A Fine Aerosol Diagram

New results from the Cassini spacecraft reveal the chain of events (so to speak) that leads to the formation of complex aerosols in its atmosphere. Aside from the spiffy science, the NASA announcement includes the very nice diagram pictured above.

What I like about the graphic is that it tells the story very plainly and simply, yet with considerable detail and substantial visual interest: nice little PAHs and aerosols, decent image of Titan’s surface, Saturn in the background (tilted too much with respect to the ring plane, but that’s nothing new), and so on. It even includes altitude info on the right-hand side clearly indicating where specific processes take place. All in all, a lot of info packed into a single image.

And anther detail. I’m already on record as not being a fan of lens flares in the fulldome environment, and in general, I seem them as kind of cheesy. But this might be the first time I’ve seen a lens flare used as a didactic element, suggesting the flow of photons from the Sun. Nice touch!

The only thing that gives me pause is the depiction of “energetic particles” as little arrows pointing away from Saturn. The particles are trapped in Saturn’s magnetic field, so they aren’t really shooting out of the planet in straight lines, which makes that depiction a little deceptive. But then, the only real solution would be to depict Saturn’s magnetic field with particles streaming from it, and that might be a little cumbersome. So I suppose I can forgive the diagrammatic shorthand.

Another more mundane quibble. The NASA webpage for the diagram include links to smaller versions at 1600×1200, 1028×768, and 800×600, but those are all windowboxed versions of the (obviously portrait, not landscape) diagram. Thus, the only version of above image that you can download at its original aspect ratio is the full-resolution version: a whopping 2000×2776 pixels! Not the greatest for, say, linking to blog entries.

Anyway, nice work, Cassinifolk! I like the diagram. And the story it tells…

Subjective Lakes

A Cassini press release describes the identification of lakes on the surface of Titan, the large moon of Saturn’s visited by the Huygens probe a couple years back.

The image above shows a false-color representation of radar data, with low backscatter color-coded black-to-blue. I recently blogged about so-so use of false color, but I think the above image does a pretty good job. N.B., however, what the choice of color stretch is doing here. The transition from the warmish colors to the cool blue and black guides one’s eye to “read” the transition as being from solid land to liquid lakes. But we’re trusting the visualizer of the data to have performed that stretch correctly (or I should say, honestly).

This is an excellent example of how images—even those based on data—incorporate subjective elements. The eye perceives the color difference as stark and distinct, but the actual difference in pixel values might be quite small, so the color choice communicates a lot of information in this case. I’m not saying the image is lying or anything; I’m just saying that the image does not give anything near an objective sense of the data.

(There is no such thing as an objective image!)

The results are also reported in the current issue of Nature.

In Saturn’s Shadow

It’s tempting to do a simple report from the Astro-Viz ”06 workshop, since we’re starting to have conversations that might be of interest, but David Malin distracted me by presenting the above image as part of his keynote address this morning.

The Photojournal description of “In Saturn’s Shadow” tells us that the image “was created by combining a total of 165 images taken by the Cassini wide-angle camera.” We can see light scattered through the rings, as well as light cast on the dark side of the planet by the rings themselves. Obviously, one gets a sense of the extended nature of the rings as well.

“Color in the view was created by digitally compositing ultraviolet, infrared and clear filter images and was then adjusted to resemble natural color.” A sentence that gives me pause. I appreciate the description, but I’d like a little more detail (even if I think I can piece together what’s going on anyway). And the annotated image doesn’t help.

The corresponding page from the CICLOPS site provides a little more detail, describing color variations in the E ring in the “color-exaggerated” image above. Maybe there could be a link to a page describing what “color-exaggerated” means? Basically, I think they’re just trying to acquire a longer baseline (in terms of wavelength, stretching from ultraviolet to visible to infrared), thereby enhancing color contrasts.

Spiffy image, that’s for sure. Very spiffy. And it speaks to one of the points Malin made this morning: that compelling images can simply make one look more closely and phenomena, which excites curiosity and promotes thinking about the cosmos.

Speaking Warmly of Saturn

Okay, this just proves I’m a whore for astronomy images. I’d already started writing something about PET scans in relation to today’s story about the long-term effects of chemotherapy on brain function, but then I saw the press release for the above image.

In spite of the mediocre resolution (mostly because it’s a composite of infrared mapping spectrometer, which operates in a scanning, single-pixel-at-a-time mode), the image rather intuitively communicates the idea of seeing ”through” Saturn’s clouds.

As described in the caption from JPL, we’re looking at a near-infrared image of Saturn, in which the shorter-wavelength light (shown as blue-to-green) is reflected off the cloudtops whereas the longer-wavelength emission (colored red) from Saturn’s warm interior shines through in shadowed regions, less obviously in the daylit regions. Because most people (stellar astronomers excluded) think of red as warm and blue as cool, this image capitalizes on people’s natural sensibilities. Always a good thing.

This strikes me as a good image to talk about some of the confusing aspects of infrared light, which well-informed people typically perceive simply as “heat,” because that’s what they’ve been told. Of course, the problem with blackbody radiation is that there’s a big contrast issue: yeah, the lower layers of Saturn’s atmosphere may be warm, but their infrared glow gets blocked by clouds in the upper atmosphere, plus it has to compete with the bright, reflected glare of the Sun. The image above allows one to talk about those contrast issues while clearly conveying that infrared light allows us to see things we can’t in visible light. Also, the rings cut across the center of the image as a blue line, indicating that they reflect the short-wavelength infrared light but don’t emit much thermally—pretty much as one would expect from chilly rings made mostly of ice.

Speaking of a Pale Blue Dot…

I referenced this image in my Yahoo 360 blog, but it’s worth presenting again. Taken by the Cassini spacecraft (currently in orbit around Saturn), it shows Earth as a point of light viewed through Saturn’s rings. You can read more about the image on NASA’s Cassini page. As Carl Sagan wrote, regarding a similar image: “Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.”