This view of Saturn's moon Enceladus and its prominent plumes was taken by the Cassini spacecraft on April 2, 2013. Credit: NASA/JPL-Caltech/Space Science Institute.
We can never get enough of seeing those intriguing jets and plumes from Saturn’s moon Enceladus, especially this great view from the Cassini spacecraft where the plumes are back-it from the Sun while the moon’s surface is lit with reflected light from Saturn. And as you can see, those jets are still firing. There are close to 100 geyser jets of varying sizes near Enceladus’s south pole spraying water vapor, icy particles, and organic compounds out into space. If you look closely, you’ll see the entire plume is as large as the moon itself.
Can we please send another spacecraft just to study this fascinating moon?
The image was taken in blue light with the Cassini spacecraft narrow-angle camera on April 2, 2013, when Cassini was about 517,000 miles (832,000 kilometers) from Enceladus.
We all know that Saturn’s moon Enceladus has a whole arsenal of geysers jetting a constant spray of ice out into orbit (and if you didn’t know, learn about it here) but Enceladus isn’t the only place in the Saturnian system where jets can be found — there are some miniature versions hiding out in the thin F ring as well!
Watch the 50-mile-wide Prometheus dip into the F ring (CLICK TO PLAY) NASA/JPL/SSI. Animation by J. Major.
The image above, captured by the Cassini spacecraft on June 20, 2013, shows a segment of the thin, ropy F ring that encircles Saturn just beyond the A ring (visible at upper right). The bright barb near the center is what scientists call a mini jet, thought to be caused by small objects getting dragged through the ring material as a result of repeated passings by the shepherd moon Prometheus.
Coincidentally, it’s gravitational perturbations by Prometheus that help form the objects — half-mile-wide snowball-like clusters of icy ring particles — in the first place.
Unlike the dramatic jets on Enceladus, which are powered by tidal stresses that flex the moon’s crust, these mini jets are much more subtle and occur at the casual rate of 4 mph (2 meters/second)… about the speed of a brisk walk.
The reflective jets themselves can be anywhere from 25 to 112 miles (40 to 180 kilometers) long.
See more images of mini jets — also called “classic trails” — below:
Various images of mini jets captured by Cassini from 2005 to 2008.
This set of images from NASA's Cassini mission shows the turbulent power of a monster Saturn storm. The visible-light image in the back, obtained on Feb. 25, 2011, by Cassini's imaging camera, shows the turbulent clouds churning across the face of Saturn. The inset infrared image, obtained a day earlier, by Cassini's visual and infrared mapping spectrometer, shows the dredging up of water and ammonia ices from deep in Saturn's atmosphere. This was the first time water ice was detected in Saturn's atmosphere. Credit: NASA/JPL-Caltech/SSI/Univ. of Arizona/Univ. of Wisconsin
Remember the huge storm that erupted on Saturn in late 2010? It was one of the largest storms ever observed on the ringed planet, and it was even visible from Earth in amateur-sized telescopes. The latest research has revealed the tempestuous storm churned up something surprising deep within Saturn’s atmosphere: water ice. This is the first detection of water ice on Saturn, observed by the near-infrared instruments on the Cassini spacecraft.
“The new finding from Cassini shows that Saturn can dredge up material from more than 100 miles [160 kilometers],” said Kevin Baines, a co-author of the paper who works at the University of Wisconsin-Madison and NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “It demonstrates in a very real sense that typically demure-looking Saturn can be just as explosive or even more so than typically stormy Jupiter.”
While Saturn’s moons have lots of water ice, Saturn is almost entirely hydrogen and helium, but it does have trace amounts of other chemicals, including water. When we look at Saturn, we’re actually seeing the upper cloud tops of Saturn’s atmosphere, which are made mostly of frozen crystals of ammonia.
Beneath this upper cloud layer, astronomers think there’s a lower cloud deck made of ammonium hydrosulfide and water. Astronomers thought there was water there, but not very much, and certainly not ice.
This series of images from NASA’s Cassini spacecraft shows the development of the largest storm seen on the planet since 1990. These true-color and composite near-true-color views chronicle the storm from its start in late 2010 through mid-2011, showing how the distinct head of the storm quickly grew large but eventually became engulfed by the storm’s tail. Credit: NASA/JPL-Caltech/Space Science Institute
But the storm in 2010-2011 appears to have disrupted the various layers, lofting up water vapor from a lower layer that condensed and froze as it rose. The water ice crystals then appeared to become coated with more volatile materials like ammonium hydrosulfide and ammonia as the temperature decreased with their ascent, the authors said.
“The water could only have risen from below, driven upward by powerful convection originating deep in the atmosphere,” said Lawrence Sromovsky, also of the University of Wisconsin, who lead the research team. “The water vapor condenses and freezes as it rises. It then likely becomes coated with more volatile materials like ammonium hydrosulfide and ammonia as the temperature decreases with their ascent.
Big storms appear in the northern hemisphere of Saturn once every 30 years or so, or roughly once per Saturn year. The first hint of the most recent storm first appeared in data from Cassini’s radio and plasma wave subsystem on Dec. 5, 2010. Soon after that, it could be seen in images from amateur astronomers and from Cassini’s imaging science subsystem. The storm quickly grew to superstorm proportions, encircling the planet at about 30 degrees north latitude for an expanse of nearly 300,000 km (190,000 miles).
The researchers studied the dynamics of this storm, and realized that it worked like the much smaller convective storms on Earth, where air and water vapor are pushed high into the atmosphere, resulting in the towering, billowing clouds of a thunderstorm. The towering clouds in Saturn storms of this type, however, were 10 to 20 times taller and covered a much bigger area. They are also far more violent than an Earth storm, with models predicting vertical winds of more than about 300 mph (500 kilometers per hour) for these rare giant storms.
The storm’s ability to churn up water ice from great depths is evidence of the storm’s explosive power, the team said.
Their research will be published in the Sept. 9 edition of the journal Icarus.
UV image of Titan acquired by Cassini on April 13 (NASA/JPL-Caltech/SSI)
As high summer slowly but steadily approaches on Saturn, Cassini is opening a window to the seasonal changes that occur not only on the ringed planet but also its moons. Here we can see a dark band developing around Titan’s north polar latitudes, a “fancy collar” made visible in ultraviolet wavelengths.
Polar collars have previously been seen by both Hubble and Voyager 2, and in fact a southern version was observed by HST 5 years after the planet’s 1995 equinox.
This summer collar is thought to be part of a seasonal process, related to the migration of upper-level haze material within Titan’s atmosphere.
Source: CICLOPS (Cassini Imaging Central Laboratory for OPerationS)
It’s time for the Weekly Space Hangout. This is our weekly rundown on all the big space news stories of the week, explained by a dedicated team of space journalists.
Host:Fraser Cain
Panel: Alan Boyle, Brian Koberlein, Jason Major, Nicole Gugliucci
We broadcast the Weekly Space Hangout every Friday afternoon as a live Google+ Hangout. You can join us live on Google+, YouTube or right here on Universe Today every Friday at 12:00 pm Pacific / 3:00 pm Eastern.
Animation of Iapetus briefly blocking a distant bright object. (NASA/JPL-Caltech/SSI. Assembled by Jason Major.)
It’s a cosmic cover-up! No, don’t put your tinfoil* hats on, this isn’t a conspiracy — it’s just Saturn’s moon Iapetus drifting in front of the bright star Gamma Orionis (aka Bellatrix) captured on Cassini’s narrow-angle camera on August 10, 2013.
Such an event is called an occultation, a term used in astronomy whenever light from one object is blocked by another — specifically when something visually larger moves in front of something apparently smaller. (The word occult means to hide or conceal… nothing mystical implied!)
The animation above was assembled from 19 raw images publicly available on the JPL Cassini mission site, stacked in Photoshop and exported as a gif. They’ve been rotated 90º from the originals but otherwise they’re right from Cassini’s camera.
Iapetus, seen above as just a thin crescent, is best known for its two-toned appearance. One half of the 914-mile-wide moon is bright and icy, the other coated with a layer of dark reddish material, giving it a real “yin-yang” appearance. (Ok, I guess that’s a little mystical. But purely coincidental.)
The Tao of Iapetus (NASA/JPL-Caltech/SSI)
It’s thought that the dark material originates from a more distant moon, Phoebe, which is being pelted by micrometeorites and shedding its surface out into orbit around Saturn, which eventually gets scooped up by the backwards-orbiting Iapetus.
The difference in albedo affects how Iapetus absorbs solar radiation too, causing the water ice beneath the darker material to evaporate over the course of its 79-Earth-day rotation and migrate around its surface, creating a sort of positive feedback loop.
While neat to look at, occultations are important to science because they provide a way to briefly peer into a world’s atmosphere (or in a small moon’s case, exosphere). Watching how light behaves as it passes behind the limb of a planet or moon lets researchers learn details of the air around it — however tenuous — pretty much for free… no probes or flybys needed!
The occulted star above is Bellatrix, the 1.6-magnitude star that marks Orion’s left shoulder.
Iapetus orbits Saturn at the considerable distance of 2,212,889 miles (3,561,300 km). Learn more about Iapetus here, and as always you can find more fantastic Cassini images from Carolyn Porco’s team at the Space Science Institute in Boulder, Colorado at the CICLOPS site here.
Dramatic plumes, both large and small, spray water ice out from many locations along the famed "tiger stripes" near the south pole of Saturn's moon Enceladus. Credit: NASA/JPL/SSI.
The geyser jets of Enceladus don’t shoot out in a continuous stream, but are more like an adjustable garden hose nozzle, says Cassini scientist Matt Hedman, author of a new paper about the inner workings of this fascinating tiger-striped moon. Observations from Cassini has found that the bright plume emanating from Enceladus’ south pole varies predictably. The fluctuating factor appears to be how far or close Enceladus is to its home planet, Saturn.
Scientists have hypothesized that the intensity of the jets likely varied over time, but until now had not been able to show they changed in a recognizable pattern. Hedman and colleagues were able to see the changes by examining infrared data of the plume as a whole, obtained by Cassini’s visual and infrared mapping spectrometer (VIMS), and looking at data gathered since 2004 when Cassini entered Saturn’s orbit. In 2005, the jets that form the plumes were discovered.
“The way the jets react so responsively to changing stresses on Enceladus suggests they have their origins in a large body of liquid water,” said Christophe Sotin, a co-author and Cassini team member. “Liquid water was key to the development of life on Earth, so these discoveries whet the appetite to know whether life exists everywhere water is present.”
This set of images from NASA’s Cassini mission shows how the gravitational pull of Saturn affects the amount of spray coming from jets at the active moon Enceladus. Enceladus has the most spray when it is farthest away from Saturn in its orbit (inset image on the left) and the least spray when it is closest to Saturn (inset image on the right). Credit: NASA/JPL-Caltech/University of Arizona/Cornell/SSI.
The scientists say this new finding adds to evidence that a liquid water reservoir or ocean lurks under the icy surface of the moon. This is the first clear observation the bright plume emanating from Enceladus’ south pole varies predictably. The findings were published in a scientific paper in this week’s edition of Nature.
The VIMS instrument, which enables the analysis of a wide range of data including the hydrocarbon composition of the surface of another Saturnian moon, Titan, and the seismological signs of Saturn’s vibrations in its rings, collected more than 200 images of the Enceladus plume from 2005 to 2012.
These data show the plume was dimmest when the moon was at the closest point in its orbit to Saturn. The plume gradually brightened until Enceladus was at the most distant point, where it was three to four times brighter than the dimmest detection. This is comparable to moving from a dim hallway into a brightly lit office.
Adding the brightness data to previous models of how Saturn squeezes Enceladus, the scientists deduced the stronger gravitational squeeze near the planet reduces the opening of the tiger stripes and the amount of material spraying out. They think the relaxing of Saturn’s gravity farther away from planet allows the tiger stripes to be more open and for the spray to escape in larger quantities.
“Cassini’s time at Saturn has shown us how active and kaleidoscopic this planet, its rings and its moons are,” said Linda Spilker, Cassini project scientist at JPL. “We’ve come a long way from the placid-looking Saturn that Galileo first spied through his telescope. We hope to learn more about the forces at work here as a microcosm for how our Solar System formed.”
Enceladus has likely been subject to other gravitational forces over time as well. Previous studies have shown that over hundreds of millions of years, an existing gravitational interaction between Enceladus and another moon, Dione, has caused the orbit of Enceladus to grow increasingly more elongated, or eccentric.
In turn, this produced much more tidal stress in the past and scientists think that contributed to the wide-scale fracturing and friction within Enceladus’ icy crust. The friction leads to melting of internal ice and produces an ocean and eruptions of water and organics on the surface.
It’s time for another Weekly Space Hangout, where a dedicated team of space journalists run down all the big stories in space and astronomy for the week of July 26, 2013.
We record the Weekly Space Hangout live as a Google+ Hangout on Air every Friday at Noon Pacific, 3:00 pm Eastern. You can watch the show live on Google+, or here on Universe Today. But you can also watch the archive after the fact, if live video isn’t your thing.
The face of Earth aimed toward Cassini during imaging on July 19, 2013
So along with the rest of the world, you smiled. You waved. You went outside on July 19, wherever you were, and looked upwards and out into the solar system knowing that our robotic representative Cassini would be capturing a few pixels’ worth of photons bouncing off our planet when they eventually reached Saturn, 900 million miles away. But did Cassini actually capture any photons coming from where you were? The image above will tell you.
Assembled by the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo (where the enormous 305-meter radio telescope is located) this image shows what side of Earth was facing Cassini when its “pale blue dot” images were obtained, at approximately 22:47 UTC (Cassini time.)
Didn’t make it into Cassini’s photo? That’s ok… maybe MESSENGER had already caught you earlier that very same day:
The view of Earth seen by MESSENGER from Mercury on July 19, 2013
Before Cassini took its images — several hours before, in fact — the MESSENGER spacecraft was holding some photo shoots of its own from 61 million miles in the other direction!
The image above shows the side of Earth that was facing Mercury on the morning of July 19, 2013, when MESSENGER was acquiring images in our direction during a hunt for any possible satellites of the innermost planet.
Earth was as bright (-4.8 magnitude) as the maximum brightness of Venus at the moment the image was taken from Mercury.
Of course, in both series of images specific details of our planet can’t be made out — Earth was barely more than a pixel in size (regardless of any bloom caused by apparent brightness.) Clouds, countries, continents, oceans… the entire population of our world, reduced to a single point of light — a “mote of dust suspended in a sunbeam.”
For both portrayals, high-resolution black and white images from the GOES East and Meteosat meteorological satellites were combined with color information from NASA Visible Earth to generate true-color images of our planet as it would have looked to each respective imaging spacecraft… if they had the impossibly-precise optics to resolve Earth from such distances, of course.
But it’s ok that they don’t… we can still use our imaginations.
Earth from the geostationary weather satellite GOES East on July 19, 2013 at 5 PM EST. This is approximately the view that Cassini would have had of Earth during imaging.
Image credits: PHL @ UPR Arecibo, NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington, NERC Satellite Station, Dundee University, Scotland. Thanks to Prof. Abel Méndez (PHL/UCR) for the heads-up on these.
The Day the Earth Smiled: Sneak Preview. In this rare image taken on July 19, 2013, the wide-angle camera on NASA's Cassini spacecraft has captured Saturn's rings and our planet Earth and its moon in the same frame. Image Credit: NASA/JPL-Caltech/Space Science Institute
The Day the Earth Smiled: Sneak Preview
In this rare image taken on July 19, 2013, the wide-angle camera on NASA’s Cassini spacecraft has captured Saturn’s rings and our planet Earth and its moon in the same frame. Image Credit: NASA/JPL-Caltech/Space Science Institute
See below our wider context mosaic of the Earth, Saturn and its majestic rings[/caption]
Breathtaking raw images of the Earth and Saturn system snapped by NASA’s Cassini spacecraft on July 19 during the worldwide ‘Wave at Saturn’ campaign are streaming back across 1 billion miles of interplanetary space.
Science team members are now busily processing the images to create individual color composites and a panoramic view of the ‘pale blue dot’ and the entire Saturnian system.
NASA just released the first individual color composite focusing on Earth – see above. And its spectacular!
See below our preliminary mosaic showing the Earth in context with nearly half of Saturn and floating in between its incomparably majestic rings.
Partial context mosaic of the Earth and Saturn taken by NASA’s Cassini orbiter on July 19, 2013. This mosaic was assembled from five wide angle camera raw images and offers a sneak peek of the complete panorama. Credit: NASA/JPL-Caltech/Ken Kremer/Marco Di Lorenzo
To capture all of Saturn and its wide swath of rings, Cassini’s wide angle camera snapped a mosaic of 33 footprints.
“At each footprint, images were taken in different spectral filters for a total of 323 images,” says Carolyn Porco, Cassini Imaging Team leader of the Space Science Institute in Boulder, Colo.
Cassini took the pictures of Earth between 2:27 and 2:42 p.m. PDT on Friday, July 19 from a distance of about 898 million miles (1.44 billion kilometers) away from the home to every human being that has ever lived.
The images show the Earth and the Moon as dots barely about a pixel wide but do reveal the ‘pale blue dot’ that is home to all of humanity and our whitish colored neighbor.
Distant views of the Earth from our robotic explorers, especially from the outer reaches of our Solar System, are few and far between, and are therefore events for space and astronomy enthusiasts and everyone else to savor.
“One of the most exciting Cassini events in 2013 will be the unusual opportunity on July 19 to image the whole Saturn system as it is backlit by the sun,” explained Linda Spilker, Cassini project scientist of NASA’s Jet Propulsion Laboratory, Pasadena, Calif.
“With Saturn covering the harsh light of the sun, we will be gathering unique ring science and also catching a glimpse of our very own home planet.”
Cassini previously took an absolutely fabulous mosaic of Saturn and Earth back in 2006 that stands as one of the landmark images of the space age.
Besides being picturesque, such mosaics also serve science. For example, the 2006 image “revealed that the dusty E ring, which is fed by the water-ice plume of the moon Enceladus, had unexpectedly large variations in brightness and color around its orbit,” says Spilker.
“We’ll want to see how that looks seven Earth years and a Saturnian season later, giving us clues to the forces at work in the Saturn system. We’ll do this analysis by collecting data from our visual and infrared mapping spectrometer, composite infrared mapping spectrometer and ultraviolet imaging spectrograph in addition to the imaging cameras.”
This simulated view from NASA’s Cassini spacecraft shows the expected positions of Saturn and Earth on July 19, 2013, around the time Cassini will take Earth’s picture. Cassini will be about 898 million miles (1.44 billion kilometers) away from Earth at the time. That distance is nearly 10 times the distance from the sun to Earth. Image credit: NASA/JPL-Caltech
“July 19 marked the first time people on Earth had advance notice their planet’s portrait was being taken from interplanetary distances,” says NASA.
I waved fondly at Saturn and hope you had the chance to wave at Saturn from all across the globe. NASA reports that nearly 20,000 participated in organized events. Countless others waved too.
Cassini was launched in 1997 and achieved orbit at Saturn in 2004. The mission is scheduled to continue until 2017 when it will commit a suicide death dive into the gas giant.
“We can’t see individual continents or people in this portrait of Earth, but this pale blue dot is a succinct summary of who we were on July 19,” said Spilker in a NASA statement.
“Cassini’s picture reminds us how tiny our home planet is in the vastness of space, and also testifies to the ingenuity of the citizens of this tiny planet to send a robotic spacecraft so far away from home to study Saturn and take a look-back photo of Earth.”
JPL Waves at Saturn
As NASA’s Cassini spacecraft turned its imaging cameras to Earth, scientists, engineers and visitors at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., gathered to wave at our robotic photographer in the Saturn system on July 19, 2013. Credit: NASA/JPL-Caltech
