Author Topic: weathEU - Titan's Nitrogen and Methane/Ethane weather  (Read 29521 times)

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weathEU - Titan's Nitrogen and Methane/Ethane weather
« on: August 16, 2009, 20:41:59 »
Titan's Weather System




Titan is a massive moon, larger than Mercury, a very cold Moon (-180C, 94 Kelvin) yet it has a weather system with its atmosphere mainly Nitrogen and a  frozen Methane/Ethane cloud system.

Although Titan is a frozen moon it has geological features similar to earth and other planets. How can Titan and these other planets (Earth, Mars, Mercury, Venus?) have what we are told are similar liquid erosion formed landscapes?

Ethane is interesting in that it has been found not just on Earth, Pluto and Titan and the 4 Gas Giants (Jupiter, Saturn, Uranus, and Neptune) but also in Comet Hyakutake and other comets.

The articles quoted below are the orginal summaries or press release of the research papers about Titans Tropical storm clouds and the discovery in August 2008 of a massive storm system.



A 25 minute video (Titans tropical storm clouds) from Henry Roe and Mike Brown (astronomers) who discuss the finding of Titans methane clouds in the Saturn moons "tropics".

The links below are brief "new reports" that sum up and add additional background information.

Storm Clouds Found on Saturn's Moon - aol news
Scientists Spot Massive Methane Rainstorm on Saturn's Moon - abc news

Below are the press releases with more detail and information about Titans Methane/Ethane tropical storm clouds

Lowell Observatory - Clouds Discovered over Titan's Tropics

Caltech  - Scientists Discover Storms in the Tropics of Titan

Mike Brown - The long road to a Titan storm - personal story of those involed

NSF - Gemini Observatory captures first images of clouds over the tropics of Titan

University of Hawaii, Institute for Astronomy - Huge Storm Detected on Titan

National Science Foundation (NSF) - Methane Clouds Observed Near Titan's Equator May Explain Presence of Riverbeds on the Surface

Nature letters - Storms in the tropics of Titan



« Last Edit: August 17, 2009, 03:23:12 by electrobleme »

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Clouds Discovered over Titan's Tropics
« Reply #1 on: August 16, 2009, 20:46:45 »
Clouds Discovered over Titan's Tropics


Quote
In a case of persistent interplanetary detective work using powerful ground-based telescopes, a team of astronomers located and tracked the first bright but transient clouds over tropical latitudes on Saturn's moon Titan. The astronomers used the Gemini North telescope and NASA's Infrared Telescope Facility (IRTF) in an almost-nightly observing program providing new insights into the nature of Titan's tropospheric (low-elevation) clouds. The team's paper, Storms in the tropics of Titan, will be published in the August 13, 2009 edition of the journal Nature. The astronomers observed a convective pulse at mid-latitudes that generated a wave in Titan's atmosphere. This wave went on to trigger cloud formation over both the equatorial and south polar regions. These new observations of this type of equatorial cloud may help explain the formation of liquid methane-carved channels and rivers located in the vicinity of the Huygens probe landing site.

"These types of dramatic global weather events on Titan are rare and only last a few weeks," said Henry Roe, Lowell Observatory astronomer and team member. "The best way to observe them and understand how they compare with more normal weather on Titan is through a coordinated effort obtaining frequent observations on several telescopes." The observing team consists of Lowell astronomer Henry Roe; Emily Schaller, a Hubble Fellow now working at the University of Arizona's Lunar and Planetary Laboratory; and Caltech's Tapio Schneider and Michael Brown.

Using the 3.0-meter NASA Infrared Telescope Facility (IRTF), operated by the Institute for Astronomy, University of Hawaii, and The Gemini North 8.0-meter telescope, the team made many observations over a longer than two-year period. During this period, which covered the mid-to-late northern spring season on Titan, they observed remarkably few clouds anywhere on Titan. On April 13, 2008 observations with the IRTF showed a dramatic increase in cloud activity on Titan. The next night, and for many nights thereafter, they acquired quick imaging snapshots of Titan using the larger Gemini North telescope. These images revealed that the initial cloud system was at 30 deg S latitude, but within days additional clouds appeared over Titan's tropics and south polar region. "It was as though we observed a giant storm covering South Africa that days later caused clouds to form over Antarctica and Indonesia," said team member Schaller.

Titan, Saturn's largest moon, is larger than Mercury and Pluto and is the only moon in our solar system to be surrounded by an atmosphere. While weather on Earth is based on water, on Titan conditions are too cold for liquid water to exist. However, conditions on Titan are just right for weather to be methane based. In January 2005 NASA's Cassini mission deployed the Huygens probe into Titan's atmosphere. The probe landed near Titan's equator and returned images of channels and dry streambeds. This posed a conundrum as weather models predicted that Titan's equatorial regions were a desert and should never be cloud covered or receive rainfall. These same models predicted the south polar clouds the team had earlier observed during early southern summer on Titan, but the models indicated that these south polar clouds should have disappeared by mid-to-late summer.

By observing clouds in the equatorial region, where clouds were never expected to form, and in the south polar region, where clouds were not expected to form in the current season, this new research has shown that clouds can form in times and places not predicted by the current generation of computer weather models of Titan's atmosphere. On Titan strong storm activity in one area can trigger clouds and storms elsewhere on the moon. "These observations show that the channels and streambeds in Titan's tropical desert can be explained by infrequent but strong downpours, much like many of the landforms here in the Southwestern United States," said Roe.

"Titan's year is 30 Earth years long and so far we've only been observing Titan with this type of precision and frequency for less than one Titanian season," said Roe. "Imagine trying to understand Earth's weather having only seen what happens in January, February, and part of March. We have our work cut out for us to continue watching the weather on Titan for many more years."

Funding for this research was provided by NASA's Planetary Astronomy Program and from a NSF Planetary Astronomy Grant. Support was also made through the Hubble Postdoctoral Fellowship. The IRTF is operated by the University of Hawaii under a cooperative agreement with the Planetary Astronomy Program of the NASA Science Mission Directorate. Gemini Observatory is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation on behalf of the International Gemini partnership.
Lowell Observatory - Clouds Discovered over Titan's Tropics
« Last Edit: August 16, 2009, 21:15:53 by electrobleme »

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Caltech Scientists Discover Storms in the Tropics of Titan
« Reply #2 on: August 16, 2009, 21:05:46 »

Caltech Scientists Discover Storms in the Tropics of Titan





Quote
For all its similarities to Earth—clouds that pour rain (albeit liquid methane not liquid water) onto the surface producing lakes and rivers, vast dune fields in desert-like regions, plus a smoggy orange atmosphere that looks like Los Angeles's during fire season—Saturn's largest moon, Titan, is generally "a very bland place, weatherwise," says Mike Brown of the California Institute of Technology (Caltech).
Adaptive optics image from Gemini Observatory of Titan passing nearly directly in front of Saturn. Titan, as usual, looks quite bland, with no hint of clouds.
[Credit: Gemini Observatory/AURA/Henry Roe, Lowell Observatory]

"We can watch for years and see almost nothing happen. This is bad news for people trying to understand Titan's meteorological cycle, as not only do things happen infrequently, but we tend to miss them when they DO happen, because nobody wants to waste time on big telescopes—which you need to study where the clouds are and what is happening to them—looking at things that don't happen," explains Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.

However, just because weather occurs "infrequently" doesn't mean it never occurs, nor does it mean that astronomers, in the right place at the right time, can't catch it in the act.

That's just what Emily Schaller—then a graduate student of Brown's—and colleagues accomplished when they observed, in April 2008, a large system of storm clouds appear in the apparently dry mid-latitudes and then spread in a southeastward direction across the moon. Eventually, the storm generated a number of bright but transient clouds over Titan's tropical latitudes, a region where clouds had never been seen—and, indeed, where it was thought they were extremely unlikely to form.

Schaller, now a Hubble Postdoctoral Fellow at the University of Arizona, Brown, and their colleages; Henry Roe, a former Caltech postdoctoral scholar in Brown’s group, now at the Lowell Observatory in Flagstaff; and Tapio Schneider, a professor of environmental science and engineering at Caltech, describe their work, and its implications for climate on Titan, in the August 13 issue of Nature.

"A couple of years ago, we set up a highly efficient system on a smaller telescope to figure out when to use the biggest telescopes," Brown says. The first telescope, NASA's Infrared Telescope Facility, on Mauna Kea, takes a spectrum of Titan almost every single night. "From that we can't tell much, but we can say 'no clouds,' 'a few clouds,' or, if we get lucky 'monster clouds,'" he explains.

Schaller explains, "The period during which I was collecting data for my thesis, sadly, corresponded entirely to an extended period of essentially no clouds, so we never really got to show the full power of the combined telescopes. But then, after finishing and turning in my thesis, I walked back across campus to my office to look at the data from the previous night to find that Titan suddenly had the biggest clouds ever. I like to think it was Titan’s graduation gift to me. Or perhaps a bad joke."
A major storm erupts in the desert tropics of Titan.
[Credit: Emily Schaller et al./Gemini Observatory]

The day after the telescope's big find (and Schaller’s thesis submission), Schaller, Brown, and Roe began tracking the clouds with the large Gemini telescope on Mauna Kea and watched this system evolve for a month. "And what a cool show it was," Brown says.

"The first cloud was seen near the tropics and was caused by a still-mysterious process, but it behaved almost like an explosion in the atmosphere, setting off waves that traveled around the planet, triggering their own clouds. Within days a huge cloud system had covered the south pole, and sporadic clouds were seen all the way up to the equator."

Schneider, an expert on atmospheric circulations, was instrumental in helping to sort out the complicated chain of events that followed the initial outburst of cloud activity.

"The monthlong event has many important implications for understanding the hydrological cycle on Titan," says Brown, "but one of the reasons I am most excited about it is that it shows clouds near the equator—where the [European Space Agency's] Huygens probe landed—for the first time. For a while now, people have speculated that the equatorial regions are simply too dry to ever have significant clouds."

And yet, the images snapped by the Huygens probe in January 2005, as it descended through Titan's soupy atmosphere and toward the surface, revealed small-scale channels and streams, which looked just like features created by fluids—by water, here on Earth, and on Titan, probably by liquid methane.

Experts had speculated for years on how there could be streams and channels in a region with no rain. The new results suggest those speculations may prove unneccessary. "No one considered how storms in one location can trigger them in many other locations," says Brown.

The paper, "Storms in the tropics of Titan," appears in the August 13 issue of Nature. The research was supported by a Hubble Postdoctoral Fellowship (to Schaller), the NASA Planetary Astronomy Program, and a Planetary Astronomy Grant from the National Science Foundation.

For more information about the discovery, go to http://www.mikebrownsplanets.com.

View a video of astronomers Henry Roe and Mike Brown discussing recently announced observations of storm clouds in the tropics of Titan.
Caltech Scientists Discover Storms in the Tropics of Titan



« Last Edit: August 16, 2009, 21:16:29 by electrobleme »

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Re: weathEU - Titan's Nitrogen and Methane/Ethane weather
« Reply #3 on: August 16, 2009, 21:14:51 »

The long road to a Titan storm

Quote
Look in your newspaper this Saturday, and you may see a paragraph about Saturn’s moon Titan and a giant storm that moved across the surface last May and what that means. With luck they’ll even print it with a tiny little picture of Titan to catch your eye. Your response, if you have one, will likely be “huh.” It’s OK. I’m not offended. It’s hard to distill the richness of a full scientific paper into a paragraph. And it’s even harder, still, to distill the richness of a decade of scientific inquiry into a short scientific paper. But if you’re curious about what that little paragraph means, and how it came to be in your newspaper, and what we’ve been doing for the past decade, read on. It’s a long story, but that’s somewhat of the point.

I became interested in Titan ten years ago, almost as a matter of convenience. It was an excellent solar system target for the then-new technique of Adaptive Optics, which attempts to undo some of the effects of the smearing of starlight caused by Earth’s atmosphere. Titan was a great target because it is just small enough to be completely smeared by the atmosphere, but big enough that, if you could unsmear it, you would still have a nice view. Just as importantly, no one had ever had a nice view of the surface of Titan before because the satellite it covered in a thick layer of smog which mostly doesn’t let light penetrate to the surface. When the Voyager spacecrafts flew by, they took pictures of Titan which look like a big orange billiard ball. I should have said, though, that visible light doesn’t penetrate to the surface. On the earth, red light penetrates smog better than blue light (hence the nice red sunsets on a smoggy day in Los Angeles). The same happens on Titan. Red penetrates better than blue, but infrared penetrates better still. In fact, if you go far enough into the infrared, you can take a picture of Titan and almost not notice any smog there at all. Conveniently, the new technique of Adaptive Optics works best in the infrared. Hence Titan became a natural target to try out the new techniques on. Antonin Bouchez, then a relatively new graduate student at Caltech, signed on to do this project as part of his Ph.D. thesis.

Our first goals were to obtain maps of the then-almost-totally-unknown surface of Titan. And what a strange looking surface it turned out to be! We speculated endlessly about what all of those dark and bright spots on the surface might be (for the most part it is fair to say that we – and everyone else – had no idea whatsoever until we got better images from Cassini a few years later). And then, in late 2001, we found a cloud sitting at the south pole of Titan.

A cloud!

It doesn’t sound like such a big deal, except that it had long been predicted that Titan was incapable of having clouds. Occasionally there was speculation that clouds of methane might be present, but that, if so, they would be tightly confined to the equator. And yet there it indisputably was: a cloud at the south pole.

Antonin and I were so astounded by this that we put Sarah Horst, then an undergraduate at Caltech, at work looking through a tiny 14-inch telescope on the roof of the astronomy building at Caltech. We had developed some special telescope filters which would – we hoped – be capable of penetrating the haze deck and seeing if Titan got a little brighter due to a cloud or two. We wouldn’t be able to tell anything else, but that would be enough to go back to the giant Keck telescope and say “Look now! There will be a cloud!”

It worked. Just a month after our first cloud detection Sarah saw something that looked just like what we expected a cloud to look like. We called people at the Keck telescope and begged them to snap a picture, and there it was. A much bigger splotch, still near the south pole.

I’m an astronomer, not a meteorologist. I had to spend six months learning about how clouds worked, trying to understand precisely why people thought they wouldn’t occur on Titan, and figuring out what was wrong. On a long summertime flight across the country where we continuously skirted afternoon thunderstorms, it all came together: no one had ever previously bothered to consider the effect of Titan’s surface heating. Like Arizona on a summer afternoon, Titan’s surface can heat up and eventually drive convective clouds over it. On Titan, though, it doesn’t happen in the afternoon. It happens in the summertime, when the south pole spends something like 10 years in continuous sunlight.

It was a compelling story, and, I think true. But, even better, it made some fairly clear predictions. The clouds were at the south pole when we discovered them only because it was very close to southern summer solstice. Titan (and Saturn) takes 30 years to go around the sun, so its seasons are quite long. But if you had the patience to watch, you should see the clouds move from the south pole to the north pole over the next 15 years before coming back 15 years later.

Antonin eventually got his Ph.D. and moved on to take a job working with the technical team continuing the development of Adaptive Optics at the Keck Observatory. It was the perfect place to be. Whenever there was a spare moment or two at the telescope, he would swing it over towards Titan and snap a picture. The clouds were nonstop. Sometimes there were just a few tiny specks, but occasionally there would be a huge outburst. It was a thrilling show to watch.

Emily Schaller entered graduate school at Caltech at just about that time, and she decided to do her thesis on watching and understanding these developing clouds on Titan. The first year was exciting, indeed. She saw a monster cloud system cover the south pole of Titan and remain for more than a month (disappearing just as one of the first close Cassini flybys went in to take pictures; Cassini saw a few wispy little clouds but missed almost all of the action). Henry Roe, a recently graduated Ph.D. from the University of California at Berkeley who had been using the Adaptive Optics on the Gemini telescope to study Titan, moved down to Caltech to work with us, and the odd discoveries about the clouds poured in. They appeared to finally move north from the pole; they appeared tied to one spot at 40 degrees south latitude for a while; they untied themselves; bright clouds in one spot seemed to foretell bright clouds in another. It was clear that we were amateurs here. We enlisted the help of Tapio Schneider, a professor of environmental engineering at Caltech and one of the world’s experts on atmospheric circulations, to help us make sense of what was going on. Things were finally falling into place.

In one final piece of exceedingly clever astronomy, Emily Schaller replaced our clunky nightly observations with a 14-inch Celestron, originally begun by Sarah Horst, with a sleek set of nightly observations from NASA’s Infrared Telescope Facility on top of Mauna Kea. The IRTF would take a quick spectrum of Titan every night possible, and Emily could quickly look at the rainbow of infrared light to tell precisely how many clouds were there. And when they looked good, she could tell Henry Roe, who would get the Gemini telescope to examine them.

And then the clouds stopped.

For years and years Emily would look at her data in the morning and walk across the hall to my office to mournfully say “no clouds again last night.” Seeing no clouds is scientifically interesting, and she dutifully wrote papers and indeed an entire chapter of her Ph.D. thesis demonstrating and trying to explain this years-long lack of clouds. But, really, I understood. Explaining a lack of something is not nearly as satisfying as actually getting to see something happen. As her advisor, I would have been happy to fly to Titan to perform a little cloud-seeding, but no one had yet figured out exactly what chemicals or incantations might do the trick.

On April 14th last year, Emily walked across the Caltech campus to finally turn in her thesis. Then she did what she did most mornings: she walked to her office, downloaded the data from the night before, and checked to see if Titan had clouds. That morning, I suspect, she came close to falling out of her chair. She was likely exhausted from those final stretches of thesis writing, and I am sure that the first time she plotted her data she did what I always do when I see something astounding: she assumed she had made a mistake. She probably re-downloaded the data, double-checked the coordinates, and shook herself a little more awake. But it was no mistake. Titan suddenly had the largest cloud system seen in years. She likes to say it was Titan throwing a graduation party for her. But I know better: I think Titan likes to hide its secrets as long as possible, and knew it was finally safe to let go.

The scientific paper that Emily wrote along with Henry, Tapio, and I that appears in Nature describes the big cloud outburst and its scientific implications. And the implications are pretty fascinating. This big cloud outburst – the biggest ever seen – began in the tropics of Titan, where it has been speculated that clouds, if they ever form, should be weak wispy things. The tropics are where, of course, the Huygens spacecraft that landed on Titan took dramatic images of things that look like stream beds and shorelines and carved channels. How could those be at the equator if there are never clouds and never rain? People asked.

This discovery doesn’t actually answer that question, because we don’t know why there was a huge outburst of clouds in the tropics of Titan. But it does perhaps answer that lingering question: How could those be at the equator if there is never rain? Because there is rain.

Now, however, I am going to allow myself to speculate a bit more than we were comfortable speculating in the scientific paper. I am going to ask: Why? Why were there clouds in the tropics? Why did they appear suddenly at one spot? What is going on?

What I think is going on (again, I warn you, rampant speculation follows…) is that Titan occasionally burps methane, and I think Emily found one of the burps. For many years scientists have wondered where all of the methane in Titan’s atmosphere comes from, and, I think, here is the answer. The surface occasionally releases methane. Call it what you want. Methane geysers? Cryovolcanoe? Titanian cows? Whatever happens, the methane gets injected into the atmosphere and, at that location, instantly forms a huge methane cloud. Massive rainout ensues downwind. The stream channels, the shorelines, and everything else in the otherwise desert-seeming regions are carved in massive storms.

Evidence? Evidence? Where’s the evidence? You scream. Fair enough. I am giving you a snapshot of how science is done, and, at this point, this is the hypothesis stage. Or hunch. Or speculation. This hunch is the type that then guides what we go off to try to observe next. What will we see? Will the spot Emily found burp again? That would be pretty striking confirmation. Will other spots blow? (I should mention that we do indeed think we saw a different spot burp a few years ago).

At this point we have observed Titan well for about 7 years, from the winter southern solstice until the northern spring equinox, which actually just occurred last week, the terrestrial equivalent of late December to late March. What will the rest of the year reveal? We’re still watching, waiting. Maybe in 23 years, when we’ve finally seen an entire season, we’ll call it a day.
Mike Brown's Planets - The long road to a Titan storm


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Ground-based telescope captures first visual images of storm clouds over the tropics of Saturn's largest moon

Quote
Taking advantage of advanced techniques to correct distortions caused by Earth's atmosphere, astronomers used the NSF-supported Gemini Observatory to capture the first images of clouds over the tropics of Titan, Saturn's largest moon.

The images clarify a long-standing mystery linking Titan's weather and surface features, helping astronomers better understand the moon of Saturn, viewed by some scientists as an analog to Earth when our planet was young.

The effort also served as the latest demonstration of adaptive optics, which use deformable mirrors to enable NSF's suite of ground-based telescopes to capture images that in some cases exceed the resolution of images captured by space-based counterparts.

Emily Schaller from the University of Hawai'i, Henry Roe from Lowell Observatory, and Tapio Schneider and Mike Brown, both of Caltech, reported their findings in the Aug. 13, 2009, issue of Nature.

"Adaptive optics are helping our ground-based telescopes accomplish feats that have until now been capable only with telescopes in space," said Brian Patten, a program director in NSF's Astronomy Division. "Now, we can remove the affects of the atmosphere, capturing images that in some cases exceed the resolution of those captured by space-based telescopes. Investments in adaptive optics technology are really starting to pay off."

On Titan, clouds of light hydrocarbons, not water, occasionally emerge in the frigid, dense atmosphere, mainly clustering near the poles, where they feed scattered methane lakes below.

Closer to the moon's equator, clouds are rare, and the surface is more similar to an arid, wind-swept terrain on Earth. Observations by space probes suggest evidence for liquid-carved terrain in the tropics, but the cause has been a mystery.

Regular monitoring of Titan's infrared spectrum suggests clouds increased dramatically in 1995 and 2004, inspiring astronomers to watch closely for the next brightening, an indicator of storms that could be imaged from Earth.

Schaller and her colleagues used NASA's Infrared Telescope Facility (IRTF), situated on Hawaii's Mauna Kea, to monitor Titan on 138 nights over a period of two years, and on April 13, 2008, the team saw a tell-tale brightening.

The researchers then turned to the NSF-supported Gemini North telescope, an 8-meter telescope also located on Mauna Kea, to capture the extremely high-resolution infrared snapshots of Titan's cloud cover, including the first storms ever observed in the moon's tropics.

The team suggests that the storms may yield precipitation capable of feeding the apparently liquid-carved channels on the planet's surface, and also influenced weather patterns throughout the moon's atmosphere for several weeks.
NSF - Storm Clouds Over Titan

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Huge Storm Detected on Titan - University of Hawaii, Institute for Astronomy


Quote
A paper that describes the first storm observed in the tropical latitudes of Saturn's moon Titan will be published in the journal Nature on August 13. The rain from large clouds such as these is actually liquid methane and may be responsible for forming the channels and other features near the equator observed by the Huygens probe in 2005. The lead author, Dr. Emily Schaller, wrote the paper while working as a Hubble Fellow at the University of Hawaii, Institute for Astronomy.

The huge storm, observed with the NASA Infrared Telescope Facility and the Gemini North telescope on Mauna Kea, Hawaii, covered over almost 1.2 million square miles (three million square kilometers, about the size of India). While the diameter of Earth is 7,926 miles (12,756 km), Titan’s is 3,193 miles (5,150 km), just slightly larger than Mercury, the smallest planet in our solar system.

Titan is the only moon in the solar system with a thick atmosphere, and like Earth, it has a weather cycle, including clouds and rain. However, on Titan, the substance that forms clouds and rains down on the surface is not water but methane (natural gas). It is so cold on Titan (-288°F,
-178°C) that methane is a liquid, and there are “boulders” made of frozen water rather than rock.

Clouds on Titan are generally much smaller and occur much more infrequently than on Earth, which led scientists to wonder how the rivers and channels seen by the Cassini spacecraft and the Huygens probe were formed. “After three years of observing Titan and finding little to no cloud activity, Titan suddenly put on quite a show,” quipped Schaller.

Unlike the large channels on Mars, which were probably carved millions or billions of years ago by liquid water, Titan’s carved surface features, like those on Earth, are still being formed today. Observations over the next several years by telescopes on Earth and by instruments aboard Cassini will continue to reveal more clues about the meteorology and geology of this world, which has many similarities to our own.

The Cassini-Huygens mission was launched in 1997 and arrived at Saturn in July 2004. Cassini completed its initial four-year mission to explore the Saturn system in June 2008. It is now working on an extended mission, seeking answers to new questions raised during its first years at Saturn. The Huygens probe separated from the Cassini orbiter on December 25, 2004, and landed on Titan, Saturn’s largest moon, on January 14, 2005. It continued to transmit information for over an hour despite a hard landing and Titan’s high atmospheric pressure.

The other authors of the paper, “Storms in the tropics of Titan,” are H. G. Roe (Lowell Observatory), and T. Schneider and M. E. Brown (both California Institute of Technology).
Huge Storm Detected on Titan
« Last Edit: August 16, 2009, 22:16:43 by electrobleme »

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The Huygens probe discovered fluid-formed channels in the arid equatorial regions of Titan, Saturn's largest moon




Quote
On Titan, Saturn's largest moon, methane clouds drift through a dense, nitrogen-rich atmosphere, clustering mainly in the polar regions. Methane lakes dot Titan's surface, also at high latitudes. Closer to the moon's equator, by contrast, clouds appear rarely if at all, and the surface seems arid. But in January 2005, the Huygens probe, after detaching from the Cassini spacecraft and descending through Titan's atmosphere, gave planetary scientists their first close-up view of the moon's surface. Huygens imaged small channels and river beds at low latitudes, in regions that scientists had assumed to be devoid of flowing liquids that could carve such features. Now, astronomers working at Earth-based telescopes have for the first time observed, near Titan's equator, large and persistent clouds that might be capable of raining liquid methane onto the surface.

Titan's equatorial plane is tilted at about 27 degrees from the plane of the solar system. That creates seasons, as the apparent position of the sun in Titan's sky ranges from 27 degrees north of its equator to 27 degrees south during the course of Saturn's 30-year orbit. Using adaptations of the computer models used to study Earth's climate, planetary scientists have found that clouds are most likely to form predominantly at Titan's poles during polar summers, when the sun is high in the sky in those regions. Only at those times, the models suggest, is the sun's heat enough to drive atmospheric convections that will send methane-laden "air" upward, where the methane will cool and condense to produce clouds.

That predicted pattern is broadly consistent with observations to date, which indicate that clouds on Titan are generally sparse, typically covering less than 1 percent of the moon's visible surface area, and concentrated toward the poles. But in September 1995, and October 2004, cloud coverage rose as high as 7 percent for periods of up to a month, episodes that may have produced significant amounts of methane rain. To better understand these sporadic events, Emily Schaller of the University of Hawaii and her colleagues at the Lowell Observatory in Flagstaff, Ariz., and the California Institute of Technology began a project to regularly monitor cloud coverage on Titan.

At visible wavelengths, Titan's hazy atmosphere--whose surface pressure is about one and half times that of Earth's--gives it a fuzzy, opaque appearance. At certain infrared wavelengths, however, the atmosphere is transparent while methane clouds are highly reflective. Schaller and her colleagues used NASA's Infrared Telescope Facility (IRTF), situated on Hawaii's Mauna Kea, to check Titan's infrared brightness as many nights as they could. IRTF measures the brightness of Titan as a whole, so when it revealed an increase in infrared reflectivity, the team turned to another telescope, Gemini North, to see where on Titan that infrared light was coming from. Gemini North, also on Mauna Kea, is one of a pair of 8-meter infrared telescopes funded in part by the National Science Foundation; its twin is Gemini South in the Chilean Andes. The Gemini telescopes achieve high resolution through the use of adaptive optics, meaning that the shape of their mirrors can be rapidly tweaked to overcome the blurring of images that results from light passing through the Earth's turbulent atmosphere.

In just over two years, the Titan monitoring program acquired 138 nights of observations, and on April 13, 2008, Schaller says, the effort finally paid off. After IRTF reported brightening of the moon, observations by Gemini North revealed cloud cover extending across the moon's middle latitudes, from 14 degrees south to 44 degrees south. Over the next few days, this large cloud spread southward, until on April 17, Titan's rotation took it out of view from Earth. The following day clouds appeared at even lower latitudes, from 20 degrees south to 12 degrees south--closer to the equator than clouds had ever been seen before. Clouds also appeared in the polar regions. A similar pattern recurred about a week later, as the large mid-latitude cloud rotated back into view again.

Schaller and her colleagues offer a theoretical argument indicating that the initial mid-latitude cloud formation could have triggered the formation of clouds in both the polar and equatorial regions via large-scale atmospheric waves. Such waves occur in Earth's atmosphere and are known to propagate weather systems around the globe.

The equatorial clouds seem substantial enough, the astronomers say in the August 13 issue of Nature, to produce methane rains that could, from time to time, create and shape the channels and apparent riverbeds imaged by Huygens. What remains puzzling, though, is why the mid-latitude cloud formed in the first place. Some surface features on Titan hint at the occurrence of "cryovolcanism," in which water-ice melts and flows, perhaps also releasing methane that was trapped in the frozen surface. Rising heat and freed methane could both lead to the formation of clouds. But observations from Cassini show that the surface of Titan above which the mid-latitude cloud formed "seems completely unremarkable," Schaller says. It's possible, she adds, that a convergence of purely atmospheric phenomena could have brought the initial cloud into being.

Regardless of their origin, the possibility that clouds can form sporadically at almost all latitudes of Titan suggests that closer examination of its surface will reveal an abundance of features created by flows of liquid methane, Schaller says.
NSF - Methane Clouds Observed Near Titan's Equator May Explain Presence of Riverbeds on the Surface

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Storms in the tropics of Titan
« Reply #7 on: August 17, 2009, 03:21:13 »
Storms in the tropics of Titan
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E. L. Schaller1, H. G. Roe2, T. Schneider3,4  &  M. E. Brown3

   1. Institute for Astronomy, University of Hawaii, Honolulu, Hawaii 96822, USA
   2. Lowell Observatory, Flagstaff, Arizona 86001, USA
   3. Geological and Planetary Sciences,
   4. Environmental Science and Engineering, California Institute of Technology, Pasadena, California 91125, USA

Methane clouds, lakes and most fluvial features on Saturn's moon Titan have been observed in the moist high latitudes, while the tropics have been nearly devoid of convective clouds and have shown an abundance of wind-carved surface features like dunes. The presence of small-scale channels and dry riverbeds near the equator observed by the Huygens probe9 at latitudes thought incapable of supporting convection (and thus strong rain) has been suggested to be due to geological seepage or other mechanisms not related to precipitation. Here we report the presence of bright, transient, tropospheric clouds in tropical latitudes. We find that the initial pulse of cloud activity generated planetary waves that instigated cloud activity at other latitudes across Titan that had been cloud-free for at least several years. These observations show that convective pulses at one latitude can trigger short-term convection at other latitudes, even those not generally considered capable of supporting convection, and may also explain the presence of methane-carved rivers and channels near the Huygens landing site.
Nature - Storms in the tropics of Titan


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A Tropical Tempest on Titan
« Reply #8 on: August 17, 2009, 03:29:33 »
A Tropical Tempest on Titan
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A Tropical Tempest on Titan
There's an old saying that describes the weather in Maine as "9 months of wintah, and 3 months of damn poor sleddin'." But even the hardiest Mainer would be challenged by the climate on Saturn's big moon Titan, where "wintah" lasts 7½ years, temperatures struggle to reach -290°F (-178°C), the ground is rock-hard water ice, and a mix of liquid methane and ethane rains from the sky.

Understandably, planetary scientists are eager to learn more about Titan's remarkable atmosphere. Although an opaque hydrocarbon smog lingers constantly in the dense air, which consists almost entirely of nitrogen with a dash of methane, ground-based observers have become adept at exploiting specific infrared wavelengths to peer deep into the troposphere (its weather layer) and even down to the surface.

An observing team led by Emily Schaller (University of Hawaii) and Henry Roe (Lowell Observatory) has been keeping very close tabs on Titan's weather. In fact, Schaller's Caltech doctoral thesis hinged on analyzing the moon's long-term climatic characteristics. Using a sensitive spectrometer with NASA's 3-meter Infrared Telescope Facility on Mauna Kea, the team set up a long-running "storm watch" — 138 nights over 2.2 years — for signs of sporadic methane-cloud buildups, as had occurred in 1995 and 2004. Whenever it looked like a storm might be brewing, the observers switched to an infrared imager on the much larger Gemini North telescope, also on Mauna Kea.

Unfortunately, Titan just wouldn't cooperate, because during all that time clouds typically covered only 0.3% of the disk. (By comparison, Earth averages 65% cloud cover.) But on April 14, 2008, literally minutes after turning in her thesis, Schaller discovered that a monstrous storm had mushroomed in the moon's troposphere the night before. "I like to think it was Titan's graduation gift to me," quips Schaller, "or perhaps a bad joke."

Storm clouds on Titan
During April and May 2008, a major storm appeared in Titan's atmosphere. A green box highlights a region centered on 15°S, 250°W, where surface activity might have triggered the rare outbreak. Observers used the Gemini North telescope to acquire these images at 2.1 microns. Labels give the date and the longitude at the center of Titan's disk. Click on the image to see the full series.
Gemini Obs. / AURA / H. Roe / E. Schaller
Cruel twists of fate aside, for the next few weeks Titan's atmosphere put on quite a show. The hurricane-size storm had erupted at mid-southern latitudes, but soon more cloud clusters popped up nearer the equator (where they'd never occurred before) and close to the south pole. Clearly, something was amiss with theorists' climate models. Clearly, Roe admits, "We don't yet understand the atmosphere of Titan."

As the team describes in the August 13th issue of Nature, the tropical and polar outbreaks probably resulted from powerful pulses of wave energy, called Rossby waves, that slowly spread outward from the original storm cell like ripples expanding from where a tossed rock enters a pond. These waves, well known in Earth's atmosphere, can alter the temperature and induce convective activity as they pass through humid air masses.

More intriguing is speculation about what triggered such a rare outbreak in the first place. The source region seems to be centered at 15° south, 250° west, where images from the Cassini orbiter show that the Titanian terrain is rather bland. But it wouldn't take much, Roe explains, to create the large-scale convection for storm clouds to form. Perhaps a cryogenic slurry of ammonia-charged water erupted onto the surface, causing the overlying atmosphere to become warmer, more humid, and ripe for cloud formation. Even a slight heating of the surface from below could have spawned the storm.

You can bet that Cassini scientists will be paying special attention to this region the next time their spacecraft passes within view of it. Maybe they'll find the landscape awash with fresh ice flows. Or perhaps they'll just find it awash, recently drenched by a methane-ethane deluge from the storm clouds that passed overhead.
Sky and Telescope - A Tropical Tempest on Titan