Surf’s Up on Titan! Cassini May Have Spotted Waves in Titan’s Seas

Cassini VIMS image of specular reflections in one of Titan's lakes from a flyby on July 24, 2012 (NASA/JPL-Caltech/SSI/Jason W. Barnes et al.)

It’s no surprise that Titan’s north polar region is covered with vast lakes and seas of liquid methane — these have been imaged many times by Cassini during its ten years in orbit around Saturn. What is surprising though is just how incredibly smooth the surfaces of these lakes have been found to be.

One would think that such large expanses of surface liquid — some of Titan’s seas are as big the Great Lakes — would exhibit at least a little surface action on a world with an atmosphere as dense as Titan’s. But repeated radar imaging has shown their surfaces to be “as smooth as the paint on a car.” Over the past several years scientists have puzzled over this anomaly but now they may have truly seen the light — that is, reflected light from what could actually be waves on Titan!

Seasonal winds may be finally kicking up waves in Titan's lakes. (Illustration © Ron Miller.)
Seasonal winds may be finally kicking up waves in Titan’s lakes. (Illustration © Ron Miller.)

Using data acquired during flybys of Titan in 2012 and 2013, planetary scientist Jason Barnes from the University of Idaho and a team of researchers from several other institutions including JPL, Cornell, and MIT, have identified what might be waves in the surface of Punga Mare, one of Titan’s biggest lakes.

For a sense of scale, Lake Victoria, the largest lake in Africa, could fit lengthwise across Titan’s 380-km (236-mile) -wide Punga Mare.

Read more: Titan’s North Pole is Loaded with Lakes

Variations in specular highlights in four pixels observed in the surface of Punga Mare by Cassini’s VIMS (Visible and Infrared Mapping Spectrometer) have been interpreted by the team as being the result of waves — or, perhaps more accurately, ripples, seeing as that they are estimated to be a mere 2 centimeters in height.

Still, based on what’s been observed thus far on Titan, that’s downright choppy.

If the Cassini observations interpreted by Barnes et al. are indicative of waves in Punga Mare, they could also explain previous specular variations seen in other bodies of liquid, like the smaller Kivu Lacus (top image).

Map of Titan's northern "Land o' Lakes" made from Cassini radar imaging passes (NASA/JPL/USGS)
Map of Titan’s northern “Land o’ Lakes” made from Cassini high-resolution radar imaging (NASA/JPL/USGS)

“If correct this discovery represents the first sea-surface waves known outside of Earth.”

– Jason W. Barnes et al.

Then again, wave action isn’t the only possible answer. Similar varied specular highlights could also be caused by a wet surface — like a methane mud flat. Further observations will be needed to rule out other possibilities and obtain a more accurate “surf forecast” for Titan.

The findings were presented by Jason Barnes at the 45th Lunar and Planetary Science Conference in Houston on March 17, 2014. Read the team’s abstract here, and read more in this article by Alexandra Witze on Nature News.

Happy Holidays from Cassini!

Saturn makes a beautifully striped ornament in this natural-color image, showing its north polar hexagon and central vortex (Credit: NASA/JPL-Caltech/Space Science Institute)

Cassini couldn’t make it to the mall this year to do any Christmas shopping but that’s ok: we’re all getting something even better in our stockings than anything store-bought! To celebrate the holiday season the Cassini team has shared some truly incredible images of Saturn and some of its many moons for the world to “ooh” and “ahh” over. So stoke the fire, pour yourself a glass of egg nog, sit back and marvel at some sights from a wintry wonderland 900 million miles away…

Thanks, Cassini… these are just what I’ve always wanted! (How’d you know?)

Saturn’s southern hemisphere is growing more and more blue as winter approaches there — a coloration similar to what was once seen in the north when Cassini first arrived in 2004:

Saturn's southern hemisphere images from a million miles away (Credit: NASA/JPL-Caltech/Space Science Institute)
Saturn’s southern hemisphere images from a million miles away (Credit: NASA/JPL-Caltech/Space Science Institute)

(The small dark spot near the center right of the image above is the shadow of the shepherd moon Prometheus.)

Titan and Rhea, Saturn’s two largest moons, pose for Cassini:

Rhea (front) and Titan, images by Cassini in June 2011 (Credit: NASA/JPL-Caltech/Space Science Institute)
Rhea (front) and Titan, images by Cassini in June 2011 (Credit: NASA/JPL-Caltech/Space Science Institute)

The two moons may look like they’re almost touching but in reality they were nearly half a million miles apart!

Titan’s northern “land of lakes” is visible in this image, captured by Cassini with a special spectral filter able to pierce through the moon’s thick haze:

Titan images by Cassini on Oct. 7, 2013 (Credit: NASA/JPL-Caltech/Space Science Institute)
Titan images by Cassini on Oct. 7, 2013 (Credit: NASA/JPL-Caltech/Space Science Institute)

Read more: Titan’s North Pole is Loaded with Lakes

The frozen, snowball-like surface of the 313-mile-wide moon Enceladus:

Enceladus: a "snowball in space" (Credit: NASA/JPL-Caltech/Space Science Institute)
Enceladus: a highly-reflective and icy “snowball in space” (Credit: NASA/JPL-Caltech/Space Science Institute)

(Even though Enceladus is most famous for its icy geysers, first observed by Cassini in 2005, in these images they are not visible due to the lighting situations.)

Seen in a different illumination angle and in filters sensitive to UV, visible, and infrared light the many fractures and folds of Enceladus’ frozen surface become apparent:

View of the trailing face of Enceladus (Credit: NASA/JPL-Caltech/Space Science Institute)
View of the trailing face of Enceladus (Credit: NASA/JPL-Caltech/Space Science Institute)

Because of Cassini’s long-duration, multi-season stay in orbit around Saturn, researchers have been able to learn more about the ringed planet and its fascinating family of moons than ever before possible. Cassini is now going into its tenth year at Saturn and with much more research planned, we can only imagine what discoveries (and images!) are yet to come in the new year(s) ahead.

“Until Cassini arrived at Saturn, we didn’t know about the hydrocarbon lakes of Titan, the active drama of Enceladus’ jets, and the intricate patterns at Saturn’s poles,” said Linda Spilker, the Cassini project scientist at NASA’s Jet Propulsion Laboratory. “Spectacular images like these highlight that Cassini has given us the gift of knowledge, which we have been so excited to share with everyone.”

Read more about the images above and see even more on the CICLOPS  Imaging Team website, and see the NASA press release here.

Thanks to Carolyn Porco, Cassini Imaging Team Leader, for the heads-up on these gifs — er, gifts!

New Flyover Video Takes You on a Tour of Titan’s Lake Region

This colorized mosaic from NASA's Cassini mission shows the most complete view yet of Titan's northern land of lakes and seas. Saturn's moon Titan is the only world in our solar system other than Earth that has stable liquid on its surface. The liquid in Titan's lakes and seas is mostly methane and ethane. Image credit: NASA/JPL-Caltech/ASI/USGS

Saturn’s moon Titan has the only known liquid lakes beyond planet Earth, and new data from the Cassini spacecraft’s radar instrument provides an intriguing 3-D flyover of these hydrocarbon lakes and seas at the north pole region. Steve Wall, Cassini acting radar team lead, provided a guided tour as he presented the video at the American Geophysical Union conference in San Francisco, noting that the vertical heights are exaggerated tenfold and the data has been colorized, both for visual effect.

The video starts by zooming into the southern end of Kraken Mare, the largest of Titan’s seas, and as you fly a little farther, Wall said the things that look like little islands are just noise in the radar data. Next, comes Ligea Mare, with its rugged coastline, and you’ll see that the liquid flow into the surrounding terrain, which appear like river valleys.

The “smooth” area that stretches farther from Ligea Mare is actualy not so smooth, but is just an area when the science team doesn’t have topographical data yet.

The video then continues to other smaller lakes that are nestled into valleys and rugged terrain.

“Learning about surface features like lakes and seas helps us to understand how Titan’s liquids, solids and gases interact to make it so Earth-like,” said Wall. “While these two worlds aren’t exactly the same, it shows us more and more Earth-like processes as we get new views.”

The new data is not only visually stunning, but provides previously unknown details about these lakes and the region. For example, Kraken Mare is more extensive and complex than previously thought. They also show nearly all of the lakes on Titan fall into an area covering about 600 miles by 1,100 miles (900 kilometers by 1,800 kilometers). Only 3 percent of the liquid at Titan falls outside of this area.

“Scientists have been wondering why Titan’s lakes are where they are. These images show us that the bedrock and geology must be creating a particularly inviting environment for lakes in this box,” said Randolph Kirk, a Cassini radar team member at the U.S. Geological Survey in Flagstaff, Ariz. “We think it may be something like the formation of the prehistoric lake called Lake Lahontan near Lake Tahoe in Nevada and California, where deformation of the crust created fissures that could be filled up with liquid.”

Additionally, scientists now know that Ligeia Mare is about 560 feet (170 meters) deep. This is the first time scientists have been able to plumb the bottom of a lake or sea on Titan. This was possible partly because the liquid turned out to be very pure, allowing the radar signal to pass through it easily. The liquid surface may be as smooth as the paint on our cars, and it is very clear to radar eyes.

“Ligeia Mare turned out to be just the right depth for radar to detect a signal back from the sea floor, which is a signal we didn’t think we’d be able to get,” said Marco Mastrogiuseppe, a Cassini radar team associate at Sapienza University of Rome. “The measurement we made shows Ligeia to be deeper in at least one place than the average depth of Lake Michigan.”

The new results indicate the liquid is mostly methane, somewhat similar to a liquid form of natural gas on Earth.

Sources: AGU press conference, JPL press release

Ghostly Pic Of Saturn’s Moon Shows It Rising From The Deep

Titan imaged by the Cassini spacecraft. Credit: NASA/JPL-Caltech/Space Science Institute

Sunlight can do fun things in space. For example: this recent picture of Titan (a moon of Saturn) shows sunlight hitting the moon’s surface as well as a southern vortex, just visible in the shadows of the picture.

“The sunlit edge of Titan’s south polar vortex stands out distinctly against the darkness of the moon’s unilluminated hazy atmosphere,” NASA stated. “The Cassini spacecraft images of the vortex led scientists to conclude that its clouds form at a much higher altitude — where sunlight can still reach — than the surrounding haze.”

Titan has intrigued scientists for decades, since the Voyager spacecraft first revealed it as a world socked in by orange haze. Cassini dropped off a lander on the surface, called Huygens, which took pictures on the surface in 2005. Besides that, the orbiter has revealed a lot about lakes, rain and other features of the moon in the year since.

Cassini has been orbiting the moon since 2004 and is still busily producing science, but there are concerns that NASA’s budget situation could cause the agency to shut down operations on the still-healthy spacecraft. There are no other missions to Saturn or Titan booked yet, although scientists do have intriguing ideas for exploration.

Titan’s North Pole is Loaded With Lakes

Titan's north pole is home to many methane lakes. Credit: NASA

A combination of exceptionally clear weather, the steady approach of northern summer, and a poleward orbital path has given Cassini — and Cassini scientists — unprecedented views of countless lakes scattered across Titan’s north polar region. In the near-infrared mosaic above they can be seen as dark splotches and speckles scattered around the moon’s north pole. Previously observed mainly via radar, these are the best visual and infrared wavelength images ever obtained of Titan’s northern “land o’ lakes!”

 

Titan is currently the only other world besides Earth known to have stable bodies of liquid on its surface, but unlike Earth, Titan’s lakes aren’t filled with water — instead they’re full of liquid methane and ethane, organic compounds which are gases on Earth but liquids in Titan’s incredibly chilly -290º F (-180º C) environment.

While one large lake and a few smaller ones have been previously identified at Titan’s south pole, curiously almost all of Titan’s lakes appear near the moon’s north pole.

Infrared observations of Titan's northern lakes (NASA/JPL-Caltech/SSI)
Infrared observations of Titan’s northern lakes. The cross marks Titan’s geographic north pole. (NASA/JPL-Caltech/SSI)

For an idea of scale, the large lake at the upper right above (and the largest lake on Titan) Kraken Mare is comparative in size to the Caspian Sea and Lake Superior combined. Kraken Mare is so large that sunlight was seen reflecting off its surface in 2009. Punga Mare, nearest Titan’s pole, is 240 miles (386 km) across.

Besides revealing the (uncannily) smooth surfaces of lakes — which appear dark in near-infrared wavelengths but would also be darker than the surrounding landscape in visible light —  these Cassini images also show an unusually bright terrain surrounding them. Since the majority of Titan’s lakes are found within this bright region it’s thought that there could be a geologic correlation; is this Titan’s version of karst terrain, like what’s found in the southeastern U.S. and New Mexico? Could these lakes be merely the visible surfaces of a vast underground hydrocarbon aquifer? Or are they shallow pools filling depressions in an ancient lava flow?

Annotated infrared mosaic of Titan's north pole (NASA/JPL-Caltech/SSI)
Annotated infrared mosaic of Titan’s north pole (NASA/JPL-Caltech/SSI)

Or, are they the remains of once-larger lakes and seas which have since evaporated? The orange-hued regions in the false-color mosaic may be evaporite — the Titan equivalent of salt flats on Earth. The evaporated material is thought to be organic chemicals originally from Titan’s haze particles that were once dissolved in liquid methane.

“Is this an indication that with increased warmth, the seas and lakes are starting to evaporate, leaving behind a deposit of organic material,” wrote Carolyn Porco, Cassini Imaging Team Leader, in an email earlier today. “…in other words, the Titan equivalent of a salt-flat?”

The largest lake at Titan’s south pole, Ontario Lacus, has been previously compared to such an ephemeral lake in Namibia called the Etosha Pan. (Read more here.)

These observations are only possible because of the extended and long-term study of Saturn and its family of moons by the Cassini spacecraft, which began with its establishing orbit in 2004 and has since continued across multiple seasons over a third of the ringed planet’s year. The existence of methane lakes on Titan is undoubtedly fascinating, but how deep the lakes are, where they came from and how they behave in Titan’s environment have yet to be discovered. Luckily, the changing season is on our side.

“Titan’s northern lakes region is one of the most Earth-like and intriguing in the solar system,” said Linda Spilker, Cassini project scientist, based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We know lakes here change with the seasons, and Cassini’s long mission at Saturn gives us the opportunity to watch the seasons change at Titan, too. Now that the sun is shining in the north and we have these wonderful views, we can begin to compare the different data sets and tease out what Titan’s lakes are doing near the north pole.”

The images shown above were obtained by Cassini’s visual and infrared mapping spectrometer (VIMS) during a close flyby of Titan on Sept. 12, 2013.

Read more on the Cassini Imaging Central Laboratory for Operations (CICLOPS) site here and on the NASA site here.

“But how thrilling it is to still be uncovering new territory on this fascinating moon… a place that, until Cassini’s arrival at Saturn nearly 10 years ago, was the largest single expanse of unseen terrain we had remaining in our solar system. Our adventures here have been the very essence of exploration. And it’s not over yet!”

– Carolyn Porco on Facebook

An illustration of a Titanic lake by Ron Miller. All rights reserved. Used with permission.
An illustration of a Titanic lake © Ron Miller. All rights reserved.

Also, check out a corresponding article and intriguing illustration of robotic Titan exploration by space artist extraordinaire Ron Miller on io9.com.

Ice Volcanoes Likely Alter Titan’s Surface Brightness: Study

Titan peeks from behind two of Saturn's rings. Another small moon Epimetheus, appears just above the rings. Credit: NASA/JPL/Space Science Institute

Icy volcanoes are likely responsible for changes in brightness on the surface of Titan, the largest moon of Saturn, according to a new study.

Images with the Cassini spacecraft’s visual and infrared mapping spectrometer revealed the brightness, or albedo, of two equatorial areas changing during the study period. Tui Regio (which got darker from 2005 to 2009) and Sotra Patera (which got brighter from 2005 to 2006).

The researchers also pointed to “volcanic-like features” in these areas as evidence that the potential cryovolcanoes, as these icy volcanoes are known, might be connected to an ocean on Titan.

Top: Sotra Patera, a cryovolcanic candidate on Titan that has a one-kilometer crater. (Credit: NASA/JPL Caltech/USGS/University of Arizona). Bottom: The Kirishima volcano in Japan, a terrestrial analogue (Credit: USGS).
Top: Sotra Patera, a cryovolcanic candidate on Titan that has a one-kilometer crater. (Credit: NASA/JPL Caltech/USGS/University of Arizona). Bottom: The Kirishima volcano in Japan, a terrestrial analogue (Credit: USGS).

“All of these features, plus a need for a methane reservoir and volcanic activity to replenish the methane in the atmosphere, is compatible with the theory of active cryovolcanism on Titan,” stated Anezina Solomonidou , a planetary geologist with the Paris Observatory as well as the National and Kapodistrian University of Athens.

“These results have important implications for Titan’s potential to support life, as these cryovolcanic areas might contain environments that could harbor conditions favorable for life,” Solomonidou added.

Of note, Titan also has a fresh-looking surface with few craters on it, indicating that something might be altering the surface. “Its landscape is remarkably Earth-like with dunes and lakes, erosion due to weathering and tectonic-like features,” a statement on the research added.

There’s been chatter about cryovolcanoes on Titan before. In 2010, researchers said a chain of peaks found on the moon could be evidence of this type of feature. However, a 2012 preliminary California Institute of Technology weather model of the moon explained many of its features without necessarily needing to rely on cryovolcanoes.

Source: European Planetary Science Congress

Titan Has a Fancy Collar

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)

Cassini Flyby Will Look for Waves on Titan’s Seas

A dense network of small rivers or swampy areas appears to connect some of the seas on Saturn's moon Titan, as seen in this comparison of data of the same area from two instruments on NASA's Cassini spacecraft. Images from the radar instrument are on the left and images from the visual and infrared mapping spectrometer (VIMS) are on the right. Credit: NASA/JPL-Caltech/University of Arizona

Are there waves on Titan’s lakes and seas? Cassini scientists say that the best chance of answering this question is with the May 23 flyby of Titan, when the Cassini spacecraft will be just 970 km (603 miles) over Titan’s biggest ‘lake,’ the northern sea named Ligeia Mare.

Lakes, seas, and rivers were discovered on Titan by Cassini in 2005, and since then, scientists and space enthusiasts have been intrigued about the possibility of what could be found in these bodies of hydrocarbon liquid. Future potential missions such as paddleboats have even been proposed.

Lakes, seas and rivers of liquid hydrocarbons cover much of the Titan’s northern hemisphere. Additionally, these hydrocarbons may rain down on the surface. The questions is, are these frigid liquid bodies capable of producing wave action, or would they be a rigid type of frigid? With surface temperature at -178 degrees Celsius (-289 degrees Fahrenheit), Titan’s environment is too cold for life as we may know it, but its environment, rich in the building blocks of life, is of great interest to astrobiologists.

Additionally, new models of Titan’s atmosphere prediction that as the seasons change in Titan’s northern hemisphere, waves could ripple across the moon’s hydrocarbon seas, and possibly even hurricanes could begin to swirl over these areas, too. The model predicting waves tries to explain data from the moon obtained so far by Cassini.

“If you think being a weather forecaster on Earth is difficult, it can be even more challenging at Titan,” said Scott Edgington, Cassini’s deputy project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We know there are weather processes similar to Earth’s at work on this strange world, but differences arise due to the presence of unfamiliar liquids like methane. We can’t wait for Cassini to tell us whether our forecasts are right as it continues its tour through Titan spring into the start of northern summer.”

For the flyby on May 23, the altimetry data that will be collected by the radar instrument could show whether the surface of that sea is thick like molasses or as thin as liquid water on Earth.

In addition, radar will look for changes in small northern lakes last observed in previous flybys, the T-16 and T-19 flybys.
This flyby is a carefully planned sibling of the following flyby; the combination of the data from T-91 and T-92 will provide stereo views of the same geography, which will tell us about the depth of the lake walls.

Stay tuned! See the Cassini flyby page for more info, and read more about the new models of Titan’s atmosphere here.

IMG004815-br500

Cassini Says “Senkyo Very Much”

Narrow-angle camera image of Titan from Cassini (NASA/JPL-Caltech/Space Science Institute)

In this image acquired on January 5, Cassini’s near-infrared vision pierced Titan’s opaque clouds to get a glimpse of the dark dune fields across a region called Senkyo.

The vast sea of dunes is composed of solid hydrocarbon particles that have precipitated out of Titan’s atmosphere. Also visible over Titan’s southern pole are the rising clouds of the recently-formed polar vortex.

For a closer look at Titan’s dunes (and to find out what the name Senkyo means) keep reading…

In the image above north on Titan is up and rotated 18 degrees to the right. It was taken using a spectral filter sensitive to wavelengths of near-infrared light centered at 938 nanometers.

The view was obtained at a distance of approximately 750,000 miles (1.2 million kilometers) from Titan.

Titan’s hydrocarbon dunes are found across the moon in a wide swath within 30 degrees of the equator and are each about a kilometer wide and tens to hundreds of kilometers long… and in some cases stand over 100 meters tall. (Source: Astronomy Now.)

Titan dunes Jan 2007
Radar image of Titan’s dunes acquired on Jan. 13, 2007. This view is 160 kilometers (100 miles) high by 150 kilometers (90 miles) wide. (NASA/JPL)

Observations of the dunes with Cassini and ESA’s Huygens probe during its descent onto Titan’s surface have shown that the moon experiences seasonally-shifting equatorial winds during equinoxes, similar to what occurs over the Indian Ocean between monsoon seasons.

The name Senkyo refers to the Japanese realm of serenity and freedom from wordly cares and death… in line with the IAU convention of naming albedo features on Titan after mythological enchanted places.

Click here for an earlier view of Senkyo, and follow the Cassini mission here.

Color-composite of Titan made from raw Cassini images acquired on April 13, 2013 (added 4/17) NASA/JPL/SSI. Composite by J. Major.
Color-composite of Titan made from raw Cassini images acquired on April 13, 2013 (added 4/17) NASA/JPL/SSI. Composite by J. Major.

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 28th 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 3rd 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.
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 28th 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 6th.

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 25th. 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).
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?