Posted on by Jason Major

Pictures From T-86: Cassini’s Latest Flyby of Titan

On September 26-27 Cassini executed its latest flyby of Titan, T-86, coming within 594 miles (956 km) of the cloud-covered moon in order to measure the effects of the Sun’s energy on its dense atmosphere and determine its variations at different altitudes.

The image above was captured as Cassini approached Titan from its night side, traveling about 13,000 mph (5.9 km/s). It’s a color-composite made from three separate raw images acquired in red, green and blue visible light filters.

Titan’s upper-level hydrocarbon haze is easily visible as a blue-green “shell” above its orange-colored clouds.

Cassini captured this image as it approached Titan’s sunlit limb, grabbing a better view of the upper haze. Some banding can be seen in its highest reaches.

The haze is the result of UV light from the Sun breaking down nitrogen and methane in Titan’s atmosphere, forming hydrocarbons that rise up and collect at altitudes of 300-400 kilometers. The sea-green coloration is a denser photochemical layer that extends upwards from about 200 km altitude.

In this image, made from data acquired on Sept. 27, Titan’s south polar vortex can be made out just within the southern terminator. The vortex is a relatively new feature in Titan’s atmosphere, first spotted earlier this year. It’s thought that it’s a region of open-cell convection forming above the moon’s pole, a result of the approach of winter to Titan’s southern half.

Read: Cassini Spots Surprising Swirls Above Titan’s South Pole

This T-86 flyby was was one of a handful of opportunities to profile Titan’s ionosphere from the outermost edge of Titan’s atmosphere. In addition Cassini was able to look for any changes to Ligeia Mare, a methane lake last observed in spring of 2007.

Now that Titan has been under scrutiny for a full year of Saturn’s seasons — which lasts 29.7 Earth-years — astronomers now know that varying amounts of solar radiation can drastically change situations both within Saturn’s atmosphere and on its surface.

“As with Earth, conditions on Titan change with its seasons. We can see differences in atmospheric temperatures, chemical composition and circulation patterns, especially at the poles,” said Dr. Athena Coustenis from the Paris-Meudon Observatory in France. “For example, hydrocarbon lakes form around the north polar region during winter due to colder temperatures and condensation. Also, a haze layer surrounding Titan at the northern pole is significantly reduced during the equinox because of the atmospheric circulation patterns. This is all very surprising because we didn’t expect to find any such rapid changes, especially in the deeper layers of the atmosphere.”

“It’s amazing to think that the Sun still dominates over other energy sources even as far out as Titan, over 1.5 billion kilometres from us.”
– Dr. Athena Coustenis, Paris-Meudon Observatory

The image above, acquired on Sept. 28, was added to this post on Oct. 1. It was taken from a distance of  649,825 miles (1,045,792 kilometers.)

Cassini’s next targeted approach to Titan — T-87 — will occur on November 13.

Get more news from the Cassini mission here.

Image credits: NASA/JPL/Space Science Institute. All color composites by Jason Major. Images have not been validated or calibrated by the SSI team.

 

(Do you love the Cassini mission as much as we do? Vote on your favorite Cassini “Shining Moment” here, in honor of the 15th anniversary of Cassini’s launch on October 15! Amazing to think it’s already been 15 years — 8 of those in orbit around Saturn!)

Posted on by Fraser Cain

Weekly Space Hangout – Sept. 27, 2012

This was an action-packed episode of the Weekly Space Hangout. Lots of stories, very little time.

Participants: Mike Wall, Alan Boyle, Ian O’Neill, Nancy Atkinson, Jason Major

Host: Fraser Cain

Want to watch us record the show live? Point your browser at next week’s event page to put the recording right into your calendar.

Posted on by Nancy Atkinson

Paddleboat Mission to Titan Proposed

Three concepts for the TALISE boat mission to Titan: screw propelled (left), paddle wheels (center) and inflatable wheels (right). Credit: Urdampilleta, et al.

Is sending a boat to Titan an outlandish idea? Maybe, said a group of European scientists and engineers, but they’re working on a plan. The Titan Lake In-situ Sampling Propelled Explorer (TALISE) proposes a sending an instrument-laden boat-probe to Saturn’s largest moon that could be propelled by paddles, inflatable wheels or screws. The probe would land in the middle of Ligeia Mare – Titan’s biggest lake, near the moon’s north pole — then set sail for the coast, taking scientific measurements along the way.

“The main innovation in TALISE is the propulsion system,” says Igone Urdampilleta from SENER, an engineering company in Spain and a member of the TALISE team. “This allows the probe to move, under control, from the landing site in the lake, to the closest shore. The displacement capability would achieve the obtaining of liquid and solid samples from several scientific interesting locations on Titan’s surface such as the landing place, along the route towards the shore and finally at the shoreline.”

In a presentation at the European Planetary Science Congress on September 27, 2012, the TALISE team says that since Titan has a thick atmosphere, a diameter between that of Earth and the planet Mercury, and a network of seas, lakes and rivers, it is in many respects more like a planet than a moon.

And it’s time to go there and do a little in-situ science. The principle objective of the mission would be to characterize Titan’s environment and the chemical composition of the lakes and terrain.

While the Cassini-Huygens mission landed the Huygens probe on Titan in 2005, it transmitted data for only about 90 minutes after touchdown. The TALISE mission would last six months to a year.

Images from the Cassini mission show river networks draining into the lakes in Titan’s north polar region. Credit: NASA/JPL/USGS

The Cassini orbiter has confirmed that lakes, seas and rivers of liquid hydrocarbons cover much of the Titan’s northern hemisphere, and these hydrocarbons may rain down on the surface, forming the frigid liquid bodies. 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, the team said.

“The chemical composition of the lakes of Titan is still not well determined,” the TALISE team wrote in their abstract. “The detection of other compounds and the investigation of influence of both, photochemistry and the atmosphere on the chemical composition of liquids of Titan lakes remain challenging in the absence of in situ measurements. Therefore, it is next step to understand the Titan lakes environment, its relationship with the climate behavior, the surrounding solid substrate and analyze the organic inventory including the possibility of prebiotic compounds.”

The actual configuration of the boat is still under consideration, and they are considering various in-situ propulsion methods through the liquid hydrocarbon seas. In addition to paddle wheels, screw propulsion and inflatable wheels, they are also looking at tank wheels, air propeller, liquid propeller and a hovercraft design.

The TALISE concept is being developed as a partnership between SENER and the Centro de Astrobiología in Madrid, Spain, and the mission is still in the very early stages of feasibility studies and preliminary mission architecture design, but they are hoping to be ready for a future space science mission call for proposals.

Sources: EPSC, TALISE team abstract

Posted on by John Williams

Changing Hues Signal Transition of Seasons at Saturn

The giant moon Titan passes in front of Saturn in this natural-color, wide-angle view from NASA’s Cassini spacecraft. Image Credit: NASA/JPL-Caltech/SSI

[SPOILER ALERT: Viewing these images will force you to change your computer wallpaper]

Here on Earth, it’s almost time for the burst of fall color that signals the change of seasons in the Northern Hemisphere. Saturn’s color too is transforming subtly as the gas giant slips into a Saturnian spring and autumn as seen in this series of true-color images from NASA’s Cassini spacecraft.

Titan, a moon larger than the planet Mercury, hangs before the rings and changing colors of Saturn in the first of four spectacular images release by NASA and the Cassini Imaging Central Laboratory for Operations (CICLOPS).

“For no other reason than that they are gorgeous, the Cassini imaging team is releasing today a set of fabulous images of Saturn and Titan…in living color…for your day-dreaming enjoyment,” said Carolyn Porco, Cassini imaging team lead based at the Space Science Institute in Boulder, Colordo, in an email blast.

When Cassini arrived at Saturn eight years ago, the planet’s northern hemisphere, locked in winter, showed azure blue. Now as winter passes to the southern hemisphere, the colors are reversing as the blue fades from the north and rises in the south.

“Note that our presence at Saturn for the last eight years has made possible the sighting of subtle changes with time, and one such change is obvious here,” Porco said. “As the seasons have advanced, and spring has come to the north and autumn to the south throughout the Saturn system, the azure blue in the northern winter Saturnian hemisphere that greeted Cassini upon its arrival in 2004 is now fading; and it is now the southern hemisphere, in its approach to winter, that is taking on a bluish hue.”

Scientists believe that the increasing blue color in the south likely is due to the increasing intensity of ultraviolet light from the Sun which produces the haze. Methane in the atmosphere also absorbs light toward the red end of the spectrum while reflecting blue light. This view looks from just above the ring plane with the Sun shining from above casting broad shadows on the colorful clouds of Saturn. The image was taken on May 6, 2012 from about 778,000 kilometers (483,000 miles) from Titan.

Some of the views, including this image of a vortex at Titan’s south pole are only possible because of a newly tilted, or inclined, orbit that takes Cassini high over the poles of Saturn and its moons. Scientists first noticed the detached mass of clouds over the south pole in March. The swirling mass of the vortex stands out clearly against the golden cloud deck surrounding Titan.

The recently formed south polar vortex stands out against Titan in this natural-color view from NASA’s Cassini spacecraft. Image Credit: NASA/JPL-Caltech/SSI

Sunlight scattering through Titan’s atmosphere forms a ring of color as NASA’s Cassini spacecraft cruises along the night side of Saturn’s largest moon. Image Credit: NASA/JPL-Caltech/SSI

A glowing hint of the polar vortex shows in this image looking toward the night-time, Saturn-facing side of Titan. Sunlight scattering through Titan’s atmosphere forms the ring of color in this image taken about 216,000 kilometers (134,000 miles) from Titan.

Saturn’s rings cut colorful Titan in half in this image from NASA’s Cassini spacecraft. Image Credit: NASA/JPL-Caltech/SSI

The rings obscure Titan in the final image of the quartet. The image is taken from just above the northern, sunlit side of the ring plane. Saturn’s shadow cast along the rings create the dark swath in the center of the image but if you look close, you can see a tiny sliver of Titan through the Cassini Division, the largest gap in Saturn’s wide rings.

“Cassini has been in orbit now for the last eight years, and despite the fact that we can’t know exactly what the next five years will show us, we can be certain that whatever it is will be wondrous,” said Porco.

About the author: John Williams is owner of TerraZoom, a Colorado-based web development shop specializing in web mapping and online image zooms. He also writes the award-winning blog, StarryCritters, an interactive site devoted to looking at images from NASA’s Great Observatories and other sources in a different way. A former contributing editor for Final Frontier, his work has appeared in the Planetary Society Blog, Air & Space Smithsonian, Astronomy, Earth, MX Developer’s Journal, The Kansas City Star and many other newspapers and magazines.

Posted on by Jason Major

Surprising Swirls Above Titan’s South Pole

View of Titan's South Pole, showing a vortex. Credit: NASA

Thanks to Cassini’s new vantage point granted by its inclined orbit researchers have gotten a new look at the south pole of Titan, Saturn’s largest moon. What they’ve recently discovered is a swirling vortex of gas forming over the moon’s pole, likely the result of the approach of winter on Titan’s southern hemisphere.

What we’re seeing here is thought to be an open cell convection process in Titan’s upper atmosphere. In open cells, air sinks in the center of the cell and rises at the edge, forming clouds at cell edges. However, because the scientists can’t see the layer underneath the layer visible in these new images, they don’t know what other mechanisms may be at work.

A stable atmospheric event that’s found here on Earth as well, open cell convection can be compared to the action of boiling water.

Titan has already been seen to have a thicker area of high-altitude haze over its north pole, and as autumn progresses toward winter in Titan’s south during the course of Saturn’s 29.7-year-long orbit this may very well be the beginnings of a southern polar hood.

An animation of this southern vortex can be found here.

“We suspect that this maelstrom, clearly forming now over the south pole and spinning more than forty times faster than the moon’s solid body, may be a harbinger of what will ultimately become a south polar hood as autumn there turns to winter.  Of course, only time will tell.”

– Carolyn Porco, Cassini Imaging Team Leader

Discoveries like this are prime examples of why it was so important for Cassini to have an extended, long-duration mission around Saturn, so that seasonal changes in the planet and moons could be closely observed. New seasons bring new surprises!

The southern vortex structure was also captured in raw images acquired by Cassini on June 28. A color-composite made from three of those raw images is below (the vortex can be seen at center just right of the terminator):

You can find more images from Cassini on the CICLOPS Imaging Team site.

Image credits: NASA/JPL/Space Science Institute. Bottom RGB composite by Jason Major.

Posted on by Jason Major

Titan’s Tides Suggest a Subsurface Sea

Saturn’s hazy Titan is now on the short list of moons that likely harbor a subsurface ocean of water, based on new findings from NASA’s Cassini spacecraft.

As Titan travels around Saturn during its 16-day elliptical orbits, it gets rhythmically squeezed by the gravitational pull of the giant planet — an effect known as tidal flexing (see video below.) If the moon were mostly composed of rock, the flexing would be in the neighborhood of around 3 feet (1 meter.) But based on measurements taken by the Cassini spacecraft, which has been orbiting Saturn since 2004, Titan exhibits much more intense flexing — ten times more, in fact, as much as 30 feet (10 meters) — indicating that it’s not entirely solid at all.

Instead, Cassini scientists estimate that there’s a moon-wide ocean of liquid water beneath the frozen crust of Titan, possibly sandwiched between layers of ice or rock.

“Short of being able to drill on Titan’s surface, the gravity measurements provide the best data we have of Titan’s internal structure.”

– Sami Asmar, Cassini team member at JPL

“Cassini’s detection of large tides on Titan leads to the almost inescapable conclusion that there is a hidden ocean at depth,” said Luciano Iess, the paper’s lead author and a Cassini team member at the Sapienza University of Rome, Italy. “The search for water is an important goal in solar system exploration, and now we’ve spotted another place where it is abundant.”

Although liquid water is a necessity for the development of life, the presence of it alone does not guarantee that alien organisms are swimming around in a Titanic underground ocean. It’s thought that water must be in contact with rock in order to create the necessary building blocks of life, and as yet it’s not known what situations may exist around Titan’s inner sea. But the presence of such an ocean — possibly containing trace amounts of ammonia — would help explain how methane gets replenished into the moon’s thick atmosphere.

“The presence of a liquid water layer in Titan is important because we want to understand how methane is stored in Titan’s interior and how it may outgas to the surface,” said Jonathan Lunine, a Cassini team member at Cornell University, Ithaca, N.Y. “This is important because everything that is unique about Titan derives from the presence of abundant methane, yet the methane in the atmosphere is unstable and will be destroyed on geologically short timescales.”

The team’s paper appears in today’s edition of the journal Science. Read more on the Cassini mission site here.

Top image: artist’s concept showing a possible scenario for the internal structure of Titan. (A. Tavani). Side image: An RGB-composite color image of Titan and Dione in front of Saturn’s face and rings, made from Cassini images acquired on May 21, 2011. (NASA/JPL/SSI. Composite by J. Major.)

Posted on by Nancy Atkinson

Cassini Spies a Possible ‘Oasis’ on Titan

Saturn's rings lie in the distance as the Cassini spacecraft looks toward Titan and its dark region called Shangri-La, east of the landing site of the Huygens Probe. Image Credit: NASA/JPL-Caltech/Space Science Institute

From a JPL press release:

New data from the Cassini spacecraft shows enduring methane lakes in the equatorial regions on Saturn’s moon Titan. Previous models of the frigid liquids on Titan’s surface showed standing bodies of liquid would only exist at the poles, but one of the newly found “tropical” lakes appears to be about half the size of Utah’s Great Salt Lake, with a depth of at least 3 feet (1 meter).

Where could the liquid for these lakes come from? “A likely supplier is an underground aquifer,” said Caitlin Griffith, the paper’s lead author and a Cassini team associate at the University of Arizona, Tucson. “In essence, Titan may have oases.”

Understanding how lakes or wetlands form on Titan helps scientists learn about the moon’s weather. Like Earth’s hydrological cycle, Titan has a “methane” cycle, with methane rather than water circulating. In Titan’s atmosphere, ultraviolet light breaks apart methane, initiating a chain of complicated organic chemical reactions. But existing models haven’t been able to account for the abundant supply of methane.

“An aquifer could explain one of the puzzling questions about the existence of methane, which is continually depleted,” Griffith said. “Methane is a progenitor of Titan’s organic chemistry, which likely produces interesting molecules like amino acids, the building blocks of life.”

Global circulation models of Titan have theorized that liquid methane in the moon’s equatorial region evaporates and is carried by wind to the north and south poles, where cooler temperatures cause methane to condense. When it falls to the surface, it forms the polar lakes. On Earth, water is similarly transported by the circulation, yet the oceans also transport water, thereby countering the atmospheric effects.

The latest results come from Cassini’s visual and infrared mapping spectrometer, which detected the dark areas in the tropical region known as Shangri-La, near the spot where the European Space Agency’s Huygens probe landed in 2005. When Huygens landed, the heat of the probe’s lamp vaporized some methane from the ground, indicating it had landed in a damp area.

Areas appear dark to the visual and infrared mapping spectrometer when liquid ethane or methane are present. Some regions could be shallow, ankle-deep puddles. Cassini’s radar mapper has seen lakes in the polar region, but hasn’t detected any lakes at low latitudes.

The tropical lakes detected by the visual and infrared mapping spectrometer have remained since 2004. Only once has rain been detected falling and evaporating in the equatorial regions, and only during the recent expected rainy season. Scientists therefore deduce the lakes could not be substantively replenished by rain.

“We had thought that Titan simply had extensive dunes at the equator and lakes at the poles, but now we know that Titan is more complex than we previously thought,” said Linda Spilker, the Cassini project scientist based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Cassini still has multiple opportunities to fly by this moon going forward, so we can’t wait to see how the details of this story fill out.”

The findings appear in this week’s issue of the journal Nature.

Posted on by Jason Major

On the Edge of Titan

Titan's haze-covered limb seen by Cassini on June 6

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Here’s a quick look at one of my favorite cosmic photo subjects – the varying layers of atmosphere that enshroud Saturn’s enormous moon Titan. The image above is a color-composite made from three raw images acquired by Cassini during its latest flyby.

On June 7 Cassini approached Titan within 596 miles (959 km) and imaged portions of the moon’s northwest quadrant with its radar instrument, as well as conducted further investigations of areas near the equator where surface changes were detected in 2010.

The image here was assembled from three raw images captured in red, green and blue visible light channels. It reveals some structure in the upper hydrocarbon haze layers that extend upwards above the moon’s opaque orange clouds — reaching 400-500 km in altitude, Titan’s atmosphere is ten times thicker than Earth’s!

The June 6 flyby was the second in a series of passes that will take Cassini into a more inclined orbit, where it will reside for the next three years as it investigates Saturn’s polar regions and obtains better views of its ring system.

Read more about the flyby here.

Image: NASA/JPL/Space Science Institute. Composite by J. Major.

Posted on by Jason Major

A New Angle on Titan

Color-composite image of Titan and Saturn. There are few confirmed craters on Titan, and the ones that have been spotted are much shallower than expected. Image Credit: NASA/JPL/SSI/J. Major

Here’s a great shot of Titan and Saturn acquired by Cassini on May 6, 2012 just after a pass by the haze-covered moon. It’s a color-composite made from images taken in Cassini’s red, green and blue color channels, and the resulting image was color adjusted a bit to appear more “Saturny”.

UPDATE 7/2/12: The image above is featured in today’s Astronomy Picture of the Day (APOD)… check it out here.

Cassini also made some closer passes of Titan on May 6, taking images within about 710,000 km. After recent passes of Encealdus and Dione, Cassini buzzed past Titan in preparation of a targeted flyby on May 22, after which it will head up and out out of the “moonplane” in order to get a better view of Saturn’s rings and upper latitudes.

After that, Cassini won’t be playing amongst the moons again for three years, so images like this will be a rarity for a while.

Another image of Titan, closer-in and set against Saturn’s rings and clouds, shows the fine, transparent structure of the moon’s upper atmospheric haze layers:

Created by the breakdown of methane in Titan’s opaque atmosphere by UV radiation, the haze is composed of complex hydrocarbons that extend outwards up to ten times the thickness of Earth’s atmosphere!

(The RGB layers weren’t available for this particular view, so there’s no color version of it.)

Check out previous images from Cassini’s flyby of Dione and Enceladus, and follow along with the Cassini mission on the JPL site here.

Top image: Color-composite image of Titan and Saturn (NASA/JPL/SSI/J. Major) Bottom image: Titan in blue wavelength against Saturn (NASA/JPL/SSI)

Posted on by Jason Major

African Lake Has a Twin on Titan

Titan's Ontario Lacus is found to bear a striking resemblance to Namibia's Etosha Pan. (NASA/JPL/ESA)

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A large lake on Saturn’s cloud-covered Titan seems very similar to the Etosha Pan, a salt-encrusted dry lakebed in northern Namibia that periodically fills with water. As it turns out, Titan’s “great lake” may also be temporary.

Ontario Lacus, so named because of its similarity both in shape and size to Lake Ontario here on Earth, was first discovered near the south pole of Titan by the Cassini spacecraft in 2009. Its smooth, dark appearance in radar images indicated a uniform and reflective surface, implying a large — although likely shallow — body of liquid.

Of course, on Titan the liquid isn’t water — it’s methane, which is the main ingredient of the hydrologic cycle found on the giant moon. That far from the Sun the temperatures at Titan’s poles fall to a frigid -300ºF (-185ºC), much too cold for water to exist as a liquid and so, on this world, methane has taken its place.

A research team led by Thomas Cornet of the Université de Nantes, France has taken a closer look at Cassini’s radar data of Ontario Lacus and found evidence of channels carved into the southern portion. According to the team, this likely indicates that the lakebed surface is exposed.

Cassini image of Ontario Lacus. (NASA/JPL/SSI)

“We conclude that the solid floor of Ontario Lacus is most probably exposed in those areas,” said Cornet.

In addition, sediment layers surrounding the lake suggest that the liquid level has varied.

All in all, this reveals a striking resemblance between Ontario Lacus and Namibia’s Etosha Pan — an “ephemeral lake” that is dry for much of the year, occasionally filling with a shallow layer of water which evaporates, leaving salty rings of sediment.

The inherent otherworldly nature of Etosha Pan is further underlined — and perhaps foreshadowed! — by its use as a backdrop in the 1968 sci-fi film 2001: A Space Odyssey.

Although Ontario Lacus was initially thought to be permanently filled with liquid hydrocarbons, the team’s findings draw a strong correlation with this well-known Earthly environment, suggesting a much more temporary nature and showing the value of comparative research.

Satellite image of Etosha Pan, acquired on April 28, 2012. (Chelys/EOSnap)

“These results emphasise the importance of comparative planetology in modern planetary sciences,” said Nicolas Altobelli, Cassini project scientist for ESA.”Finding familiar geological features on alien worlds like Titan allows us to test the theories explaining their formation.”

Read the press release from ESA here.

Image credits: Cassini radar image JPL/NASA. Envisat radar image ESA. Composite image: LPGNantes.