Sunday, April 16, 2006

Here. There. Everywhere! (Part 2)

Earlier, I made a post about all the fun stuff going on over at Mars right now. But as I stated in the beginning of that post, that's far from the only extraterrestrial expedition going on right now.

Also of note is the Cassini spacecraft which is off at Saturn. It arrived there in June of 2004 and has been returning some excellent data, and more importantly for those not in the field, pictures.

One of my favourites is this one:

The thin blue line across this image is Saturn's rings viewed edge on. Visible also, are a few of Saturn's moons (which ones I'm not sure).

Saturn's moons are of special interest as well. One of the most interesting ones is named Titan. For a long time, astronomers have known that Titan has significant atmosphere. In fact, it's atmosphere is 60% greater than Earth's! And even though it's classified as a moon, it's larger than either Mercury or Pluto.

But although Titan does have a noteable atmosphere, it's not about to be a vacation spot any time soon. Being that it orbits along with Saturn at 9.5 times the distance from the sun that the Earth does, it's a chilly place. Additionally, that atmosphere isn't going to be good for your health. It's composed mostly of nitrogen. The ~2% that's not is complex molecules such as ethane, acetylene, and propane, as well as a little bit of argon, carbon dioxide, carbon monoxide, and others gasses.

Quite often, when people hear that Titan's atmosphere contains such volatile gasses, they ask if is going to explode. The answer is no. To ignite such gasses requires the presence of oxygen which is non-existant on Titan.

But that's not what makes Titan interesting. It's possible that there's actually liquid on Titan's surface. Not liquid water of course (it's far too cold for that), but instead, liquid ethane. The reasoning behind this has to do with the requirements for various chemicals to be in different states. The main determinants of the state of a compound are temperature and pressure (some of you may recall something called Standard Temperature and Pressure, STP, from your high school chemistry courses).

These two properties work against eachother. The higher the temperature is, the more likely a given chemical is to be in a vapor form. The higher the pressure is, the more the chemical will be in a dense liquid or solid state. Each molecule has its own specific balance of these to determine forms. But it just so happens that at Titan, the pressure and temperature are just right for ethane to be in liquid form.

Thus, astronomers suspected that Titan may actually have complete oceans of ethane. Images from wavelengths of light that could penetrate the hazy atmosphere showed large dark spots that appeared to be extremely smooth like just such an ocean would be. One of those spots can be seen in the upper left of this image:

So what's the best way to find out if this is true or not? The obvious answer is to go there. That's why the Cassini mission carried along a small lander called Huygens. Given that it was possible that they would be landing in an ocean, the lander was designed to float. This lander was dropped off at Titan and parachuted through the atmosphere and returned the first images from the surface:

Hardly the exciting dynamic surface that we were all hoping for. But that's not the only picture the lander took. It also took a large number of pictures as it parachuted down.

In this, we can see the lighter land area, which is positively filled with features very similar to drainage canals on Earth. These features all head to lower altitudes where there's a large dark area that is relatively featureless. This implies that the canals have emptied their liquid into a basin, which evaporates after eroding the surface, which accounts for the featureless appearance. Thus, it appears that, although Titan isn't going to be good for going swimming, you might have to bring an umbrella if ever we visit.

When Cassini was first launched, it was thought that most of Saturn's other moons were rather bland. Many of them were quite large, but lacked the interesting, large scale features of Titan. Moons such as Enceladus appeared to be featureless discs:

However, on getting there, Cassini discovered that these moons were far more interesting. Iapetus was one of the first moons that caught a bit of attention. It had long been known to have some rather irregular constrasts on its surface in which a good portion of the surface was significantly brighter (the measure of how well an object like moons reflect light is called albedo) than the rest. This became even more striking when the first close up pictures were returned:

Another thing that was gleaned from these images is a strange ridge along the moon. The combination of these two features led astronomers to believe that Iapetus had undergone a massive impact. The bright spot would have been caused by freshly revealed material that had not yet had time to be dirtied. The ridge would have been the shockwave that propagated through the moon until resolidifying.

But this wasn't the only interesting feature that was discovered on Saturn's moons. Enceladus, ended up having deep grooves in the surface:

These grooves ended up becoming very important last month, even grabbing the front page on a local newspaper or two. The reason: jets of liquid water spurted from them. While at least two moons of Jupiter are known to have subsurface oceans of liquid water, no one had suspected that Enceladus harbored such a secret. However, unlike with Jupiter's water filled moons, Enceladus' water must be close to the surface in order to erupt as it does. This gives astrobiologists an exciting new prospect in the search for possible extraterrestrial life.

Although other moons have interseting features, those have been the major highlights thus far. But Cassini's mission is far from finished.

So that's it for tonight. In my next update on what's going on around the solar system, I'll either be talking about what's happening at Venus, or some interesting plans for the moon.

NOTE: All images in this post are copyrighted to NASA and/or their respective creators.


Anonymous said...

greets! I noticed an incoming link to my site from this post. I looked to see where the link was from and noticed it in an image that doesn't show. I have set up my web server to disable the display of images when they're called from websites other than my own (to save in bandwidth usage).

If you wish to display that image, I invite you to save the individual images from my post that contains (what I think is) the image you wanted to display and upload 'em to your own site. I'd also appreciate a link to where you got 'em from if you're willing to add it. (I've no problems with your displaying the images themselves, as they came from NASA/ESA/UofA. I'd feel differently if you were to do the same to one of my own fotos, tho).


Jon Voisey said...

I apologize for hotlinking the image. Generally I do host the images that I use, but unfortunately, my computer has been down and the computers in the library I'm using don't have FTP clients to upload the images to my webspace.

Once I get my computer working again, I had every intention of rehosting the images.

I appreciate your concerns and will gladly give sources. Thanks also giving me the link to the actual post as I generally find the images from google's image search and not through the main page of sites.