surface may be as smooth as the paint on our cars, and it is very clear to radar eyes.

“Ligeia Mare turned out to be just the right depth for radar to detect a signal back from the sea floor, which is a signal we didn’t think we’d be able to get,” said Marco Mastrogiuseppe, a Cassini radar team associate at Sapienza University of Rome. “The measurement we made shows Ligeia to be deeper in at least one place than the average depth of Lake Michigan.”

The new results indicate the liquid is mostly methane, somewhat similar to a liquid form of natural gas on Earth.

Sources: AGU press conference, JPL press release

Posted on by Elizabeth Howell

Ghostly Pic Of Saturn’s Moon Shows It Rising From The Deep

Titan imaged by the Cassini spacecraft. Credit: NASA/JPL-Caltech/Space Science Institute

Sunlight can do fun things in space. For example: this recent picture of Titan (a moon of Saturn) shows sunlight hitting the moon’s surface as well as a southern vortex, just visible in the shadows of the picture.

“The sunlit edge of Titan’s south polar vortex stands out distinctly against the darkness of the moon’s unilluminated hazy atmosphere,” NASA stated. “The Cassini spacecraft images of the vortex led scientists to conclude that its clouds form at a much higher altitude — where sunlight can still reach — than the surrounding haze.”

Titan has intrigued scientists for decades, since the Voyager spacecraft first revealed it as a world socked in by orange haze. Cassini dropped off a lander on the surface, called Huygens, which took pictures on the surface in 2005. Besides that, the orbiter has revealed a lot about lakes, rain and other features of the moon in the year since.

Cassini has been orbiting the moon since 2004 and is still busily producing science, but there are concerns that NASA’s budget situation could cause the agency to shut down operations on the still-healthy spacecraft. There are no other missions to Saturn or Titan booked yet, although scientists do have intriguing ideas for exploration.