A dense network of small rivers or swampy areas appears to connect some of the seas on Saturn's moon Titan, as seen in this comparison of data of the same area from two instruments on NASA's Cassini spacecraft. Images from the radar instrument are on the left and images from the visual and infrared mapping spectrometer (VIMS) are on the right. Credit: NASA/JPL-Caltech/University of Arizona
Are there waves on Titan’s lakes and seas? Cassini scientists say that the best chance of answering this question is with the May 23 flyby of Titan, when the Cassini spacecraft will be just 970 km (603 miles) over Titan’s biggest ‘lake,’ the northern sea named Ligeia Mare.
Lakes, seas, and rivers were discovered on Titan by Cassini in 2005, and since then, scientists and space enthusiasts have been intrigued about the possibility of what could be found in these bodies of hydrocarbon liquid. Future potential missions such as paddleboats have even been proposed.
Lakes, seas and rivers of liquid hydrocarbons cover much of the Titan’s northern hemisphere. Additionally, these hydrocarbons may rain down on the surface. The questions is, are these frigid liquid bodies capable of producing wave action, or would they be a rigid type of frigid? With surface temperature at -178 degrees Celsius (-289 degrees Fahrenheit), Titan’s environment is too cold for life as we may know it, but its environment, rich in the building blocks of life, is of great interest to astrobiologists.
Additionally, new models of Titan’s atmosphere prediction that as the seasons change in Titan’s northern hemisphere, waves could ripple across the moon’s hydrocarbon seas, and possibly even hurricanes could begin to swirl over these areas, too. The model predicting waves tries to explain data from the moon obtained so far by Cassini.
“If you think being a weather forecaster on Earth is difficult, it can be even more challenging at Titan,” said Scott Edgington, Cassini’s deputy project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We know there are weather processes similar to Earth’s at work on this strange world, but differences arise due to the presence of unfamiliar liquids like methane. We can’t wait for Cassini to tell us whether our forecasts are right as it continues its tour through Titan spring into the start of northern summer.”
For the flyby on May 23, the altimetry data that will be collected by the radar instrument could show whether the surface of that sea is thick like molasses or as thin as liquid water on Earth.
In addition, radar will look for changes in small northern lakes last observed in previous flybys, the T-16 and T-19 flybys.
This flyby is a carefully planned sibling of the following flyby; the combination of the data from T-91 and T-92 will provide stereo views of the same geography, which will tell us about the depth of the lake walls.
Saturn seen by the Cassini spacecraft in late 2012. If you look carefully, you can spot the shadow of Mimas in the image. Credit: NASA/JPL-Caltech/Space Science Institute
The mystery of Saturn’s bright, youthful appearance is a step closer to resolution. And it actually has to do with gas.
Layers of gas within the ringed giant trap heat emanating from the center, preventing the planet from cooling off as it was expected to do as it aged, according to a model developed by a European science team.
“Scientists have been wondering for years if Saturn was using an additional source of energy to look so bright, but instead our calculations show that Saturn appears young because it can’t cool down,” stated Gilles Chabrier, a physics and astronomy professor at the University of Exeter and part of the research team.
“Instead of heat being transported throughout the planet by large scale (convective) motions, as previously thought, it must be partly transferred by diffusion across different layers of gas inside Saturn. These separate layers effectively insulate the planet and prevent heat from radiating out efficiently. This keeps Saturn warm and bright.”
A raw image of Saturn taken May 4, 2013, as seen through the eyes of the Cassini probe. Credit: NASA/JPL/Space Science Institute
You can also see layered convection on Earth, pointed out scientists. In this instances, salty water stays underneath colder and less salty liquid. The salt trap stops water from moving between the layers, also stopping heat from transferring.
The findings were published in Nature Geoscience and included participation from the University of Exeter in England and the Ecole Normale Supérieure de Lyon in France.
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Plumes from Enceladus' geysers are illuminated by reflected light from Saturn. Credit: NASA/JPL-Caltech, Space Science Institute.
According to planetary scientist and Cassini imaging team leader Carolyn Porco, about 98 geyser jets of all sizes near Enceladus’s south pole are spraying water vapor, icy particles, and organic compounds out into space. The spray from those geysers are evident in this new image from Cassini, showing a big, beautiful plume, illuminated by light reflected off of Saturn. Look closely to see that the plume is as large as the moon itself.
Cassini first discovered the jets of water ice particles in 2005, and since then scientists have been trying to learn more about how they behave, what they are made of and – most importantly – where they are coming from. The working theory is that Enceladus has a liquid subsurface ocean, and pressure from the rock and ice layers above combined with heat from within force the water up through surface cracks near the moon’s south pole. When this water reaches the surface it instantly freezes, sending plumes of ice particles hundreds of miles into space.
A patchwork network of frozen ridges and troughs cover the face of Enceladus. Credit: NASA/ESA, image processed by amateur astronomer Gordan Ugarkovic.
Cassini has flown through the spray several times now, and instruments have detected that aside from water and organic material, there is salt in the icy particles. The salinity is the same as that of Earth’s oceans.
Enceladus is just 504 kilometers (313 miles) across, but it potentially could be one of the best spots in the solar system for finding life.
The top image was taken on January 18, 2013. This view looks toward the Saturn-facing side of Enceladus, and was taken when Cassini was approximately 483,000 miles (777,000 kilometers) from Enceladus. Image scale is 3 miles (5 kilometers) per pixel.
The second, face-on, color view of Enceladus was taken by the Cassini spacecraft on January 31 2011, from a distance of 81,000 km, and processed by amateur astronomer Gordan Ugarkovic.
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Daphnis' gravity disturbs the edges of the Keeler Gap as it travels along
Captured on January 15, this narrow-angle Cassini image shows an outer portion of Saturn’s A ring on the left and the ropy F ring crossing on the right. The thin black line near the A ring’s bright edge is the Keeler Gap, a 22-mile-wide space cleared by the passage of Daphnis, a shepherd moon barely 5 miles (about 7.5 km) across. As it travels around Saturn within the gap its gravity perturbs the fine icy particles within the rings, sending up rippling waves both before and behind it — visible here near the upper center.
From Cassini’s distance of 870,000 miles (1.4 million km) Daphnis itself is just barely visible as a single pixel within the Gap — can you see it? If not, click below…
There it is:
Highlighting Daphnis inside the Keeler Gap
While lacking the murky mystery of Titan’s atmosphere, Enceladus’ dramatic jets and the tortured and cratered surfaces found on Dione, Rhea, Mimas and many of Saturn’s larger icy moons, little Daphnis has always fascinated me because of the scalloped waves it kicks up within Saturn’s rings. Eventually these waves settle back down, but at their highest they can extend a mile or two above and below the ring plane!
Daphnis’ wake casts peaked shadows on the rings
This effect was most pronounced during Saturn’s spring equinox in August 2009 when sunlight was striking the rings edge-on, creating strong shadows from any areas of relief.
Imagine the impressive view you’d have if you were nearby, positioned just above the rings as Daphnis approached and hurtled past, the rings rising up in mile-high peaks from the moon’s gravity before smoothing out again. Incredible!
Daphnis seen by Cassini in June 2010 (NASA/JPL/SSI)
And I’m not the only one to imagine such a scene either — apparently artist Erik Svensson is also intrigued by Daphnis, enough to have been inspired to create the image below. How very cool!
Like its larger shepherd moon sister Prometheus, Daphnis may be little but still has a big effect on the icy stuff that makes up Saturn’s iconic rings.
And for lots more views of Daphnis click here (but watch out, it may just become your favorite moon too!)
Image credits: NASA/JPL-Caltech/Space Science Institute.
Narrow-angle camera image of Titan from Cassini (NASA/JPL-Caltech/Space Science Institute)
In this image acquired on January 5, Cassini’s near-infrared vision pierced Titan’s opaque clouds to get a glimpse of the dark dune fields across a region called Senkyo.
The vast sea of dunes is composed of solid hydrocarbon particles that have precipitated out of Titan’s atmosphere. Also visible over Titan’s southern pole are the rising clouds of the recently-formed polar vortex.
For a closer look at Titan’s dunes (and to find out what the name Senkyo means) keep reading…
In the image above north on Titan is up and rotated 18 degrees to the right. It was taken using a spectral filter sensitive to wavelengths of near-infrared light centered at 938 nanometers.
The view was obtained at a distance of approximately 750,000 miles (1.2 million kilometers) from Titan.
Titan’s hydrocarbon dunes are found across the moon in a wide swath within 30 degrees of the equator and are each about a kilometer wide and tens to hundreds of kilometers long… and in some cases stand over 100 meters tall. (Source: Astronomy Now.)
Radar image of Titan’s dunes acquired on Jan. 13, 2007. This view is 160 kilometers (100 miles) high by 150 kilometers (90 miles) wide. (NASA/JPL)
Observations of the dunes with Cassini and ESA’s Huygens probe during its descent onto Titan’s surface have shown that the moon experiences seasonally-shifting equatorial winds during equinoxes, similar to what occurs over the Indian Ocean between monsoon seasons.
The name Senkyo refers to the Japanese realm of serenity and freedom from wordly cares and death… in line with the IAU convention of naming albedo features on Titan after mythological enchanted places.
Click here for an earlier view of Senkyo, and follow the Cassini mission here.
Color-composite of Titan made from raw Cassini images acquired on April 13, 2013 (added 4/17) NASA/JPL/SSI. Composite by J. Major.
The Cassini spacecraft observes three of Saturn's moons set against the darkened night side of the planet. Credit: NASA/JPL/Space Science Institute
Anyone looking for miscellanies from the early days of the Solar System can likely find them all in one place: the Saturn system. A new analysis of data from the Cassini spacecraft suggests that Saturn’s moons and rings are “antiquities” from around the time of our Solar System’s very beginnings.
“Studying the Saturnian system helps us understand the chemical and physical evolution of our entire solar system,” said Cassini scientist Gianrico Filacchione, from Italy’s National Institute for Astrophysics. “We know now that understanding this evolution requires not just studying a single moon or ring, but piecing together the relationships intertwining these bodies.”
The rings, moons, moonlets, and other debris date back more than 4 billion years. They are from around the time that the planetary bodies in our neighborhood began to form out of the protoplanetary nebula, the cloud of material still orbiting the sun after its ignition as a star.
Data from Cassini’s visual and infrared mapping spectrometer (VIMS) have revealed how water ice and also colors — which are the signs of non-water and organic materials –are distributed throughout the Saturnian system. The spectrometer’s data in the visible part of the light spectrum show that coloring on the rings and moons generally is only skin-deep.
Using its infrared range, VIMS also detected abundant water ice – too much to have been deposited by comets or other recent means. So the authors deduce that the water ices must have formed around the time of the birth of the solar system, because Saturn orbits the sun beyond the so-called “snow line.” Out beyond the snow line, in the outer solar system where Saturn resides, the environment is conducive to preserving water ice, like a deep freezer. Inside the solar system’s “snow line,” the environment is much closer to the sun’s warm glow, and ices and other volatiles dissipate more easily.
The effects of the small moon Prometheus loom large on two of Saturn’s rings in this image taken a short time before Saturn’s August 2009 equinox. Credit: NASA
The colored patina on the ring particles and moons roughly corresponds to their location in the Saturn system. For Saturn’s inner ring particles and moons, water-ice spray from the geyser moon Enceladus has a whitewashing effect.
Farther out, the scientists found that the surfaces of Saturn’s moons generally were redder the farther they orbited from Saturn. Phoebe, one of Saturn’s outer moons and an object thought to originate in the far-off Kuiper Belt, seems to be shedding reddish dust that eventually rouges the surface of nearby moons, such as Hyperion and Iapetus.
A rain of meteoroids from outside the system appears to have turned some parts of the main ring system – notably the part of the main rings known as the B ring — a subtle reddish hue. Scientists think the reddish color could be oxidized iron — rust — or polycyclic aromatic hydrocarbons, which could be progenitors of more complex organic molecules.
One of the big surprises from this research was the similar reddish coloring of the potato-shaped moon Prometheus and nearby ring particles. Other moons in the area were more whitish.
“The similar reddish tint suggests that Prometheus is constructed from material in Saturn’s rings,” said co-author Bonnie Buratti, a VIMS team member based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Scientists had been wondering whether ring particles could have stuck together to form moons — since the dominant theory was that the rings basically came from satellites being broken up. The coloring gives us some solid proof that it can work the other way around, too.”
“Observing the rings and moons with Cassini gives us an amazing bird’s-eye view of the intricate processes at work in the Saturn system, and perhaps in the evolution of planetary systems as well,” said Linda Spilker, Cassini project scientist, based at JPL. “What an object looks like and how it evolves depends a lot on location, location, location.”
Filacchione’s paper has been published in the Astrophysical Journal.
Saturn's moon Enceladus sprays its salty sea out into space. Those plumes are rich in phosphates. (NASA/JPL/SSI/J. Major)
Thanks to the Cassini mission we’ve known about the jets of icy brine spraying from the south pole of Saturn’s moon Enceladus for about 8 years now, but this week it was revealed at the 44th Lunar and Planetary Science Conference outside Houston, Texas that Enceladus’ jets very likely reach all the way down to the sea — a salty subsurface sea of liquid water that’s thought to lie beneath nearly 10 kilometers of ice.
Enceladus’ jets were first observed by the Cassini spacecraft in 2005. The jets constantly spray fine particles of ice into space which enter orbit around Saturn, creating the hazy, diffuse E ring in which Enceladus resides.
Emanating from deep fissures nicknamed “tiger stripes” that gouge the 512-km (318-mile) -wide moon’s south pole the icy jets — and the stripes — have been repeatedly investigated by Cassini, which has discovered that not only do the ice particles contain salts and organic compounds but also that the stripes are surprisingly warm, measuring at 180 Kelvin (minus 135 degrees Fahrenheit) — over twice as warm as most other regions of the moon.
Where the jets are getting their supply of liquid water has been a question scientists have puzzled over for years. Is friction caused by tidal stresses heating the insides of the stripes, which melts the ice and shoots it upwards? Or do the fissures actually extend all the way down through Enceladus’ crust to a subsurface ocean of liquid water, and through tidal pressure pull vapor and ice up to the surface?
“Baghdad Sulcus,” one of many tiger stripe fissures on Enceladus (NASA/JPL/SSI)
Researchers are now confident that the latter is the case.
In a presentation at the Lunar and Planetary Science Conference titled “How the Jets, Heat and Tidal Stresses across the South Polar Terrain of Enceladus Are Related” (see the PDF here) Cassini scientists note that the amount of heating due to tidal stress seen along Enceladus’ tiger stripes isn’t nearly enough to cause the full spectrum of heating observed, and the “hot spots” that have been seen don’t correlate with the type of heating caused by shear friction.
Instead, the researchers believe that heat energy is being carried upwards along with the pressurized water vapor from the subsurface sea, warming the areas around individual vents as well as serving to keep their channels open.
With 98 individual jets observed so far on Enceladus’ south polar terrain and surface heating corresponding to each one, this scenario, for lack of a better term… seems legit.
What this means is that not only does a moon of Saturn have a considerable subsurface ocean of liquid water with a heat source and Earthlike salinity (and also a bit of fizz) but also that it’s spraying that ocean, that potentially habitable environment, out into local space where it can be studied relatively easily — making Enceladus a very intriguing target for future exploration.
“To touch the jets of Enceladus is to touch the most accessible salty, organic-rich, extraterrestrial body of water and, hence, habitable zone, in our solar system.”
– Cassini imaging team leader Carolyn Porco et al.
Enceladus is actively spraying its habitable zone out into space (NASA/JPL/SSI)
Research notes via C. Porco, D. DiNino, F. Nimmo, CICLOPS, Space Science Institute at Boulder, CO, and Earth and Planetary Sciences at UC Santa Cruz, CA.
Top image: color-composite of Enceladus made from raw Cassini images acquired in 2010. The moon is lit by reflected light from Saturn while the jets are backlit by the Sun.
The dark hot spot in this false-color image from NASA's Cassini spacecraft is a window deep into Jupiter's atmosphere. All around it are layers of higher clouds, with colors indicating which layer of the atmosphere the clouds are in. Image credit: NASA/JPL-Caltech/SSI/GSFC
In the swirling canopy of Jupiter’s atmosphere, cloudless patches are so exceptional that the big ones get the special name “hot spots.” Exactly how these clearings form and why they’re only found near the planet’s equator have long been mysteries. Now, using images from NASA’s Cassini spacecraft, scientists have found new evidence that hot spots in Jupiter’s atmosphere are created by a Rossby wave, a pattern also seen in Earth’s atmosphere and oceans. The team found the wave responsible for the hot spots glides up and down through layers of the atmosphere like a carousel horse on a merry-go-round.
“This is the first time anybody has closely tracked the shape of multiple hot spots over a period of time, which is the best way to appreciate the dynamic nature of these features,” said the study’s lead author, David Choi, a NASA Postdoctoral Fellow working at NASA’s Goddard Space Flight Center in Greenbelt, Md. The paper is published online in the April issue of the journal Icarus.
Choi and his colleagues made time-lapse movies from hundreds of observations taken by Cassini during its flyby of Jupiter in late 2000, when the spacecraft made its closest approach to the planet. The movies zoom in on a line of hot spots between one of Jupiter’s dark belts and bright white zones, roughly 7 degrees north of the equator. Covering about two months (in Earth time), the study examines the daily and weekly changes in the sizes and shapes of the hot spots, each of which covers more area than North America, on average.
Much of what scientists know about hot spots came from NASA’s Galileo mission, which released an atmospheric probe that descended into a hot spot in 1995. This was the first, and so far only, in-situ investigation of Jupiter’s atmosphere.
“Galileo’s probe data and a handful of orbiter images hinted at the complex winds swirling around and through these hot spots, and raised questions about whether they fundamentally were waves, cyclones or something in between,” said Ashwin Vasavada, a paper co-author who is based at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and who was a member of the Cassini imaging team during the Jupiter flyby. “Cassini’s fantastic movies now show the entire life cycle and evolution of hot spots in great detail.”
Because hot spots are breaks in the clouds, they provide windows into a normally unseen layer of Jupiter’s atmosphere, possibly all the way down to the level where water clouds can form. In pictures, hot spots appear shadowy, but because the deeper layers are warmer, hot spots are very bright at the infrared wavelengths where heat is sensed; in fact, this is how they got their name.
One hypothesis is that hot spots occur when big drafts of air sink in the atmosphere and get heated or dried out in the process. But the surprising regularity of hot spots has led some researchers to suspect there is an atmospheric wave involved. Typically, eight to 10 hot spots line up, roughly evenly spaced, with dense white plumes of cloud in between. This pattern could be explained by a wave that pushes cold air down, breaking up any clouds, and then carries warm air up, causing the heavy cloud cover seen in the plumes. Computer modeling has strengthened this line of reasoning.
In this series of images from NASA’s Cassini spacecraft, a dark, rectangular hot spot (top) interacts with a line of vortices that approaches from on the upper-right side (second panel). Image credit: NASA/JPL-Caltech/SSI/GSFC
From the Cassini movies, the researchers mapped the winds in and around each hot spot and plume, and examined interactions with vortices that pass by, in addition to wind gyres, or spiraling vortices, that merge with the hot spots. To separate these motions from the jet stream in which the hot spots reside, the scientists also tracked the movements of small “scooter” clouds, similar to cirrus clouds on Earth. This provided what may be the first direct measurement of the true wind speed of the jet stream, which was clocked at about 300 to 450 mph (500 to 720 kilometers per hour) — much faster than anyone previously thought. The hot spots amble at the more leisurely pace of about 225 mph (362 kilometers per hour).
By teasing out these individual movements, the researchers saw that the motions of the hot spots fit the pattern of a Rossby wave in the atmosphere. On Earth, Rossby waves play a major role in weather. For example, when a blast of frigid Arctic air suddenly dips down and freezes Florida’s crops, a Rossby wave is interacting with the polar jet stream and sending it off its typical course. The wave travels around our planet but periodically wanders north and south as it goes.
The wave responsible for the hot spots also circles the planet west to east, but instead of wandering north and south, it glides up and down in the atmosphere. The researchers estimate this wave may rise and fall 15 to 30 miles (24 to 50 kilometers) in altitude.
The new findings should help researchers understand how well the observations returned by the Galileo probe extend to the rest of Jupiter’s atmosphere. “And that is another step in answering more of the questions that still surround hot spots on Jupiter,” said Choi.
