Quantum Rocketry

Europa, the second Galilean moon of Jupiter, has been my favorite planetary body for a long time. The reason I like Europa so much is that it’s a world whose orbital dynamics with Jupiter, its orbital resonances with the other Galilean moons, and its own rigid-body dynamics have a strong hand in creating its surface features – and giving it the potential to harbor life. It’s one of perhaps two or three extraterrestrial places in the Solar System where we might hope to find life. Europa is also easier to get to than Enceladus or Titan. As such, I think it ought to be one of the highest-priority exploration targets for robotic space probes. (Human exploration would be nice, too, but if you think radiation exposure on the way to Mars is hard, you don’t even want to consider putting people in the Jovian system!)

Thanks to magnetometer measurements and images from the Galileo mission, it’s pretty much established at this point that Europa has an icy outer shell over a global liquid ocean, with a rocky core on the inside.^* The only question is how thick that ice shell is – I’ve read estimates ranging from 10 meters to 100 kilometers, with a pretty high confidence of ones to tens of kilometers. The ice shell gives rise to a number of interesting surface features. A particularly cool sort of feature, found with global extent across Europa, is the double ridge.

A prominent double-ridge feature on Europa, most likely a crack in the icy shell

Planetary scientists have a number of models for how these double ridges form, and they generally seem to agree that the ridges mark the locations of cracks in the ice crust. One especially well-established model suggests that these cracks occur when Jupiter raises tides in Europa’s ocean – just like how the Moon raises tides in terrestrial oceans, but much stronger, because Jupiter is frakking huge compared to Earth’s moon. Europa’s ice crust bulges out over the ocean’s tidal swell and then cracks under the incredible stress. (I like to take a moment to think about the mindbogglingness of that statement: the whole moon’s surface cracks. I’ve stood on a frozen pond when a crack pings through the foot or so of ice on top of the water – Just imagine standing on Europa when this happens!) Once a crack forms, the tides don’t go away. As Europa rotates, about once every three and a half Earth days, the tides periodically lever these cracks apart and squeeze them back together again. In this model, every time the cracks gape open the subsurface ocean gets exposed to space. The surface water boils and rapidly crusts over with ice, and when the cracks get smushed closed, all this ice gets crushed up and forced to the top and bottom of the crack, forming the ridges. The ridges appear in pairs because the crack opens up again after that. These double-ridge features are mounds of crushed ice flanking passages into Europa’s ocean!^†

Dr. Richard Greenberg is a planetary scientist who thinks that these cracks in the ice shell might be potential sites for life to take hold. Unlike the rest of the subsurface ocean, they get exposed to sunlight, which means that photosynthesis could take place. The periodic in-and-out forcing of the crack would also drive strong currents, which is another energy source Europan life could use. (Those aren’t the only energy sources: other possibilities include thermal gradients in the water, volcanic vents on the ocean floor, or even induction as Europa travels through the Jovian magnetic field.) Of course, that life would also have to adapt to the crack opening and closing once every 3 1/2 Earth days!^‡

Europa's possible ice-fissure biosphere (from New Scientist; click for full article)

We do at least know, from the Galileo mission, that these cracks often have accompanying veneers of organic (e.g. carbon-based) molecules and salts splashed onto the ice surface. This is why the cracks appear as brown stripes in large-scale context images. The crack/veneer combination suggests that there are organic molecules and salts in the Europan ocean, and that those compounds get pumped to the surface through these cracks.

So, let’s take stock: Europa is the only extraterrestrial world with a global liquid water ocean, there is a definite possibility for life in that ocean, and these double-ridged cracks are a possible gateway into the alien biosphere.

Well, then, let’s go diving! Read on for my concept system architecture for an ambitious Europan ocean-exploring mission, which I call the Ice Fracture Explorer.

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…full of unsolved yet soluble mysteries!

Mysterious craters on Mars

I’m shamelessly bouncing all you readers over to the Bad Astronomy blog for this post, which is a great outline of the detective process that is planetary geology. It’s also a great illustration of how much context matters and how leaping to conclusions is…bad. AND it’s a good demonstration that, when there are several hypotheses in consideration, elements of each could be synthesized into the proper conclusion.

All things for us to keep in mind, in science and in everyday life!

(Also, way cool pictures that are reminders of TOTALLY AWESOME events in the past!)

I spent the week of the Fourth of July with my girlfriend’s family in Gatlinburg, Tennessee, right next to the Great Smoky Mountains National Park. I have driven through the southeastern United States twice, but never had a chance to get out of the car and look around much, so I was very happy to add a new area of the country to the places I’ve visited and go take a look at my 7th National Park. (Everglades, Zion, Grand Canyon, Mesa Verde, Bryce Canyon, and Petrified Forest were the previous six.) We landed in Nashville Airport, made a valiant attempt to dodge all the country music, picked up our rental car, and then drove though the countryside for four hours before coming in to Gatlinburg, driving up a mountain, and arriving at her family’s swanky rental cabin. (I shall skip over describing the übercheesiness that is Gatlinburg itself.) An impressive view greeted us out the back porch…

Gatlinburg

They don’t call them the Smoky Mountains for nothing. It was pretty hazy most of the time I was there, so we got a lot of views of faded ridgelines marching off into the distance, covered by lush deciduous forests. Of course, as this was a family event, we spent most of our time in that cabin and generally had a great time. But my girlfriend and I managed to make two highly successful jaunts into Smoky Mountains NP.

The first was a bike around the 11-mile Cades Cove Loop Road. This loop starts at a visitor center an hour’s drive into the park and circumnavigates a flat expanse of farmland in the middle of the mountains. Even the drive in was fun – it reminded me quite a bit of the drive from my home to Williams on Rt. 2, on the part around the Mohawk Trail. Makes sense – the Berkshires and Appalachians formed in similar orogenies, though the scales were far different. Anyway, a farming community has existed in Cades Cove since the first settlers made it that far west and persists today. The loop road winds along what were – to an Ithaca biker – gentle hills and afforded us a lot of panoramic views as well as some brief visits to historic buildings. (The Park Service calls the Loop Road a “moderately difficult” bike. That was definitely on account of the condition of the rental bikes, and that they tell you not to use the front derailleur – I think the one on my girlfriend’s bike was actually disabled. Fortunately, I had my multitool….)

View from the Cades Cove Loop Road

There were quite a few panoramic views from the road. Cars and cyclists share the road, and despite the many pullouts, traffic was slow as the people in cars paused to take photos. I was happy to be a bit more mobile and flexible!

Cades Cove panorama

At the far end of the loop was another visitor center built near the old farming community’s mill – which looked very picturesque among all the trees! I had a fun time playing with the CDHK high-dynamic-range script on my little Canon point-and-shoot to get a picture of the half-shaded, half-sunlit mill building:

Cades Cove mill

Inside the mill, they sell corn meal ground at the site. Of course, we weren’t going to hump any of that out the remaining 5 miles on our clunker rental bikes! After pausing awhile for lunch – which gave us an opportunity to improve my blood sugar, the water level in our bottles, and the worst of the derailleur problems on our bikes – we set off again. I was most interested in the scenery of Cades Cove, as after seeing one or two of the historic old houses, you’ve pretty much seen ‘em all. However, there were still interesting historical tidbits to be had. Here’s a pretty cool grave we found in the cemetery around the Primitive Baptist Church:

Murdered by Rebs!

Our bike tour finished with a close encounter. On the way back, all the cars on the road suddenly jammed up, with occasional people pointing out of rolled-down windows. I cast a look off to one side and spotted a BEAR. I skidded to a stop, and it turned out to be a mother black bear with two cubs, rooting around in the shrubbery. They had warned us about bears at the visitor center, but I took those warning in the same way I take any warning about animals in parks – yeah, yeah, okay, if I see a bear I’ll be sure to keep that stuff in mind! Little did I know that they give these warning in the Smoky Mountains because you will probably run into bears. I took some grainy movies before they got too close for us to do anything but get back on the bikes and get going. We had no windows to roll up!

After the Cades Cove bike, we collapsed at the lodge. The next day, though, we were feeling intrepid enough to be looking at hikes in the park, and based on the description alone we picked out Chimney Tops trail. This was a big win.

Chimney Tops is a 2-mile trail to the summit of a mountain right next to LeConte Peak, the highest point in the park. The last mile of the two gets steeper and steeper, ending with a bare-rock climb. I, my girlfriend, and her cousin were very excited as we set off.

One of the first things to strike my about this hike was how lush everything was. I’m used to forests that consist large of trees and ground cover, like those in New England. Whenever I see a different forest ecosystem things seem a little funny to me. So far, the weirdest to me has been the ponderosa pine forest around the Grand Canyon, which consists of huge ponderosas and nothing else. Well, Smoky Mountains National Park is at the other extreme: solid green growing things from ground level up to the canopy.

Chimney Tops Trail

(Other great examples here and here.) We even managed to spot a Jordan’s Red-Cheeked Salamander in all that foliage – a salamander species found only in this National Park! Shortly thereafter, we almost had another encounter with a black bear, as we saw some fellow hikers hoof it down the trail to us and tell us that they were doubling back a bit to avoid a bear that had burst out of the undergrowth right in front of them. We didn’t see the bear – only some wet footprints a few minutes later.

Chimney Tops Trail reminded me a little bit of Angel’s Landing in Zion National Park – though the climates, geology, and trails had plenty of differences, of course – in that it ends with hikers climbing out onto a spur of rock that sticks out into a valley. So, as the hike got steeper and steeper, eventually it turned into this!

Scaling the summit

Pausing at a convenient stopping point partway up those rocks, I turned to one side and snapped the following panorama, a preview of what we saw at the very top.

Panorama near the top

Finally, after a bit of exciting scrabbling, we got to wedge ourselves into some crevices at the top and have a good look around. Scenic! (Click to panoramify.)

Chimney Tops summit panorama

Have I mentioned that I love my little Canon SD1000, which fits in my pocket, has a nice panorama mode, and lets me take HDR photos with CHDK? In fact, the HDR tricks I’ve been playing with were wonderful up on Chimney Tops, because they let me combine exposures to get some good shots of the progressively faded mountain ridges staggering off into the distance over the near hills. One such example:

HDR of mountain ridges

And another, capturing the tip of the mountain spur forming the Chimney Tops:

HDR mountain rock spur

Under the shade of the trees it had been nice and cool, but as we came out onto the bare rocks it warmed up. As we snacked, sitting on the mountain, the sun was flirting with the edges of some clouds. Coupled with the haze and humidity, this meant that we got a pretty nice optics show of sunbeams blazing down on the distant mountains. I tried to capture some of that with my camera, too, but found it about as difficult as the one time I was in a position to photograph the aurora borealis. Still, I got a few nice images!

Smoky Mountain sunbeams

I even figured out how to postprocess the living heck out of one panorama to bring out the sunbeams without totally destroying the rest of the image. I quite like the result, below! You’ll want to click on this one.

Smoky Mountains sunbeams

Maybe next time, I’ll have to try and time that hike for sunset or sunrise!

After a good deal of gawking, it was time to head back. Of course, climbing up the rocks and climbing down the rocks are two different problems, and we were a bit slower picking our way down the steep surfaces. This is the best picture I got that gives a real sense of going down. Notice all the deformation in the tilted stratigraphy, with girlfriend and her cousin for scale. (The runner-up is this photo.)

Going down!

I’ve gotta say that the Smoky Mountains were definitely worth a visit, and I’d happily recommend Chimney Tops as a good morning or afternoon hike. I like hiking, and I like our National Parks, so I was happy for the chance to get to see another in an area of the country I haven’t been to.That’s one of the things I like best about the United States: we’ve got so much stuff within our borders, but everyone uses the same money, understands English, and follows the same road signs. And sometimes we even feel like protecting what we have, so we can go into these spectacular places!

Gatlinburg ridges at sunrise

See all my pictures on Picasa - I had fun tweaking them all on the plane back to Ithaca!

I know I am not at my blogging best when I just write, “hey, look at these spectacular images!” But…look at these spectacular images!

An image-of-the-day gadget on my iGoogle home page showed me this picture, which I subsequently spent about a half hour trying to locate at a primary-source web site. It is wicked cool.

Possible Cyclic Bedding in Arabia Terra (HiRISE/MRO)

Click to go to this image’s description page on the University of Arizona HiRISE site. (Be sure to bookmark the 2560×1600 wallpaper version!!!)

I really want to know how these terraced buttes got to be the way they are…it looks like they must have been eroded in stages, with each layer from the top getting peeled back successively, but somehow the individual layers hold together – those are some pretty steep walls. I can see in the southwestern portion of this image that some of the terrace walls are eroding away in chunks; there are a couple good fallen boulders over there. The layers might be some kind of sandstone, because they haven’t eroded away in lots of rocks and boulders, so they don’t seem very friable, but there’s obviously a lot of source material for dunes in this area so the butte walls might be getting ground down into very small grains. I’m not sure what the fluvial history of Arabia Terra is – on Earth, that would be bound to play an important role in creating landforms like this.

I also really love the expression of the more recent aeolian features in this area. Looks like there are prevailing north-south winds on the east side of this image (I’m going to say the wind blows to the north because the north sides of the dunes look more like slip faces to me), but from the east-moving dunes in the terraced valley-like feature at center bottom and the east-west oriented ripples on the larger dune field, the winds are apparently going in rather circuitous routes around these buttes. There are also some confusingly-oriented dunes and ripples in the southwest portion of this image, probably from the wind winding around all the rocky towers. (In my mind, I can hear it whistling.)

Looks like the valley from which the east-going dunes have traveled is an exposed outcrop of one of the terrace layers. This image can resolve objects less than a meter in size, so the various crisscrossing dark lines in the light-toned outcrop might be joints or something.

Anyway, this is not a new image and I haven’t studied or researched this stuff…I just saw it today and wrote a little stream of consciousness of geological ideas. I just think this image looks beautiful and I want to send some rovers/people there. Any planetary science guys want to comment?

Last, and just for grins, here are some goodies I turned up in my search for that image on the UA HiRISE site. Here we have some dramatic contrast between dunes and some lighter, rockier topographically high areas:

Pitted Layers Northeast of Hellas Region

Here’s some great layer exposures around some hills – and if you zoom into the large version of this one, you can find some wild and interesting ripple patterns:

Light-Toned Rock Exposures in Noctis Labyrinthus

Thus ends today’s amateur geology geekage.