Posted on by Nancy Atkinson

Titan + Dione = New Desktop

Titan and Dione as seen by Cassini. Credit: NASA/JPL/Space Science Institute

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Another stunning image from the Cassini spacecraft, suitable for wallpaper on your desktop. Click image for larger version, or click here for a large 1.125 MB version.

This is Saturn’s moon Dione, in crisp detail, against a hazy, ghostly Titan. Simply stunning.

The “wispy” terrain on Dione is visible, and on Titan are hints of atmospheric banding around Titan’s north pole. This view looks toward the Saturn-facing hemisphere of Dione (1123 kilometers, 698 miles across) and Titan (5150 kilometers, 3200 miles across), and was taken on April 10, 2010.

No images available yet from Cassini’s extremely close flyby of Titan over the weekend where it buzzed the hazy moon at an altitude of just 880 kilometers (547 miles) above the surface.

That is 70 kilometers (43 miles) lower than it has ever been at Titan before. The reason for attempting such a close pass is to try and establish if Titan has a magnetic field of its own. But the Cassini team went through hours and hours of calculations for this close flyby, as Titan’s atmosphere applies torque to objects flying through it, much the same way the flow of air would wiggle your hand around if you stuck it outside a moving car window. According to the Cassini website, when engineers calculated the most stable and safe angle for the spacecraft to fly, they found it was almost the same as the angle that would enable Cassini to point its high-gain antenna to Earth. So they cocked the spacecraft a fraction of a degree, enabling them to track the spacecraft in real-time during its closest approach. They set up the trajectory with thrusters firing throughout the flyby to maintain pointing automatically.

The images and data gathered should be amazing, as if everything went as planned, the flyby ended with the ultra violet imaging spectrograph (UVIS) instrument capturing a stellar occultation outbound from Titan. We’ll keep you posted!

Source: CICLOPS, Carolyn Porco on Twitter

Posted on by Nancy Atkinson

Alien Life on Titan? Hang on Just a Minute…

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

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Two papers released last week detailing oddities found on Titan have blown the top off the ‘jumping to conclusions’ meter, and following media reports of NASA finding alien life on Saturn’s hazy moon, scientists are now trying to put a little reality back into the news. “Everyone: Calm down!” said Cassini imaging team leader Carolyn Porco on Twitter over the weekend. “It is by NO means certain that microbes are eating hydrogen on Titan. Non-bio explanations are still possible.” Porco also put out a statement on Monday saying such reports were “the unfortunate result of a knee-jerk rush to sensationalize an exciting but rather complex, nuanced and emotionally-charged issue.”

Astrobiologist Chris McKay told Universe Today that life on Titan is “certainly the most exciting, but it’s not the simplest explanation for all the data we’re seeing.”

McKay suggests everyone needs to take the Occam’s Razor approach, where the simplest theory that fits the facts of a problem is the one that should be selected.

The two papers suggest that hydrogen and acetylene are being depleted at the surface of Titan. The first paper by Darrell Strobel shows hydrogen molecules flowing down through Titan’s atmosphere and disappearing at the surface. This is a disparity between the hydrogen densities that flow down to the surface at a rate of about 10,000 trillion trillion hydrogen molecules per second, but none showing up at the surface.

“It’s as if you have a hose and you’re squirting hydrogen onto the ground, but it’s disappearing,” Strobel said. “I didn’t expect this result, because molecular hydrogen is extremely chemically inert in the atmosphere, very light and buoyant. It should ‘float’ to the top of the atmosphere and escape.”

The other paper (link not yet available) led by Roger Clark, a Cassini team scientist, maps hydrocarbons on Titan’s surface and finds a surprising lack of acetylene. Models of Titan’s upper atmosphere suggest a high level of acetylene in Titan’s lakes, as high as 1 percent by volume. But this study, using the Visual and Infrared Mapping Spectrometer (VIMS) aboard Cassini, found very little acetylene on Titan’s surface.

Of course, one explanation for both discoveries is that something on Titan is consuming the hydrogen and acetylene.

Even though both findings are important, McKay feels the crux of any possible life on Titan hinges on verifying Strobel’s discovery about the lack of hydrogen.

“To me, the whole thing hovers on this determination of whether there is this flux of hydrogen is real,” McKay said via phone. “The acetylene has been missing and the ethane has been missing, but that certainly doesn’t generate a lot of excitement, because how much is supposed to be there depends on how much is being made. There are a lot of uncertainties.”

McKay stressed both results are still preliminary and the hydrogen loss in particular is the result of a computer calculation, and not a direct measurement. “It is the result of a computer simulation designed to fit measurements of the hydrogen concentration in the lower and upper atmosphere in a self-consistent way,” he said in a statement he put out over the weekend. “It is not presently clear from Strobel’s results how dependent his conclusion of a hydrogen flux into the surface is on the way the computer simulation is constructed or on how accurately it simulates the Titan chemistry.”

However, the findings are interesting for astrobiology, and would require the actual existence of methane-based life, a theory McKay himself proposed five years ago, which he described today as an “odd idea.”

In 2005, McKay and Heather Smith (McKay and Smith, 2005) suggested that methane-based life (rather than water-based) called methanogens on Titan could consume hydrogen, acetylene, and ethane. The key conclusion of that paper 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.”

Even though the two new papers seem to show evidence for all three of these on Titan, McKay said this is a still a long way from “evidence of life”. However, it is extremely interesting.

But what does McKay really think?

“Unfortunately, if I was betting, the most likely explanation is that Darrel’s (Strobel) results are wrong and that further analysis will show there is another explanation for the data he is trying to fit, besides the strong flux of hydrogen into the surface. I would be very happy if we did confirm all that data, but we do have to take it in steps.”

McKay provided 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,” McKay said.

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,” McKay said.

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 (Astrobiology, vol. 5, no. 4., p. 560-567.).

McKay said if further analysis shows that a strong flux of hydrogen into the surface really is happening, “then my first two explanations are no longer options and we are then left with two really quite remarkable alternatives, either there is some mysterious metalysis going on, which at 95 k is really hard to imagine, and would have enormous implications for things like chemical engineering. And the second alternative is that there is life, which is even more amazing.”

“So to make process on this,” McKay continued, “we have to confirm Darrel’s result that there is hydrogen being fluxed onto the surface of Titan, that is really way unexpected, and unfortunately, it constitutes extraordinary claims that need extraordinary evidence. Darrel’s paper is just a first step in that.”

What does McKay think about the rash of media reports claiming life on Titan?

“Well, I think it reflects our human fascination and desire to find life out there,” he said. “We want it to be true. When we’re given a set of facts, if they are consistent with biology we jump to that explanation first. The most biologically interesting explanation is the first one we look to. We ought to give that a name — something like ‘Carl Sagan’s Razor’ as opposed to ‘Occam’s Razor,’ which would say that ‘The most exciting explanation is assumed to be true until it is proven false.'”

You can read all of McKay’s written response on the CICLOPS website, which Porco said will be “the first installment in a new feature on the CICLOPS website, called ‘Making Sense of the News’, where from time to time, scientists, both involved in Cassini and not, will be invited to comment on new developments that bear on the exploration of the solar system and the study of planetary systems, including our own.”

Posted on by Nancy Atkinson

Early Faint Sun Paradox Explained?

Titan's thick haze. Image: NASA/JPL/Space Science Institute.

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Models of the Sun’s evolution indicate it was as much as 30 percent less luminous during Earth’s early history than it is now. But, somehow the surface of the planet was warm enough for primordial life to emerge. A new study and a look at Saturn’s moon Titan has provided clues for how the Sun could have kept the early Earth warm enough. Scientists say a thick organic haze that enshrouded early Earth several billion years ago may have been similar to the haze that covers Titan and would have protected emerging life on the planet from the damaging effects of ultraviolet radiation, while warming the planet, as well.

Eric Wolf from the University of Colorado-Boulder and his team believe the organic haze was made up primarily of methane and nitrogen chemical byproducts created by reactions with light. If the particles clumped together in larger, complex structures, an arrangement known as a fractal size distribution, then the smallest particles would interact with the shortwave radiation, while the larger structures made out of the smaller particles would affect longer wavelengths. Not only would the haze have shielded early Earth from UV light, it would have allowed gases like ammonia to build up, causing greenhouse warming and perhaps helped to prevent the planet from freezing over.

Other researchers including Carl Sagan have proposed possible solutions to this “Early Faint Sun” paradox, which generally involved atmospheres with powerful greenhouse gases that could have helped insulate the Earth. But while those gases would have blocked the radiation, it wouldn’t have warmed Earth enough for life to form.

“Since climate models show early Earth could not have been warmed by atmospheric carbon dioxide alone because of its low levels, other greenhouse gases must have been involved,” said Wolf. “We think the most logical explanation is methane, which may have been pumped into the atmosphere by early life that was metabolizing it.”

Lab simulations helped researchers conclude that the Earth haze likely was made up of irregular “chains” of aggregate particles with greater geometrical sizes, similar to the shape of aerosols believed to populate Titan’s thick atmosphere. The arrival of the Cassini spacecraft at Saturn in 2004 has allowed scientists to study Titan, the only moon in the solar system with both a dense atmosphere and liquid on its surface.

During the Archean period there was no ozone layer in Earth’s atmosphere to protect life on the planet, said Wolf. “The UV shielding methane haze over early Earth we are suggesting not only would have protected Earth’s surface, it would have protected the atmospheric gases below it — including the powerful greenhouse gas, ammonia — that would have played a significant role in keeping the early Earth warm.”

The researchers estimated there were roughly 100 million tons of haze produced annually in the atmosphere of early Earth during this period. “If this was the case, an early Earth atmosphere literally would have been dripping organic material into the oceans, providing manna from heaven for the earliest life to sustain itself,” said team member Brian Toon, also from CU-Boulder.

“Methane is the key to make this climate model run, so one of our goals now is to pin down where and how it originated,” said Toon. If Earth’s earliest organisms didn’t produce the methane, it may have been generated by the release of gasses during volcanic eruptions either before or after life first arose — a hypothesis that will requires further study.

This new study will likely re-ignite interest in a controversial experiment by scientists Stanley Miller and Harold Urey in the 1950s in which methane, ammonia, nitrogen and water were combined in a test tube. After Miller and Urey ran an electrical current through the mixture to simulate the effects of lightning or powerful UV radiation, the result was the creation of a small pool of amino acids — the building blocks of life.

“We still have a lot of research to do in order to refine our new view of early Earth,” said Wolf. “But we think this paper solves a number of problems associated with the haze that existed over early Earth and likely played a role in triggering or at least supporting the earliest life on the planet.”

Sources: CU-Boulder, Science

Posted on by Nancy Atkinson

Incredible Images of Enceladus From Cassini’s Latest Flyby

Titan, Saturn's rings and Enceladus. Credit: NASA/JPL/SSI

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Wow. Cassini the artist has struck again, this time with amazing images from the close flyby of Enceladus that we wrote a preview about earlier this week. Cassini flew by Enceladus during the early hours of May 18 UTC, coming within about 435 kilometers (270 miles) of the moon’s surface. The raw images came in late last night, and in my inbox this morning was an email from Stuart Atkinson, (no relation, but great name) alerting me to the treasures. Stu himself has called this image “the new iconic image of the space age,” and Emily Lakdawalla of the Planetary Blog has called these images “some of the most amazing Cassini has captured yet.”

What you’re seeing here is hazy Titan, backlit by the Sun, with Saturn’s rings in the foreground– plus, at the way bottom is the limb of the night side of Enceladus’ south pole. Emily has created a flipped, annotated image (plus there’s more Enceladus jaw-droppers below:

nceladus, Titan, and the rings of Saturn (explained) Credit: NASA/JPL/SSI/annotated by Emily Lakdawa. Click for larger version.

The 'fountains' of Enceladus. Credit: NASA/JPL/SSI

Three huge “fountains” of Enceladus geysers are visible in this raw image taken by Cassini on May 18, 2010. The camera was pointing toward Enceladus at approximately 14,972 kilometers away, and the image was taken using the CL1 and CL2 filters. Emily, with her photo editing prowess, has created a movie from four different images as Cassini cruised closer to the moon.

Astro0 on UnmannedSpaceflight.com has put the two different images together to create a collage of what it would have looked like if the plumes were visible in the image with Titan. Gorgeous! Plus, here’s a color version Astro0 created.

Plus there’s this very interesting raw image from Cassini:

Raw image from Cassini on May 18. Credit: NASA/JPL/SSI

Explanations anyone?

Cassini will be flying by Titan in the early hours of May 20 UTC, coming within 1,400 kilometers (750 miles) of the surface. Although Cassini will primarily be doing radio science during this pass to detect subtle variations in the gravitational tug on the spacecraft by Titan, hopefully we’ll see some new visible light images of Titan, as well.

For more images from Cassini, see the Cassini website, and the section for the raw images.

Posted on by Nancy Atkinson

Cassini’s Cruise: Close Flybys of Two Moons in Less Than Two Days

On the left, Saturn's moon Enceladus is backlit by the sun, showing the fountain-like sources of the fine spray of material that towers over the south polar region. On the right, is a composite image of Titan. Image credit: NASA/JPL/SSI and NASA/JPL/University of Arizona

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It’s a space navigator’s dream! The Cassini spacecraft will perform close flybys of two of Saturn’s most enigmatic moons all within less than 48 hours, and with no maneuvers in between. Enceladus and Titan are aligned just right so that Cassini can catch glimpses of these two contrasting moons – one a geyser world and the other an analog to early Earth.

Cassini will make its closest approach to Enceladus late at night on May 17 Pacific time, which is in the early hours of May 18 UTC. The spacecraft will pass within about 435 kilometers (270 miles) of the moon’s surface.

The main scientific goal at Enceladus will be to watch the sun play peekaboo behind the water-rich plume emanating from the moon’s south polar region. Scientists using the ultraviolet imaging spectrograph will be able to use the flickering light to measure whether there is molecular nitrogen in the plume. Ammonia has already been detected in the plume and scientists know heat can decompose ammonia into nitrogen molecules. Determining the amount of molecular nitrogen in the plume will give scientists clues about thermal processing in the moon’s interior.

Then on to Titan: the closest approach will take place in the late evening May 19 Pacific time, which is in the early hours of May 20 UTC. The spacecraft will fly to within 1,400 kilometers (750 miles) of the surface.

Cassini will primarily be doing radio science during this pass to detect the subtle variations in the gravitational tug on the spacecraft by Titan, which is 25 percent larger in volume than the planet Mercury. Analyzing the data will help scientists learn whether Titan has a liquid ocean under its surface and get a better picture of its internal structure. The composite infrared spectrometer will also get its southernmost pass for thermal data to fill out its temperature map of the smoggy moon.

Cassini has made four previous double flybys and one more is planned in the years ahead.

For more information on the Enceladus flyby, dubbed “E10,” see this link.

For more information on the Titan flyby, dubbed “T68,” see this link.

Source: JPL

Posted on by Nancy Atkinson

Incredible! Cassini as Houdini Cuts Titan in Half

Saturn's rings, made dark in part as the planet casts its shadow across them, cut a striking figure before Saturn's largest moon, Titan. Credit: NASA/JPL/Space Science Institute

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There’s nothing up the sleeves of the Cassini imaging team in this image; it is real! Is the moon Titan being cut in half by Saturn’s rings? What is actually happening here is that the middle part of the rings are made dark as Saturn casts its shadow across them. Cassini was just in the right place at the right time, making it appear as though Titan is being sliced in half! The night side of the planet is to the left, out of the frame of the image. Illuminated Titan can be seen above, below and through gaps in the rings. Click the image for a larger version.

As an added benefit in this shot, Mimas (396 kilometers, 246 miles across) is near the bottom of the image, and Atlas (30 kilometers, 19 miles across) can barely be detected near the thin F ring just above the center right of the image. Lit terrain seen here is the area between the leading hemisphere and Saturn-facing side of Titan (5,150 kilometers, 3,200 miles across). This view looks toward the northern, sunlit side of the rings from just above the ringplane.

Below are a few more magical images from Cassini:

Here the moon Enceladus appears strung along a wispy ring of Saturn, likely the G ring. Look close and Enceladus’ plumes are visible, too.

Enceladus and a wispy ring. Credit: NASA/JPL/Space Science Institute
Pandora and Epimetheus sit on Saturn's rings. Credit: NASA/JPL/Space Science Institute

Two of Saturn’s small moons appear to be sitting on Satun’s thin F ring in this image.

From the CICLOPS website:

Pandora (81 kilometers, 50 miles across) is on the left, and Epimetheus (113 kilometers, 70 miles across) is on the right. This view looks toward the northern, sunlit side of the rings from just above the ringplane. Both moons are closer to Cassini than the rings are. Pandora is slightly closer to Cassini than Epimetheus here.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Nov. 23, 2009. The view was acquired at a distance of approximately 1.3 million kilometers (808,000 miles) from Pandora and Epimetheus. Image scale is 8 kilometers (5 miles) per pixel.

For more great images from Cassini (which I contend is actually an artist and not a magician!) go to the CICLOPS website and NASA’s Cassini website.

Posted on by Nancy Atkinson

Life on Titan Could Be Smelly and Explosive

Artist concept of Methane-Ethane lakes on Titan (Credit: Copyright 2008 Karl Kofoed). Click for larger version.

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Could there be life on Titan? If so, one astrobiologist says humans probably couldn’t be in the same room with a Titanian and live to tell about it. “Hollywood would have problems with these aliens” said Dr. William Bains. “Beam one onto the Starship Enterprise and it would boil and then burst into flames, and the fumes would kill everyone in range. Even a tiny whiff of its breath would smell unbelievably horrible. But I think it is all the more interesting for that reason. Wouldn’t it be sad if the most alien things we found in the galaxy were just like us, but blue and with tails?”

While giving an obvious nod to the recent movie “Avatar,” Bains’ research provides insight to the difficulties we might encounter – beyond cultural – if we ever meet up with alien life. There could be unintended harmful consequences for one species, or both.

Bains is working to find out just how extreme the chemistry of life can be. Life on Titan, Saturn’s largest moon, represents one of the more bizarre scenarios being studied. While images sent back by the Cassini/Huygens mission might make Titan look Earth-like and maybe even inviting, it has a thick atmosphere of frozen, orange smog. At ten times our distance from the Sun, it is a frigid place, with a surface temperature of -180 degrees Celsius. Water is permanently frozen into ice and the only liquid available is liquid methane and ethane.

So instead of water based-life (like us), life on Titan would likely be based on methane.

“Life needs a liquid; even the driest desert plant on Earth needs water for its metabolism to work. So, if life were to exist on Titan, it must have blood based on liquid methane, not water. That means its whole chemistry is radically different. The molecules must be made of a wider variety of elements than we use, but put together in smaller molecules. It would also be much more chemically reactive,” said Bains.

Additionally, Bains said a metabolism running in liquid methane would have to be built of smaller molecules than terrestrial biochemistry.

“Terrestrial life uses about 700 molecules, but to find the right 700 there is reason to suppose that you need to be able to make 10 million or more,” Bains said. “The issue is not how many molecules you can make, but whether you can make the collection you need to assemble a metabolism.”

Bains said doing such assembling is like trying to find bits of wood in a lumber-yard to make a table.

“In theory you only need 5,” he said. “But you may have a lumber-yard full of offcuts and still not find exactly the right five that fit together. So you need the potential to make many more molecules than you actually need. Thus the 6-atom chemicals on Titan would have to include much more diverse bond types and probably more diverse elements, including sulphur and phosphorus in much more diverse and (to us) unstable forms, and other elements such as silicon.”

Energy is another factor that would affect the type of life that could evolve on Titan. With Sunlight a tenth of a percent as intense on Titan’s surface as on the surface of Earth, energy is likely to be in short supply.

“Rapid movement or growth needs a lot of energy, so slow-growing, lichen-like organisms are possible in theory, but velociraptors are pretty much ruled out,” said Bains.

Whatever life may be on Titan, at least we know there won’t be a Jurassic Park.

Bains, whose research is carried out through Rufus Scientific in Cambridge, UK, and MIT in the USA, is presenting his research at the National Astronomy Meeting in Glasgow, Scotland on April 13, 2010.

Source: RAS NAM

Posted on by John Carl Villanueva

What Is A Moon?

Full Moon
Full Moon

Before the invention of the telescope in the early 1600’s, man just knew of the Moon — a round, mysterious astronomical object that people would gaze up to in the night sky. As time progressed however, astronomers discovered that the moon isn’t exactly unique to earthlings, and other planets had their own moons. So exactly what is a moon?

A moon is defined to be a celestial body that makes an orbit around a planet, including the eight major planets, dwarf planets, and minor planets. A moon may also be referred to as a natural satellite, although to differentiate it from other astronomical bodies orbiting another body, e.g. a planet orbiting a star, the term moon is used exclusively to make a reference to a planet’s natural satellite.

The first moons to be discovered outside of the Earth’s moon were the Galilean moons of Jupiter, named after astronomer and discoverer Galileo Galilei. The moons Io, Europa, Ganymede, and Callisto are Jupiter’s largest and only the first four to be revealed, as to date, the planet has 63 moons.

Other than the four Galilean moons, Saturn’s Titan and Neptune’s Triton are two other moons which are comparable in size to the Earth’s Moon. In fact, these seven moons are the largest natural satellites in the solar system, measuring more than 3,000 kilometers in diameter. Only the inner planets Mercury and Venus have no moons.

An interesting fact about some of the solar system’s largest moons that most people may not be aware of is that a few of them are geologically active. While we may not see the Moon spewing lava or displaying any evidence of tectonic activity, Jupiter’s Io and Europa, Saturn’s Titan and Enceladus, and Neptune’s Triton have been found to be volcanically active bodies.

If the moon count had a grand total of just one in the olden times, that number has ballooned to 336 as of July 2009, with 168 moons orbiting the six planets, while the rest are moons of dwarf planets, asteroids moons, and natural satellites of Trans-Neptunian objects.

As more and more discoveries are made however, astronomers may find it more difficult to put a really defining line on what can or what can’t be classified as a moon. For instance, can you consider a 10-inch rock that’s orbiting Jupiter a moon? If yes, then there could be thousands or even millions of moons out there. If not, then where do you draw the line? Obviously, even the size of an “official” moon is still up for debate, so other than the simple definition of it being a natural satellite of a planet, there really is no clear cut answer to the question, “What is a moon?”.

Here in Universe Today, we have a nice collection of articles that explain why the Moon landings could not have been faked. Here are some of them:

Moon Rocks – Discusses how the Moon rocks are one of the most tangible objects that prove the landings took place.

Moon Landing Hoax – An explanation that counters some of the points raised by skeptics

Apollo 11 Hoax – another point for point discussion by Jerry Coffey

TV – Alert: Mythbusters and the Moon Hoax Myth – a teaser for the Mythbusters episode featuring the so-called hoax. You’ll find the comments below that article equally interesting, by the way.

Here’s an article from NASA that debunks the hoax theory using the Moon rock arguments. Another article about Moon rocks from the same site.

Episodes about the moon from Astronomy Cast. Lend us your ears!

Shooting Lasers at the Moon and Losing Contact with Rovers
The Moon Part I

References:
NASA Solar System Exploration: Moons of Jupiter
NASA Solar System Exploration: Moons

Posted on by Nicholos Wethington

A Double-Dose of Cassini Goodness

The Cassini mission is just a non-stop faucet of fantastic images! Here are two that were released today, for your viewing pleasure. The first image, above, is an eclipse of Saturn’s moon Tethys, which lies in the background, by Dione. The three images were each taken one minute apart.

As you can see, from Cassini’s perspective Dione passes right in front of Tethys. Make no mistake in thinking that these two Saturnian companions are close together in this shot, however; Dione, the moon in the foreground, is 2.2 million kilometers (1.4 million miles) from the Cassini spacecraft, while Tethys is 2.6 million kilometers (1.6 million miles) away.

An interesting feature of the image is how Tethys appears brighter on the side of the moon opposite the Sun. This is because Saturn, which lies out of the image to the right, is reflecting light from the Sun back onto the moon. Dione is not being backlit by Saturn from the vantage point of Cassini, so its face that is opposite the Sun appears darker.

Visible on Tethys is the Odysseus Crater, which spans a whopping 400km (240 miles). Given that Tethys is only 1,062 kilometers, or 660 miles across, the crater appears very large in comparison to the moon. It also makes the moon very much resemble the Death Star from Star Wars, don’t you think? These images were taken using Cassini’s narrow-angle camera on Nov. 28, 2009.

This second image is a synthetic aperture radar image of the surface of Saturn’s moon Titan. In the lower right and upper center of the image, the two wrinkly features are actually small Titanian mountains. What exactly causes the grooves in these mountains has still to be determined.

On Earth, the shifting of tectonic plates can form such structures, as well as the processes of water flowing, freezing, and melting.

Since Titan has an atmosphere composed mostly of methane and ethane, and experiences rain much like here on Earth, it’s quite possible that these processes are the cause of such features.

Because the illumination of this image comes from the radar on Cassini, the peaks of these formations should be the brightest. As is visible, this isn’t the case. Notice how the left side of the upper mountain in the image, and right side of the lower-right mountain are brighter. The materials that make up the darker and lighter areas are the cause for this lighting effect.

The image represents a patch of Titan’s surface 250 km (155 miles) high and 285 km (180 miles) wide, and the resolution is about 350 meters (1,150 feet) per pixel, and it was taken on December 28th, 2009.

Source: Cassini Equinox Mission, here and here.

Posted on by Nicholos Wethington

Sailing the Seas of Titan

Titan's Ligeia Mare. Credit: NASA/JPL/USGS

The first interplanetary nautical craft may be a boat to explore the methane seas of Titan. A proposed mission to Titan would explore some of its largest seas, including Ligeia Mare (pictured) or the Kraken Mare, both of which are in the northern hemisphere of the foggy moon of Saturn. The concept has been studied for over two years by scientific team led by Ellen Stofan of Proxemy Research, Inc. in Washington DC, and has recently been submitted to NASA.

The concept is under consideration by NASA to be one of the Discovery Class missions – low-cost, high-return missions, which include the MESSENGER and Kepler missions. If chosen, the Titan Mare Explorer (TiME), could launch as early as January of 2015, and would make port at Titan in June of 2023. The total proposed cost of TiME is currently estimated at $425 million. Stofan described the proposal at this year’s American Geophysical Union meeting in San Fransisco, CA.

Lakes, seas, and rivers were discovered on Titan by the Cassini spacecraft in 2005. Since then, the weather and climate patterns of the moon have been scrutinized by scientists, leading to the discovery of both fog and rain.

Of course, the proposed boat wouldn’t be the first craft to land on Titan – that distinction is held by the Huygens probe, which as part of the Cassini mission landed on Titan on January 14th, 2005 and for three hours took images and scientific data which it sent back to Earth. Huygens touched down on dry land, though it was designed to operate on either land or ocean.

Proposed instruments for the boat include a mass spectrometer, sonar, cameras and meteorology instruments. TiME would investigate the chemical composition of the seas of Titan, as well as monitor the cycle of ethane and methane on the moon (called the “methane-ologic” cycle), a process that scientists are just beginning to understand. The sonar would be used just like it is on submarines and boats here on Earth – to map the depth of the seas, as well as get an accurate image of the sea bottom.

Since the cloudy and foggy surface of Titan sees little sunlight, the boat is proposed to be powered by an Advanced Stirling Radioisotope Generator. These types of engines, called Stirling engines after the inventor, Robert Stirling, use a radioactive source such as plutonium to heat a gas in one chamber, and as it flows to a cooler chamber the flow is turned into mechanical energy with a very high rate of efficiency.

If the boat is seaworthy, it may set a precedent to give us Earthlubbers a chance at understanding the only other body in our Solar System with lakes and seas on its surface (though Europa and Enceladus are thought to have watery oceans under their crusts). By comparing the methane-ologic cycle on Titan with the Earth’s hydrologic cycle, scientists could gain a more intricate knowledge of the large-scale impact of these cycles.

Source: Physorg, Ellen Stofan’s presentation (available here in PDF)