Saturn Archives

April 10, 2013December 23, 2015 by Nancy Atkinson

Rain is Falling from Saturn’s Rings

This artist's concept illustrates how charged water particles flow into the Saturnian atmosphere from the planet's rings, causing a reduction in atmospheric brightness. Credit: NASA/JPL-Caltech/Space Science Institute/University of Leicester

Astronomers have known for years there was water in Saturn’s upper atmosphere, but they weren’t sure exactly where it was coming from. New observations have found water is raining down on Saturn, and it is coming from the planet’s rings.

“Saturn is the first planet to show significant interaction between its atmosphere and ring system,” said James O’Donoghue, a postgraduate researcher at the University of Leicester and author of a new paper published in the journal Nature. “The main effect of ring rain is that it acts to ‘quench’ the ionosphere of Saturn, severely reducing the electron densities in regions in which it falls.”

Using the Keck Observatory, O’Donoghue and a team of researchers found charged water particles falling from the planet’s rings into Saturn’s atmosphere. They also found the extent of the ring-rain is far greater, and falls across larger areas of the planet, than previously thought. The work reveals the rain influences the composition and temperature structure of parts of Saturn’s upper atmosphere.

O’Donoghue said the ring’s effect on electron densities is important because it explains why, for many decades, observations have shown electron densities to be unusually low at some latitudes at Saturn.

“It turns out a major driver of Saturn’s ionospheric environment and climate across vast reaches of the planet are ring particles located 120,000 miles [200,000 kilometers] overhead,” said Kevin Baines, a co-author on the paper, from the Jet Propulsion Laboratory. “The ring particles affect which species of particles are in this part of the atmospheric temperature.”

In the early 1980s, images from NASA’s Voyager spacecraft showed two to three dark bands on Saturn and scientists theorized that water could have been showering down into those bands from the rings. Then astronomers using ESA’s Infrared Observatory discovered the presence of trace amounts of water in Saturn’s atmosphere back in 1997, but couldn’t really find an explanation for why it was there and how it got there.

Then in 2011 observations with the Herschel space observatory determined water ice from geysers on Enceladus formed a giant ring of water vapor around Saturn.

But the bands seen by Voyager were not seen again until 2011 as well, when the team observed the planet with Keck Observatory’s NIRSPEC, a near-infrared spectrograph that combines broad wavelength coverage with high spectral resolution, allowing the observers to clearly see subtle emissions from the bright parts of Saturn.

The ring rain’s effect occurs in Saturn’s ionosphere (Earth has a similar ionosphere), where charged particles are produced when the otherwise neutral atmosphere is exposed to a flow of energetic particles or solar radiation. When the scientists tracked the pattern of emissions of a particular hydrogen molecule consisting of three hydrogen atoms (rather than the usual two), they expected to see a uniform planet-wide infrared glow.

What they observed instead was a series of light and dark bands with a pattern mimicking the planet’s rings. Saturn’s magnetic field “maps” the water-rich rings and the water-free gaps between rings onto the planet’s atmosphere.

They surmised that charged water particles from the planet’s rings were being drawn towards the planet by Saturn’s magnetic field and neutralizing the glowing triatomic hydrogen ions. This leaves large “shadows” in what would otherwise be a planet-wide infrared glow. These shadows cover 30 to 43 percent of the planet’s upper atmosphere surface from around 25 to 55 degrees latitude. This is a significantly larger area than suggested by the Voyager images.

Both Earth and Jupiter have a very uniformly glowing equatorial region. Scientists expected this pattern at Saturn, too, but they instead saw dramatic differences at different latitudes.

“Where Jupiter is glowing evenly across its equatorial regions, Saturn has dark bands where the water is falling in, darkening the ionosphere,” said Tom Stallard, one of the paper’s co-authors at Leicester. “We’re now also trying to investigate these features with an instrument on NASA’s Cassini spacecraft. If we’re successful, Cassini may allow us to view in more detail the way that water is removing ionized particles, such as any changes in the altitude or effects that come with the time of day.”

Sources: Keck Observatory
, Nature.

April 8, 2013December 23, 2015 by David Dickinson

The Return of Saturn: A Guide to the 2013 Opposition

A fine recent view of Saturn as captured by Daniel Robb. (Credit & Copyright: Daniel Robb/Universe Today flickr community. All rights reserved).

A star party favorite is about to return to evening skies.

The planet Saturn can now be spied low to the southeast for northern hemisphere observers (to the northeast for folks in the southern) rising about 1-2 hours after local sunset this early April. That gap will continue to close until Saturn is opposite to the Sun in the sky later this month and rises as the Sun sets.

Opposition occurs on April 28^th at 8:00 UT/4:00AM EDT. Saturn will shine at magnitude +0.1 and appear 18.8” in diameter excluding the rings, which give it a total angular diameter of 43”.

Saturn has just passed into the faint constellation Libra for 2013, although its springtime retrograde loop will bring it back into Virgo briefly. Both the 2013 and 2014 opposition will occur in Libra. Saturn will also pass 26’ from +4.2 Kappa Virginis on July 3^rd as it moves back into Virgo while in retrograde before resuming direct motion back into Libra.

Saturn currently lies about 15° to the lower left of the +1.04 magnitude star Spica, also known as Alpha Virginis. Remember the handy saying to “Spike to Spica” from the handle of the Big Dipper asterism to locate the region. Another handy finder tip; stars twinkle, planet generally don’t. That is, unless your skies are extremely turbulent!

With an orbital period 29.46 years, Saturn moves slowly eastward year to year, taking 2-3 years to cross through each constellation along the ecliptic.

Oppositions are roughly 378 days apart and thus move forward on our calendar by about two weeks a year. Successive oppositions also move about 13° eastward per year.

Saturn as imaged by the author on June 11th, 2012.

Oppositions of the ringed planet are also currently becoming successively favorable for southern observers over the coming years. Saturn crossed into the southern celestial hemisphere some years back, and will be at its southernmost in 2018.

Saturn won’t pass north of the celestial equator again until early 2026. Saturn is 15 million kilometres farther from us than opposition last year as its moving toward aphelion in 2018.

Saturn will reach eastern quadrature this summer on July 28^th and stand its highest south at sunset northern hemisphere observers. South of the equator, it will pass directly overhead or transit to the north. Saturn will be with us for most of the remainder of 2013 in evening skies until reaching solar conjunction on November 6^th.

Looking at Saturn with binoculars, you’ll immediately note that something is amiss.

You’re getting a view similar to that of Galileo, who sketched Saturn as a sort of “double handled cup.” In fact, it wasn’t until 1655 that Christian Huygens correctly hypothesized that the rings of Saturn are a flat disk that is not physically in contact with the planet.

Huygens also discovered the large moon Titan. Shining at magnitude +8.5 and taking 16 days to orbit Saturn, Titan is the second largest moon in our solar system after Ganymede. Titan would easily be a planet in its own right if it orbited the Sun. Titan is easily picked out observing Saturn at low power through a telescope.

Saturn's system of moons visible through a small telescope. orientation is for May 9th, 2013. (Created by the author using Starry Night). — Saturn’s system of moons visible through a small telescope. orientation is for May 9th, 2013. (Created by the author using Starry Night).

Observing Saturn at slightly higher magnification, five moons interior to Titan become apparent. From outside in, they are Rhea, Dione, Tethys, Enceladus, and Mimas. Exterior to Titan is the curious moon of Iapetus. Taking 79 days to complete one orbit of Saturn, Iapetus varies in brightness from magnitude +11.9 to +10.2, or a factor of over 5 times. Arthur C. Clarke placed the final monolith in the book adaptation of 2001: A Space Odyssey on Iapetus for this reason. Close-ups from the Cassini spacecraft reveal a two-faced world covered with a dark leading hemisphere and a bright trailing side, but alas, no alien artifacts.

But the centerpiece of observing Saturn through a telescope is its brilliant and complex system of rings. The A, B, and C rings are easily apparent through a backyard telescope, as is the large spacing known as the Cassini Gap.

The rings are also currently tilted in respect to our Earthly vantage point. The rings were edge-on in 2009 and vanish when this occurs every 15-16 years.

This year, we see the rings of Saturn at a respectable 19 ° opening and widening. The rings will appear at their widest at over 25° in 2017 and then become edge-on again in 2025.

The average tilt of Saturn's ring system as seen from Earth spanning 2008-2026. (Graph created by author). — The average tilt (in degrees) of Saturn’s ring system as seen from Earth spanning 2008-2026. (Graph created by author).

The ring system of Saturn adds 0.7 magnitudes of overall brightness to the planet at opposition this year.

Another interesting optical phenomenon to watch for in the days leading up to opposition is known as the “opposition surge” in brightness, or the Seeliger effect. This is a retro-reflector effect familiar to many as high-beam headlights strike a highway sign. Think of the millions of particles making up Saturn’s rings as tiny little “retro-reflectors” focusing sunlight back directly along our line of sight. The opposition surge has been noted for other planets, but it’s most striking for Saturn when its rings are at their widest.

The disk of Saturn will cast a shadow straight back onto the rings around opposition and thus vanish from our view. The shadow across the back of the rings will then become more prominent over subsequent months, reaching its maximum angle at quadrature this northern hemisphere summer and then beginning to slowly slide back behind the planet again. A true challenge is to glimpse the disk of the through the Cassini gap in the rings… you’ll need clear steady skies and high magnification for this one!

It’s also interesting to note a very shallow partial lunar eclipse occurs with Saturn nearby just three days prior to opposition on April 25^th. Saturn will appear 4° north of the Moon and it may be just possible to image both in the same frame.

The location of Saturn and the Full Moon during the April 25th partial eclipse. (Created by the author using Starry Night).

Saturn takes about 30 years to make its way around the zodiac. I remember just beginning to observe Saturn will my new 60mm Jason refractor as a teenager in 1983 as it crossed the constellation Virgo.Hey, I’ve been into astronomy for over one “Saturnian year” now… where will the next 30 years find us?

March 28, 2013December 23, 2015 by Nancy Atkinson

Solar System Antiquities Abound in Saturn’s Rings

The Cassini spacecraft observes three of Saturn's moons set against the darkened night side of the planet. Credit: NASA/JPL/Space Science Institute

Anyone looking for miscellanies from the early days of the Solar System can likely find them all in one place: the Saturn system. A new analysis of data from the Cassini spacecraft suggests that Saturn’s moons and rings are “antiquities” from around the time of our Solar System’s very beginnings.

“Studying the Saturnian system helps us understand the chemical and physical evolution of our entire solar system,” said Cassini scientist Gianrico Filacchione, from Italy’s National Institute for Astrophysics. “We know now that understanding this evolution requires not just studying a single moon or ring, but piecing together the relationships intertwining these bodies.”

The rings, moons, moonlets, and other debris date back more than 4 billion years. They are from around the time that the planetary bodies in our neighborhood began to form out of the protoplanetary nebula, the cloud of material still orbiting the sun after its ignition as a star.

Data from Cassini’s visual and infrared mapping spectrometer (VIMS) have revealed how water ice and also colors — which are the signs of non-water and organic materials –are distributed throughout the Saturnian system. The spectrometer’s data in the visible part of the light spectrum show that coloring on the rings and moons generally is only skin-deep.

Using its infrared range, VIMS also detected abundant water ice – too much to have been deposited by comets or other recent means. So the authors deduce that the water ices must have formed around the time of the birth of the solar system, because Saturn orbits the sun beyond the so-called “snow line.” Out beyond the snow line, in the outer solar system where Saturn resides, the environment is conducive to preserving water ice, like a deep freezer. Inside the solar system’s “snow line,” the environment is much closer to the sun’s warm glow, and ices and other volatiles dissipate more easily.

The effects of the small moon Prometheus loom large on two of Saturn's rings in this image taken a short time before Saturn's August 2009 equinox. Credit: NASA — The effects of the small moon Prometheus loom large on two of Saturn’s rings in this image taken a short time before Saturn’s August 2009 equinox. Credit: NASA

The colored patina on the ring particles and moons roughly corresponds to their location in the Saturn system. For Saturn’s inner ring particles and moons, water-ice spray from the geyser moon Enceladus has a whitewashing effect.

Farther out, the scientists found that the surfaces of Saturn’s moons generally were redder the farther they orbited from Saturn. Phoebe, one of Saturn’s outer moons and an object thought to originate in the far-off Kuiper Belt, seems to be shedding reddish dust that eventually rouges the surface of nearby moons, such as Hyperion and Iapetus.

A rain of meteoroids from outside the system appears to have turned some parts of the main ring system – notably the part of the main rings known as the B ring — a subtle reddish hue. Scientists think the reddish color could be oxidized iron — rust — or polycyclic aromatic hydrocarbons, which could be progenitors of more complex organic molecules.

One of the big surprises from this research was the similar reddish coloring of the potato-shaped moon Prometheus and nearby ring particles. Other moons in the area were more whitish.

“The similar reddish tint suggests that Prometheus is constructed from material in Saturn’s rings,” said co-author Bonnie Buratti, a VIMS team member based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Scientists had been wondering whether ring particles could have stuck together to form moons — since the dominant theory was that the rings basically came from satellites being broken up. The coloring gives us some solid proof that it can work the other way around, too.”

“Observing the rings and moons with Cassini gives us an amazing bird’s-eye view of the intricate processes at work in the Saturn system, and perhaps in the evolution of planetary systems as well,” said Linda Spilker, Cassini project scientist, based at JPL. “What an object looks like and how it evolves depends a lot on location, location, location.”

Filacchione’s paper has been published in the Astrophysical Journal.

Source: JPL

March 19, 2013December 23, 2015 by Jason Major

Enceladus’ Jets Reach All the Way to its Sea

Saturn's moon Enceladus sprays its salty sea out into space. Those plumes are rich in phosphates. (NASA/JPL/SSI/J. Major)

Thanks to the Cassini mission we’ve known about the jets of icy brine spraying from the south pole of Saturn’s moon Enceladus for about 8 years now, but this week it was revealed at the 44th Lunar and Planetary Science Conference outside Houston, Texas that Enceladus’ jets very likely reach all the way down to the sea — a salty subsurface sea of liquid water that’s thought to lie beneath nearly 10 kilometers of ice.

Enceladus’ jets were first observed by the Cassini spacecraft in 2005. The jets constantly spray fine particles of ice into space which enter orbit around Saturn, creating the hazy, diffuse E ring in which Enceladus resides.

Emanating from deep fissures nicknamed “tiger stripes” that gouge the 512-km (318-mile) -wide moon’s south pole the icy jets — and the stripes — have been repeatedly investigated by Cassini, which has discovered that not only do the ice particles contain salts and organic compounds but also that the stripes are surprisingly warm, measuring at 180 Kelvin (minus 135 degrees Fahrenheit) — over twice as warm as most other regions of the moon.

Where the jets are getting their supply of liquid water has been a question scientists have puzzled over for years. Is friction caused by tidal stresses heating the insides of the stripes, which melts the ice and shoots it upwards? Or do the fissures actually extend all the way down through Enceladus’ crust to a subsurface ocean of liquid water, and through tidal pressure pull vapor and ice up to the surface?

"Baghdad Sulcus," one of many tiger stripe fissures on Enceladus (NASA/JPL/SSI) — “Baghdad Sulcus,” one of many tiger stripe fissures on Enceladus (NASA/JPL/SSI)

Researchers are now confident that the latter is the case.

In a presentation at the Lunar and Planetary Science Conference titled “How the Jets, Heat and Tidal Stresses across the South Polar Terrain of Enceladus Are Related” (see the PDF here) Cassini scientists note that the amount of heating due to tidal stress seen along Enceladus’ tiger stripes isn’t nearly enough to cause the full spectrum of heating observed, and the “hot spots” that have been seen don’t correlate with the type of heating caused by shear friction.

Instead, the researchers believe that heat energy is being carried upwards along with the pressurized water vapor from the subsurface sea, warming the areas around individual vents as well as serving to keep their channels open.

With 98 individual jets observed so far on Enceladus’ south polar terrain and surface heating corresponding to each one, this scenario, for lack of a better term… seems legit.

What this means is that not only does a moon of Saturn have a considerable subsurface ocean of liquid water with a heat source and Earthlike salinity (and also a bit of fizz) but also that it’s spraying that ocean, that potentially habitable environment, out into local space where it can be studied relatively easily — making Enceladus a very intriguing target for future exploration.

“To touch the jets of Enceladus is to touch the most accessible salty, organic-rich, extraterrestrial body of water and, hence, habitable zone, in our solar system.”

– Cassini imaging team leader Carolyn Porco et al.

Enceladus is actively spraying its habitable zone out into space (NASA/JPL/SSI)

Research notes via C. Porco, D. DiNino, F. Nimmo, CICLOPS, Space Science Institute at Boulder, CO, and Earth and Planetary Sciences at UC Santa Cruz, CA.

Top image: color-composite of Enceladus made from raw Cassini images acquired in 2010. The moon is lit by reflected light from Saturn while the jets are backlit by the Sun.

March 12, 2013April 26, 2016 by Jason Major

Saturn to Shed its Spooky Spokes for Summer

Cassini image of Saturn's rings from Dec. 20, 2012 (NASA/JPL-Caltech/SSI)

As Saturn steadily moves along its 29.7-year-long orbit toward summertime in its northern hemisphere NASA’s Cassini spacecraft is along for the ride, giving astronomers a front-row seat to seasonal changes taking place on the ringed planet.

One of these fluctuations is the anticipated disappearance of the “spokes” found in the rings, a few of which can be seen above in an image captured on Dec. 20 of last year.

First identified by Voyager in 1980, spokes are ghostly streaks of varying size and brightness that stretch radially across Saturn’s ring system. They orbit around the planet with the ring particles and can last for hours before fading away.

*Under the right lighting conditions spokes can appear dark, as seen in this image from Jan. 2010 (NASA/JPL/SSI)*

One of the most elusive and transient of features found on Saturn, spokes are thought to be made up of larger microscopic particles of ice — each at least a micron or more — although exactly what makes them gather together isn’t yet known.

They are believed to be associated with interactions between ring particles and Saturn’s electromagnetic field.

“The spokes are most prominent at a point in the rings where the ring particles are moving at the same speed as Saturn’s electromagnetic field,” said Brad Wallis, Cassini rings discipline scientist. “That idea and variations of it are still the most prominent theories about the spokes.”

Other researchers have suggested that they may be caused by electron beams issuing outwards along magnetic field lines from lightning storms in Saturn’s atmosphere.

Regardless of how they are created, spokes are more often observed when sunlight is striking the rings edge-on — that is, during the spring and autumn equinoxes. Perhaps the increased solar radiation along Saturn’s equator increases the formation of lightning-generating storms, in turn creating more spokes? It’s only a guess, but Cassini — and astronomers — will be watching to see if these furtive features do in fact fail to appear during Saturn’s northern summer, the height of which arrives in 2016.

These are the Last Close-up Images of the Moon Rhea from Cassini

Cassini looks over the heavily cratered surface of Rhea during the spacecraft's flyby of the moon on March 10, 2012. Credit: NASA/JPL-Caltech/SSI.

“Take a good, long, luxurious look at these sights from another world,” said Cassini Imaging Team Leader Carolyn Porco, “as they will be the last close-ups you’ll ever see of this particular moon.”

On Saturday, March 9, 2013 Cassini made the last close flyby of Rhea during its mission, coming within 620 miles (997km) of the surface of the moon. Cassini’s mission is slated to end in 2017 with a controlled fall into Saturn’s atmosphere. Cassini has been in orbit around Saturn since 2004 and is in its second mission extension.

“Our mission at Saturn has been ongoing for nearly 9 years and is slated to continue for another 4,” Porco said in an email message. “Targeted flybys of the moons Dione, in June and August of 2015, and Enceladus, in October and December of 2015, are all that remains on the docket for detailed exploration of Saturn’s medium-sized moons.”

See more below:

This raw, unprocessed image of Rhea was taken on March 9, 2013. Credit: NASA/JPL-Caltech/Space Science Institute

Besides these great final shots, NASA said the primary purpose of this last close flyby of Rhea was to probe the internal structure of the moon by measuring the gravitational pull of Rhea against the spacecraft’s steady radio link to NASA’s Deep Space Network here on Earth. The results will help scientists understand whether the moon is homogeneous all the way through or whether it has differentiated into the layers of core, mantle and crust.

In addition, Cassini’s imaging cameras will take ultraviolet, infrared and visible-light data from Rhea’s surface. The cosmic dust analyzer will try to detect any dusty debris flying off the surface from tiny meteoroid bombardments to further scientists’ understanding of the rate at which “foreign” objects are raining into the Saturn system.

“We’re nearing the end of this historic expedition,” Porco said. “Let’s enjoy the finale while we can.”

This raw, unprocessed image of Rhea was taken on March 10, 2013 and received on Earth March 10, 2013. The camera was pointing toward Rhea at approximately 280,317 kilometers away, and the image was taken using the CL1 and CL2 filters. Credit: NASA/JPL-Caltech/SSI

See more of the raw images from the flyby at the CICLOPS website.

March 4, 2013December 23, 2015 by Nancy Atkinson

Stunning Views of Venus, All the Way from Saturn

Venus appears just off the edge of the dark disc of Saturn, in the upper part of the image, directly above the white streak of Saturn's G ring. Credit: NASA/JPL-Caltech/Space Science Institute

Two amazing images from the Cassini spacecraft today: We know how brightly Venus shines in our own night sky; now here’s visual proof it shines brightly even in the skies above Saturn. In one image it shines so brightly that it is even visible looking through Saturn’s rings! But in this absolutely stunning shot, above, Venus appears as a morning star, just off the edge of the planet. From Cassini, you’re looking directly above the edge of Saturn’s G ring to see the white dot, which is Venus. Lower down, Saturn’s E ring makes an appearance, looking blue thanks to the scattering properties of the dust that comprises the ring. (A bright spot near the E ring is a distant star, the Cassini CICLOPS team says.)

This beautiful image was taken on January 4, 2013.

On average, Venus and Saturn are about 1,321,200,000 km (820,955,619 mi or 8.83 astronomical units) apart, so that’s a nice, long distance shot! Venus is brighter in Saturn’s skies than Earth is, however, because Venus is covered in thick sulfuric acid clouds, making it very bright.

And here’s the other great shot, showing Saturn and its rings in true color:

NASA's Cassini spacecraft spies the bright, cloudy terrestrial planet, Venus. Credit: NASA/JPL-Caltech/Space Science Institute — NASA’s Cassini spacecraft spies the bright, cloudy terrestrial planet, Venus. Credit: NASA/JPL-Caltech/Space Science Institute

Venus is the white dot, just above and to the right of the image center. Again, its amazing that it shines through the rings.

This view looks toward the unilluminated side of the rings from about 17 degrees below the ring plane, and was taken in visible light (and it is a true-color image) with the Cassini spacecraft wide-angle camera on Nov. 10, 2012.

In an email about these images, Cassini imaging team lead Carolyn Porco said that even though Venus reaches nearly 900 degrees Fahrenheit (500 degrees Celsius) and has a surface pressure 100 times that of Earth’s, Venus is considered a twin of our planet because of their similar sizes, masses, rocky compositions and close orbits.

And so, she pointed out, “Think about Venus the next time you find yourself reveling in the thriving flora, balmy breezes, and temperate climate of a lovely day on Earth, and remember: you could be somewhere else!”

See more about these images at the CICLOPS (Cassini Imaging Central Laboratory for Operations) website.

February 28, 2013December 23, 2015 by Jason Major

A New Look at Saturn’s Northern Hexagon

Raw Cassini image captured on 26 Feb. 2013 (NASA/JPL/SSI)

Freshly delivered from Cassini’s wide-angle camera, this raw image gives us another look at Saturn’s north pole and the curious hexagon-shaped jet stream that encircles it, as well as the spiraling vortex of clouds at its center.

Back in November we got our first good look at Saturn’s north pole in years, now that Cassini’s orbit is once again taking it high over the ringplane. With spring progressing on Saturn’s northern hemisphere the upper latitudes are getting more and more sunlight — which stirs up storm activity in its atmosphere.

The bright tops of upper-level storm clouds speckle Saturn’s skies, and a large circular cyclone can be seen near the north pole, within the darker region contained by the hexagonal jet stream. This could be a long-lived storm, as it also seems to be in the images captured on November 27.

About 25,000 km (15,500 miles) across, Saturn’s hexagon is wide enough to fit nearly four Earths inside!

The Saturn hexagon as seen by Voyager 1 in 1980 (NASA)

The hexagon was originally discovered in images taken by the Voyager spacecraft in the early 1980s. It encircles Saturn at about 77 degrees north latitude and is estimated to whip around the planet at speeds of 354 km/h (220 mph.)

Watch a video of the hexagon in motion here.

The rings can be seen in the background fading into the shadow cast by the planet itself. A slight bit of ringshine brightens Saturn’s nighttime limb.

Cassini was approximately 579,653 kilometers (360,180 miles) from Saturn when the raw image above (W00079643) was taken.

Image credit: NASA/JPL/Space Science Institute

January 14, 2013December 23, 2015 by Nancy Atkinson

Saturn’s Mini-Moons Align for Family Portrait

Saturn, its rings and three moons are visible in this image from Cassini. Credit: NASA/ESA

It’s a good thing NASA labeled the moons in this image of Saturn, because they are pretty hard to see. But they are there, keeping each other company in this Cassini spacecraft image of Saturn’s night side. And as the Cassini team says, it seems fitting that they should do so since in Greek mythology, their namesakes were brothers.

In Greek mythology these three were all sons of Iapetus (another of Saturn’s moons), and supposedly Prometheus and Epimetheus were tasked with creating humans. Prometheus was a pretty good sort, and gave gifts to humans like fire; Epimetheus gave humans evil – not so good. And famously, Atlas ended up having the weight of the world on his shoulders.

But in science, Prometheus the moon is about 86 kilometers across (53 miles) and is located just inside the F ring in this image, while Epimetheus is about 113 kilometers across (70 miles) and is farther from the rings, due right of Prometheus in this image. Atlas is the tiny guy (30 kilometers across (19 miles) and can be just barely seen between the A and F rings almost right below Epimetheus,

This view looks toward the unilluminated side of the rings from about 30 degrees below the ringplane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Sept. 19, 2012.

The view was obtained at a distance of approximately 2.2 million kilometers (1.4 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 96 degrees. Image scale is 128 kilometers (80 miles) per pixel. Epimetheus has been brightened by a factor of 1.5 and Atlas’ brightness has been enhanced by a factor of 3 relative to the rings and Prometheus to improve visibility.

You can see an unlabeled version here.

January 14, 2013December 23, 2015 by Nancy Atkinson

What Happened During the Huygens Mission?

Artist depiction of Huygens landing on Titan. Credit: ESA

It was eight years ago on January 14, 2005 that the Huygens spacecraft descended through Titan’s murky atmosphere and touched down – if a bit precariously – by bouncing, sliding and wobbling across the surface of Saturn’s largest moon Titan. This was the first time a probe had touched down on an alien world in the outer Solar System.

But that surface wasn’t quite what we expected.

While earlier studies of data from Huygens determined the surface of Titan to be quite soft, scientists now think the surface consisted of a hard outer crust but is soft underneath, so that if an object put more pressure on the surface, it sank in significantly.

“It is like snow that has been frozen on top,” said Erich Karkoschka, a co-author of a paper published in October 2012. “If you walk carefully, you can walk as on a solid surface, but if you step on the snow a little too hard, you break in very deeply.”

The scientists think that Huygens landed in something similar to a flood plain on Earth, but that it was dry at the time. The analysis reveals that, on first contact with Titan’s surface, Huygens dug a hole 12 cm deep, before bouncing out onto a flat surface.

The probe, tilted by about 10 degrees in the direction of motion, then slid 30–40 cm across the surface.

A new animation. top of the event has been created using real data recorded by Huygen’s instruments, allowing us to witness this historical moment as if we had been there.

ESA explains:

The animation takes into account Titan’s atmospheric conditions, including the Sun and wind direction, the behaviour of the parachute (with some artistic interpretation only on the movement of the ropes after touchdown), and the dynamics of the landing itself.

Even the stones immediately facing Huygens were rendered to match the photograph of the landing site returned from the probe, which is revealed at the end of the animation.

Split into four sequences, the animation first shows a wide-angle view of the descent and landing followed by two close-ups of the touchdown from different angles, and finally a simulated view from Huygens itself – the true Huygens experience.

Also, a ‘fluffy’ dust-like material – most likely organic aerosols that are known to drizzle out of the Titan atmosphere – was thrown up and suspended for around four seconds around the probe following the impact. The dust was easily lifted, suggesting it was most likely dry and that there had not been any ‘rain’ of liquid ethane or methane for some time prior to the landing.

Huygens was released from the Cassini spacecraft on Christmas Day 2004, and arrived at Titan three weeks later. The probe began transmitting data to Cassini four minutes into its descent and continued to transmit data after landing at least as long as Cassini was above Titan’s horizon, for about 90 minutes, and radio telescopes on Earth continued to receive Huygen’s signal well past the expected lifetime of the craft.

Cassini was supposed to receive Huygen’s signal over two channels, but because of an operational commanding error, only one channel was used. This means that only 350 pictures were received instead of 700 that were expected. All Doppler radio measurements between Cassini and Huygens were lost as well; however, Doppler radio measurements of Huygens from Earth were made, though not as accurate as the expected measurements that Cassini would have made. But when added to accelerometer sensors on Huygens and VLBI tracking of the position of the Huygens probe from Earth, reasonably accurate wind speed and direction measurements could still be derived.

You can see images from the Huygens mission here.

Huygens is currently the most distant landing of any craft launched from Earth. Cassini has been in orbit around Saturn since July 2004, and will continue operations until 2017.

Sources: ESA, Wiki