Cassini Equinox & Solstice Mission, (nine year extension)!!.

[EarthlingX]

http://www.physorg.com : What is Consuming Hydrogen and Acetylene on Titan?

June 3, 2010


This artist concept shows a mirror-smooth lake on the surface of the smoggy moon Titan. Image credit: NASA/JPL

(PhysOrg.com) -- Two new papers based on data from NASA's Cassini spacecraft scrutinize the complex chemical activity on the surface of Saturn's moon Titan. While non-biological chemistry offers one possible explanation, some scientists believe these chemical signatures bolster the argument for a primitive, exotic form of life or precursor to life on Titan's surface. According to one theory put forth by astrobiologists, the signatures fulfill two important conditions necessary for a hypothesized "methane-based life."

One key finding comes from a paper online now in the journal Icarus that shows hydrogen molecules flowing down through Titan's atmosphere and disappearing at the surface. Another paper online now in the Journal of Geophysical Research maps hydrocarbons on the Titan surface and finds a lack of acetylene.

The absence of detectable acetylene on the Titan surface can very well have a non-biological explanation, said Mark Allen, principal investigator with the NASA Astrobiology Institute Titan team. Allen is based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. Allen said one possibility is that sunlight or cosmic rays are transforming the acetylene in icy aerosols in the atmosphere into more complex molecules that would fall to the ground with no acetylene signature.

"Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed," Allen said. "We have a lot of work to do to rule out possible non-biological explanations. It is more likely that a chemical process, without biology, can explain these results - for example, reactions involving mineral catalysts."

"These new results are surprising and exciting," said Linda Spilker, Cassini project scientist at JPL. "Cassini has many more flybys of Titan that might help us sort out just what is happening at the surface."

 

[3488]

The 110 x 88 x 62 km sized icy moon Pandora, seen by Cassini on: Thursday 3rd June 2010.

A view of a slim crescent Enceladus on: Monday 17th May 2010. South Plar geysers appear to be waning, though this appears to be a short exposure shot.

Andrew Brown.

 

[3488]

On Thursday 3rd June 2010, Cassini passed about 100,000 KM of Saturn's second largest moon, the 1,528 KM wide Rhea. Clickable thumbnails.



The following day, Friday 4th June 2010, hazez were recorded in Titan's stratosphere.



Titan on Saturday 5th June 2010. IR filter.


Andrew Brown.

 

[EarthlingX]

http://www.ciclops.org : Have we discovered evidence for life on Titan?

by Chris McKay, NASA Ames Research Center, Moffett Field CA. (chris.mckay@nasa.gov)

Recent results from the Cassini mission suggest that hydrogen and acetylene are depleted at the surface of Titan. Both results are still preliminary and the hydrogen loss in particular is the result of a computer calculation, and not a direct measurement. However the findings are interesting for astrobiology. Heather Smith and I, in a paper published 5 years ago (McKay and Smith, 2005) suggested that methane-based (rather than water-based) life – ie, organisms called methanogens -- on Titan could consume hydrogen, acetylene, and ethane. The key conclusion of that paper (last line of the abstract) was "The results of the recent Huygens probe could indicate the presence of such life by anomalous depletions of acetylene and ethane as well as hydrogen at the surface."

Now there seems to be evidence for all three of these on Titan. Clark et al. (2010, in press in JGR) are reporting depletions of acetylene at the surface. And it has been long appreciated that there is not as much ethane as expected on the surface of Titan. And now Strobel (2010, in press in Icarus) predicts a strong flux of hydrogen into the surface.

This is a still a long way from "evidence of life". However, it is extremely interesting.

...

In conclusion, there are four possibilities for the recently reported findings, listed in order of their likely reality:

1. The determination that there is a strong flux of hydrogen into the surface is mistaken. It will be interesting to see if other researchers, in trying to duplicate Strobel's results, reach the same conclusion.

2. There is a physical process that is transporting H2 from the upper atmosphere into the lower atmosphere. One possibility is adsorption onto the solid organic atmospheric haze particles which eventually fall to the ground. However this would be a flux of H2, and not a net loss of H2.

3. If the loss of hydrogen at the surface is correct, the non-biological explanation requires that there be some sort of surface catalyst, presently unknown, that can mediate the hydrogenation reaction at 95 K, the temperature of the Titan surface. That would be quite interesting and a startling find although not as startling as the presence of life.

4. The depletion of hydrogen, acetylene, and ethane, is due to a new type of liquid-methane based life form as predicted (Benner et al. 2004, McKay and Smith 2005, and Schulze-Makuch and Grinspoon 2005).

 

[brandbll]

Fresh raw images :

http://saturn.jpl.nasa.gov/photos/raw/?start=1&storedQ=2233046

N00154189.jpg was taken on May 23, 2010 and received on Earth May 24, 2010. The camera was pointing toward TITAN at approximately 1,719,330 kilometers away, and the image was taken using the CL1 and CB3 filters. This image has not been validated or calibrated.

http://saturn.jpl.nasa.gov/photos/raw/?start=5&storedQ=2233046

Any idea on why that dark circle occurrs in both pictures on the right hand side?

 

[3488]

Hi Brandon,

It is a tiny impact crater on the optics by a dust particle. It will be there for the rest of Cassini's mission & beyond.

I think it has already been there for some time, but because Titan is bright & of low contrast, any defects like that are more obvious. Image processing will remove it.

Andrew Brown.

 

[brandbll]

Hi Brandon,

It is a tiny impact crater on the optics by a dust particle. It will be there for the rest of Cassini's mission & beyond.

I think it has already been there for some time, but because Titan is bright & of low contrast, any defects like that are more obvious. Image processing will remove it.

Andrew Brown.

That's sort of what i figured. Is there a shield that normally covers the lense when it is not being used, and if so do they have a picture of when the dust particle struck the lense? Thanks again for the help Andrew!

 

[EarthlingX]

http://www.ciclops.org : Encke Gap Ringlets

Kinky, discontinuous ringlets occupy the Encke Gap in Saturn's A ring in the middle of this Cassini image.


This view looks toward the northern, unilluminated side of the rings from about 17 degrees below the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 8, 2010. The view was acquired at a distance of approximately 1.6 million kilometers (1 million miles) from Saturn. Image scale is 9 kilometers (6 miles) per pixel.

 

[EarthlingX]

A bit late, but anyway :

saturn.jpl.nasa.gov : Happy Birthday to Giovanni Domenico Cassini, Born June 8, 1625.

Happy Birthday to Giovanni Domenico Cassini, Born June 8, 1625.
June 5, 2009

Cassini, namesake of the Cassini Orbiter, discovered four moons of Saturn and the large gap in Saturn's rings, now called the Cassini division. He also was the first director of the Paris Observatory, measured the sun's apparent motion through the sky, and even approximated the distance from the Earth to the Sun. In addition, he used the shadows of Jupiter's moons and shadows on Jupiter's surface to determine the length of Jupiter's day, and he is also credited with discovering Jupiter's Great Red Spot!

http://www.nasa.gov/worldbook/cassini_gio_worldbook.html

Wiki : Giovanni Domenico Cassini

 

[EarthlingX]

http://www.ciclops.org : On Either Side

A pair of small moons join Saturn's second largest moon in this Cassini image spotlighting Rhea in front of the rings.

Rhea (1528 kilometers, 949 miles across) is in the center foreground. Janus (179 kilometers, 111 miles across) can be seen beyond the rings on the right of the image. Prometheus (86 kilometers, 53 miles across) is visible orbiting between the main rings and the thin F ring on the left of the image.



Lit terrain seen on Rhea is on the area between that moon's trailing hemisphere and anti-Saturn side. This view looks toward the northern, sunlit side of the rings from just above the ringplane.

The image was taken in visible red light with the Cassini spacecraft narrow-angle camera on March 28, 2010. The view was acquired at a distance of approximately 1.9 million kilometers (1.2 million miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 105 degrees. Janus and Prometheus are both about 2.5 million kilometers (1.6 million miles) away. Scale is 11 kilometers (7 miles) per pixel on Rhea and about 15 kilometers (9 miles) per pixel on Janus and Prometheus.

http://www.ciclops.org : Tethys in the Fore

The moon Tethys occupies the right foreground of this Saturnian scene.

This view looks toward the anti-Saturn side of Tethys (1062 kilometers, 660 miles across) and toward the northern, sunlit side of the rings from just above the ringplane.



The image was taken with the Cassini spacecraft wide-angle camera on Nov. 23, 2009 using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers. The view was obtained at a distance of approximately 1.4 million kilometers (870,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 79 degrees. Image scale is 78 kilometers (49 miles) per pixel.

http://www.ciclops.org : Closest View of Helene

Cassini snapped this image during the spacecraft's closest flyby of Saturn's moon Helene on March 3, 2010.



See PIA09015 for the previous closest view of Helene (33 kilometers, 21 miles across). The small moon leads Dione by 60 degrees in the moons' shared orbit. Helene is a "Trojan" moon of Dione, named for the Trojan asteroids that orbit 60 degrees ahead of and behind Jupiter as it circles the Sun.

Lit terrain seen here is on the anti-Saturn side of Helene. The south pole of the moon is in the lower right of the image.

The image was taken in visible light with the Cassini spacecraft wide-angle camera. The view was obtained at a distance of approximately 1,900 kilometers (1,200 miles) from Helene and at a Sun-Helene-spacecraft, or phase, angle of 90 degrees. Scale in the original image was 235 meters (770 feet) per pixel. The image has been magnified by a factor of two and contrast-enhanced to aid visibility.

90 deg Rotated, enlarged crop :

 

[EarthlingX]

http://www.ciclops.org : Rev133: Jun 11 - Jun 27 '10

Cassini nears the end of its extended tour of the Saturn system with the 16-day-long Rev133, the spacecraft's 134th orbit around the Ringed Planet. This is the last full orbit of its first extended mission, which ends on July 1. Cassini begins Rev133 on June 11 at its farthest distance from Saturn, called apoapse. At this point, Cassini is 2.23 million kilometers (1.38 million miles) from Saturn's cloud tops. Cassini is now in a slightly inclined orbit, but will spend most of its camera observing time imaging Saturn's largest moon, Titan.

Cassini's ISS camera system starts its observations for Rev133 the day after apoapse by acquiring calibration images for its narrow-angle camera. These images will use stars in the Hyades open star cluster, and Theta Tauri in particular. On June 13, Cassini will image Titan from a distance of 3.26 million kilometers (2.02 million miles). Cassini will be searching for clouds across the eastern Aztlan, Quivira, and Fensal regions of Titan in this distant observation.

On June 19 at 07:02 UTC, Cassini will reach the periapse of Rev133, its closest point to Saturn in the orbit. At periapse, the spacecraft will be 97,949 kilometers (60,862 miles) above Saturn's cloud tops. A few minutes after periapse, Cassini will perform one of its closest encounters with the small satellite Pan to date, at a distance of 29,333 kilometers (18,226 miles). Unfortunately, no imaging is planned for this encounter.

Cassini encounters Titan on June 21 at 01:27 UTC for the 71st time. This is the second of two encounters in the month of June and is the last Titan encounter of Cassini's first extended mission, though 56 more are planned during the seven-year, second extended mission, known as the Cassini Solstice Mission. The close approach distance for the encounter (known as T70) is 955 kilometers (593 miles), close to the altitude limit for Cassini at Titan. This flyby will allow for imaging of the anti-Saturn hemisphere of Titan outbound to the encounter. For much of the inbound segment of the encounter, when only a thin crescent will be visible, the Composite Infrared Spectrometer (CIRS), Visual and Infrared Mapping Spectrometer (VIMS), and ISS teams will control spacecraft pointing, or be "prime." First up is CIRS, which will acquire a distant observation of the crescent of Titan, staring at the limb of Titan in order to acquire far-infrared spectra of Titan's haze layers. Next, ISS will spend an hour taking a photometric observation of Titan using the wide-angle camera. Afterward, CIRS will take a series of infrared spectral observations measuring the composition of Titan's atmosphere by performing the following: several limb scans in the mid-infrared at different northern latitudes around Titan's bright limb, far-infrared scans across the night side of the satellite, and far-infrared stares at the bright limb. At closest approach, the Radio Science Subsystem (RSS) team will have Cassini point its high-gain antenna at Earth in order to monitor how the spacecraft's signal is affected by the gravity of nearby Titan. The degree of this effect, called Doppler shift, and how it changes over the course of the flyby, can provide information on Titan's internal structure and any heterogeneity that might exist in Titan's lithosphere.

blogs.jpl.nasa.gov : Cassini to Swing Low Into Titan’s Atmosphere

This weekend, Cassini will embark on an exciting mission: trying to establish if Titan, Saturn’s largest moon, possesses a magnetic field of its own. This is important for understanding the moon’s interior and geochemical evolution.

For Titan scientists, this is one of the most anticipated flybys of the whole mission. We want to get as close to the surface with our magnetometer as possible for a one-of-a-kind scan of the moon. Magnetometer team scientists (including me) have a reputation for pushing the lower limits. In a world of infinite possibilities, we would have liked many flybys at 800 kilometers. But we went back and forth a lot with the engineers, who have to ensure the safety of the spacecraft and fuel reserves. We agreed on one flyby at 880 kilometers (547 miles) and both sides were happy.

Cassini flies to within 880 kilometers (547 miles) of Titan’s surface during its 71st flyby of Titan, known as “T70,” the lowest in the entire mission. Image credit: NASA/JPL/Space Science Institute
› Full image and caption

saturn.jpl.nasa.gov : Insider's Cassini: 'Going Low at T-70'

Jun. 17, 2010

Todd J. Barber, Cassini lead propulsion engineer

As summer begins in Earth’s northern hemisphere, our thoughts turn to barbeques, long evenings, and maybe even dipping our toes in the pool. The Cassini spacecraft will celebrate Earth’s summer solstice with a bold “toe-dip” of its own this Sunday evening (PDT), plunging deeper into Titan’s atmosphere than it ever has before. I recently interviewed Julie Webster, the Spacecraft Operations Team Manager (and my immediate boss) about this unique event as Cassini’s Equinox Mission nears completion. Believe it or not, the first work for “going low at T-70” began nearly 3.5 years ago. We knew that Titan closest approaches below 940 to 970 kilometers (584 to 603 miles) in altitude had some non-zero risk of spacecraft tumbling, depending on the spacecraft pointing (or attitude). But the question familiar to every limbo fan (“How low can you go?”) was investigated extensively. The team decided to look at an 880 kilometers (547 miles) altitude flyby: not too much of a change, but enough to make our magnetometer scientists salivate, since their instrument's sensitivity for understanding the Titan subsurface structure increases as the inverse fourth power of distance to the center of Titan. Interestingly enough, at the minimum torque attitude (which was still excellent for science, by the way), there was margin against tumbling at 880 kilometers! However, the margins were tighter for aero-heating thermal limits on the spacecraft (specifically, the stellar reference units) — in fact, the thermal limits were the ultimate driver in selecting a closest approach altitude no lower than 880 kilometers.

http://www.ciclops.org : By Bright Rings

A pair of Saturn's small moons orbit near the planet's rings which appear well illuminated in this Cassini view.



Janus (179 kilometers, 111 miles across) is near the center of the image and is farther than the rings from Cassini. Pandora (81 kilometers, 50 miles across) is on the left. This view looks toward the northern, sunlit side of the rings from just above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 17, 2010. The view was acquired at a distance of approximately 2.7 million kilometers (1.7 million miles) from Janus and Pandora. Image scale is 16 kilometers (10 miles) per pixel.

Crop and a slight enlargement :

http://www.ciclops.org : Titan's Dark Senkyo

Cassini looks toward the dark Senkyo region on Saturn's moon Titan.



Senkyo is the dark region on the right. Two other dark regions, Aztlan (left) and Fensal (left, north of Aztlan), are also shown here. The bright area south of the equator is called Tsegihi. See PIA11636 for a closer view of Senkyo and to learn more. This view looks toward the Saturn-facing side of Titan (5150 kilometers, 3200 miles across). North on Titan is up and rotated 9 degrees to the left.

The image was taken with the Cassini spacecraft narrow-angle camera on April 8, 2010 using a spectral filter sensitive to wavelengths of near-infrared light centered at 938 nanometers. The view was obtained at a distance of approximately 2.1 million kilometers (1.3 million miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 33 degrees. Image scale is 12 kilometers (8 miles) per pixel.

http://www.ciclops.org : Slender Rings

Like a thin thread strung perpendicular to the crescent of the planet, Saturn's rings are seen edge-on by Cassini.



This view looks toward the northern, sunlit side of the rings from just above the ringplane. The image was taken in visible red light with the Cassini spacecraft wide-angle camera on Dec. 8, 2009. The view was acquired at a distance of approximately 1.4 million kilometers (870,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 140 degrees. Image scale is 79 kilometers (49 miles) per pixel.

 

[3488]

Cassini to swoop to 880 KM of Titan in the closest pass yet on: Monday 21st June 2010 (Solstice on Earth).

This will be the first time Cassini dips right into Titan's Ionosphere & the magnetomoter will be able to detect once & for all, if Titan possesses an active magnetosphere.

IMO, I say no, gravity data seems to suggest that the interior of Titan resembles that of the giant Jupiter moon Callisto, which the Galileo spacecraft revealed is fairly homogenous, a mix of rock & ice, rather than Callisto's neighbouring sibling Ganymede, which is highy evolved internally & resembles the Earth & Mercury with the level of internal differentiation.

We'll see.

Andrew Brown.

 

[RVHM]

Echoing a question seen elsewhere on this site, would it be possible to eventually use Titan's atmosphere to aerobrake Cassini into an orbit around it?

 

[3488]

Hi RVHM,

Most likely no. Cassini was never designed for aerobraking. There have been suggestions of pointing the HGA in direction of travel, etc during close Titan passes. The amount of deceleration required to put Cassini in a Titancentric orbit is just too much. Also to make it worthwhile, it would need to be a polar orbit so the entire globe of Titan is covered, that would be even more difficult.

It is a nice idea, but no, it would not work. What would be doable is frequent Titan passes at different points & latitudes, but the problem with that is the mission would just be limited to Titan with distant Saturn observations. If Cassini is still working well, lets continue getting as much as possible through out the system, particularly further Enceladus & Dione passes too.

Andrew Brown.

 

[RVHM]

Hi RVHM,

Most likely no. Cassini was never designed for aerobraking. There have been suggestions of pointing the HGA in direction of travel, etc during close Titan passes. The amount of deceleration required to put Cassini in a Titancentric orbit is just too much. Also to make it worthwhile, it would need to be a polar orbit so the entire globe of Titan is covered, that would be even more difficult.

It is a nice idea, but no, it would not work. What would be doable is frequent Titan passes at different points & latitudes, but the problem with that is the mission would just be limited to Titan with distant Saturn observations. If Cassini is still working well, lets continue getting as much as possible through out the system, particularly further Enceladus & Dione passes too.

Andrew Brown.

Thank you. It's a pity, let's wait for a Titan-dedicated probe then.

 

[EarthlingX]

Let's play some golf :

http://www.ciclops.org : GOLF SECTOR 6

What will it be like to do ordinary things on the extraordinary alien worlds of our solar system? For instance, will we still play our favorite games? In 1971, during the Apollo 14 mission, astronaut Alan Shepard hit a few golf balls on Earth's moon, where the gravity is six times weaker than on Earth. But what if you took a swing on Hyperion, where the gravity is 500 times weaker than on Earth? How gently would you have to swing to prevent the ball from going into orbit?

GOLF SECTOR 6 is an easy-to-play, Flash-based golf game that lets you tee off on Saturn's moons. It is based on some of our most stunning images returned from the high resolution cameras onboard the Cassini spacecraft that have been processed by CICLOPS and released to the public here on this website. Each of Saturn's moons has its own weak gravity, which should keep things interesting, so be sure to take that into account when you make your swing! Just like golfing on Earth, the goal is to hit the ball into the hole -- or in this case, the crater! -- using the smallest number of swings.

 

[CalliArcale]

Oh, that sounds like a blast! I have got to try that out!

By now, Cassini has completed its closest-ever pass of Titan. Now we just have to hold our breath and wait for the data to come back!

 

[RVHM]

Oh, that sounds like a blast! I have got to try that out!

By now, Cassini has completed its closest-ever pass of Titan. Now we just have to hold our breath and wait for the data to come back!

You wrote this quite a while ago, so the data should already be here no?

 

[EarthlingX]

saturn.jpl.nasa.gov : Dione and Ghostly Titan

June 21, 2010



The surface of Saturn's moon Dione is rendered in crisp detail against a hazy, ghostly Titan.

A portion of the ''wispy'' terrain of Dione's trailing hemisphere can be seen on the right (see Wispy Marble). Also visible in this image are hints of atmospheric banding around Titan's north pole. To learn more about the northern bands, see Bands of Titan and Northern Bands. This view looks toward the Saturn-facing hemisphere of Dione (1,123 kilometers, or 698 miles across) and Titan (5,150 kilometers, or 3,200 miles across).

The image was taken in visible blue light with the Cassini spacecraft narrow-angle camera on April 10, 2010. The view was acquired at a distance of approximately 1.8 million kilometers (1.1 million miles) from Dione and 2.7 million kilometers (1.7 million miles) from Titan. Scale in the original image was 11 kilometers (7 miles) per pixel on Dione and 16 kilometers (10 miles) on Titan. The image has been magnified by a factor of 1.5 and contrast-enhanced to aid visibility.

 

[EarthlingX]

Oh, that sounds like a blast! I have got to try that out!

By now, Cassini has completed its closest-ever pass of Titan. Now we just have to hold our breath and wait for the data to come back!

You wrote this quite a while ago, so the data should already be here no?

Not yet :

saturn.jpl.nasa.gov : TITAN 133TI(T70) MISSION DESCRIPTION (pdf)

June 20, 2010

Page 11 :

T16:23:00 Jun 21 17:40 Jun 21 10:40 T70+14h56m Playback of T70 DataMadrid
T22:00:00 Jun 21 23:17 Jun 21 16:17 T70+20h33m Playback of T70 DataGoldstone
T04:56:00 Jun 23 06:13 Tue Jun 22 11:13 PM T70+02d03h Turn cameras to Titan

but soon

 

[3488]

Hi EarthlingX,

Like calliarcale, I too a am impatient, but yes that is going to be one hell of a data set.

Glad Cassini did NOT enter Titan's atmosphere by accident, always a risk with such a pass (bit like MESSENGER impacting Mercury or Cassini impacting one of the other moons by accident). :shock: :shock:

The Dione transiting Titan image, remember that, I did some enhancements myself & mine are very nearly as good as NASA's own. :mrgreen:

Andrew Brown.

 

[EarthlingX]

Yes, i remember that awesome pass

Have it on a disk too

 

[EarthlingX]

blogs.jpl.nasa.gov : Super Swooper: Cassini wraps up its lowest pass through Titan atmosphere

June 21st, 2010

On Sunday evening, my eyes were glued to eight windows on my computer screen, watching data pop up every few seconds. NASA’s Cassini spacecraft was making its lowest swing through the atmosphere of Saturn’s moon Titan and I was on the edge of my seat. Trina Ray, a Titan orbiter science team co-chair, was keeping me company. Five other members of my team were also at JPL. Between us, we were keeping an eye on about 2,000 data channels.

One of the 34-meter antennas at the Deep Space Network’s Goldstone complex, DSS-24, was pointed at Saturn and listening for the signal that was expected to be here in just a few minutes. The data would be arriving at my computer as quickly as they could be sent back to Earth, though there was an agonizing hour-and-18-minute delay because of the distance the data had to travel. (We call this flyby T70, but it is actually Cassini’s 71st flyby of Titan.)

 

[3488]

Titan images starting to come in from T70 on Monday 21st June 2010 very close pass.

Andrew Brown.

 

[EarthlingX]

http://www.ciclops.org : Tethys and Darker Dione

Saturn's moon Dione, in the foreground of this Cassini image, appears darker than the moon Tethys.



Tethys appears brighter because it has a higher albedo than Dione, meaning Tethys reflects more sunlight. This higher albedo is due to Tethys being closer to the moon Enceladus and the E ring which coats these moons in fresh, bright debris spewing from Enceladus. See PIA08921 and PIA11688 to learn more.

Because of the particular viewing geometry here, lit terrain seen here is on the anti-Saturn side of Dione (1123 kilometers, 698 miles across) while lit terrain on Tethys (1062 kilometers, 660 miles across) is on the leading hemisphere of that moon.

The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on March 23, 2010. The view was obtained at a distance of approximately 1.2 million kilometers (745,000 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 88 degrees. The view was obtained at a distance of approximately 1.8 million kilometers (1.1 million miles) from Tethys and at a Sun-Tethys-spacecraft, or phase, angle of 88 degrees. Image scale is 7 kilometers (4 miles) per pixel on Dione and 11 kilometers (7 miles) per pixel on Tethys.

Crop and enlargement :