NASA Cassini sunny Hydrocarbon seas on Titan

This near-infrared, colour mosaic from NASA's Cassini spacecraft shows the sun glinting off of Titan's north polar seas.

While Cassini has captured, separately, views of the polar seas and the sun glinting off of them in the past, this is the first time both have been seen together in the same view.

The sunglint, also called a specular reflection, is the bright area near the 11 o'clock position at upper left.

This mirror-like reflection, known as the specular point, is in the south of Titan's largest sea, Kraken Mare, just north of an island archipelago separating two separate parts of the sea.

This particular sunglint was so bright as to saturate the detector of Cassini's Visual and Infrared Mapping Spectrometer (VIMS) instrument, which captures the view.

It is also the sunglint seen with the highest observation elevation so far, the sun was a full 40 degrees above the horizon as seen from Kraken Mare at this time, much higher than the 22 degrees seen in PIA18433.

Because it was so bright, this glint was visible through the haze at much lower wavelengths than before, down to 1.3 microns.

The southern portion of Kraken Mare (the area surrounding the specular feature toward upper left) displays a "bathtub ring," a bright margin of evaporate deposits, which indicates that the sea was larger at some point in the past and has become smaller due to evaporation.

The deposits are material left behind after the methane & ethane liquid evaporates, somewhat akin to the saline crust on a salt flat.

The highest resolution data from this flyby, the area seen immediately to the right of the sunglint, cover the labyrinth of channels that connect Kraken Mare to another large sea, Ligeia Mare.

Ligeia Mare itself is partially covered in its northern reaches by a bright, arrow-shaped complex of clouds.

The clouds are made of liquid methane droplets, and could be actively refilling the lakes with rainfall.

The view was acquired during Cassini's August 21, 2014, flyby of Titan, also referred to as "T104" by the Cassini team.

The view contains real colour information, although it is not the natural color the human eye would see.

Here, red in the image corresponds to 5.0 microns, green to 2.0 microns, and blue to 1.3 microns.

These wavelengths correspond to atmospheric windows through which Titan's surface is visible. The unaided human eye would see nothing but haze.

Credit: NASA/JPL-Caltech/University of Arizona/University of Idaho

NASA Cassini: MIPT researcher models Titan's atmosphere

Titan’s atmosphere. Image from the Cassini orbiter.

Credit: Nasa

A researcher from Moscow Institute of Physics and Technology (MIPT), Prof. Vladimir Krasnopolsky, who heads the Laboratory of High Resolution Infrared Spectroscopy of Planetary Atmospheres, has published the results of the comparison of his model of Titan's atmosphere with the latest data.

Vladimir Krasnopolsky

The article in the journal Icarus compares the chemical composition of Titan's atmosphere with parameters predicted by a mathematical model.

The atmosphere of Saturn's largest moon, Titan, was described by a model that took into account the presence of 83 neutral molecules, 33 ions and 420 different chemical reactions between them.

Despite the fact that Titan is located much further from the Sun than the Earth and that radiation flux coming from the Sun to the moon is 100 times lower, the intensity of UV rays is enough to spur photochemical reactions in the upper layers of Titan's atmosphere.

Cassini orbiter

The data regarding the composition of Titan's atmosphere, which is 1.6 times denser near the surface than the Earth's air, was obtained from several sources, mainly the Cassini orbiter.

It was equipped with a number of gauges, including ultraviolet and infrared spectrometers and equipment for studying the ions that were drawn into space.

Within ten years in Saturn's orbit, a plasma complex and a mass spectrometer designed specifically for this research project gathered enough data to compare it with mathematical models.

IRAM ground submillimeter telescope

In addition to Cassini, part of the data was obtained using the IRAM ground submillimeter telescope and the Hershel infrared space observatory.

Data on the distribution of aerosol particles in Titan's atmosphere was received from a unique space capsule, Huygens, which landed on Titan for the first time in the history of mankind and sent the first photos of its surface.

Comparing this data with the previously developed model, Krasnopolsky showed that the theoretical description of Titan's atmosphere matches the reality quite accurately.

There are discrepancies, however, but they are caused by inevitable measurement errors – so far, the concentrations of many substances are approximate.

The most important thing is not the absolute matching of specific parameters but the correctness of the general model of chemical processes.

"The coherence of the model with reality means that we can correctly tell where different substances go from Titan's ionosphere and where they come from," Krasnopolsky said.

Krasnopolsky is considered a leading global expert on the atmosphere of celestial bodies of the solar system.

He has participated in the creation of spectrometers for a variety of spacecraft, including the legendary Voyagers and the first Soviet interplanetary probes.

NASA Cassini: Titan's Icy Ocean has extra high salt content

Researchers found that Titan's ice shell, which overlies a very salty ocean, varies in thickness around the moon, suggesting the crust is in the process of becoming rigid. 

Credit: NASA /JPL /SSI /Univ. of Arizona /G. Mitri /University of Nantes

Scientists analyzing data from NASA Cassini mission have firm evidence the ocean inside Saturn's largest moon, Titan, might be as salty as the Earth's Dead Sea.

The new results come from a study of gravity and topography data collected during Cassini's repeated flybys of Titan during the past 10 years.

Using the Cassini data, researchers presented a model structure for Titan, resulting in an improved understanding of the structure of the moon's outer ice shell.

The findings are published in this week's edition of the journal Icarus.

"Titan continues to prove itself as an endlessly fascinating world, and with our long-lived Cassini spacecraft, we're unlocking new mysteries as fast as we solve old ones," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, who was not involved in the study.

Additional findings support previous indications the moon's icy shell is rigid and in the process of freezing solid.

Researchers found that a relatively high density was required for Titan's ocean in order to explain the gravity data.

This indicates the ocean is probably an extremely salty brine of water mixed with dissolved salts likely composed of sulphur, sodium and potassium.

The density indicated for this brine would give the ocean a salt content roughly equal to the saltiest bodies of water on Earth.

"This is an extremely salty ocean by Earth standards," said the paper's lead author, Giuseppe Mitri of the University of Nantes in France.

"Knowing this may change the way we view this ocean as a possible abode for present-day life, but conditions might have been very different there in the past."

Cassini data also indicate the thickness of Titan's ice crust varies slightly from place to place.

The researchers said this can best be explained if the moon's outer shell is stiff, as would be the case if the ocean were slowly crystalizing, and turning to ice.

Otherwise, the moon's shape would tend to even itself out over time, like warm candle wax.

This freezing process would have important implications for the habitability of Titan's ocean, as it would limit the ability of materials to exchange between the surface and the ocean.

A further consequence of a rigid ice shell, according to the study, is any outgassing of methane into Titan's atmosphere must happen at scattered "hot spots," like the hot spot on Earth that gave rise to the Hawaiian Island chain.

Titan's methane does not appear to result from convection or plate tectonics recycling its ice shell.

How methane gets into the moon's atmosphere has long been of great interest to researchers, as molecules of this gas are broken apart by sunlight on short geological timescales.

Titan's present atmosphere contains about five percent methane. This means some process, thought to be geological in nature, must be replenishing the gas.

The study indicates that whatever process is responsible, the restoration of Titan's methane is localized and intermittent.

"Our work suggests looking for signs of methane outgassing will be difficult with Cassini, and may require a future mission that can find localized methane sources," said Jonathan Lunine, a scientist on the Cassini mission at Cornell University, Ithaca, New York, and one of the paper's co-authors. "As on Mars, this is a challenging task."

More information: Icarus, www.sciencedirect.com/science/… ii/S0019103514001444

NASA Cassini: Carolyn Porco talks about her life and experiences as a Saturn explorer - Video

Cassini mission scientist Carolyn Porco talks about her life and experiences as a Saturn explorer.

This interview, in which Porco discusses her fascination with astronomy and planets, and how that fascination led her down her remarkable career path, was conducted by space historian Andrew Chalkin, and it is just so wonderful to watch.

Porco's love of scientific investigation and passion for what she does is so compelling, it's hard not to get lost in her stories of coming up in the Bronx, her accounts of past missions, and her continued enthusiasm for the science that she and the Cassini team are busy conducting to this day.

More information on the Saturn and the Cassini mission

NASA Cassini Image: Looking beyond Saturn to view Uranus

This view from NASA's Cassini spacecraft features a blue planet, but unlike the view from July 19, 2013 (PIA17172 The Day the Earth Smiled) that featured our home planet, this blue orb is Uranus, imaged by Cassini for the first time.

Credit: NASA /JPL-Caltech /Space Science Institute

Uranus is a pale blue in this natural colour image because its visible atmosphere contains methane gas and few aerosols or clouds.

Methane on Uranus and its sapphire-coloured sibling, Neptune, absorbs red wavelengths of incoming sunlight, but allows blue wavelengths to escape back into space, resulting in the predominantly bluish color seen here.

Cassini imaging scientists combined red, green and blue spectral filter images to create a final image that represents what human eyes might see from the vantage point of the spacecraft.

Uranus

Uranus has been brightened by a factor of 4.5 to make it more easily visible. The outer portion of Saturn's A ring, seen at bottom right, has been brightened by a factor of two.

The bright ring cutting across the image center is Saturn's narrow F ring.

Uranus was approximately 28.6 astronomical units from Cassini and Saturn when this view was obtained.

An astronomical unit is the average distance from Earth to the sun, equal to 93,000,000 miles (150,000,000 kilometers).

Neptune

The view was acquired by the Cassini narrow-angle camera at a distance of approximately 614,300 miles (988,600 kilometers) from Saturn on April 11, 2014.

Image scale at Uranus is approximately 16,000 miles (25,700 kilometers) per pixel.

Image scale at Saturn's rings is approximately 4 miles (6 kilometers) per pixel.

In the image, the disk of Uranus is just barely resolved.

The solar phase angle at Uranus, seen from Cassini, is 11.9 degrees.

Nasa Cassini: Saturn's moon Pan in the Encke gap in Saturn's rings

Credit: NASA /JPL-Caltech /Space Science Institute

Saturn's moon Pan, named for the Greek god of shepherds, rules over quite a different domain: the Encke gap in Saturn's rings.

Pan (17 miles, or 28 kilometers across) keeps the Encke gap open through its gravitational influence on the ring particles nearby.

This view looks toward the sunlit side of the rings from about 48 degrees above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 25, 2013.

The view was obtained at a distance of approximately 1.4 million miles (2.3 million kilometers) from Pan and at a Sun-Pan-spacecraft, or phase, angle of 87 degrees. Image scale is 9 miles (14 kilometers) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.

The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C.

The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL.

The imaging operations center is based at the Space Science Institute in Boulder, Colo.

NASA Cassini Image: Familiar forms on Titan's dunes

Credit: NASA/JPL-Caltech

The moons of our Solar System are brimming with unusual landscapes.

However, sometimes they look a little more familiar, as in this new radar image from the Cassini orbiter.

The image shows dark streaks carved into dunes reminiscent of those we might find on a beach on Earth, or raked with flowing lines in a Japanese Zen garden—but this scene is actually taking place on Saturn's moon Titan.

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.

These grains are shunted around by winds shifting over the moon's surface. These winds aren't particularly fast—only moving at around 1 m/s—but they blow in opposing directions throughout the year, causing Titan's 'sand' to pile up in certain places over time.

Titan seems to be full of features and phenomena that are quite familiar to those found on Earth.

Since Cassini arrived in the Saturn system in 2004, and dropped off ESA's Huygens probe in 2005, scientists have been studying the similarities between Titan and Earth by exploring sand dunes, channels and lakes of liquid ethane and methane scattered across its surface.

While previous images have spotted these eerily familiar patterns on Titan's dunes, this new image shows them in greater detail.

The image was obtained by Cassini's Titan radar mapper on 10 July 2013, by a team led by Steve Wall at NASA's Jet Propulsion Laboratory in California, USA.

The horizontal seam near the centre is an artifact of radar image data processing.

Nasa Cassini: Liquid Hydrogen provides important data for planetary models

The gas giant Jupiter, captured by the US-European space ship Cassini-Huygens. 

Credit: NASA/JPL/Space Science Institute

Using DESY's X-ray laser FLASH, researchers took a sneak peek deep into the lower atmospheric layers of giant gas planets such as Jupiter or Saturn.

The observations of the team around lead author Dr. Ulf Zastrau from the University of Jena reveal how liquid hydrogen becomes a plasma, and provide information on the material's thermal conductivity and its internal energy exchange, which are important ingredients for planetary models.

The hydrogen jet inside the sample chamber. 

Credit: Sven Toleikis/DESY

The scientists present their experiments in Friday's issue of the scientific journal Physical Review Letters.

The atmosphere of gas giants consists mainly of hydrogen, which is the most abundant chemical element in the universe.

"We have very little experimental knowledge about the hydrogen in the interior of such planets," says Zastrau. "This is despite our very good theoretical models."

The researchers therefore decided to use cold liquid hydrogen as a sample of the planetary atmosphere.

"Liquid hydrogen has a density that corresponds to that of the lower atmosphere of such giant gas planets," explains Zastrau.

The scientists used DESY's X-ray laser FLASH to heat liquid hydrogen, almost instantaneously, from minus 253 to around 12,000 degrees Celsius and simultaneously observed the properties of the element during the heating process.

Hydrogen is the simplest atom of the periodic table, consisting of a single proton in the atomic nucleus, which is orbited by a single electron. Normally, hydrogen occurs as a molecule consisting of two atoms.

Ulf Zastrau

The X-ray laser pulse initially heats only the electrons. These slowly transfer their energy to the protons, which are around 2,000 times heavier, until a thermal equilibrium is reached.

The molecular bonds break during this process, and a plasma of electrons and protons is formed.

Although this process takes many thousands of collisions between electrons and protons, the studies showed that the thermal equilibrium is attained in just under a trillionth of a second (a picosecond).

Thomas Tschentscher

"Our experiment showed us the way of how to investigate dense plasmas with X-ray lasers," says Dr. Thomas Tschentscher, scientific director of the European XFEL X-ray laser, at which experiments will be possible in 2017.

"This method opens up the road for further studies, e.g. of denser plasmas of heavier elements and mixtures, as they occur in the interior of planets."

"Hopefully, the results will provide us among others with an experimentally based answer to the question, why the planets discovered outside our solar system do not exist in all imaginable combinations of properties as age, mass, size or elemental composition, but may be allocated to certain groups."

More Information: “Resolving ultra-fast heating of dense cryogenic hydrogen”; U. Zastrau et al.; Physical Review Letters, 2014; DOI: 10.1103/PhysRevLett.

NASA Cassini: Rhea's Day in the Sun

A nearly full Rhea shines in the sunlight in this recent Cassini image. 

Rhea (949 miles, or 1,527 kilometers across) is Saturn's second largest moon.

Lit terrain seen here is on the Saturn-facing hemisphere of Rhea. 

North on Rhea is up and rotated 43 degrees to the left. 

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 10, 2013.

The view was obtained at a distance of approximately 990,000 miles (1.6 million kilometers) from Rhea. 

Image scale is 6 miles (9 kilometers) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. 

The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. 

The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. 

The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission, and saturn.jpl.nasa.gov. 

The Cassini imaging team homepage.
Image Credit: NASA/JPL-Caltech/Space Science Institute

NASA Cassini nears 100th Titan flyby with a look back

This artist’s concept shows a possible model of Titan’s internal structure that incorporates data from NASA’s Cassini spacecraft. 

In this model, Titan is fully differentiated, which means the denser core of the moon has separated from its outer parts. 

This model proposes a core consisting entirely of water-bearing rocks and a subsurface ocean of liquid water. 

The mantle, in this image, is made of icy layers, one that is a layer of high-pressure ice closer to the core and an outer ice shell on top of the sub-surface ocean. 

Credit: A. D. Fortes/UCL/STFC

Ten years ago, we knew Titan as a fuzzy orange ball about the size of Mercury. We knew it had a nitrogen atmosphere—the only known world with a thick nitrogen atmosphere besides Earth but what might lie beneath the hazy air was still just a guess.

On March 6, NASA’s Cassini spacecraft will swoop down within 933 miles (1,500 kilometers) of Titan to conduct its 100th flyby of the Saturn moon.

Each flyby gives us a little more knowledge of Titan and its striking similarities to our world.

Even with its cold surface temperatures of minus 290 degrees Fahrenheit (94 kelvins), Titan is like early Earth in a deep freeze.

Since its 2004 arrival at Saturn, Cassini's radar instrument has identified remarkable surface features on Titan.

The features include lakes and seas made of liquid methane and ethane, which are larger than North America's Great Lakes, and an extensive layer of liquid water deep beneath the surface.

Organic molecules abound in Titan's atmosphere, formed from the breakup of methane by solar radiation.

Michael Malaska

A recent innovation was the discovery that radar could be used to determine the depth of a Titan sea.

"It's something we didn't think we could do before," said Michael Malaska, an affiliate of the Cassini radar team at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

"The radar can measure the depth by receiving two different bounces: one from the surface and one from the bottom of the sea."

"This technique was used to determine that Ligeia Mare, the second largest sea on Titan, is about 160 meters [525 feet] deep."

"When coupled with some laboratory experiments, it gives us information about the composition of the liquid in Ligeia Mare, too."

As spring turns to summer in Titan's northern hemisphere for the first time since Cassini arrived at Saturn, scientists are looking forward to entering potentially the most exciting time for Titan weather - with waves and winds picking up.

With increasing sunlight, the north polar lakes and seas can now be seen in near-infrared images, enabling scientists to learn more about their composition and giving them clues about the surrounding terrain.

Jonathan Lunine

"Methane is not only in the atmosphere, but probably in the crust," said Jonathan Lunine, a scientist on the Cassini mission at Cornell University, Ithaca, N.Y.

"It's a hint there are organics not only in Titan's air and on the surface, but even in the deep interior, where liquid water exists as well."

"Organics are the building blocks of life, and if they are in contact with liquid water, there could be a chance of finding some form of life."

Linda Spilker

Linda Spilker, Cassini project scientist at JPL, speculated on the type of life that could exist.

"The astrobiological potential for Titan is two-fold," she said. "Could a unique form of methane-based life exist in Titan's liquid lakes and seas? With a global ocean of liquid water beneath its icy crust, could life exist in Titan's subsurface ocean?"

Although the official Cassini mission name for this flyby is T-99, it is, in fact, the 100th targeted Titan flyby of the mission.

Why the discrepancy? An extra flyby was inserted early in the mission, after the Titan flybys had been named.

NASA Cassini: Saturn's moon Prometheus sculpting the F Ring

Saturn's moons create art on the canvas of Saturn's rings with gravity as their tool. 

Here Prometheus is seen sculpting the F ring while Daphnis (too small to discern in this image) raises waves on the edges of the Keeler gap.

Prometheus (53 miles, or 86 kilometers across) is just above image center while Daphnis (5 miles, or 8 kilometers across), although too small to see in its location in the Keeler gap just to the right of center, can be located by the waves it creates on the edges of the gap. 

Prometheus and stars have been brightened by a factor of 2 relative to the rest of the image to enhance their visibility.

There are 20 stars visible in this image.

This view looks toward the unilluminated side of the rings from about 53 degrees below the ringplane. 

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 25, 2013.

The view was acquired at a distance of approximately 1.2 million miles (1.9 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 111 degrees. 

Image scale is 7 miles (11 kilometers) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. 

The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C.

The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL.

The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit saturn.jpl.nasa.gov . 

The Cassini imaging team homepage is at ciclops.org .

Image credit: NASA/JPL-Caltech/Space Science Institute

NASA Cassini: Mystery of the missing waves on Titan

This image shows the first flash of sunlight reflected off a lake on Saturn's moon Titan. Credit: NASA/JPL/University of Arizona/DLR

One of the most shocking discoveries of the past 10 years is how much the landscape of Saturn's moon Titan resembles Earth.

Like our own blue planet, the surface of Titan is dotted with lakes and seas; it has river channels, islands, mud, rain clouds and maybe even rainbows. The giant moon is undeniably wet.

The "water" on Titan is not, however, H2O. With a surface temperature dipping 290 degrees F below zero, Titan is far too cold for liquid water.

Instead, researchers believe the fluid that sculpts Titan is an unknown mixture of methane, ethane, and other hard-to-freeze hydrocarbons.

The idea that Titan is a wet world with its own alien waters is widely accepted by planetary scientists.

Nothing else can account for the observations: NASA's Cassini spacecraft has flown by Titan more than 90 times since 2004, pinging the Moon with radar and mapping its lakes and seas.

ESA's Huygens probe parachuted to the surface of Titan in 2005, descending through humid clouds and actually landing in moist soil.

Yet something has been bothering Alex Hayes, a planetary scientist on the Cassini radar team at Cornell University.

If Titan is really so wet, he wonders, "Where are all the waves?"

Here on Earth, bodies of water are rarely still. Breezes blowing across the surface cause waves to ripple and break; raindrops striking sea surfaces also provide some roughness.

Yet on Titan, the lakes are eerily smooth, with no discernable wave action down to the millimeter scale, according to radar data from Cassini.



"We know there is wind on Titan," says Hayes. "The moon's magnificent sand dunes [prove] it."

Add to that the low gravity of Titan-only 1/7th that of Earth-which offers so little resistance to wave motion, and you have a real puzzle.

NASA's Cassini Image: Titan's Ligeia Mare - Second largest liquid lake

Ligeia Mare represents the second largest known body of liquid on Saturn's moon, Titan, shown here in a false-colour image obtained by NASA's Cassini mission. 

Ligeia Mare contains liquid hydrocarbons, such as ethane and methane, and makes up one of the many seas and lakes located in Titan's north polar region. 

The image consists of a false-colour mosaic of synthetic aperture radar images obtained by the Cassini spacecraft between February 2006 and April 2007. 

In this image, liquids, dark to the radar, appear black and the solid surface of Titan, which appears bright to the radar, appears yellow. 

Image released May 22, 2013.

NASA Cassini Finds Hints of Geological Activity on Saturn Moon Dione

The NASA Cassini spacecraft swooped in for a close-up of the cratered, fractured surface of Saturn's moon Dione in this image taken during the spacecraft's Jan. 27, 2010, non-targeted flyby.

Image credit: NASA /JPL-Caltech /Space Science Institute.

From a distance, most of the Saturnian moon Dione resembles a bland cueball.

Thanks to close-up images of a 500-mile-long (800-kilometer-long) mountain on the moon from NASA's Cassini spacecraft, scientists have found more evidence for the idea that Dione was likely active in the past. It could still be active now.

Bonnie Buratti

"A picture is emerging that suggests Dione could be a fossil of the wondrous activity Cassini discovered spraying from Saturn's geyser moon Enceladus or perhaps a weaker copycat Enceladus," said Bonnie Buratti of NASA's Jet Propulsion Laboratory in Pasadena, Calif., who leads the Cassini science team that studies icy satellites.

"There may turn out to be many more active worlds with water out there than we previously thought."

Other bodies in the solar system thought to have a subsurface ocean - including Saturn's moons Enceladus and Titan and Jupiter's moon Europa - are among the most geologically active worlds in our solar system.

They have been intriguing targets for geologists and scientists looking for the building blocks of life elsewhere in the solar system.

The presence of a subsurface ocean at Dione would boost the astrobiological potential of this once-boring iceball.

Hints of Dione's activity have recently come from Cassini, which has been exploring the Saturn system since 2004.

This image, which is composed of data obtained by NASA's Cassini spacecraft, shows the topography of a mountain known as Janiculum Dorsa on the Saturnian moon Dione. 

Image credit: NASA/JPL-Caltech/SSI/Brown

The spacecraft's magnetometer has detected a faint particle stream coming from the moon, and images showed evidence for a possible liquid or slushy layer under its rock-hard ice crust.

Other Cassini images have also revealed ancient, inactive fractures at Dione similar to those seen at Enceladus that currently spray water ice and organic particles.

The mountain examined in the latest paper -- published in March in the journal Icarus -- is called Janiculum Dorsa and ranges in height from about 0.6 to 1.2 miles (1 to 2 kilometers).

The moon's crust appears to pucker under this mountain as much as about 0.3 mile (0.5 kilometer).

Noah Hammond

"The bending of the crust under Janiculum Dorsa suggests the icy crust was warm, and the best way to get that heat is if Dione had a subsurface ocean when the ridge formed," said Noah Hammond, the paper's lead author, who is based at Brown University, Providence, R.I.

Dione gets heated up by being stretched and squeezed as it gets closer to and farther from Saturn in its orbit.

With an icy crust that can slide around independently of the moon's core, the gravitational pulls of Saturn get exaggerated and create 10 times more heat, Hammond explained.

Other possible explanations, such as a local hotspot or a wild orbit, seemed unlikely.

Scientists are still trying to figure out why Enceladus became so active while Dione just seems to have sputtered along.

Perhaps the tidal forces were stronger on Enceladus, or maybe the larger fraction of rock in the core of Enceladus provided more radioactive heating from heavy elements.

Read more here