Category Archives: Gas giants Saturn, Jupiter, et al

Gas giants Saturn, Jupiter, et al, Space Science

Cassini: Propellers in Saturn’s rings and a hexagon on its north pole

The Cassini spacecraft returns more amazing pictures of the Saturn system:

Cassini Targets a Propeller in Saturn’s A Ring 

NASA’s Cassini spacecraft captured these remarkable views of a propeller feature in Saturn’s A ring on Feb. 21, 2017. These are the sharpest images taken of a propeller so far, and show an unprecedented level of detail. The propeller is nicknamed “Santos-Dumont,” after the pioneering Brazilian-French aviator.

This observation was Cassini’s first targeted flyby of a propeller. The views show the object from vantage points on opposite sides of the rings. The top image looks toward the rings’ sunlit side, while the bottom image shows the unilluminated side, where sunlight filters through the backlit ring.

The two images presented as figure A are reprojected at the same scale (0.13 mile or 207 meters per pixel) in order to facilitate comparison. The original images, which have slightly different scales, are also provided here, without reprojection, as figure B; the sunlit-side image is at left, while the unlit-side image is at right.

The original images, which have slightly different scales, are seen here without reproduction; the sunlit-side image is at left, while the unlit-side image is at right. › Full image

Cassini scientists have been tracking the orbit of this object for the past decade, tracing the effect that the ring has upon it. Now, as Cassini has moved in close to the ring as part of its ring-grazing orbits, it was able to obtain this extreme close-up view of the propeller, enabling researchers to examine its effects on the ring. These views, and others like them, will inform models and studies in new ways going forward.

Like a frosted window, Saturn’s rings look different depending on whether they are seen fully sunlit or backlit. On the lit side, the rings look darker where there is less material to reflect sunlight. On the unlit side, some regions look darker because there is less material, but other regions look dark because there is so much material that the ring becomes opaque.

Observing the same propeller on both the lit and unlit sides allows scientists to gather richer information about how the moonlet affects the ring. For example, in the unlit-side view, the broad, dark band through the middle of the propeller seems to be a combination of both empty and opaque regions.

The propeller’s central moonlet would only be a couple of pixels across in these images, and may not actually be resolved here. The lit-side image shows that a bright, narrow band of material connects the moonlet directly to the larger ring, in agreement with dynamical models. That same thin band of material may also be obscuring the moonlet from view.

Lengthwise along the propeller is a gap in the ring that the moonlet has pried open. The gap appears dark on both the lit and unlit sides. Flanking the gap near the moonlet are regions of enhanced density, which appear bright on the lit side and more mottled on the unlit side.

One benefit of the high resolution of these images is that, for the first time, wavy edges are clearly visible in the gap. These waves are also expected from dynamical models, and they emphasize that the gap must be sharp-edged. Furthermore, the distance between the wave crests tells scientists the width of the gap (1.2 miles or 2 kilometers), which in turn reveals the mass of the central moonlet. From these measurements, Cassini imaging scientists deduce that the moonlet’s mass is comparable to that of a snowball about 0.6 mile (1 kilometer) wide.

For the original images (figure B), the lit-side image has a scale of 0.33 mile (530 meters) per pixel in the radial (or outward from Saturn) direction and 0.44 mile (710 meters) per pixel in the azimuthal (or around Saturn) direction. The different scales are the result of Cassini’s vantage point being off to the side of the propeller, rather than directly above it. The unlit-side image has a scale of 0.25 (410 meters) per pixel in both directions.

In order to preserve its original level of detail, the image has not been cleaned of bright blemishes due to cosmic rays and to charged particle radiation from Saturn.

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.

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

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At the Center 

Saturn’s North Pole

The north pole of Saturn sits at the center of its own domain. Around it swirl the clouds, driven by the fast winds of Saturn. Beyond that orbits Saturn’s retinue of moons and the countless small particles that form the ring.

Although the poles of Saturn are at the center of all of this motion, not everything travels around them in circles. Some of the jet-stream patterns, such as the hexagon-shaped pattern seen here, have wavy, uneven shapes. The moons as well have orbits that are elliptical, some quite far from circular.

This view looks toward the sunlit side of the rings from about 26 degrees above the ring plane. The image was taken with the Cassini spacecraft wide-angle camera on Dec. 2, 2016 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 890 nanometers.

The view was acquired at a distance of approximately 619,000 miles (996,000 kilometers) from Saturn. Image scale is 37 miles (60 kilometers) per pixel.

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.

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

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Europa, Titan, & other deep space sites, Gas giants Saturn, Jupiter, et al, Space Science

Cassini: Magnetic anomaly leads to an ocean world circling Saturn

Saturn’s little moon Enceladus has turned out to be one of the most interesting objects in the solar system:

Cassini: Mission to Saturn: An Ice World…With an Ocean?
How a puzzling sensor reading transformed NASA’s
Cassini Saturn mission and created a new target in the search
for habitable worlds beyond Earth.

On Feb. 17, 2005, NASA’s Cassini spacecraft was making the first-ever close pass over Saturn’s moon Enceladus as it worked through its detailed survey of the planet’s icy satellites. Exciting, to be sure, just for the thrill of exploration. But then Cassini’s magnetometer instrument noticed something odd.

Since NASA’s two Voyager spacecraft made their distant flybys of Enceladus about 20 years prior, scientists had anticipated the little moon would be an interesting place to visit with Cassini. Enceladus is bright white — the most reflective object in the solar system, in fact — and it orbits in the middle of a faint ring of dust-sized ice particles known as Saturn’s E ring. Scientists speculated ice dust was being kicked off its surface somehow. But they presumed it would be, essentially, a dead, airless ball of ice.

What Cassini saw didn’t look like a frozen, airless body. Instead, it looked something like a comet that was actively emitting gas. The magnetometer detected that Saturn’s magnetic field, which envelops Enceladus, was perturbed above the moon’s south pole in a way that didn’t make sense for an inactive world. Could it be that the moon was actively replenishing gases it was breathing into space?

Thus began a hunt for clues that has turned out to be Cassini’s most riveting detective story.

“Enceladus was so exciting that, instead of just three close flybys planned for our four-year primary mission, we added 20 more, including seven that went right through the geysers at the south pole,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California.

By following the trail of scientific breadcrumbs, Cassini eventually found that Enceladus harbors a global ocean of salty water under its icy crust, possibly with hydrothermal vents on its seafloor. The trail of clues that began with a puzzling magnetometer reading led to an understanding that the moon — and perhaps many small, icy moons like it throughout the cosmos — could potentially have the ingredients needed for life.

“Half the excitement of doing science is that you sometimes find yourself going in a totally different direction than you expected, which can lead to amazing discoveries,” said Spilker. “That little anomaly in Cassini’s magnetometer signal was unusual enough that it eventually led us to an ocean world.”

For a timeline of Cassini’s Enceladus discoveries, visit: http://go.nasa.gov/2k0CRP3

Launched in 1997, the Cassini mission is currently in its final year of operations, performing weekly ring-grazing dives just past the outer edge of Saturn’s rings. In April, the spacecraft will begin its Grand Finale, plunging through the gap between the rings and the planet itself, leading up to a final plunge into Saturn on September 15.

Illustration showing the bending of Saturn’s magnetic field near Enceladus that was detected by Cassini’s magnetometer. Credit: NASA/JPL-Caltech > Full image and caption

Cassini has been touring the Saturn system since arriving in 2004 for an up-close study of the planet, its rings and moons, and its vast magnetosphere. Cassini has made numerous dramatic discoveries, besides the activity at Enceladus, including liquid methane seas on another moon, Titan.

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the mission for NASA’s Science Mission Directorate, Washington. JPL designed, developed and assembled the Cassini orbiter.

More information about Cassini:

Europa, Titan, & other deep space sites, Gas giants Saturn, Jupiter, et al, Space Science

Cassini views the little moon Daphnis up close

In early January, the Cassini spacecraft took this marvelous shot of the small moon Daphnis as it travels along in a gap in Saturn’s rings: Cassini: Mission to Saturn: Daphnis Up Close 

The wavemaker moon, Daphnis, is featured in this view, taken as NASA’s Cassini spacecraft made one of its ring-grazing passes over the outer edges of Saturn’s rings on Jan. 16, 2017. This is the closest view of the small moon obtained yet. Daphnis (5 miles or 8 kilometers across) orbits within the 42-kilometer (26-mile) wide Keeler Gap. Cassini’s viewing angle causes the gap to appear narrower than it actually is, due to foreshortening. The little moon’s gravity raises waves in the edges of the gap in both the horizontal and vertical directions. Cassini was able to observe the vertical structures in 2009, around the time of Saturn’s equinox. [Full caption and larger images]
Check out the latest Cassini shots from the Saturnian system in the Mission to Saturn Images gallery and the Raw Images gallery. 

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Gas giants Saturn, Jupiter, et al, Space Science, Space Systems

Cassini returns detailed views of Saturn’s rings

NASA’s Cassini probe at Saturn returns amazing views of the outer rings as it makes its final orbits before plunging into the planet’s atmosphere on September 15th :

Close Views Show Saturn’s Rings in Unprecedented Detail

Newly released images showcase the incredible closeness with which NASA’s Cassini spacecraft, now in its “Ring-Grazing” orbits phase, is observing Saturn’s dazzling rings of icy debris.

This Cassini image features a density wave in Saturn’s A ring (at left) that lies around 134,500 km from Saturn. Density waves are accumulations of particles at certain distances from the planet. This feature is filled with clumpy perturbations, which researchers informally refer to as “straw.” Image Credit: NASA/JPL-Caltech/Space Science Institute › Full image and caption

The views are some of the closest-ever images of the outer parts of the main rings, giving scientists an eagerly awaited opportunity to observe features with names like “straw” and “propellers.” Although Cassini saw these features earlier in the mission, the spacecraft’s current, special orbits are now providing opportunities to see them in greater detail. The new images resolve details as small as 0.3 miles (550 meters), which is on the scale of Earth’s tallest buildings.

Cassini is now about halfway through its penultimate mission phase — 20 orbits that dive past the outer edge of the main ring system. The ring-grazing orbits began last November, and will continue until late April, when Cassini begins its grand finale. During the 22 finale orbits, Cassini will repeatedly plunge through the gap between the rings and Saturn. The first finale plunge is scheduled for April 26.

This image from NASA’s Cassini mission shows a region in Saturn’s A ring. The level of detail is twice as high as this part of the rings has ever been seen before. The view contains many small, bright blemishes due to cosmic rays and charged particle radiation near the planet. Image Credit: NASA/JPL-Caltech/Space Science Institute › Full image and caption

For now, the veteran spacecraft is shooting past the outer edges of the rings every week, gathering some of its best images of the rings and moons. Already Cassini has sent back the closest-ever views of small moons Daphnis and Pandora.

Some of the structures seen in recent Cassini images have not been visible at this level of detail since the spacecraft arrived at Saturn in mid-2004. At that time, fine details like straw and propellers — which are caused by clumping ring particles and small, embedded moonlets, respectively — had never been seen before. (Although propellers were present in Cassini’s arrival images, they were actually discovered in later analysis, the following year.)

This image shows a region in Saturn’s outer B ring. NASA’s Cassini spacecraft viewed this area at a level of detail twice as high as it had ever been observed before. And from this view, it is clear that there are still finer details to uncover. Image Credit: NASA/JPL-Caltech/Space Science Institute › Full image and caption

Cassini came a bit closer to the rings during its arrival at Saturn, but the quality of those arrival images (examples: 1, 2, 3) was not as high as in the new views. Those precious few observations only looked out on the backlit side of the rings, and the team chose short exposure times to minimize smearing due to Cassini’s fast motion as it vaulted over the ring plane. This resulted in images that were scientifically stunning, but somewhat dark and noisy.

In contrast, the close views Cassini has begun capturing in its ring-grazing orbits (and soon will capture in its Grand Finale phase) are taking in both the backlit and sunlit side of the rings. Instead of just one brief pass lasting a few hours, Cassini is making several dozen passes during these final months.

“As the person who planned those initial orbit-insertion ring images — which remained our most detailed views of the rings for the past 13 years — I am taken aback by how vastly improved are the details in this new collection,” said Cassini Imaging Team Lead Carolyn Porco, of Space Science Institute, Boulder, Colorado. “How fitting it is that we should go out with the best views of Saturn’s rings we’ve ever collected.”

After nearly 13 years studying Saturn’s rings from orbit, the Cassini team has a deeper, richer understanding of what they’re seeing, but they still anticipate new surprises.

“These close views represent the opening of an entirely new window onto Saturn’s rings, and over the next few months we look forward to even more exciting data as we train our cameras on other parts of the rings closer to the planet,” said Matthew Tiscareno, a Cassini scientist who studies Saturn’s rings at the SETI Institute, Mountain View, California. Tiscareno planned the new images for the camera team.

Launched in 1997, Cassini has been touring the Saturn system since arriving in 2004 for an up-close study of the planet, its rings and moons, and its vast magnetosphere. Cassini has made numerous dramatic discoveries, including a global ocean with indications of hydrothermal activity within the moon Enceladus, and liquid methane seas on another moon, Titan.

This image shows a region in Saturn’s outer B ring. NASA’s Cassini spacecraft viewed this area at a level of detail twice as high as it had ever been observed before. Image Credit: NASA/JPL-Caltech/Space Science Institute › Full image and caption

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA’s Jet Propulsion Laboratory in Pasadena, California, manages the mission for the agency’s Science Mission Directorate in Washington. JPL is a division of Caltech in Pasadena. The Cassini imaging operations center is based at Space Science Institute in Boulder, Colorado.

For more information about Cassini, visit:

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Gas giants Saturn, Jupiter, et al, Space participation, Space Science

Help choose Juno’s next image targets on Jupiter

Help select spots on Jupiter for the Juno spacecraft to image on its next pass close to the planet:

Public to Choose Jupiter Picture Sites for NASA Juno 

This amateur-processed image was taken on Dec. 11, 2016, at 9:27 a.m. PST (12:27 p.m. EST), as NASA’s Juno spacecraft performed its third close flyby of Jupiter. At the time the image was taken, the spacecraft was about 15,200 miles (24,400 kilometers) from the gas giant planet. The citizen scientist (Eric Jorgensen) cropped the JunoCam image and enhanced the color to draw attention to Jupiter’s swirling clouds southeast of the “pearl.” The “pearl” is one of eight massive rotating storms at 40 degrees south latitude on Jupiter, known colloquially as the “string of pearls.” The processing of this image highlights the turbulence of the clouds in the south temperate belt of the planet. [Other image sizes]
Where should NASA’s Juno spacecraft aim its camera during its next close pass of Jupiter on Feb. 2? You can now play a part in the decision. For the first time, members of the public can vote to participate in selecting all pictures to be taken of Jupiter during a Juno flyby. Voting begins Thursday, Jan. 19 at 11 a.m. PST (2 p.m. EST) and concludes on Jan. 23 at 9 a.m. PST (noon EST).

“We are looking forward to people visiting our website and becoming part of the JunoCam imaging team,” said Candy Hansen, Juno co-investigator from the Planetary Science Institute, Tucson, Arizona. “It’s up to the public to determine the best locations in Jupiter’s atmosphere for JunoCam to capture during this flyby.”

NASA’s JunoCam website can be visited at: www.missionjuno.swri.edu/junocam

The voting page for this flyby is available at: www.missionjuno.swri.edu/junocam/voting/

JunoCam will begin taking pictures as the spacecraft approaches Jupiter’s north pole. Two hours later, the imaging will conclude as the spacecraft completes its close flyby, departing from below the gas giant’s south pole. Juno is currently on its fourth orbit around Jupiter. It takes 53 days for Juno to complete one orbit.

“The pictures JunoCam can take depict a narrow swath of territory the spacecraft flies over, so the points of interest imaged can provide a great amount of detail,” said Hansen. “They play a vital role in helping the Juno science team establish what is going on in Jupiter’s atmosphere at any moment. We are looking forward to seeing what people from outside the science team think is important.”

There will be a new voting page for each upcoming flyby of the mission. On each of the pages, several points of interest will be highlighted that are known to come within the JunoCam field of view during the next close approach. Each participant will get a limited number of votes per orbit to devote to the points of interest he or she wants imaged. After the flyby is complete, the raw images will be posted to the JunoCam website, where the public can perform its own processing.

“It is great to be able to share excitement and science from the Juno mission with the public in this way,” said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio. “Amateur scientists, artists, students and whole classrooms are providing the world with their unique perspectives of Jupiter. I am really pleased that this website is having such a big impact and allowing so many people to join the Juno science team. The public involvement is really affecting how we look at the most massive planetary inhabitant in our solar system.”

During the Feb. 2 flyby, Juno will make its closest approach to Jupiter at 4:58 a.m. PST (7:58 a.m. EST), when the spacecraft is about 2,700 miles (4,300 kilometers) above the planet’s swirling clouds.

JunoCam is a color, visible-light camera designed to capture remarkable pictures of Jupiter’s poles and cloud tops. As Juno’s eyes, it will provide a wide view of Jupiter over the course of the mission, helping to provide context for the spacecraft’s other instruments. JunoCam was included on the spacecraft primarily for public engagement purposes, although its images also are helpful to the science team.

NASA’s Jet Propulsion Laboratory, Pasadena, California, manages the Juno mission for the principal investigator, Scott Bolton, of Southwest Research Institute in San Antonio. The Juno mission is part of the New Frontiers Program managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for NASA’s Science Mission Directorate. Lockheed Martin Space Systems, Denver, built the spacecraft. JPL is a division of Caltech in Pasadena, California.

More information on the Juno mission is available at:

The public can follow the mission on Facebook and Twitter at:

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