Category Archives: Cassini

Ithaca Chasma

Lots of Cassini related items lately, mostly our last looks at the Saturnian system. Cassini completed the first gap encounter. This image came a few days ago well in advance of the flyby, it is the moon Tethys, and the Ithaca Chasma.

From NASA:

The low angle of the sun over Tethys’ massive canyon, Ithaca Chasma (near the terminator, at right), highlights the contours of this enormous rift.

Ithaca Chasma is up to 60 miles (100 kilometers) wide, and runs nearly three-fourths of the way around icy Tethys (660 miles or 1,062 kilometers across). The canyon has a maximum depth of nearly 2.4 miles (4 kilometers) deep.

The giant crater Odysseus — usually one of Tethys’ most recognizable features– is barely seen in profile along the limb, at upper left.

This view looks toward the Saturn-facing hemisphere of Tethys. North on Tethys is up and rotated 5 degrees to the left. The image was taken in green light with the Cassini spacecraft narrow-angle camera on Jan. 30, 2017.

The view was obtained at a distance of approximately 221,000 miles (356,000 kilometers) from Tethys. Image scale is 1 mile (2 kilometers) per pixel.

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

Through The Gap

Here is one of the images returned from Cassini, it is a raw image with no processing.

This is some welcome news!

NASA – NASA’s Cassini spacecraft is back in contact with Earth after its successful first-ever dive through the narrow gap between the planet Saturn and its rings on April 26, 2017. The spacecraft is in the process of beaming back science and engineering data collected during its passage, via NASA’s Deep Space Network Goldstone Complex in California’s Mojave Desert. The DSN acquired Cassini’s signal at 11:56 p.m. PDT on April 26, 2017 (2:56 a.m. EDT on April 27) and data began flowing at 12:01 a.m. PDT (3:01 a.m. EDT) on April 27.

“In the grandest tradition of exploration, NASA’s Cassini spacecraft has once again blazed a trail, showing us new wonders and demonstrating where our curiosity can take us if we dare,” said Jim Green, director of the Planetary Science Division at NASA Headquarters in Washington.

As it dove through the gap, Cassini came within about 1,900 miles (3,000 kilometers) of Saturn’s cloud tops (where the air pressure is 1 bar — comparable to the atmospheric pressure of Earth at sea level) and within about 200 miles (300 kilometers) of the innermost visible edge of the rings.

While mission managers were confident Cassini would pass through the gap successfully, they took extra precautions with this first dive, as the region had never been explored.

“No spacecraft has ever been this close to Saturn before. We could only rely on predictions, based on our experience with Saturn’s other rings, of what we thought this gap between the rings and Saturn would be like,” said Cassini Project Manager Earl Maize of NASA’s Jet Propulsion Laboratory in Pasadena, California. “I am delighted to report that Cassini shot through the gap just as we planned and has come out the other side in excellent shape.”

The gap between the rings and the top of Saturn’s atmosphere is about 1,500 miles (2,000 kilometers) wide. The best models for the region suggested that if there were ring particles in the area where Cassini crossed the ring plane, they would be tiny, on the scale of smoke particles. The spacecraft zipped through this region at speeds of about 77,000 mph (124,000 kph) relative to the planet, so small particles hitting a sensitive area could potentially have disabled the spacecraft.

As a protective measure, the spacecraft used its large, dish-shaped high-gain antenna (13 feet or 4 meters across) as a shield, orienting it in the direction of oncoming ring particles. This meant that the spacecraft was out of contact with Earth during the ring-plane crossing, which took place at 2 a.m. PDT (5 a.m. EDT) on April 26. Cassini was programmed to collect science data while close to the planet and turn toward Earth to make contact about 20 hours after the crossing.

Cassini’s next dive through the gap is scheduled for May 2.

Image and caption: NASA/JPL-Caltech/Space Science Institute

Cassini’s First Dive

Cassini is making its first dive inside the gap between Saturn and the ring system. What will happen? We don’t really know for sure but we are going to find out. I will be checking shortly after 08:00 UT / 0400 ET to see what happened and if all goes really well we might even have some images.


Here’s the time line and kind of what is expected from NASA:
NASA’s Cassini spacecraft is set to make its first dive through the narrow gap between Saturn and its rings on April 26, 2017. Because that gap is a region no spacecraft has ever explored, Cassini will use its dish-shaped high-gain antenna (13 feet or 4 meters across) as a protective shield while passing through the ring plane. No particles larger than smoke particles are expected, but the precautionary measure is being taken on the first dive. The Cassini team will use data collected by one of the spacecraft’s science instruments (the Radio and Plasma Wave Subsystem, or RPWS) to ascertain the size and density of ring particles in the gap in advance of future dives. As a result of its antenna-forward orientation, the spacecraft will be out of contact with Earth during the dive.

Below is a list of milestones expected to occur during the event, if all goes as planned:

— 5 p.m. PDT (8 p.m. EDT) on April 25: Cassini is approaching Saturn over the planet’s northern hemisphere in advance of its first of 22 planned dives through the gap between the planet and its rings.

— 1:34 a.m. PDT (4:34 a.m. EDT) on April 26: As it passes from north to south over Saturn, Cassini begins a 14-minute turn to point its high-gain antenna into the direction of oncoming ring particles. In this orientation, the antenna acts as a protective shield for Cassini’s instruments and engineering systems.

— 2 a.m. PDT (5 a.m. EDT) on April 26: Cassini crosses the ring plane during its dive between the rings and Saturn. The spacecraft’s science instruments are collecting data, but Cassini is not in contact with Earth at this time.

No earlier than around midnight PDT on April 26 (3 a.m. EDT on April 27): Earth has its first opportunity to regain contact with Cassini as the giant, 230-foot (70-meter) Deep Space Network antenna at Goldstone, California, listens for the spacecraft’s radio signal.

— Likely no earlier than 12:30 a.m. PDT (3:30 a.m. EDT) on April 27: Images are scheduled to become available from the spacecraft.

Artistic rendering: Credits: NASA/JPL-Caltech

Last Look at Titan

Click the image for a larger view.

From NASA:

NASA’s Cassini spacecraft has had its last close brush with Saturn’s hazy moon Titan and is now beginning its final set of 22 orbits around the ringed planet.

The spacecraft made its 127th and final close approach to Titan on April 21 at 11:08 p.m. PDT (2:08 a.m. EDT on April 22), passing at an altitude of about 608 miles (979 kilometers) above the moon’s surface.

Cassini transmitted its images and other data to Earth following the encounter. Scientists with Cassini’s radar investigation will be looking this week at their final set of new radar images of the hydrocarbon seas and lakes that spread across Titan’s north polar region. The planned imaging coverage includes a region previously seen by Cassini’s imaging cameras, but not by radar. The radar team also plans to use the new data to probe the depths and compositions of some of Titan’s small lakes for the first (and last) time, and look for further evidence of the evolving feature researchers have dubbed the “magic island.”

“Cassini’s up-close exploration of Titan is now behind us, but the rich volume of data the spacecraft has collected will fuel scientific study for decades to come,” said Linda Spilker, the mission’s project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California.


Cassini Looking Home

Cassini looks back towards home. This is what we look like from Saturn, although I brightened the Moon up a little. The top image is the original released version and the second is one where I cropped and enlarged the section with the Earth and Moon for visibility.

Very nice indeed!

The release from NASA:

This view from NASA’s Cassini spacecraft shows planet Earth as a point of light between the icy rings of Saturn.

The spacecraft captured the view on April 12, 2017 at 10:41 p.m. PDT (1:41 a.m. EDT). Cassini was 870 million miles (1.4 billion kilometers) away from Earth when the image was taken. Although far too small to be visible in the image, the part of Earth facing toward Cassini at the time was the southern Atlantic Ocean.

Earth’s moon is also visible to the left of our planet in a cropped, zoomed-in version of the image (Figure 1).

The rings visible here are the A ring (at top) with the Keeler and Encke gaps visible, and the F ring (at bottom). During this observation Cassini was looking toward the backlit rings, making a mosaic of multiple images, with the sun blocked by the disk of Saturn.

Seen from Saturn, Earth and the other inner solar system planets are all close to the sun, and are easily captured in such images, although these opportunities have been somewhat rare during the mission. The F ring appears especially bright in this viewing geometry.

Image: NASA / Cassini Imaging Team

Last Titan Flyby

By this time the Cassini spacecraft has made its final close flyby of the Saturn moon Titan. This will allow one last look at the hydrocarbon lakes and surface of the moon, via radar of course, Titan is shrouded in a thick haze.

The encounter will alter the orbit of Cassini and start the final phase of the epic mission – The Grand Finale.

Here’s a video of how it will all came together in a video entitled “Crazy Engineering Astrodynamics”

The Grand Finale

Here is the preview of The Grand Finale or the end of the Cassini Mission. What you are seeing is the entire press announcement and you will get to hear great questions and answers.

The last phase begins in just a few weeks and ends after orbits between the inner rings and Saturn itself. What is in that gap? Could be a “white-knuckled” encounter or clear ride looking at the ring-plane or Saturn’s upper atmosphere very close up.

No matter, the Cassini mission sets the “remote planetary exploration bar” pretty high and especially when you think about this mission from the international teamwork and co-operative side of things. This is yet another example of what can be done when all involved work together, space sciences are really lucky in this respect and would seem to provide a good example to follow.



Saturn’s Crescent

NASA’s caption:
Although only a sliver of Saturn’s sunlit face is visible in this view, the mighty gas giant planet still dominates the view.

From this vantage point just beneath the ring plane, the dense B ring becomes dark and essentially opaque, letting almost no light pass through. But some light reflected by the planet passes through the less dense A ring, which appears above the B ring in this photo. The C ring, silhouetted just below the B ring, lets almost all of Saturn’s reflected light pass right through it, as if it were barely there at all. The F ring appears as a bright arc in this image, which is visible against both the backdrop of Saturn and the dark sky. (For a diagram showing the names and positions of the rings see PIA08389.)

This view looks toward the unilluminated side of the rings from about 7 degrees below the ring plane. The image was taken in green light with the Cassini spacecraft wide-angle camera on Jan. 18, 2017.

The view was acquired at a distance of approximately 630,000 miles (1 million kilometers) from Saturn. Image scale is 38 miles (61 kilometers) per pixel.

NASA/JPL-Caltech/Space Science Institute

Saturn’s Fine ‘A’ Ring

It would be interesting to know how the different sized constituents of the ring are distributed. I would think they would grade out by size.

From Cassini:
NASA’s Cassini spacecraft zoomed in on Saturn’s A ring, revealing narrow, detailed structures that get even finer as the cameras’ resolution increases. Even at this level of detail, it is still not fine enough to resolve the individual particles that make up the ring.

High-resolution images like this help scientists map the fine structure of Saturn’s rings. Features less than a half a mile (one kilometer) in size are resolvable here. But the particles in the A ring typically range in size from several meters across down to centimeters, making them still far too small to see individually here.

This view looks toward the sunlit side of the rings from about 38 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 9, 2017.

The view was obtained at a distance of approximately 70,000 miles (113,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 11 degrees. Image scale is 2,300 feet (690 meters) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute

You’ve Probably Never Seen a Moon Like Pan

Just when you thought a moon was a more-or-less spherical body, we have the Saturn moon Pan.  What in the world universe would create this?

From NASA:
These two images from NASA’s Cassini spacecraft show how the spacecraft’s perspective changed as it passed within 15,300 miles (24,600 kilometers) of Saturn’s moon Pan on March 7, 2017. This was Cassini’s closest-ever encounter with Pan, improving the level of detail seen on the little moon by a factor of eight over previous observations.

The views show the northern and southern hemispheres of Pan, at left and right, respectively. Both views look toward Pan’s trailing side, which is the side opposite the moon’s direction of motion as it orbits Saturn.

Cassini imaging scientists think that Pan formed within Saturn’s rings, with ring material accreting onto it and forming the rounded shape of its central mass, when the outer part of the ring system was quite young and the ring system was vertically thicker. Thus, Pan probably has a core of icy material that is denser than the softer mantle around it.

The distinctive, thin ridge around Pan’s equator is thought to have come after the moon formed and had cleared the gap in the rings in which it resides today. At that point the ring was as thin as it is today, yet there was still ring material accreting onto Pan. However, at the tail end of the process, that material was raining down on the moon solely in (or close to) its equatorial region. Thus, the infalling material formed a tall, narrow ridge of material. On a larger, more massive body, this ridge would not be so tall (relative to the body) because gravity would cause it to flatten out. But Pan’s gravity is so feeble that the ring material simply settles onto Pan and builds up. Other dynamical forces keep the ridge from growing indefinitely.

These views are also presented in stereo (3-D) in PIA21435. The images are presented here at their original size.

The views were acquired by the Cassini narrow-angle camera at distances of 15,275 miles or 24,583 kilometers (left view) and 23,199 miles or 37,335 kilometers (right view). Image scale is 482 feet or 147 meters per pixel (left view) and about 735 feet or 224 meters per pixel (right view).

See PIA09868 and PIA11529 for more distant context views of Pan.

Image: NASA/JPL-Caltech/Space Science Institute