Cassini Completes Final -- and Fateful -- Titan Flyby
This unprocessed image of Saturn's moon Titan was captured by NASA's Cassini spacecraft during its final close flyby of the hazy, planet-sized moon on April 21, 2017.
Credits: NASA/JPL-Caltech/Space Science Institute
This unprocessed image of Saturn's moon Titan was captured by NASA's Cassini spacecraft during its final close flyby of the hazy, planet-sized moon on April 21, 2017.
Credits: NASA/JPL-Caltech/Space Science Institute
This unprocessed image of Saturn's moon Titan was captured by NASA's Cassini spacecraft during its final close flyby of the hazy, planet-sized moon on April 21, 2017.
Credits: NASA/JPL-Caltech/Space Science Institute
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.
Gateway to the Grand Finale
The flyby also put Cassini on course for its dramatic last act, known as the Grand Finale. As the spacecraft passed over Titan, the moon's gravity bent its path, reshaping the robotic probe's orbit slightly so that instead of passing just outside Saturn's main rings, Cassini will begin a series of 22 dives between the rings and the planet on April 26. The mission will conclude with a science-rich plunge into Saturn's atmosphere on Sept. 15.
"With this flyby we're committed to the Grand Finale," said Earl Maize, Cassini project manager at JPL. "The spacecraft is now on a ballistic path, so that even if we were to forgo future small course adjustments using thrusters, we would still enter Saturn's atmosphere on Sept. 15 no matter what."
Cassini received a large increase in velocity of approximately 1,925 mph (precisely 860.5 meters per second) with respect to Saturn from the close encounter with Titan.
After buzzing Titan, Cassini coasted onward, reaching the farthest point in its orbital path around Saturn at 8:46 p.m. PDT (11:46 p.m. EDT) on April 22. This point, called apoapse, is where each new Cassini lap around Saturn begins. Technically, Cassini began its Grand Finale orbits at this time, but since the excitement of the finale begins in earnest on April 26 with the first ultra-close dive past Saturn, the mission is celebrating the latter milestone as the formal beginning of the finale.
The spacecraft's first finale dive will take place on April 26 at 2 a.m. PDT (5 a.m. EDT). The spacecraft will be out of contact during the dive and for about a day afterward while it makes science observations from close to the planet. The earliest time Cassini is scheduled to make radio contact with Earth is 12:05 a.m. PDT (3:05 a.m. EDT) on April 27. Images and other data are expected to begin flowing in shortly after communication is established.
Some key numbers for Cassini's Grand Finale and final plunge into Saturn.
Credits: NASA/JPL-Caltech
A new narrated, 360-degree animated video gives viewers a sense of what it might be like to fly alongside Cassini as it makes one of its Grand Finale dives.
NASA VR: Cassini's Grand Finale (360 view)
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Dark Chasm
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.
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.
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Pan Anaglyph (3-D)
These stereo views, or anaglyphs, highlight the unusual, quirky shape of Saturn's moon Pan. They appear three-dimensional when viewed through red-blue glasses with the red lens on the left.
The views show the northern and southern hemispheres of Pan, at left and right, respectively. They have been rotated to maximize the stereo effect.
Standard (non-stereo) versions of these views are presented in PIA21436.
Pan has an average diameter of 17 miles (28 kilometers). The moon orbits within the Encke Gap in Saturn's A ring. See PIA09868 and PIA11529for more distant context views of Pan.
Both of these views look toward Pan's trailing side, which is the side opposite the moon's direction of motion as it orbits Saturn.
These views were acquired by the Cassini narrow-angle camera on March 7, 2017, at distances of approximately 16,000 miles or 25,000 kilometers (left view) and 21,000 miles or 34,000 kilometers (right view).
Image scale in the original images is about 500 feet (150 meters) per pixel (left view) and about 650 feet (200 meters) per pixel (right view). The images have been magnified by a factor of two from their original size.
Quelle: NASA
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Update: 27.04.2017
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Nasa waits on Cassini radio contact from Saturn
Controllers and scientists must wait until Thursday to hear from Cassini.
The probe was due early on Wednesday to make the first of 22 dives in between Saturn's cloudtops and the inner edge of its spectacular rings.
The daredevil flights are designed to gather pictures and other science data of unprecedented resolution.
But Cassini was out of radio contact for the duration of the plunge and is not scheduled to re-establish communications for another day.
Because the probe was moving so fast - at over 110,000km/h (70,000mph) - there was some risk attached to flying through the ring plane.
An impact with even a tiny ice or rock particle at that velocity could do a lot of damage, and so the decision was made to point Cassini's big antenna in the direction of travel, to act as a shield.
But, of course, that meant it could not also then talk to Earth at the same time.
Assuming all goes well, 21 similar dives will be made over the course of the next five months before the probe dumps itself in the atmosphere of Saturn. With so little fuel left in its tanks, Cassini cannot continue its mission for much longer.
Image copyrightNASA/JPL-CALTECHImage captionThe final orbits are designed so that Cassini comes in over the north pole
The US space agency (Nasa) is calling the gap-runs the "grand finale", in part because of their ambition. They promise pictures of unparalleled resolution and science data that finally unlocks key puzzles about the make-up and history of this huge world.
"We're going to top off this mission with a lot of new measurements - some amazing new data," said Athena Coustenis from the Paris Observatory in Meudon, France.
"We're expecting to get the composition, structure and dynamics of the atmosphere, and fantastic information about the rings," she told the BBC.
A key objective is to determine the mass and therefore the age of the rings. The more massive they are, the older they are likely to be - perhaps as old as Saturn itself.
Scientists will do this by studying how the velocity of the probe is altered as it flies through the gravity field generated by the planet and the great encircling bands of ice.
"In the past, we were not able to determine the mass of the rings because Cassini was flying outside them," explained Luciano Iess of the Sapienza University of Rome, Italy.
"Essentially, the contribution of the rings to the gravity field was mixed up with the oblateness of Saturn. It was impossible. But by flying between the rings and the planet, Cassini will be able to disentangle the two effects.
"We're able to tell the velocity of Cassini to an accuracy of a few microns per second. This is indeed fantastic when you think Cassini is more than one billion kilometres away from the Earth."
Having the mass number might not straightforwardly resolve the age issue, however, cautioned Nicolas Altobelli, who is project scientist for Nasa's Cassini mission partner, the European Space Agency.
"We still need to understand the rings' composition. They are made of very nearly pure water-ice. If they're very old, formed at the same time as Saturn, how come they still look so fresh when they're constantly bombarded with meteorite material?" he pondered.
One possibility is that the rings are actually very young, perhaps the remains of a giant comet that got too close to Saturn and broke apart into innumerable fragments.
Coustenis, Iess and Altobelli discussed the end phases of the Cassini mission here in Vienna at the General Assembly of the European Geosciences Union.
The earliest that Cassini is expected to radio home is 07:00 GMT (08:00 BST) on Thursday. Contact should come through Nasa's 70m-wide Deep Space Network antenna at Goldstone, California.
If a stable communications link is established, pictures and other data ought to start coming down about half an hour later.
Image copyrightNASA/JPL-CALTECHImage captionArtwork: Some of the best science of the mission could come out these final orbits
Quelle: BBC
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NASA Spacecraft Dives Between Saturn and Its Rings
This unprocessed image shows features in Saturn's atmosphere from closer than ever before. The view was captured by NASA's Cassini spacecraft during its first Grand Finale dive past the planet on April 26, 2017. Credit: NASA/JPL-Caltech/Space Science Institute › Larger view
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.
Launched in 1997, Cassini arrived at Saturn in 2004. Following its last close flyby of the large moon Titan on April 21 PDT (April 22 EDT), Cassini began what mission planners are calling its "Grand Finale." During this final chapter, Cassini loops Saturn approximately once per week, making a total of 22 dives between the rings and the planet. Data from this first dive will help engineers understand if and how they will need to protect the spacecraft on its future ring-plane crossings. The spacecraft is on a trajectory that will eventually plunge into Saturn's atmosphere -- and end Cassini's mission -- on Sept. 15, 2017.
More information about Cassini's Grand Finale, including images and video, is available at:
The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. JPL, a division of Caltech in Pasadena, California, manages the mission for NASA's Science Mission Directorate. JPL designed, developed and assembled the Cassini orbiter.
Quelle: NASA
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Update: 2.05.2017
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Dust-free space near Saturn baffles Cassini scientists
Unexpected 'big empty' region inside rings will allow NASA to collect more data on next dive.
NASA/JPL-CALTECH
Scientists, coming to grips with recent data from the Cassini spacecraft, are baffled by the lack of dust in the 2,000 kilometre-wide region between Saturn and its rings.
Data collected by Cassini during its first dive through the region on 26 April shows the region to be largely free of any sort of debris.
“The region between the rings and Saturn is ‘the big empty’, apparently,” said Cassini project manager Earl Maize.
But the unexpected finding has been a boon for the spacecraft’s engineers who now won’t have to shield its saucer shape antenna from damaging dust particles.
That means Cassini will now be able to collect data and make observations all the way through its next dive through the ring plane.
“Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected,” said Maize.
An artist's concept shows how Cassini is able to detect radio signals from lightning on Saturn using its Radio and Plasma Wave Science instrument. Lightning strokes emit electromagnetic energy across a broad range of wavelengths.
NASA/JPL-CALTECH
As the RPWS hits particles of dust the data are converted to audio format – pops and cracks that cover 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, they got whistles and squeaks.
“It was a bit disorienting – we weren't hearing what we expected to hear,” said William Kurth, RPWS team leader.
“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.”
Cassini will cross through the ring plane on 2 May 19:38 UTC.
It is scheduled for another 21 dives – four passing through the innermost fringes of the giant planet’s rings.
Hexagon Eye of Saturn Stares into Space in Stunning Photo
NASA's Cassini spacecraft captured this image of Saturn's north polar vortex and surrounding hexagonal jet stream on Jan. 22, 2017, from a distance of about 560,00 miles (900,000 kilometers).
Credit: NASA/JPL-Caltech/Space Science Institute
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Saturn never blinks.
The ringed planet's bizarre "eye" — its north polar vortex and surrounding hexagonal jet stream — stares impassively out into space in an amazing photo by NASA's Saturn-orbiting Cassini probe.
Though NASA released the image just Monday (May 8), Cassini actually snapped it on Jan. 22. At the time, the spacecraft was about 560,000 miles (900,000 kilometers) from the gas giant's cloud tops, agency officials said.
The photo has a resolution of about 33 miles (54 km) per pixel, they added.
Saturn's hexagon is about 20,000 miles (32,000 km) wide and consists of air traveling at about 200 mph (320 km/h), scientists have said. Other planets, including Earth, are known to have jet streams, but none of them remotely resemble Saturn's north polar hexagon.
The strange feature was first spotted in the early 1980s by NASA's Voyager mission. Cassini has gotten some good looks at the hexagon since August 2009, when spring arrived in Saturn's northern hemisphere and the sun began flooding the area with 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," NASA officials wrote in an image description Monday. "In addition to being low in the sky (just like summer at Earth's poles), the sun is nearly 10 times as distant from Saturn as from Earth. This results in the sunlight being only about 1 percent as intense as at our planet."
The $3.2 billion Cassini-Huygens mission is a joint effort involving NASA, the European Space Agency and the Italian Space Agency. The Cassini spacecraft launched in October 1997 and arrived at Saturn in July 2004. (Huygens was a piggyback lander that touched down on Saturn's largest moon, Titan, in January 2005.)
The Cassini orbiter is nearing the end of its impressive mission, which discovered liquid-hydrocarbon seas on Titan and a buried, potentially life-supporting ocean on the Saturn moon Enceladus, among other accomplishments.
Late last month, Cassini began the "Grand Finale" phase of its mission, a series of 22 dives between Saturn and the planet's innermost rings. On Sept. 15, the orbiter will end its life with an intentional dive into Saturn's thick atmosphere, a maneuver designed to ensure that the probe doesn't contaminate Titan or Enceladus with microbes from Earth.
Quelle: SC
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Cassini downlinks view of Titan’s methane clouds on third loop inside rings
Cassini took this picture of Titan’s northern cloud bands Sunday from a distance of more than 300,000 miles (500,000 kilometers). Credit: NASA/JPL-Caltech/Space Science Institute
The Cassini spacecraft captured captivating images of wispy methane clouds suspended above Titan’s hydrocarbon lakes as the probe headed for its third shot through Saturn’s ring gap Tuesday.
The distant pictures, taken from a range of more than 300,000 miles (500,000 kilometers), were recorded Sunday as Saturn’s gravity tugged NASA’s Cassini spacecraft toward its third pass between the planet’s atmosphere and rings.
Cassini crossed Saturn’s ring plane at 0613 GMT (2:13 a.m. EDT) Tuesday, passing about 1,680 miles (2,710 kilometers) from the upper fringes of the planet’s hydrogen-helium atmosphere. That is the closest Cassini has come to Saturn to date, but future flybys will swing even closer to the planet’s cloud tops.
NASA confirmed Cassini weathered the trip through the ring gap as expected. Tuesday’s encounter was the first time the spacecraft stayed in contact with Earth during a ring gap passage.
The images of Titan released Tuesday show bands of methane clouds over the moon’s northern hemisphere. Scientists were predicting cloud formations in Titan’s northern latitudes ahead of the moon’s northern summer solstice a few weeks away.
Titan’s seasons change as Saturn orbits the sun every 29 years, exposing the moon’s northern and southern hemispheres to more sunlight along the way, driving the moon’s weather patterns and moisture cycles.
“These are some of the most intensely bright clouds Cassini has observed on Titan, likely due to high-cloud tops,” NASA officials wrote in a release accompanying the images. “This activity also represents the most extensive cloud outburst on Titan since clouds reappeared at northern mid-latitudes in early 2016.”
Two versions of an image of Titan’s clouds are presented here, one with stronger enhancement (figure A) and one with much softer enhancement (figure B). Credit: NASA/JPL-Caltech/Space Science Institute
The images show a belt of “dunelands” near Titan’s equator, and pockmarked features near the top of one of the pictures are seas of methane and ethane.
Cassini made its 127th and last close flyby of Titan on April 22, but the orbiter will continue long-distance observations as it circles Saturn in the final months of its mission. The spacecraft gathered radar data on the moon’s terrain and hydrocarbon lakes during the April 22 swingby.
Titan’s surface temperature is a frigid minus 292 degrees Fahrenheit (minus 180 degrees Celsius), much too cold for liquid water. But Titan, the only moon in the solar system with a dense atmosphere, experiences day/night cycles and seasons remarkably similar to Earth, with fluctuations in rainfall, cloud patterns and temperatures.
Scientists believe Titan, Saturn’s largest moon, also hides an underground ocean of salty liquid water and ammonia.
After looking at Titan on the inbound leg of its most recent orbit, Cassini’s radio instrument focused on gravity field measurements to study Saturn’s interior and rings as the craft sailed through the ring gap Tuesday.
Cassini will make 19 more flights inside Saturn’s rings, with the next ring crossing set for May 15. Running low on fuel, the mission will end Sept. 15 with a destructive dive into Saturn’s atmosphere.
Quelle: SN
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Update: 16.05.2017
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Wow! Saturn Casts Shadow on Rings in Gorgeous Cassini Photo
NASA's Cassini spacecraft captured this image of Saturn's shadow covering part the planet's rings on Feb. 3, 2017.
Credit: NASA/JPL-Caltech/Space Science Institute
Saturn's shadow takes a bite out of the planet's iconic rings in a stunning new photo by NASA's Cassini spacecraft.
The gas giant's shadow has been shrinking since August 2009, when spring came to Saturn's northern hemisphere, and will continue to do so until summer arrives there on May 24, NASA officials said.
Saturn's rotational axis is tilted relative to the sun, so the ringed planet has seasons, just like Earth does. Saturn seasons each last more than seven Earth years, because it takes the ringed planet more than 29 years to make one lap around the sun.
Cassini captured the newly released photo on Feb. 3, when the probe was about 760,000 miles (1.2 million kilometers) from Saturn, and about 10 degrees above the ring plane, they added.
Cassini has been studying Saturn, its rings and many moons up close for nearly 13 years, but that groundbreaking work is nearly done. The probe is now in the "Grand Finale" phase of its mission, which consists of 22 dives through the gap between Saturn's cloud tops and its innermost rings.
The fourth of these dives, in fact, occurs today.
Cassini's $3.2 billion mission — a joint effort of NASA, the European Space Agency and the Italian Space Agency — will come to an end on Sept. 15 with an intentional death dive into Saturn's thick atmosphere.
This maneuver is intended to ensure that the probe doesn't contaminate Titan or Enceladus, two Saturn moons that might be capable of supporting life, with microbes from Earth, NASA officials have said.
