cassini

The Biggest Storm Ever on a Small, Small World

esiegel — Fri, 13 Jul 2012 15:28:48 +0000

The Biggest Storm Ever on a Small, Small World

"For most of the history of our species we were helpless to understand how nature works. We took every storm, drought, illness and comet personally. We created myths and spirits in an attempt to explain the patterns of nature." -Ann Druyan

Here on Earth, we are well aware of how devastating storms can be. From hurricanes to flash floods, an unpredictable change in weather can turn a serene setting into a catastrophe in no time at all. The clouds that fill the skies can often portend what type of weather is coming, and to me, the most impressive and fearsome of all is the rare and remarkable supercell.

Image credit: Sean Heavey / Barcroft Media, from Glasgow, Montana.

The least common and most severe type of thunderstorm, supercells form when a warm, moist layer of air (typically found above a cold layer, since heat rises) slides below an even higher-elevation cold layer. The wind shear from this motion causes vorticity, or a spinning motion, of the air in the warm layer. As the warm air tries to rise through the cold layer, the rotating vortex becomes vertical, and creates a mesocyclone, which can lead to tornadoes in the most catastrophic of cases.

Image credits: Vanessa Ezekowitz, retrieved from the wikipedia page for supercell.

Even in cases where tornadoes do not form, the supercell storm provides a spectacular deluge and incredible wind speeds.

Image credit: Martin Kucera of http://www.floridalightning.com/.

Under the most extreme circumstances, many tornadoes erupt and the storm -- although usually brief -- can literally destroy an entire town, as was the case a year ago in Joplin, MO. As seen from space, only the flat top of the supercell was visible, blinding us to the destruction that was occurring underneath.

Image credit: NASA / GOES-13 satellite, of the 2011 Joplin, MO supercell.

It will come as no surprise that raging storms like this are not unique to Earth. In fact, they are common and can last for extremely long durations on gas giants like Jupiter and Saturn.

Image credit: NASA/JPL/Space Science Institute, by Cassini/CICLOPS.

But what may be surprising is that on a relatively small world in our Solar System -- on Saturn's largest moon, Titan -- what appears to be a long-lived supercell storm may, in fact, be raging over its polar region. In the image above, you can see what looks like a cloudy hood over Titan's north pole; this was taken in 2004, when Titan's northern hemisphere was experiencing winter. The atmosphere of Titan extends so high, however -- it's 10 times as thick as Earth's atmosphere -- that sunlight was able to hit the upper atmosphere above the pole, creating that cold-warm-cold layer necessary to produce a giant supercell!

Well, Saturn experienced its equinox back in 2009, and so now we have the onset of winter in the southern hemisphere. And guess what Cassini saw as it flew over Titan's south pole?

Image credit: NASA/JPL-Caltech/Space Science Institute, from Cassini/CICLOPS.

Does this swirling, gaseous formation look like anything you've seen before? Titan's south pole is in the process of forming a vortex that will very likely give rise to a southern polar hood as winter arrives! As the amazing Carolyn Porco states:

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

Don't believe it? View Cassini's video of the storm yourself!

I can't help but marvel at this storm, rotating at 40 times the speed of Titan itself, and wonder at the titanic catastophes occurring on the world below. With more than 100 miles of atmosphere to see through, we are ill-equipped to find out how this cyclonic polar storm is affecting the terrain below, but I wouldn't be at all surprised if we found out (with the next Saturn mission, nudge-nudge) that there wasn't a torrential methane rain with cyclonic winds reaching down miles upon miles.

Can a storm on a world like this reach the surface? I don't know, but I sure hope we get to find out!

esiegel Fri, 07/13/2012 - 11:28

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Astronomy

Solar System

atmosphere

carolyn porco

Are those transient white flecks in the last image lighting? (Or just noise?)

Because it looks so much like a cell I was wondering if this couldn't be a gas outburst, or a volcano cloud. You can see something similar halfway this page in the case of the Mount Pinatubo super eruption:
http://www.geolsoc.org.uk/gsl/education/page3042.html

You'd need to find evidence that supports that, chelle, since a storm cell already describes the measured phenomena.

Otherwise, not much point entertaining the notion. It -could- be something else, but no reason to consider it.

Rather like Ethan's take on string theory at the moment.

Isn't it great how we learn about climate by studying *other* planets and moons as well?

@ Dale:

Noise by cosmic radiation et cetera is a common phenomena in images from spacecrafts, affects solid state pixels, memories; plus you have sundry transmission dropouts. If it is black, it is often a damaged pixel in solid state camera I think. If it is white, I would guess CR hit the pixel.

I'm sure they are on the lookout for sprites et cetera discharges.

@Dale

Those specks are almost certainly cosmic rays hitting the sensor. Some of them are even in neat little lines that show the path of the ray as it passes through the sensor array.

"You’d need to find evidence that supports that, chelle, since a storm cell already describes the measured phenomena."

Most likely yes. I had a vortex ring in mind that is often created by volcano's and this 'storm' with its clear edges made me think of that. Storms on our planet seem to have a more dense core, a bit the opposite of this one that seems to be fluffy on the inside.

Although I checked and there are cryovolcano's on Titan:
A cryovolcano (colloquially known as an ice volcano) is a volcano that erupts volatiles such as water, ammonia or methane, instead of molten rock. http://en.wikipedia.org/wiki/Cryovolcano

... on Titan:
http://en.wikipedia.org/wiki/Titan_(moon)#Cryovolcanism_and_mountains

Anyway that moon seems to be one of the most exciting places in our solar system to go and have a look at, Richard Brandon if you're hearing me ...

Cheers!

Vortex rings don't last long, though..

The Sirens of Titan

esiegel — Thu, 14 Jun 2012 20:00:33 +0000

The Sirens of Titan

"Everyone is a moon, and has a dark side which he never shows to anybody." -Mark Twain

Back before the telescope was invented, Saturn was known as the Old Man of the Skies. The slowest-moving of the naked-eye planets, it's the only one that would reliably be in nearly the same location, year after year. You can find it all summer, after sunset, by following the "arc" of the handle of the big dipper all the way until you run into the brightest northern-hemisphere star, Arcturus, and then speeding on to the very bright Spica. Saturn is right next door.

Image credit: EarthSky.org.

But everything got an awful lot more interesting once the telescope was developed. What was a bright, slowly moving point of light for all of humanity suddenly transformed into the ringed wonder we know today.

Image credit: BKellySky of http://bkellysky.wordpress.com/.

Saturn, as you know, has the most complex and spectacular ring system of any planet discovered so far. While you can see the ringed structure even through a good pair of binoculars, the best views come from NASA's Cassini mission, presently orbiting the ringed giant and photographing as much of it as possible.

The best picture I've ever seen of its rings? That would be this one, taken from when the Sun was directly behind the planet.

Image credit: NASA/JPL-Caltech/Space Science Institute.

But Saturn isn't all by its lonesome out there. Just as we, on Earth, have our Moon to keep us company, Saturn has a family of its own. A very, very large family, with one member that's unique in all the Solar System.

Image Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA).

Although there are more than 60 moons orbiting Saturn, the largest one, Titan -- visible here with its shadow falling on the gas giant -- is remarkable for a number of reasons.

Sure, it's big: larger than our Moon, larger than Mercury, and, at 5150 kilometers across, it's the second largest moon in the Solar System.

We've known about it for a really long time. Discovered in 1655 by Christiaan Huygens, Titan was the first moon discovered to orbit a world other than Earth or Jupiter.

Image retrieved from http://www.wingmakers.co.nz/universe/solar_system/Titan.html.

But unlike every other Moon ever discovered, and unlike even planets like Mercury and Mars, Titan is the only Moon known with an atmosphere so significant it's even thicker than the one here on Earth!

While this was long suspected, it was Voyager 1, the first spacecraft to visit Titan, that really showed us just how severe this atmosphere was.

Image credit: NASA / Voyager 1 space probe.

A thick nitrogen atmosphere, hundreds of kilometers thick, with a dense photochemical haze in the upper layers, obscures the surface from every single one of Voyager's visible-light pictures. With a surface pressure that's 60% greater than Earth's despite being just a fraction of our size and having just one-seventh of our gravity, Titan's atmosphere is actually more massive than our own.

But nitrogen is transparent to visible light; there's something more interesting than just a thick nitrogen atmosphere at work here.

Image credit: NASA/JPL-Caltech/Space Science Institute.

Thanks to the Cassini spacecraft, we were able to find methane molecules being broken apart by ultraviolet light from the Sun, producing other, more complex compounds, including ethane, acetyl alcohol, and even amino acids!

But that isn't all that Cassini came outfitted with. In addition to visible light equipment, it's also capable of seeing into the ultraviolet, which doesn't help much, but the infrared as well! Shown in red and green, below, the infrared filters allow us to see down, through the thick clouds and haze, all the way down to the surface of the most planet-like of all the moons.

Image credit: NASA/JPL-Caltech/Space Science Institute.

Initially, we couldn't tell what those dark features on Titan's surface were. Was it a vast ocean of methane, like our oceans on Earth? The chemistry, based on the temperatures and pressures present, would be close. Or is it just a case of differently-colored rock, like the maria of our Moon?

The great dark area, known as Shangri-la, was going to be the target of the first great experiment down to the surface. Because the Huygens probe, named after Titan's discoverer, was launched from Cassini, and became the first spacecraft -- in 2005 -- to land on a rocky body in the outer Solar System.

Image credits: ESA/NASA/JPL/University of Arizona.

Descending through Titan's atmosphere and landing on the plains of Shangri-la, Huygens found mountains, valleys, strong evidence of past (but not present) liquid, and a dry, dark surface. Shangri-la was no lake.

But that doesn't mean the surface of Titan looked very much like the surface of our Moon. To me, it looked much more like a rocky cove once the tide's gone out.

Image credits: ESA / NASA / JPL / University of Arizona; NASA / Apollo.

But despite not finding any liquid at its landing site, Huygens and Cassini have learned an awful lot about the surface of Titan, and there is liquid there! There's evidence that Huygens has heard a methane waterfall, methane rain, clouds and evaporation are Titan's version of a water cycle, and thanks to the power of radar imaging, Cassini has confirmed that there are liquid methane lakes near the poles!

Image credit: NASA / JPL / USGS.

Based on what we know about Titan now, after nearly a decade of Cassini imaging, the cold regions near Titan's poles have abundant liquid methane, but the warmer regions, near the equator, ought to be dry. Liquid methane in those regions wouldn't last long and ought to boil off, so knowing what we know now, a methane lake near a tropical region of Titan would be a surprise.

Image credit: NASA/JPL-Caltech/Space Science Institute.

Well, guess what? Surprise! A region about the size of the great Salt Lake, near Titan's equator, came back as a completely black area on Cassini's radar, the telltale signal of liquid methane!

Artist credit: Ron Miller.

Because of how rapidly methane evaporates, this 927-square-mile lake near the equator (and not far from the Huygens landing site) must be fed by an underground aquifer of methane, according to Cassini scientist Caitlin Griffith. According to the NASA press release:

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

So, in a world flush with amino acids, there are underground stores of liquid that flow and pool near the equator, in an environment that's not much different -- save for being significantly cooler -- than a very young Earth was. Are you thinking what I'm thinking?

Image credit: Brian Smallwood, http://www.spaceprime.com/.

Maybe, just maybe, Titan is another world in the Solar System where life, no matter how primitive, has found a way. Regardless of whether that's the case or not, we've still made an amazing breakthrough learning about the planetary science of this unique world:

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

The quest for extraterrestrial life in the Universe may take us to places vastly different from anything we've ever experienced; I can't wait to see how the details fill out, either!

esiegel Thu, 06/14/2012 - 16:00

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All this time we were looking for cryovolcanos when we should have looked for cryoaquafers!

A well rounded article as always. I didn't know about the Huygens putatively hearing waterfalls, but I do believe I've read the claim that it detected an increase in methan vapor when landing, meaning the surface was soaked, not entirely dry.

Currently Titan naively tests best for life outside of Earth, IIRC methane metabolism would use hydrogen to produce acetylene, and there is an unambigious near surface lack of the first and possibly a surplus of the other. The hydrogen lack can't be explained by atmospheric models, but could of course be explained by some nonorganic cold surface chemistry. But metabolism is good to amp up reaction rates with enzymes.

And of course a subcrustal supply of organics is good. Titan is differentiated and believed to have (unfortunately an ammonia soaked, IIRC) subsurface ocean like Europa. Water, organics, minerals and heat energy towards its core may come together, all the necessary ingredients for life.

Nit:

Saturn, as you know, has the most complex and spectacular ring system of any planet discovered so far.

True as far as planets go, we have 8 of them and don't expect more. (And the best, latest Nice models imply we ejected at least one outer Neptune.) All the other giants and neptunes observed rings are much punier: Jupiter, Neptune and I believe Uranus.

But FWIW there is at least one exoplanet (or brown dwarf) that has a much more spectacular planetary ring system:

""Eric Mamajek showed us the transit of an extrasolar ring system, the first ever observed. This research used archival photometry from two small programs dedicated to finding hot Jupiters: SuperWASP and ASAS-3. These teams made their data public and Mamajek and his team ran their stars through the data reduction pipeline, thinking they might be able to find rotation periods. But what they found was a complex, bizarre looking transit that blocked 95% of light at the transit minimum. This transit was seen in both data sets.

The team ruled out the most straightforward explanations, those of a transiting planet or circumstellar disk. The transit, lasting 52 days, is full of substructure: each day shows variations and there are times when the star returns to 100% brightness and is briefly unobscured. The simplest model, found by modeling the daily averages, is one with three sets of rings. The rings are thin and the gaps are clean. The rings have a radius of 0.1-0.4 AU – they’re huge – and under the assumption that they have a similar composition to Saturn’s rings, their mass is roughly 0.4 to 8 times the mass of the Moon.

Though Mamajek calls this transiting system “Saturn on steroids,” the astronomers aren’t sure what’s inside the rings."

Incidentally, another contextual and endearing quote from that page:

""“Planets are like cockroaches” – when we’ve seen one planetary system like this, we know there are more out there."

Oops. Aquifer, methane - my new browser default spell checker isn't really helpful.

That Titan waterfall paper was written in 2004. I recall Huygens landing on Titan in 2005. Now I haven't read the paper to see if Huygens heard a waterfall but I'll take your word for it.. :P

Let the bio-astronomers go fishing in The Great Methane Lake of Titan!!

Give them whatever they need: spacecraft, instruments, labs,.. grants.

I don't expect catfish jumping; I expect something alive!

Nice discovery for an underfunded space exploration program.

I personally am going to need a round trip SpaceX ticket for three from Earth to The Great Methane Lake, a hotel on the methane, a sailboat, dry suits, camera equipment, and a personal chef.

Ethan, I think you've overstated the "waterfalls" case. As Thomas noted, the paper you mentioned predated the Huygens landing by more than a year, and was a speculation based on the author's studies of space acoustics.

n a 2009 review (http://eprints.soton.ac.uk/71546/) Leighton states clearly that Huygens did not make any recordings of ambient sound.

Thomas and Michael,

Thank you for the correction on the Waterfalls sound. I had remembered hearing the audio file from back around the time of the Huygens landing and didn't go back and look up whether that was a simulation or an actual recording.

Looks like I'll have to refrain from mentioning that anymore; thanks for keeping me honest and setting me straight!

Ethan, you may have overstated the amino acids case as well. Is there any hard evidence for their presence, or are the paper's authors merely speculating? Since the setting is so reducing chemically, their formation and stability could be questioned.

It's ok Ethan. "Water"falls certainly exist on Titan whether we hear them or not. And the simulated sounds still sound sexy when we are tryin to impress the ladies.

And if life is a natural consequence of the universe, there is a solid chance that Titan has it. Beneath the surface are a huge number of potentially zones of habitation for convention forms of life, while the surface itself presents an awesome opportunity for completely alien forms of life.

It looks so much like a living breathing world that it's almost shocking not to see the remains of Titan pond scum lying around everywhere. We need to send probes to the poles to see what's what. Regardless Titan has my vote for second neatest rock in the Solar System (after Earth).

I have a board on Pinterest where I curate images and articles about space. It's a shame this site blocks Pinterest, even though it allows posting to Google Plus (which posts the image from the post), Twitter, etc. Please consider removing that block.

Aquifer? Maybe "methanifer."

Great article about a fascinating world. Torbjörn Larsson, your comments are very informative until you get to the statement "True as far as planets go, we have 8 of them and don’t expect more." Why is this statement of what is clearly an opinion, not a fact, relevant or necessary here? We have a lot more than 8 planets in our solar system, and the first small planet beyond Neptune may very well have a ring system of its own. New Horizons is currently turning the Hubble Space Telescope toward the planet Pluto to check for rings because of the potential hazard of the spacecraft hitting particles of a ring system we didn't know existed.

One thing I've never heard addressed is the temperature difference. Wouldn't chemistry run a lot slower at that temperature? If so, how would that effect life? Could it be that life formed on Titan a long time ago, but due to the slow metabolic rate, it hasn't had more than a few hundred generations' of evolution?

Chemical reactions would run slower than they would at higher temperatures or indeed not at all if too cold.

However, the chemical reactions produce energy at a rate that is equal to the rate of reaction times the energy released per reaction.

Therefore it depends on what chemical reactions take place to power the processes of life as to whether life will run slower.

@ Laurel Kornfeld
“True as far as planets go, we have 8 of them and don’t expect more.” Why is this statement of what is clearly an opinion, not a fact, relevant or necessary here?

Because it establishes the context in which Ethan's comment was almost certainly correct. Setting aside the "planet" debate, it is still inordinately unlikely that we will find a large planet beyond Neptune capable of supporting a massive ring structure. If Pluto has rings, then they are going to be ephemeral things that would be relevant to a mission that might pass through them and just interesting in general, but pose no threat of deposing Saturn as the King of Rings (in our solar system).

No, Pluto will not depose Saturn as King of the Rings. However, that doesn't mean Pluto isn't a planet or that small planets aren't planets or that our solar system has only eight planets, which it does not. What you really mean is that we are unlikely to find any more gas giants beyond Neptune. Larsson would have done better to specify that.

Pluto being out-massed by non-gravitationally-bound objects in its orbit by a factor of over 10:1 while the 8 planets all out-mass the rest of their orbit by a factor of at least 1000:1 is why it's not a planet. I don't see how ignoring a 5 order of magnitude gap in gravitational dominance, and the current definition of planet, would be inherently better other than it would mesh with your own personal opinion that such a gap in dominance should be ignored and the definition is hooey.

I can't wait for the day when a new generation has been raised who is no more shocked that Pluto isn't a planet than they are that Ceres isn't.

Regarding Avi and Wow's comments regarding very-slow life processes (um, I'll abbreviate that to VerSLiP), there was a recent discovery of some bacteria buried in the ocean floor from 86 MYA that are profoundly frugal and long-lived.

We used to think that life had to ultimately have energy inputs from our star, but the deep vent tube worms proved that idea wrong. Our ideas about what conditions are necessary for life get broader as we shed our terracentric views. Besides, any life there would have evolved to work within the given parameters, n'est-ce pas?

http://www.npr.org/2012/05/17/152936168/ancient-deep-sea-bacteria-are-i…

From Dust to Planets

krandall — Tue, 28 Sep 2010 14:30:00 +0000

From Dust to Planets

By Dr. Paul Estrada
Planetary physicist at the Carl Sagan Center for the Study of Life in the Universe, SETI Institute, and Gail Jacobs

If planets are a dime a dozen, moons are less than a penny each. There are at least 139 moons just within our own solar system. Most of these are the property of the gas giant planets beyond Mars. More than just a nice accompaniment to planets, moons may have habitats in which liquid water could ebb and flow - and possibly be a suitable home for life. Planetary physicist Dr. Paul Estrada investigates how moons around gas giants are formed -- an important question as its answer would give us insight into the nature of moons around the myriad gas giants we know orbit other stars.

Very briefly, describe your research project.
I have multiple projects but they do have some similarities. Basically I explore how the giant planets and their intricate satellite systems were formed from the cloud of gas and minuscule particles of dust that made up the early solar nebula. How do small grains of dust which condense from the nebula gas manifest into planet-sized-objects that contain an inventory of so many different elements and materials? The question turns out to be as complicated as the process itself. There are many physical, chemical and geological processes to consider in the difficult journey from dust to planet.

Interestingly, because the discovery of many more planets around other stars is happening at a feverish pace, and many of these planetary systems are so much different in structure from our own, it becomes even more important for us to explore what complications are involved in the very early stages of planet formation. Answers to these questions can obviously reveal information about the birth of our own solar system, but even more so help in the explanation of the diversity of planetary systems we see now, or will discover in the future.

Eskimo Nebula In 2000, the Hubble Space Telescope imaged the Eskimo Nebula that displays gas clouds so complex they are not fully understood. The nebula is clearly a planetary nebula, and the gas seen above composed the outer layers of a sun-like star only 10,000 years ago. Image credit: NASA/Andrew Fruchter (STScI)

How did you come to join the SETI Institute?
I came to the SETI Institute in 2005, after working at the NRC (National Research Council) at NASA Ames for three years. I had friends and colleagues at the Institute and I had always heard good things. I felt the Institute would be the best place for me. My experience here gets better each year.

What first sparked your interest in science and astronomy in particular?
It will sound clichÃ©, but I was a Cosmos kid. The series came out when I was around 9 years old, and I loved that show! My parents and I would watch it together every week. I truly enjoyed watching it. I may have been interested in astronomy before that, but my interest really took off from there. Needless to say, I was thrilled when I had Carl Sagan as my initial advisor while I was a student at Cornell University.

The other person who contributed to solidifying my interest would be Jeff Cuzzi. I met Jeff at a party when I was around 13. I remember this guy talking about astronomy and rings and planets and he had a whole group of kids around him. I was fascinated by that conversation. Flash forward to right before I started my undergrad program and was working at NASA Ames through an internship program for the Kuiper Airborne Observatory. I attended a talk being held in the space sciences building there, and who was giving the talk but none other than Jeff Cuzzi. Being the opportunist, I went up to him afterwards and told him the story about how we had met many years before. Then I hit him up for a job. I honestly think he felt he could not refuse! Jeff became my mentor and my relationship with him as both friend and colleague continues to this day.

What inspired you to investigate the formation and evolution of planet satellite, or moon, systems?
My interest goes back to grad school at Cornell. The problem that initially inspired me involved the outermost Galilean satellite, Callisto. The Galileo spacecraft data indicated Callisto might be what's called undifferentiated or partially differentiated. That means that essentially all of the rock has not separated from the ice and sunk to the center to form a dense core; rather, the rock and ice are still to a great degree mixed together.

Europa, Ganymede, and Callisto: Surface comparison at high spatial resolution These images show a comparison of the surfaces of the three icy Galilean satellites, Europa, Ganymede, and Callisto, scaled to a common resolution of 150 meters per picture element (pixel). Despite the similar distance of 0.8 billion kilometers to the sun, their surfaces show dramatic differences. Image credit: NASA/JPL/DLR

Satellites like Callisto and Ganymede are made of roughly 50% water/ice and 50% rock by mass. If you have a uniform mixture of rock and ice that gets thrown together fast enough, it will trap a lot of heat within the interior and eventually get hot. If it gets hot enough, the ice melts, the rock within the ice sinks, and the separation process begins. By looking at the gravitational data, it was determined that Callisto was not differentiated or separated, which piqued great interest within the scientific community. On the other hand, the gravitational data on Ganymede, the satellite interior to Callisto, was consistent with complete separation. So why is it that one satellite, similar in size and composition, is completely different from the other?

I had been working on thermal models of Callisto with Steve Squyres, my advisor at Cornell after Carl Sagan's death. I got somewhat frustrated with my numerical project, which involved a lot of debugging and coding, and I became more interested in the bigger picture. I could work on models of Callisto's internal structure and try to figure out how these states of partial differentiation occur and are maintained or I could explore the conditions of satellite formation that leads to the different states of differentiation we see. At that point, working closely with another fellow Cornellian and current SETI scientist Ignacio Mosqueira, I started focusing more on the problem of developing a unified picture that would not only explain Callisto but also find answers for satellite formation that could be applied to the other giant planets of our solar system.

What tools and information do you use that allows you to conduct your research?
Those of us involved in this field of study are fortunate to be associated with missions that send spacecraft to the outer planets. Initially the Voyager and Pioneer missions flew by the outer planets. Now we have special missions, such as Galileo that orbited Jupiter and Cassini that is orbiting Saturn. These spacecraft were able to spend a great deal of time conducting multiple fly-bys of the satellites, studying the systems and the planets and their atmospheres. Scientists can extract so much information from that data! We can study the atmosphere of Jupiter and look at the concentration of atmospheric elements to learn more about the initial state of the solar system, and the conditions that may have been present during the formation of the Galilean moons from Jupiter's disk of gas and dust.

I'm interested in what this data tells us about the kind of materials embedded into the objects that went into making the solid parts of these planets and their satellites. We see a lot of diversity in the way the satellites look. For example, we know that water is not only just a very important constituent, its ubiquitous and easy to track down. Other constituents, such as ammonia -- not so easy to find even though most of us expect that it is there. Jupiter System Montage (left): Image credit: NASA/JPL

Much of what I do is theoretical so I develop theoretical models. I take the data we see and construct a picture based on that data. If it's possible to relate what we see at Jupiter to what we see at Saturn or Uranus, I want to understand both the similarities and the differences.

Do you study both satellite and planet formation?
In looking at the satellite systems of the giant planets, we look for trends; what are the sizes of the moons, how are they distributed, what are their bulk properties? Are there some rules of formation or overall process at work that applies to all of the systems, thereby leading us to believe it's not a completely random process? It's complicated because, for one, you have to know something about how the disc of gas forms around the giant planet and what that structure is. This disk of gas and dust, or subnebula as it is called, is where the moons will eventually form. In a sense, the giant planet's satellite system is like a mini-solar system initially involving the same process of growth from dust to larger bodies like its solar nebula counterpart.

We're fortunate that the Galileo and Cassini missions have provided us with so much data with which to work. We can use the trends that we see, as well as the properties of the moons and the composition of the giant planet's atmosphere to construct a somewhat complete picture of what that early subnebula was like. On the other end, theorists can simulate the formation of the giant planet and its subnebula and we can compare the outcomes to see if our picture is right.

There are obviously many factors involved in the process of growth in the solar nebula and giant planet subnebula. I'm particularly interested in studying the process that begins with dust that evolves into objects that are known as planetesimals, which are essentially the building blocks of the planets. One of the various difficulties involved in getting from dust grains to planetesimal, or in the case of the subnebula, satellitesimal, has to do with the actual state of the nebula gas and whether it is turbulent or calm.

Omega Nebula: Close-Up of a Stellar Nursery Resembling the fury of a raging sea, this image shows a bubbly ocean of glowing hydrogen gas and small amounts of other elements such as oxygen and sulfur. Sculpted by stellar winds and radiation, these fantastic, undulating shapes lie within the stellar nursery known as M17, the Omega Nebula, some 5,500 light-years away in the nebula-rich constellation Sagittarius. The lumpy features in the dense cold gas and dust are illuminated by stars off the upper left of the image and may themselves represent sites of future star formation. Image credit: NASA, ESA, J. Hester (ASU)

Within the nebula gas are lots of dust grains of different sizes floating around at different relative speeds with respect to each other. If they're small enough, they're part of the gas and move within its eddies. At this stage, grains stick together without much difficulty because their relative speeds are low. As the particles get larger, however, they are less influenced by the gas motion and begin to jump from eddy to eddy and their relative speeds are higher, especially with respect to each other. For these larger particles, the gas is acting more like a headwind trying to slow the particle down. We've found that once particles grow to something close to a meter in size, the headwind tends to be the highest. The relative speed between these objects can get so high in fact that a barrier is reached -- these objects find it very difficult to grow further and instead are easily fragmented back into small grains. If this happens, growth stalls. Thus one of the main mysteries of planet formation is trying to explain how to overcome this barrier.

What is one of the coolest things about your project?
The state of differentiation of Saturn's moon, Titan, is between that of Callisto and Ganymede. I'm working on developing a consistent thermal evolutionary model that could explain the formation process for Ganymede, Titan and Callisto. I'd like to show you can get their different states over the age of the solar system.

Cassini Gazes at Veiled Titan (rendering): Artist's concept of Cassini's Sept. 24, 2010, flyby of Saturn's moon Titan. Image credit: NASA/JPL-Caltech

Right now, I'm doing internal modeling of these objects based on formation times that are consistent with our satellite formation models and are consistent with the size of objects from which we would expect these large satellites to accrete. Just after they complete their formation, there is still internal heat from accretion, and heat generated from the gravitational release of energy when rock separates from the ice. It turns out that the surface layers of Titan and Callisto are separated, but their deep interiors are not. On top of that, there is also internal heat from the radioactive elements which still provide heat to the present day If I can show certain parameter situations in which objects like Callisto or Titan are still differentiating, albeit very slowly, that would be pretty cool.

But perhaps the coolest thing about my projects in general is having actual data -- it's tangible. You can access the data from which you can draw these conclusions. It's almost like being there and taking a sample.

What is one of the most interesting discoveries you've made about the compositional evolution of Saturn's rings?

When I started working with Voyager data, my project involved looking at the rings and coming up with models to try and explain their composition. One of the most interesting things about the rings is they're made up almost entirely of ice. However, for anyone who has ever seen a true color picture of the rings, they certainly do not look like pure ice. It turns out it takes very little impurity, less than a fraction of a percent of material, to give the rings their distinct color. Ringscape in color (left:) Image credit: NASA/JPL/Space Science Institute

The model was based on the idea that because the rings' surface area is so huge, they are much more susceptible to micro-meteorite bombardment. Even now, there are lots of dust particles floating around in the outer solar system which pass with some regularity through the planetary systems. These dust grains impact on the satellites as well, but because the rings' surface area to mass ratio is so huge relative to a moon of the same mass, the dust actually makes a significant difference over time. Thus, micrometeorite bombardment is an extremely important piece of the rings' evolutionary puzzle because these impurities cause them to darken over time. The impacts also lead to structural changes in the rings because material gets thrown around from one ring region to another. Most of the dust particles impacting on the rings are thought to be mostly neutral and dark in color, similar to cometary dust (e.g. Haley's Comet).

Majestic Saturn, in the Infrared This false-color composite image, constructed from data obtained by NASA's Cassini spacecraft, shows Saturn's rings and southern hemisphere. The composite image was made from 65 individual observations by Cassini's visual and infrared mapping spectrometer in the near-infrared portion of the light spectrum on Nov. 1, 2008. The observations were each six minutes long. Image credit: NASA/JPL/University of Arizona

If you have an idea of what the impact rate of this dusty material is, you can simulate the evolution of the rings over time and extrapolate how long it would take to start from some initial condition involving just ice and a very small fraction of some initially unknown native, spectrally absorbing material and get the coloring that we now see. From that, we can extract information about the materials that gives the rings their characteristic color.

What do you currently consider your biggest challenge?
Funding is always a difficult process. Getting people to accept your ideas can also be a challenge. Inevitably if you're working on a problem that is important in the field, there is going to be a lot of competition for grants. In this field, people can be married to their ideas and it's hard to convince people if you have a different idea.

Why should the general public care about your research? In your opinion, what is the potential impact?
That's a difficult question to answer. There is value in pure science and research. For anyone interested in furthering the general collective knowledge of humanity, we need to know how planetary objects were formed. Once we know that, we can predict how objects in other planetary systems were formed. At some point, the answers we discover now may prove even more valuable for future research and explorations.

What motivates you?
Solving the mystery. Creating models that lead to solutions and results keeps my interest high. It may not be the final answer but it's an answer that takes us in the right direction. Science is a building process and we keep building on what was discovered years ago.

With the rapid rate of technological advancements, can the answers you're seeking be found in the next 20 years or so?
I think we can get closer to the answers. It could be that we substantiate that someone was right a long time ago but didn't have the means to model it. Obviously with technology, the ability to do things has improved but there are always more problems and they tend to increase in complexity. Qualitatively, we're always getting closer to the answers; we're probably not far off.

I'm trying to advance current knowledge significantly. Generally when you try to do this, you inevitably run into a lot of scrutiny. If you try to move in a certain direction that is quite different than someone else who has been working on the same problem for a decade, you're going to run into resistance and that's just the nature of the field. You have to be tough skinned to blaze new trails.

The Birth of Stars This new Hubble photo is but a small portion of one of the largest seen star-birth regions in the galaxy, the Carina Nebula. Towers of cool hydrogen laced with dust rise from the wall of the nebula. Image Credit: NASA, ESA, and M. Livio and the Hubble 20th Anniversary Team (STScI)

What historic personality do you admire most and why?
I admire people who espouse or inspire free thought. I always admire people, and especially the people in the past, who were willing to go against the establishment because they believed in what they were doing. People like Darwin, Galileo or Copernicus did serious research, reasoned things out in their head, and certainly in the case of Darwin, struggled with it for years before finally going public with his theories. I admire that those men challenged current thinking in a time when it was very dangerous to do so.

What was your dream job as a child?
When I think back on my youth, a love of science and astronomy was always a constant. I went through a stage where I wanted to be an astronaut; but as a kid, I wanted to be the astronaut who was traveling to other planets. Once I got old enough, I realized that was not the reality. Other interests would come and go, but astronomy was the one constant, so in a sense, I'm doing what I always wanted to do.

What is your philosophy of life?
My philosophy is to enjoy my work and what I have in my life as best I can.

How do you spend your free time?
I spend it with my family and friends. I have a 3-year old daughter, and my wife and I just had a son who is just three weeks old. My family also travels to Japan at least once a year to visit my wife's family.

Is there someone you would like to swap roles with for a day?
Strangely, I've thought about swapping roles with the President of the United States for just a day. I'm sure he has this really structured day, which is, of course, the total antithesis of my day, and he deals with so many different pressures. It must be so hectic. It would be interesting to see what it's like, especially with our current president.

What is your favorite vacation destination?
I love going to Japan, of course. Although I've been many places around the world, I found Maui to be a wonderful place. Being on a small island and feeling somewhat isolated was certainly appealing , at least for a short while. It was amazing to be on top of the Haleakala volcano, looking down to see the confines of where I was, with just ocean and the other islands beyond. That was fascinating.

If time wasn't an issue, what would you still like to learn?
I'm always interested in learning other languages. I speak Spanish and continuously trying to improve my Japanese, but learning Chinese might be practical. It would also be interesting to learn more about the medical field and become a doctor or a medical researcher. Another frontier, of course, is the ocean and there is so much that is interesting to study there as well.

krandall Tue, 09/28/2010 - 10:30

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From Galileo to Cassini -- 400 Years of Saturn's Rings

krandall — Fri, 23 Jul 2010 15:00:17 +0000

From Galileo to Cassini -- 400 Years of Saturn's Rings

By Dr. Mark R. Showalter
Planetary Astronomer at the Carl Sagan Center for the Study of Life in the Universe, SETI Institute

In 1609, Galileo introduced to the world his new invention, the astronomical telescope. It opened up new opportunities to explore a territory that all prior generations had regarded as familiar--the night sky. In short order, he was making major discoveries. But the sky is very big and Galileo's telescope was very small. He had to choose his targets carefully.

In that context, Saturn was nothing special, the least of the known planets, just a bright point in a black sky. A year elapsed before he finally peered at Saturn for the first time on July 25, 1610. Galileo immediately realized that this was something new and different, but he was unable to make sense of the view in his tiny eyepiece. He described Saturn as "triune" in form, mistaking the rings for a planet straddled by two close moons. They resemble Mickey Mouse ears in his sketch. It took the world's astronomers another half-century to figure out exactly what they all were seeing.

In 1659, Dutch astronomer Christiaan Huygens was the first to describe Saturn's rings as a flat, circular disk, and the concept of a ringed planet first entered the human imagination.

Anyone who has ever looked through a telescope will remember their first view of Saturn. Galileo's other early discoveries retain their allure: the mountains of the Moon, Venus as a waxing and waning crescent, Jupiter with its four little companion moons. But we have seen other mountains, other crescents and other moons. The rings of Saturn remain something different, something truly unearthly.

Galileo's notes and sketches survive from that night in 1610. They capture his thoughts but probably not his emotions. We scientists are taught to write dispassionately, and preferably in the passive voice. "The planet was observed....", not "What the ... is this?!" The interrobang never appears in the scientific literature.

Today, I think we have become a bit spoiled. NASA's Cassini spacecraft has been orbiting Saturn since July, 2004. Every day, it sends back remarkable new data describing the planet and its retinue of rings and moons. It has revealed plumes of dust venting from cracks in the surface of the moon Enceladus. It has shown us sunlight glinting off the smooth surface of a lake on Titan. We have seen the flashes of meteorites hitting the rings. With Saturn's new-found familiarity, we sometimes forget to be amazed.

Let me revisit one of the most famous images from the Cassini mission. It was taken a few years ago as Cassini flew through the shadow of Saturn. The view is stunning. A thin fringe of sunlight encircles an otherwise dark planet. The rings, lit from behind, show startling colors and contrasts. Surrounding it all is the faint bluish glow of the fine dust ejected by Enceladus. The picture is a mosaic of smaller images, painstakingly assembled by Cassini's imaging scientists. It is flawless.

On the left side of the mosaic, just above the rings, is a little dot. In the picture it is nothing special, just a bright pixel in a black sky. But we know better. This is planet Earth, seen from the far side of the rings of Saturn. On July 25, 1610, Galileo pointed his hand-made telescope out from Earth to see Saturn for the first time. Four hundred years later, we have a telescope of our own, far more sophisticated but still built by hand, out at Saturn, looking back.

I sometimes wonder if the flawlessness is the problem. When Cassini's images are processed to digital perfection, we unconsciously begin to regard them as the creations of some mad artist at Industrial Light and Magic, not photographs from a real camera orbiting a real planet.

As an amateur photographer, I know what happens when I point my camera toward the sun. I get lens flare, those circles of light that appear in so many of our snapshots from the beach or the ballpark. Too much sunlight bounces around inside the optics, following paths that the lens-makers did not intend, and leaving behind extraneous circles of light on the sensor or film.

Cassini's cameras are no different, and many of the images from Saturn's shadow show these familiar patterns of lens flare and saturation. These tiles were left out when the mosaic was assembled. However, they reveal a different truth, one not about Saturn but about the camera. It is imperfect. It was built by human hands.

This week, it will be easy to repeat Galileo's experiment. Shortly after sunset, look toward the west and you will see three planets in a line. The brightest is Venus. Above it and to the left is Mars, distinctly reddish but much fainter. And just beyond that, Saturn. Check them out. Any pair of binoculars has lenses far superior to the one in Galileo's invention. But be warned--what you see will not resemble the latest releases from the Cassini mission. If you are very lucky, you might make out Saturn's rings. Or maybe you will just see Mickey's ears. Or maybe just a fuzzy dot. But no matter, because you will be seeing it with your own eyes. That alone ought to be enough to inspire an interrobang or two.

Cassini image credit: NASA/JPL/Space Science Institute

Learn more about the Cassini mission.

krandall Fri, 07/23/2010 - 11:00

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I just bought a chi.. this chi to be exact. It's the goddess of all flat irons. I had a cheap Wal Mart hair iron. I used to have to wash my hair, take it into section, blow dry w/ a round brush THEN go over every piece of hair w/ my cra**y flat iron, again and again

Great Article.

You article is good...
But i have some new views of my own research,depending on you that whether you accept that or reject that....

Our life is very short my dear to understand these all things...

Among other things I do, I counsel people, but essentially my statement is that I wonder if the moon might be disintegrating and what that would do to gravity of the Earth and gravitational potentials, and the water on the earth if a great wabble were created through some sort of off beat gravity that through some asteriod hitting the earth or the moon could damage our gravitational field in some way and influence some delicate balance of our gravity in our smaller universe, still far from Andromeda... This is where my thoughts go... So, what about it? Can you give some data on this theorizing about the Earth and Universe???

Valerie.

Why do We Explore? [Life at the SETI Institute]

sb admin — Tue, 22 Jun 2010 17:15:59 +0000

Why do We Explore? [Life at the SETI Institute]

by Nathalie A. Cabrol

I realize how immodest the title of this first blog may sound and it is certainly not my intention to convince anybody that I will answer this question in the limited space allowed here or even in a lifetime. My hope is, instead, to stir thoughts and invite an exchange of diverse perspectives to make this a thread that we can all pull from time to time. It is an immense subject debated in an abundant literature, but discussing it is certainly not the exclusive privilege of those called explorers. All beings, from the greatest minds to the simplest forms of life on this planet and possibly others, are explorers. All are, thus, without exception, competent to contribute to this discussion in one form or another.

Exploring may mean a number of different things for each of us but I argue that we all do it for the same reasons, whether those are reasoned or subconscious, and that the fundamentals of why we do explore have been the same since the dawn of life on our planet. My perspective stems from a passion for exploration, for living, breathing and imagining it every day of my life and dreaming about it at night. It is fueled by a fascination for the possibility of finding life on other planets and observing life's ability to adapt on ours no matter what is thrown at it. It is also sustained by the exceptional environment of the SETI Institute where I belong. Walking down the Institute's hallways, posters and photographs take residents and visitors alike from Is there anybody out there? to Do you sincerely believe that anything can survive down here? and everywhere in between. The sky is not even the limit. It is our starting point.

There is a very large universe out there and according to the String Theory, it could be only one out of an infinity of universes. Even better for us curious minds since that's more real estate to explore! Cosmology theories and quantum physics possibly epitomize, at least to me, the human mind's ability to play with what we know of our universe and to project it into the unknown. These explorations take us beyond the limits of where, directly or indirectly, our hands can touch, our eyes can see, and our bodies can travel, to look at all the angles our imaginations can reveal. There, we embrace an addictive freedom, while still clinging to the laws of physics with which we have come to evolve. One day these laws might fall but for now, they are still what make our universe go round. We explore at microscopic to macroscopic scale but this is not a human privilege. All species that made the journey thus far with us are still here because they were greater explorers than those that did not. This takes me to what I feel strongly is the most fundamental, primeval essence of exploration: survival.

While we are seeking brethren in the universe, our own beginnings remain unclear. Life on Earth may have developed and gone extinct many times before finally taking roots on a planet heavily bombarded by asteroids and comets for hundreds of millions of years, a planet ravaged by volcanic eruptions the likes of which we do not know anymore, and by many more countless deadly threats. In such an environment, immobility and scarcity were not the name of the game. Survival resided in the diversification of environments that life could make available to itself by multiplying when it could, and by colonizing the next crack in the rock, the next rock in the field, and finally all the fields in the continent, the next continent and the next ocean in the planet, and soon (at geological scale), the next planet. This is our journey so far.

Each species goes as far and as fast as its evolutionary path can take it. This path is dictated by that species' exposure to the environment and to other species. We (as in life in general) are all trying to constantly expand our horizon, for there is gain in doing so. At the most primary level the gain is physical survival through a greater range of environments, which provide additional resources to supply a greater number of individuals of the same group. The curiosity and awe that we humans associate with exploration is a late comer. Understanding when this driving force developed is by itself a fascinating subject. I do not believe the first bacteria were curious about their environment; they simply tried to adapt to it.

Curiosity requires first questioning, which is the attribute of a number of superior species who do not simply react but rather interact with their environment. Those species also show creativity and imagination, which are both signs that they are exploring their mental and cerebral abilities. I am now going much too far outside my area of expertise and will hope that others will comment farther on this. But as far as humans go, beyond survival, exploration is certainly associated with physical, mental, and spiritual questioning that fuel each other by changing our perception of all the dimensions we know of, and give to the universe. Iterative questioning and exploring expands our imagination, thus our ability to further question and explore. The curiosity we apply to exploration is also one way for us to stimulate our imagination and gauge its validity in understanding our universe and its endless diversity. To some extent, it is the way each generation has to create its own universe.

Today, we still strive to survive but now life has also reached the point where its exploration path has come to question its own origin. Indeed, we do explore to understand where we came from and define the meaning, if any, of this wonderful universal journey of ours. It is fascinating to realize how, as we walk the Earth, the surface of other planets, soon the Milky Way and beyond, that this journey gives greater depth to our consciousness, for exploration is also very much an inward voyage. We are made of all the bricks of this universe. There is, therefore, a chance that part of this answer that we have set out to seek so far away in the unknown confines of the universe, might be within us, waiting for the time when exploration will take us back home.

sb admin Tue, 06/22/2010 - 13:15