Radar revelations from Titan

Posted: Thursday, February 08, 2007 8:04 AM by Alan Boyle

NASA / JPL

Cassini's radar readings reveal a crater (left) and a dune field (right) on Titan.

There's been a lot of weirdness in the space world this week - but if want to go beyond this planet for something really weird, the Saturnian moon Titan is a good place to look. Over the past three years, the Cassini spacecraft has been looking quite a bit, using several methods to cut through Titan's smoggy shroud. The piggyback Huygens probe descended through the murk and spotted channels that may have been cut by flowing methane. Meanwhile, instruments aboard Cassini itself peered through the haze to map strange dark areas that may be fields of hydrocarbon-laced sand.

Now a panorama from Cassini's radar imager has provided a wide-angle view of the dune fields, plus one of the few craters seen on the surface.

The longitudinal dunes appear to sweep around lighter areas of higher elevation, like sand raked around stones in a Zen garden. In this case, the sand is likely raked by Titan's strong winds. It turns out that the place has some pretty significant weather patterns, including a massive cloud system that came to light just last week.

NASA says the crater on the left side of the radar image, acquired Sept. 7, is notable because it's one of only three impact craters that have been positively identified on Titan.

While the radar team is mapping Titan's weird surface, Cassini's imaging team is churning out fresh pictures of the Saturnian system every day. So far this month, we've seen cool new views of the faint spokes in the planet's rings, a color-coded snapshot of the moon Tethys and much more.

So if you're in the mood for some all-natural weirdness rather than the tabloid variety, Cassini's got you covered.

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Comments

Titanic image, Alan! Yeah, yeah. Couldn't resist.

Siriusly, though that is in interesting radar image. Might I suggest an alternative interpretation. Not an impact crater, but a volcanic caldera surrounded by a volcanic outflow shield.

Take a look at satellite imagery of the Hawaiian volcanoes.

Stay warm!

Wade Whitlock, Aberdeen, MD (Sent Thursday, February 08, 2007 3:51 PM)

I agree on the volcanic observation...including the surruonding surface farther from the proposed cauldron. But how do you interpret the round object that is about in the center, yet appears to have left a rolling track on top of the volcanic summit and some sort of impression on the surface, too?

Terry Blunk (Sent Thursday, February 08, 2007 6:32 PM)

I very much agree with Wade. That looks like Olympus Mons on Mars! This mission sure paid off big time!

Chris Eldridge (Sent Thursday, February 08, 2007 6:36 PM)

I was hoping someone would write in about that central peak in the crater... I believe the interior structure of the crater (with a splash peak) is what has led geologists to conclude that the crater had its origins in an impact. It's true, however, that there's a shield volcano look to the material surrounding the rim.

Alan Boyle (Sent Thursday, February 08, 2007 7:07 PM)

The north rim (about 1:00) seems to be a faint trail from the edge of the rim (where it looks like the rim is a touch lower) down the right side. Maybe the crater wells up with water/lava and spills out. A much smaller thinner trail can be seen at about 11:45 and arches over to the right. Maybe the splash in the center is some kind of lava dome buildup. Maybe they are hesitant to call it a volcano knowing there probably isn’t enough internal energy left to drive it. Do we know if Titan has a magnetic field? If it is an impact, maybe it hit more face on and bulged-up the shield look. It seems that it is not an optical elusion, as there seems to be lines leading up to the rim on the entire south side – like the tracks of tumbling rocks – maybe impact rays.

Chris Eldridge (Sent Thursday, February 08, 2007 7:55 PM)

While it would appear to resemble a sheild volcano with the shading area's as potential cliff's. It could and probably is an impact crater with the ejected material blasted out of the crater. With Titan having a dense atmosphere the ejected material might possibly settle into a spherical ring with some weathering from hydrocarbons on the outer edges. The age of the structure is unknown, it could be millions of years old or have occurred <500 years ago. Even the central peak is indicative of an impact event within the photo, with a shallow hydrocarbon lake having formed therein.

I wonder what the actual depth of the structure is, what size was the impactor, and is the central peak formed from magma from deep inside the moon? Is there any outflow on the opposite side of Titan, that may resemble the Deccan Traps? The photo is very thought provoking and wonderful to see structures that have not been seen before. Well, the scientist will eventually have ideas after analizing and coming to some ideas.

Jerry M. Weikle, Virginia (Sent Thursday, February 08, 2007 8:15 PM)

Titan is not Terran, so we can't interpret it's character in earth terms. If there are only three craters identified, the one illustrated cannot be compared to what we consider a 'normal' volcano. Being that close to its primary, so close that tides raise the 'sand' there and pull it around like water (I'm comparing Titan to the Earth, aren't I?) will make a big difference there. The dark bar mentioned by Terry Blunk may be an anomaly of the camera or may be really a track left by something. We don't know how methane or hydrocarbons form into granular bits, but the tidal winds could erode mountain forms down to pieces small enough to make dunes over a long time. Could older craters have been eroded already? That could explain why only three have been found. If they were volcanic, wouldn't the red-hot lava ignite the methane atmosphere? As far as Alan's 'splash peak' is concerned, perhaps gravity of Titan prevented the formation of the rays and rilles we see on Luna outside the crater from impacts. And Titan has an active atmosphere,too, something Luna does not.

DesEmery,TheCarborundumChronicles,St.Thomas, ON,Canada (Sent Thursday, February 08, 2007 10:10 PM)

That ball in the center that left a track? One of the Titans missed his putt!

Back on track, so to speak, that central peak in the crater could also be the equivalent of a lava dome. The environment has a lower gravity and different materials, so who knows how such structures are going to appear? And what about that apparition of a shadow below the ball?

Wilbur Sitze (Sent Friday, February 09, 2007 5:14 AM)

I didn't have time to do a detailed examination of the image, unfortunately. The available resolution didn't encourage that, either. Excuses are like nostrils. Everyone has at least two!

Whether that is a "splash cone" or a volcanic "cinder cone" would make for a fine argument and need better resolution than I have. You will see similar wall formations in the shield volcanos. Just depends on composition and gravity!

Might be the 60+ year-old ocular system I'm working with, as well.

Wade Whitlock, Aberdeen, MD (Sent Friday, February 09, 2007 8:22 AM)

lol you guys are jumping to a lot of conclusions from a 2-D photograph. Don't forget that Nasa has 3-D info for all these photos too. If they say it's an impact crater, that is most likely what it is. Note that to the south-east (assuming that the top of the photo is north) of the crater, the dunes still have the same general direction as the dunes to the east.

Matt, Burlington, MA (Sent Friday, February 09, 2007 10:27 AM)

Perhaps the splash peak is actually a Santorini style lava dome reasserting itself?

JC, Riverton (Sent Friday, February 09, 2007 11:18 AM)

I was about to mention that central peak, quite obvious. Sounds to me the impact might have occured into material that was laced with moldable material, goes well with the description of the Huygens landing site which describes the soil as wet sand or meringue in feel.

Mantiss, Montreal, Canada (Sent Friday, February 09, 2007 3:12 PM)

DesEmery,that was an interesting statement "wouldn't the red-hot lava(sic) ignite the methane atmosphere". Even if the central peak wasn't a lava dome but an upwelling of ice from the deep mantle--the asteroid or impactor as it entered the atmosphere; should have ignited some of the methane in the atmosphere--to some degree. The lack of significant amounts of oxygen would have prevented further hydrocarbon deposit or lakes from igniting. CO2 does extinguish a fire. NASA needs to develope a spacetanker, quickly as this world will need the hydrocarbons for its oil resources. Or a fleet of spacetankers, for water/ice resources for terraforming Mars or Venus into something habital for the growing human population. Well, the photo is thought provoking--spend billions to terraform planets in the solar system or billions to destroy the Earth and humans likewise? Humm

Jerry M. Weikle, Virginia (Sent Friday, February 09, 2007 3:49 PM)

Jerry W. - thanks for reminding me of my own cautionary warning about considering Titan's characteristics by Earth standards - I should have thought about oxygen, or its lack, in the probability of fire. Your "wait and see" attitude is the right one. But I couldn't resist another 'peek'' at the picture. and this time I noticed that Terry Blunk's ball was the only round thing there, but the shadow of the trail leading to it looked less like a gouged out track than an actual shadow but what would be the light source and how would a shadow be formed in a pea-soup atmosphere?

DesEmery,TheCarborundumChronicles,St.Thomas,ON,Canada (Sent Saturday, February 10, 2007 1:20 AM)

Living in the Pacific Norhwest, I have a bit of a feel that while this may indeed be an impact crater it did have the continued effect of a volcano, to me it looks similar to Crater Lake, here in Oregon. An impact into an icy terrain would still create a lot of heat, especially if it were a metallic or rocky meteorite (Titanorite?) then it would be a continued heat source for a time and cause an upwelling of hydrocarbon/water 'lava'. At the 2 o'clock position there is what looks to be a 'lava' flow complete with what appears to be a small break in the crater wall. The peak in the center could easily be explained by the heat of the impact body diminishing over time and so a smaller cone could be built as the heat and 'lava' flow diminished, forming a secondary cone inside the main impact crater. there also appears to be a liquid 'lake' inside the main crater, just like our Crater Lake to boot! Just a thought, but I felt that it covered the visible attributes in this photo.

Chuck Sweet, Portland Oregon (Sent Saturday, February 10, 2007 12:32 PM)

I'm not sure if you guys are referring to that dark smug running halfway across the photo as a shadow, but that's got to be a radar anomaly of some king. These radar images are very long and they are taken around a curved surface, so it is not unlikely that the very ends (which this is at the very end) would have such anomaly.

Chuck, I love the idea of a heated impact causing an upwelling, but wouldn't that smug out the impact walls more? I guess the impact walls could be in a hard surface rock with water welling up from below.

Chris Eldridge (Sent Sunday, February 11, 2007 11:17 PM)

Now, this is the kind of rational discussion for a variety of viewpoints that I had grown to enjoy so much, Alan!

Notice the courtesy and delightful back-and-forth? No psycho- or religious babble. Just intelligent rational beings examining a phenomena an discussing cause and effect. Revel in it!

In any case, there also seems to be ejecta rays from the crater/caldera. An impact or an explosive eruption could do it. We may have a dual event per Mr. Sweet.

The big problem with interpretation is understanding the material we are observing and the characteristics of the sensor. It is OK to compare to known phenomena, as long as you are not wedded to the idea. Remember the "hamburger bun" formations on Venus and the right-angled geysers (Enceledus?)? And radar microwaves have some different adsorbtion and reflection characteristics versus optical frequencies.

Tell me this isn't fun!

Wade Whitlock, Aberdeen, MD (Sent Monday, February 12, 2007 11:25 AM)

Right, Wade ... I'll try to find someone from the Cassini team who can shed more light on the crater. I'm hoping that someone will weigh in here. Thanks for the good word!

Alan Boyle (Sent Monday, February 12, 2007 11:35 AM)

Thanks Chris, I understand your thinking on the heat/smudging of the initial impact crater, and so looked at it again with that in mind. I think I will stand by my idea though. Considering the extremely low surface temperatures, and the fact that much of the melted material would be water, with the hydrocarbons being turned into gas by the heat, there would be a 'boiling' effect (although at low temperatures). I could imagine there would be splash happening from that bubbling which would freeze, possibly even mid-air, and so actually cause more buildup of the original impact crater wall. Looking at the crater again I noticed that the crater wall is not a sharply defined item as we so often see in other impact craters, such as the moon, but instead is wider and softer in it's nature, with rounded outcroppings that lend credence to my idea, I think. I would very much like to hear from the professionals from the Cassini team and see what they think, since they have access to much better data than we do working off from a single, grainy picture.

I too enjoy the Real nature of the discussion here and hope to see and participate in it more in the future.

Chuck Sweet, Portland Oregon (Sent Monday, February 12, 2007 3:42 PM)

I had to go back and repeat the photos and descriptions of Titan, looking for all the different interpretations our people gave. Now that crater looks to me to be very old, and the terrain (?) around it appears to elevate it well above the dunes on the righthand side of the picture, I can trace out an almost circular base far beyond the crater itself. It is strange that only three such features are found on the entire moon. In some of the videos, the "icerocks" appear isolated by erosion-causing surges in the looser, small materials described as "sand." At well below zero temperatures, crystal "ice" would be as hard as rock is here on Earth. In the absence of warmth and liquid H2O could lifeforms even begin to evolve?

DesEmery,TheCarborundumChronicles,St,Thomas,ON,Canada (Sent Monday, February 12, 2007 11:46 PM)

The only form of life that I could imagine forming in such an environment would be some sort of single cell organism that would have to have an ability to metabolize the UV changed methane products that have been deposited on the surface and then washed into the gullies and 'seas' or lakes. Such an organism is likely to be rather acidic in nature and may have a protective cell wall of perhaps water ice or even crystaline carbon (yup, diamond) or silicon, much like our radiolarians or diatoms. One could even imagine that it would give off free methane so that they actually depended upon solar energy to convert the methane in the atmosphere into food for them, establishing a cycle similar to our carbon cycle here on earth. The organism may even use silicon as it's basic building block instead of carbon as we have on our planet. There may even be multicellular life forms evolve from just such a basis, or maybe even acellular life forms, ones without clearly defined cells. However, until we either send a lander with an extensive and apropriately versatile enough onboard lab or we go there ourselves with such equipment we really are not likely to know. That is unless we are able to devise good enough models and then get good enough data that matches those models from a distance. But I tend to think that unless we actually go and set foot there ourselves, and step into some pond scum (or it's equivalent), we are never really going to know.

Chuck Sweet, Portland Oregon (Sent Tuesday, February 13, 2007 6:56 AM)

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