Tag: Cassini

Data from Cassini’s last ring-diving orbits has now strengthened the hypothesis that Saturn’s rings formed very recently, just a few hundred million years ago.

Saturn acquired its jewels relatively late in life. If any astronomers had gazed at the sky in the time of the dinosaurs, they might have seen a bare and boring Saturn.

It was then that some sort of catastrophe struck the gas giant. Perhaps a stray comet or asteroid struck an icy moon, tossing its remnants into orbit. Or maybe the orbits of Saturn’s moons somehow shifted, and the resulting gravitational tug-of-war pulled a moon apart. However it happened, two new lines of evidence from Cassini make it clear that the rings were not around in the early days of the solar system 4.5 billion years ago, as scientists had long believed, says Jeff Cuzzi, a ring specialist at NASA’s Ames Research Center in Mountain View, California. “It rules out the primordial ring story,” Cuzzi says. “That’s what it looks like to me.”

At the moment there is no consensus on what might have caused the rings formation so recently.

Cool image time! The image above, cropped and reduced in resolution to show here, was created by Cassini from 42 images taken on September 13, 2017, two days before the spacecraft dived into Saturn to end its mission.

Be sure to take a look at the full image. It shows six of Saturn’s moons, as well as many stars.

Cool image time! The image on the right, reduced in resolution to post here, was taken by Cassini on August 17, 2017, one month before the spacecraft dived into Saturn to end its mission.

This view looks toward the sunlit side of the rings from about 19 degrees above the ringplane. The image was taken in green light with the Cassini spacecraft wide-angle camera on Aug. 12, 2017. Pandora was brightened by a factor of 2 to increase its visibility.

The view was obtained at a distance to Saturn of approximately 581,000 miles (935,000 kilometers) from Saturn. Image scale is 35 miles (56 kilometers) per pixel. The distance to Pandora was 691,000 miles (1.1 million kilometers) for a scale of 41 miles (66 kilometers) per pixel.

The moon Pandora can be seen in the full resolution image just beyond the outermost ring near the top of the screen.

Link here. Among a bunch of other interesting results, this one I found the most tantalizing:

The spacecraft’s Ion and Neutral Mass Spectrometer (INMS) returned a host of first-ever direct measurements of the components in Saturn’s upper atmosphere, which stretches almost to the rings. From these observations, the team sees evidence that molecules from the rings are raining down onto the atmosphere. This influx of material from the rings was expected, but INMS data show hints of ingredients more complex than just water, which makes up the bulk of the rings’ composition. In particular, the instrument detected methane, a volatile molecule that scientists would not expect to be abundant in the rings or found so high in Saturn’s atmosphere.

The results generally leave behind more questions than answers, but that is exactly why exploring the universe is so much fun.

After a seven year journey and thirteen years in orbit around Saturn, Cassini’s mission ended early this morning with a dive into Saturn’s atmosphere.

The image above, cropped to show here, is actually one from a short movie, showing Enceladus setting behind the horizon of Saturn. The images were taking two days ago, but provide a fitting image for the mission’s end.

Some of the best images from the dive, including Cassini’s last image, can be found here.

While most of the press will rightly wax eloquent about the magnificence of this mission, my focus remains on what will come next. We no longer have any way to observe what is happening on Saturn. We are blind. We should not be.

Engineers have confirmed that Cassini is now on its final approach to Saturn, with a scheduled dive into the gas giant set for Friday, September 15.

The mission’s final calculations predict loss of contact with the Cassini spacecraft will take place on Sept. 15 at 7:55 a.m. EDT (4:55 a.m. PDT). Cassini will enter Saturn’s atmosphere approximately one minute earlier, at an altitude of about 1,190 miles (1,915 kilometers) above the planet’s estimated cloud tops (the altitude where the air pressure is 1-bar, equivalent to sea level on Earth). During its dive into the atmosphere, the spacecraft’s speed will be approximately 70,000 miles (113,000 kilometers) per hour. The final plunge will take place on the day side of Saturn, near local noon, with the spacecraft entering the atmosphere around 10 degrees north latitude.

We will get Cassini’s last images about 90 minutes after its death.

The Cassini science team released two sets of images taken by the spacecraft of Saturn’s rings.

• Staggering Structure
• Colorful Structure at Fine Scales

The image above, reduced in resolution to show here, is from the second link. As they note,

The pale tan color is generally not perceptible with the naked eye in telescope views, especially given that Saturn has a similar hue.

The material responsible for bestowing this color on the rings—which are mostly water ice and would otherwise appear white—is a matter of intense debate among ring scientists that will hopefully be settled by new in-situ observations before the end of Cassini’s mission.

The different ringlets seen here are part of what is called the “irregular structure” of the B ring. Cassini radio occultations of the rings have shown that these features have extremely sharp boundaries on even smaller scales (radially, or along the direction outward from Saturn) than the camera can resolve here. Closer to Saturn, the irregular structures become fuzzier and more rounded, less opaque, and their color contrast diminishes.

Check out both. They reveal to me that our understanding of these rings remains essentially nil, even after more than a dozen years of study by Cassini.

Cool image time! The Cassini science team has assembled a short movie from 21 images taken by the spacecraft during its August 20th dive between the rings and Saturn. That animation is to the right.

Only two weeks remain in the Cassini mission. The spacecraft dives into Saturn on September 15.

The spacecraft is expected to lose radio contact with Earth within about one to two minutes after beginning its descent into Saturn’s upper atmosphere. But on the way down, before contact is lost, eight of Cassini’s 12 science instruments will be operating. In particular, the spacecraft‘s ion and neutral mass spectrometer (INMS), which will be directly sampling the atmosphere’s composition, potentially returning insights into the giant planet’s formation and evolution. On the day before the plunge, other Cassini instruments will make detailed, high-resolution observations of Saturn’s auroras, temperature, and the vortices at the planet’s poles. Cassini’s imaging camera will be off during this final descent, having taken a last look at the Saturn system the previous day (Sept. 14).

The second link above gives a detailed moment-by-moment breakdown of the final six days.

I would have posted this earlier this week, but my limited internet access made it impossible. Sorry about that.

Cool image time! The Cassini image above, cropped and reduced slightly, shows a close-up view of Saturn’s cloud tops, taken during Cassini’s May 18, 2017 fly-by.

Clouds on Saturn take on the appearance of strokes from a cosmic brush thanks to the wavy way that fluids interact in Saturn’s atmosphere. Neighboring bands of clouds move at different speeds and directions depending on their latitudes. This generates turbulence where bands meet and leads to the wavy structure along the interfaces.

What I see is a much less turbulent storm pattern, when compared with Jupiter. This is not to say that the weather of Saturn is quiet or peaceful, for it certainly cannot be, considering the gas giant’s size and the depth of the atmosphere. Still, this image suggests that the turbulence is less violent here, possibly because Saturn is farther from the Sun and is hit with less solar energy, and because Saturn is smaller and thus produces less of its own internal energy.

Either way, it is beautiful and mysterious, in the way are all such images of alien places.

Cassini is about to begin its last of five orbits of Saturn, before it is sent into the planet’s atmosphere to burn up.

Cassini will make the first of these five passes over Saturn at 12:22 a.m. EDT Monday, Aug. 14. The spacecraft’s point of closest approach to Saturn during these passes will be between about 1,010 and 1,060 miles (1,630 and 1,710 kilometers) above Saturn’s cloud tops.

The spacecraft is expected to encounter atmosphere dense enough to require the use of its small rocket thrusters to maintain stability – conditions similar to those encountered during many of Cassini’s close flybys of Saturn’s moon Titan, which has its own dense atmosphere. “Cassini’s Titan flybys prepared us for these rapid passes through Saturn’s upper atmosphere,” said Earl Maize, Cassini project manager at NASA’s Jet Propulsion Laboratory (JPL) in California. “Thanks to our past experience, the team is confident that we understand how the spacecraft will behave at the atmospheric densities our models predict.”

Cool image time! The image on the right, reduced in resolution to show here, was taken by Cassini in May and looks down at the outer rings of Saturn. The moon Prometheus can also be seen in the large gap between the main rings and the outermost F ring.

Most of the small moon’s surface is in darkness due to the viewing geometry here. Cassini was positioned behind Saturn and Prometheus with respect to the sun, looking toward the moon’s dark side and just a bit of the moon’s sunlit northern hemisphere.

Also visible here is a distinct difference in brightness between the outermost section of Saturn’s A ring (left of center) and rest of the ring, interior to the Keeler Gap (lower left).

The image clearly shows the gravitational influence of the moon on the outer ring. As Prometheus orbits past the F ring its mass creates waves through the ring’s materials.

Cool image time. One of the images released by the Cassini science team this week when it announced the first results from the spacecraft’s weekly dives between Saturn and its innermost rings was a short video made from 137 images taken on its first dive on April 26, 2017.

It is absolutely worthwhile to view this video. It begins at Saturn’s north pole, looking down into what appears to be a bottomless vortex, and continues south to almost the equator. Along the way the movie captures what seems to be innumerable horizontal bands across the gas giant’s surface. Not only are do we see the major bands that have been observed from Earth for centuries, there are bands within bands, and bands within those bands. Like a fractal it appears that the deeper you go, the more horizontal jet streams you see.

Like Juno at Jupiter, the mysteries of a gas giant like Saturn is overwhelming. This is a big and very active planet. We understand almost nothing about its weather systems, its atmosphere, and its interior. And this glimpse by Cassini is only that, a mere glimpse. When Cassini’s mission ends in September, it will leave us a treasure trove of knowledge. It will also leave us a much larger library of unanswered questions, all of which will remain unanswered until we can return, decades hence, with new probes..