Category Archives: Cassini

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.

Saturn’s Moon Dione

A beautiful look at the Saturn moon Dione and a great look at a rayed crater.  Easy to see why the rays are so bright being made of what we would think of as “super hard water ice”.

I believe this crater is Creusa. The rays are as you would expect material ejected out after an impact, in this case water ice (we think).  These rayed craters on Dione may be less than about 50 M/yr’s -old (1).  Yes, sounds like a long time but really not so much when you think about things on a solar system-evolutionary time scale.  Cassini has shown us that at least parts of the Saturn system are quite active more so than many people first belived.

NASA – Cassini captured this striking view of Saturn’s moon Dione on July 23, 2012. Dione is about 698 miles (1,123 kilometers) across. Its density suggests that about a third of the moon is made up of a dense core (probably silicate rock) with the remainder of its material being water ice. At Dione’s average temperature of -304 degrees Fahrenheit (-186 degrees Celsius), ice is so hard it behaves like rock.

The image was taken with Cassini’s narrow-angle camera at a distance of approximately 260,000 miles (418,000 kilometers) from Dione, through a polarized filter and a spectral filter sensitive to green light.

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

Titan’s Haze

A newly released Cassini image looking through Titan’s atmosphere.

Original caption: In this view, individual layers of haze can be distinguished in the upper atmosphere of Titan, Saturn’s largest moon. Titan’s atmosphere features a rich and complex chemistry originating from methane and nitrogen and evolving into complex molecules, eventually forming the smog that surrounds the moon.

This natural color image was taken in visible light with the Cassini spacecraft wide-angle camera on March 31, 2005, at a distance of approximately 20,556 miles (33,083 kilometers) from Titan. The view looks toward the north polar region on the moon’s night side. Part of Titan’s sunlit crescent is visible at right.

Credit: NASA/JPL-Caltech/Space Science Institute

Cassini’s Veil of Ice

Almost like abstract art, at least to me. The little moon Pan stands out nicely in this image too.

Original caption: Saturn’s rings, made of countless icy particles, form a translucent veil in this view from NASA’s Cassini spacecraft.

Saturn’s tiny moon Pan, about 17 miles (28 kilometers) across, orbits within the Encke Gap in the A ring. Beyond, we can see the arc of Saturn itself, its cloud tops streaked with dark shadows cast by the rings.

This image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 12, 2016, at a distance of approximately 746,000 miles (1.2 million kilometers) from Pan.

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 the California Institute of Technology 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.

Image: NASA/JPL-Caltech/Space Science Institute

A Distant Star

In a list of epic space missions to ever fly Cassini would be in good company near the top. In particular I like the star to the right of Enceladus. I am a little surprised to even see it. Generally exposure times would preclude any background stars at all, but the image was probably enhanced only enough to enhance the plumes of Enceladus the star was bright enough to show up. The question is what star was it? I like these types of mysteries, I may never solve it, however it won’t be for a lack of trying.

Original caption: Saturn’s moon Enceladus drifts before the rings, which glow brightly in the sunlight. Beneath its icy exterior shell, Enceladus hides a global ocean of liquid water. Just visible at the moon’s south pole (at bottom here) is the plume of water ice particles and other material that constantly spews from that ocean via fractures in the ice. The bright speck to the right of Enceladus is a distant star.

This image was taken in visible light with the Cassini spacecraft narrow-angle camera on Nov. 6, 2011, at a distance of approximately 90,000 miles (145,000 kilometers) from Enceladus.

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

Image: NASA/JPL-Caltech/Space Science Institute

Two Views of Saturn from Cassini

Two views of Cassini in what NASA titled “Alpha and Omega”.

NASA — These two images illustrate just how far Cassini traveled to get to Saturn. On the left is one of the earliest images Cassini took of the ringed planet, captured during the long voyage from the inner solar system. On the right is one of Cassini’s final images of Saturn, showing the site where the spacecraft would enter the atmosphere on the following day.

In the left image, taken in 2001, about six months after the spacecraft passed Jupiter for a gravity assist flyby, the best view of Saturn using the spacecraft’s high-resolution (narrow-angle) camera was on the order of what could be seen using the Earth-orbiting Hubble Space Telescope. At the end of the mission (at right), from close to Saturn, even the lower resolution (wide-angle) camera could capture just a tiny part of the planet.

The left image looks toward Saturn from 20 degrees below the ring plane and was taken on July 13, 2001 in wavelengths of infrared light centered at 727 nanometers using the Cassini spacecraft narrow-angle camera. The view at right is centered on a point 6 degrees north of the equator and was taken in visible light using the wide-angle camera on Sept. 14, 2017.

The view on the left was acquired at a distance of approximately 317 million miles (510 million kilometers) from Saturn. Image scale is about 1,900 miles (3,100 kilometers) per pixel. The view at right was acquired at a distance of approximately 360,000 miles (579,000 kilometers) from Saturn. Image scale is 22 miles (35 kilometers) 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.

For more information about the Cassini-Huygens mission visit https://saturn.jpl.nasa.gov and https://www.nasa.gov/cassini. The Cassini imaging team homepage is at https://ciclops.org.

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