Category Archives: Cassini

Saturn’s North

Take a look at the northern reaches of Saturn as Cassini did a few months ago.  The structure in the atmosphere aside from the hexagonal formation is rather remarkable.  Click the image to get a larger version.

NASA – “Hail the Hexagon” – Saturn’s hexagonal polar jet stream is the shining feature of almost every view of the north polar region of Saturn. The region, in shadow for the first part of the Cassini mission, now enjoys full sunlight, which enables Cassini scientists to directly image it in reflected light.

Although the sunlight falling on the north pole of Saturn is enough to allow us to image and study the region, it does not provide much warmth. In addition to being low in the sky (just like summer at Earth’s poles), the sun is nearly ten times as distant from Saturn as from Earth. This results in the sunlight being only about 1 percent as intense as at our planet.

This view looks toward Saturn from about 31 degrees above the ring plane. The image was taken with the Cassini spacecraft wide-angle camera on Jan. 22, 2017 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 939 nanometers.

The view was obtained at a distance of approximately 560,000 miles (900,000 kilometers) from Saturn. Image scale is 33 miles (54 kilometers) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute

Crossing “The Big Empty”

The image above (as always thanks to NASA/JPL-Caltech/Space Science Institute) was taken on 29 April 2017 and has very minimal processing.

Later today (at 19:38 UTC) the Cassini spacecraft will make its second crossing in the gap between the rings of Saturn and the planet itself.

During the first crossing the spacecraft was oriented so the four-meter wide antenna was leading the way through the gap so it could act as a shield protecting instruments on the spacecraft. Not so long ago only few could imagine flying through that 2,000 km wide gap and nobody knew what they would find.  Will this dive be the same?  We will know tomorrow.

NASA — Cassini’s Radio and Plasma Wave Science (RPWS) instrument was one of two science instruments with sensors that poke out from the protective shield of the antenna (the other being Cassini’s magnetometer). RPWS detected the hits of hundreds of ring particles per second when it crossed the ring plane just outside of Saturn’s main rings, but only detected a few pings on April 26.

When RPWS data are converted to an audio format, dust particles hitting the instrument’s antennas sound like pops and cracks, covering up the usual whistles and squeaks of waves in the charged particle environment that the instrument is designed to detect. The RPWS team expected to hear a lot of pops and cracks on crossing the ring plane inside the gap, but instead, the whistles and squeaks came through surprisingly clearly on April 26.

“The region between the rings and Saturn is ‘the big empty,’ apparently,” said Cassini Project Manager Earl Maize of NASA’s Jet Propulsion Laboratory in Pasadena, California. “Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected.”

“It was a bit disorienting — we weren’t hearing what we expected to hear,” said William Kurth, RPWS team lead at the University of Iowa, Iowa City. “I’ve listened to our data from the first dive several times and I can probably count on my hands the number of dust particle impacts I hear.”

The team’s analysis suggests Cassini only encountered a few particles as it crossed the gap — none larger than those in smoke (about 1 micron across).

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.