Category Archives: Cassini

Titan’s Lakes

The Saturn moon we know to have lakes made of liquid methane and ethane and not water. Now the formation of the lakes is being studied. Are they made from explosions? We can seriously ask these kinds of question thanks to on of the greatest planetary missions of all time — Cassini.

Image: NASA/JPL-Caltech

NASA: Using radar data from NASA’s Cassini spacecraft, recently published research presents a new scenario to explain why some methane-filled lakes on Saturn’s moon Titan are surrounded by steep rims that reach hundreds of feet high. The models suggests that explosions of warming nitrogen created basins in the moon’s crust.

Titan is the only planetary body in our solar system other than Earth known to have stable liquid on its surface. But instead of water raining down from clouds and filling lakes and seas as on Earth, on Titan it’s methane and ethane — hydrocarbons that we think of as gases but that behave as liquids in Titan’s frigid climate.

Most existing models that lay out the origin of Titan’s lakes show liquid methane dissolving the moon’s bedrock of ice and solid organic compounds, carving reservoirs that fill with the liquid. This may be the origin of a type of lake on Titan that has sharp boundaries. On Earth, bodies of water that formed similarly, by dissolving surrounding limestone, are known as karstic lakes.

The new, alternative models for some of the smaller lakes (tens of miles across) turns that theory upside down: It proposes pockets of liquid nitrogen in Titan’s crust warmed, turning into explosive gas that blew out craters, which then filled with liquid methane. The new theory explains why some of the smaller lakes near Titan’s north pole, like Winnipeg Lacus, appear in radar imaging to have very steep rims that tower above sea level — rims difficult to explain with the karstic model. 

The radar data were gathered by the Cassini Saturn Orbiter — a mission managed by NASA’s Jet Propulsion Laboratory in Pasadena, California — during its last close flyby of Titan, as the spacecraft prepared for its final plunge into Saturn’s atmosphere two years ago. An international team of scientists led by Giuseppe Mitri of Italy’s G. d’Annunzio University became convinced that the karstic model didn’t jibe with what they saw in these new images.

“The rim goes up, and the karst process works in the opposite way,” Mitri said. “We were not finding any explanation that fit with a karstic lake basin. In reality, the morphology was more consistent with an explosion crater, where the rim is formed by the ejected material from the crater interior. It’s totally a different process.”

The work, published Sept. 9 in Nature Geosciences, meshes with other Titan climate models showing the moon may be warm compared to how it was in earlier Titan “ice ages.”

Over the last half-billion or billion years on Titan, methane in its atmosphere has acted as a greenhouse gas, keeping the moon relatively warm — although still cold by Earth standards. Scientists have long believed that the moon has gone through epochs of cooling and warming, as methane is depleted by solar-driven chemistry and then resupplied.

In the colder periods, nitrogen dominated the atmosphere, raining down and cycling through the icy crust to collect in pools just below the surface, said Cassini scientist and study co-author Jonathan Lunine of Cornell University in Ithaca, New York.

“These lakes with steep edges, ramparts and raised rims would be a signpost of periods in Titan’s history when there was liquid nitrogen on the surface and in the crust,” he noted. Even localized warming would have been enough to turn the liquid nitrogen into vapor, cause it to expand quickly and blow out a crater.

“This is a completely different explanation for the steep rims around those small lakes, which has been a tremendous puzzle,” said Cassini Project Scientist Linda Spilker of JPL. “As scientists continue to mine the treasure trove of Cassini data, we’ll keep putting more and more pieces of the puzzle together. Over the next decades, we will come to understand the Saturn system better and better.”

The Cassini-Huygens mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. JPL, a division of Caltech in Pasadena, manages the mission for NASA’s Science Mission Directorate in Washington. JPL designed, developed and assembled the Cassini orbiter. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the U.S. and several European countries.

Saturn Time

We now know how long a day is on Saturn, well more accurately than we did thanks to Cassini.

The image above, thanks to NASA/JPL-Caltech/Space Science Institute comes from Mimas and Saturn of a couple years ago.

Here’s the story from NASA: Using new data from NASA’s Cassini spacecraft, researchers believe they have solved a longstanding mystery of solar system science: the length of a day on Saturn. It’s 10 hours, 33 minutes and 38 seconds.

The figure has eluded planetary scientists for decades, because the gas giant has no solid surface with landmarks to track as it rotates, and it has an unusual magnetic field that hides the planet’s rotation rate.

The answer, it turned out, was hidden in the rings.
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Titan Seen in Infrared

More excellence from Cassini. What a great value that mission was and to think there are a couple more planets out there that have only been visited during the Voyager missions.

Image: NASA/JPL-Caltech/University of Nantes/University of Arizona

From ESA (links from ESA included):    Saturn’s moon Titan is enveloped in a thick atmosphere, but through the infrared eyes of the international Cassini mission, the moon’s myriad surface features are revealed in this exquisite global mosaic.

Observing the surface of Saturn’s largest moon, Titan, in visible light is difficult due to the globe-enshrouding hazethat envelops the moon. On 14 January 2005, the mystery as to what lay beneath the thick atmosphere was revealed as ESA’s Huygens probe – carried to Titan by Cassini – made the first successful landing on a world in the outer Solar System. During the two-and-a-half hour descent under parachute, features that looked remarkably like shore lines and river systems on Earth appeared from the haze. But rather than water, with surface temperatures of around –180ºC, the fluid involved here is methane, a simple organic compound that also contributes to the moon’s obscuring atmosphere.

Thanks to Cassini, which studied Saturn and its rings and moons for thirteen years, Titan was extensively mapped and analysed. One result is this stunning sequence of images created using data acquired by Cassini’s Visual and Infrared Mapping Spectrometer (VIMS), whose infrared observations peered through Titan’s atmosphere, complementing the views obtained by Huygens during descent and on the surface. The maps combine data from the multitude of different observations made under a wide variety of illumination and viewing conditions over the course of the mission, stitched together in a seamless mosaic to provide the best representation of Titan’s surface to date.

The colours reflect variations in materials on the moon’s surface. For example, the moon’s equatorial dune fields appear a consistent brown colour, while bluish and purple hues may indicate materials enriched in water ice.

The image was first published in July 2018 – read more here about how the image was created, and enjoy a video featuring further stunning visuals here. The complete Cassini VIMS data archive of Saturn’s satellites is available here.

The Cassini mission is a cooperative project of NASA, ESA and Italy’s ASI space agency. The mission concluded in September 2017.

Cassini’s New Saturn Science

The Grand Finale Dive by the Cassini yielded new Saturn science. An appropriate end to an epic mission. This is just a start, there will be much more to come.

Click the image above (Credit: NASA/JPL-Caltech) for a larger illustration of some of the new findings.

Here’s the highlights (still waiting to read the papers):

  • Complex organic compounds embedded in water nanograins rain down from Saturn’s rings into its upper atmosphere. Scientists saw water and silicates, but they were surprised to see also methane, ammonia, carbon monoxide, nitrogen and carbon dioxide. The composition of the organics is different from that found on moon Enceladus — and also different from that on moon Titan, meaning there are at least three distinct reservoirs of organic molecules in the Saturn system.
  • For the first time, Cassini saw up close how rings interact with the planet and observed inner-ring particles and gases falling directly into the atmosphere. Some particles take on electric charges and spiral along magnetic-field lines, falling into Saturn at higher latitudes — a phenomenon known as “ring rain.” But scientists were surprised to see that others are dragged quickly into Saturn at the equator. And it’s all falling out of the rings faster than scientists thought — as much as 22,000 pounds (10,000 kilograms) of material per second.
  • Scientists were surprised to see what the material looks like in the gap between the rings and Saturn’s atmosphere. They knew that the particles throughout the rings ranged from large to small. But the sampling in the gap showed mostly tiny, nanometer-sized particles, like smoke, suggesting that some yet-unknown process is grinding up particles.
  • Saturn and its rings are even more interconnected than scientists thought. Cassini revealed a previously unknown electric-current system that connects the rings to the top of Saturn’s atmosphere.
  • Scientists discovered a new radiation belt around Saturn, close to the planet and composed of energetic particles. They found that while the belt actually intersects with the innermost ring, the ring is so tenuous that it doesn’t block the belt from forming.
  • Unlike every other planet with a magnetic field in our Solar System, Saturn’s magnetic field is almost completely aligned with its spin axis. The new data shows a magnetic-field tilt of less than 0.0095 degrees. (Earth’s magnetic field is tilted 11 degrees from its spin axis.) According to everything scientists know about how planetary magnetic fields are generated, Saturn should not have one. It’s a mystery that physicists will be working to solve.
  • Cassini flew above Saturn’s magnetic poles, directly sampling regions where radio emissions are generated. The findings more than doubled the number of direct measurements of radio sources from the planet, one of the few non-terrestrial locations where scientists have been able to study a radio-generation mechanism that is believed to operate throughout the universe.

Titan and Tethys

Another gem from the epic Cassini mission, gone but never to be forgotten. Thanks to the Cassini Imaging Team for their continued work.

NASA’s caption: Saturn’s moon Tethys disappears behind Titan as observed by Cassini on Nov. 26, 2009. Tethys is about 660 miles (1,070 kilometers) across. At about 3,200 miles (5,100 kilometers) wide, Titan is larger than the planet Mercury, and was much closer to Cassini than Tethys at the time of this image. Titan is planet-like in another way: it’s wrapped in a thick atmosphere, which can be clearly seen here where it overlaps icy Tethys in the distance beyond.

Cassini captured this natural-color image at a distance of approximately 620,000 miles (1 million kilometers) from Titan.

The Cassini spacecraft ended its mission on Sept. 15, 2017.

From The Travels of Cassini

Here’s sort of a throwback, one of Cassini’s great images newly processed.  The release title is “Translucent Arcs” and that is very descriptive. To me the image show the ring structure in terms of thickness density. Combined with the Sun-Saturn-Cassini angular configuration the rings seem to provide almost a “screen-door” effect to the scene.

This view is much different than what was published in 1622 by Fortunio Liceti in De Novis Astris et Cometis and much different than the sight from a backyard telescope.

Saturn is nothing short of breathtaking, if you’ve never seen it put it on your “bucket list” and look for suitable viewing opportunities — you might be surprised, local colleges and universities sometimes have public viewing and don’t overlook local astronomy clubs.

Here’s the caption from NASA:  Saturn’s rings are perhaps the most recognized feature of any world in our solar system. Cassini spent more than a decade examining them more closely than any spacecraft before it.

The rings are made mostly of particles of water ice that range in size from smaller than a grain of sand to as large as mountains. The ring system extends up to 175,000 miles (282,000 kilometers) from the planet, but for all their immense width, the rings are razor-thin, about 30 feet (10 meters) thick in most places.

From the right angle you can see straight through the rings, as in this natural-color view that looks from south to north. Cassini obtained the images that comprise this mosaic on April 25, 2007, at a distance of approximately 450,000 miles (725,000 kilometers) from Saturn.

The Cassini spacecraft ended its mission on Sept. 15, 2017.

Image: NASA/JPL-Caltech/Space Science Institute

Titan Seen in Infrared

Nice clean infrared views of the Saturn moon Titan. We never get to see these views of course, our view is normally of the none in the center.

Very nice work indeed.

NASA: These six infrared images of Saturn’s moon Titan represent some of the clearest, most seamless-looking global views of the icy moon’s surface produced so far. The views were created using 13 years of data acquired by the Visual and Infrared Mapping Spectrometer (VIMS) instrument on board NASA’s Cassini spacecraft. The images are the result of a focused effort to smoothly combine data from the multitude of different observations VIMS made under a wide variety of lighting and viewing conditions over the course of Cassini’s mission.

Previous VIMS maps of Titan (for example, PIA02145) display great variation in imaging resolution and lighting conditions, resulting in obvious seams between different areas of the surface. With the seams now gone, this new collection of images is by far the best representation of how the globe of Titan might appear to the casual observer if it weren’t for the moon’s hazy atmosphere, and it likely will not be superseded for some time to come.

Observing the surface of Titan in the visible region of the spectrum is difficult, due to the globe enshrouding haze that envelops the moon. This is primarily because small particles called aerosols in Titan’s upper atmosphere strongly scatter visible light. But Titan’s surface can be more readily imaged in a few infrared “windows” — infrared wavelengths where scattering and absorption is much weaker. This is where the VIMS instrument excelled, parting the haze to obtain clear images of Titan’s surface. (For comparison, Figure 1 shows Titan as it appears in visible light, as does PIA11603.)

Making mosaics of VIMS images of Titan has always been a challenge because the data were obtained over many different flybys with different observing geometries and atmospheric conditions. One result is that very prominent seams appear in the mosaics that are quite difficult for imaging scientists to remove. But, through laborious and detailed analyses of the data, along with time consuming hand processing of the mosaics, the seams have been mostly removed. This is an update to the work previously discussed in PIA20022.

Any full color image is comprised of three color channels: red, green and blue. Each of the three color channels combined to create these views was produced using a ratio between the brightness of Titan’s surface at two different wavelengths (1.59/1.27 microns [red], 2.03/1.27 microns [green] and 1.27/1.08 microns [blue]). This technique (called a “band-ratio” technique) reduces the prominence of seams, as well as emphasizing subtle spectral variations in the materials on Titan’s surface. For example, the moon’s equatorial dune fields appear a consistent brown color here. There are also bluish and purplish areas that may have different compositions from the other bright areas, and may be enriched in water ice.

For a map of Titan with latitudes, longitudes and labeled surface features, see PIA20713.

It is quite clear from this unique set of images that Titan has a complex surface, sporting myriad geologic features and compositional units. The VIMS instrument has paved the way for future infrared instruments that could image Titan at much higher resolution, revealing features that were not detectable by any of Cassini’s instruments.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for NASA’s Science Mission Directorate, Washington. The VIMS team is based at the University of Arizona in Tucson.

Crossed Rings?

How do you get a ring pattern like this around Saturn? It does not seem to be possible but after reading the caption (below), I get it.

ESA –   At first glance, Saturn’s rings appear to be intersecting themselves in an impossible way. In actuality, this view from the international Cassini spacecraft shows the rings in front of the planet, upon which the shadow of the rings is cast. And because rings like the A ring and Cassini Division, which appear in the foreground, are not entirely opaque, the outline of Saturn and those ring shadows can be seen directly through the rings themselves.

Saturn’s rings have complex and detailed structures, many of which can be seen here. In some cases, the reasons for the gaps and ringlets are known: for example, 28 km wide moon Pan – seen here as a bright speck near the image centre – keeps open the Encke gap. But in other cases, the origins and natures of gaps and ringlets are less well understood.

This view looks toward the sunlit side of the rings from about 14º above the ring plane. The image was taken in visible light with Cassini’s narrow-angle camera on 11 February 2016, and highlighted in a release published 25 April 2016. The view was acquired at a distance of 1.9 million km from Pan and at a Sun–Pan–spacecraft angle of 85º. Image scale is 10 km/pixel.

The Cassini mission is a cooperative project of NASA, ESA and Italy’s ASI space agency. The mission concluded in September 2017.

Image: NASA/JPL-Caltech/Space Science Institute

Another Look at Enceladus

We have a newly released image of the Saturn moon Enceladus. Cassini took thousands of images so there will be more as time goes by.

Thanks to NASA, JPL-Caltech and the Space Science Institute for the iamge.

Here’s the original caption:
Saturn’s rings cast shadows on the planet’s cloud tops, providing a perfect backdrop for the brilliant sphere of Saturn’s moon Enceladus. The tiny world’s bright white surface results in part from a snow of material originating from the towering plume of icy particles at Enceladus’ south pole.

This image looks toward the leading side of Enceladus (504 kilometers, or 313 miles across). North is up.

The image was taken in visible light with the Cassini spacecraft’s narrow-angle camera on June 28, 2007. The view was acquired at a distance of approximately 281,000 kilometers (175,000 miles) from Enceladus. Image scale is about 2 kilometers (1 mile) per pixel.

The Cassini spacecraft ended its mission on Sept. 15, 2017

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. 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, Colorado.