The centaur graphic heading up this week’s blog is such a piece. It illustrates a cool new result that clears up a decades-old mystery over some of the smallest objects in the Solar System that intermingle with some of the largest.
If you’re curious how the whole science-to-art process works, then please read on…
The Centaur Mystery
To astronomers, centaurs are not half-human/half-equine creatures of myth, but are a very real class of small bodies whose orbits fall amongst the gas giants in the outer Solar System. “Small body” may not be particularly descriptive, but part of the mystery surrounding these objects is whether they were rocky, like asteroids, or icy, like comets, or perhaps a mix of both.
The taxonomically-mixed name “centaur” was a nice fit the dual nature of these objects.
So if these objects are not long-term residents like the more stable asteroids or Kuiper belt the obvious question is from whence do they come? Are they somehow migrants from the asteroid belt that have made their way out past Jupiter’s orbit? Or are they more like ice-rich comets that have worked their way in from the outer Solar System? There is evidence for both kinds of objects, but it is notoriously difficult to study small objects so far out.
The Wisdom of NEOWISE
“Notoriously difficult” is not the same thing as impossible, and expanding one’s observations to include infrared light turns out to be a key to learning more. The centaurs have surrendered some of their secrets to the NEOWISE phase of the WISE (Wide-field Infrared Survey Explorer) mission. This infrared satellite orbiting the Earth completed a year-long survey of the sky, and the database of its observations continues to serve up some interesting science.
In a recent study of the infrared properties of centaurs, comparing the NEOWISE data to existing visible light observations, the researchers were able to get a better handle on the “man/horse” fraction, as it were.
It seems that about two-thirds of centaurs are actually comets! I’ll leave it an exercise to the reader to decide which half of the beast that represents in this increasingly overextended metaphor.
From Science to Art
The new understanding of these mystery objects warranted a release at NASA/JPL, and that’s when our group came into the picture. The IPAC Communications and Education (ICE) team originated as part of the Spitzer Science Center, but we work closely with a number of missions, including NEOWISE, to help develop visualizations to make the science exciting and understandable.
The first step is to brainstorm. In this case, all of the key players were local so an afternoon caffeine run was a perfect venue to bring together a couple of the principle investigators (James Bauer & Amy Mainzer), our JPL media rep (Whitney Clavin), and the viz side of the ICE group (Tim Pyle and me).
I like to try to break the result, and the resulting news story, down into bullet points. From those we can identify which are most easily incorporated into the visuals for the story. For this one:
- there is a population of objects known as “centaurs”
- they fall between the orbits of Jupiter and Neptune
- there are likely two distinct populations, both asteroid-like and comet-like
- the name derives from the split nature of the population
- NEOWISE finds they are about 2/3 cometary in nature
- combining visible and infrared data facilitates identification
Ideally we would develop one image that would capture all of these points clearly and in a visually stunning way. In reality, we generally have to concentrate on a couple key points to keep the illustration simple enough to understand .
Ultimately the goal is to develop an image that is visually appealing enough to make someone curious about the article, and give them enough visual reference that they have an easier time understanding it.
It’s kind of like making a movie poster… for science.
The image also has to work, even if it is shrunk down to a tiny inline graphic on a web page, so too much detail can be a hindrance.
We started by discussing some obvious concepts. One early idea was to show a kind of split screen view of something that was an asteroid on one side and a comet on the other. It is a simple way of communicating a duality, but we had done something similar recently for planets that might or might not be habitable and thought it was too soon to repeat that design.
We also considered how one could put the centaurs into a geographic context, falling between the orbits of Jupiter and Neptune. However, concerns over exaggerated scales, and difficulties in showing the two populations clearly made that seem untenable. If they were just mixed together it might be difficult to see there were two different kinds of objects. But if they were segregated into two halves, it might seem we were implying that the asteroids and comets fell into distinct bands.
Then someone tossed out the delightfully obvious idea of showing a mythological centaur. We all pretty much fell in love with the idea right away. People are accustomed to seeing mythological creatures in the sky because of the constellations, and adding an abstract element like that allows us to separate the populations along a division that is clearly artistic, not geographic.
Bringing a Centaur to Life
Tim started work on the graphic, and I took on the role of art/science direction. Part of my job was to make sure Tim had good reference material for the appearance of asteroids and comets.
Fortunately there are now so many wonderful images of cometary nuclei from various flyby missions it was easy to come up with a meaningfully accurate representation (though admittedly we exaggerated the amount of outgassing that would be happening so far from the sun). Interestingly, comets actually have a pretty counter-intuitive appearance. While we think of them as dirty snowballs, they are more like snowy dirt-balls that are almost sooty black. As their ices evaporate they leave behind all the dark grit, looking a bit like weeks-old snowfall in a Manhattan gutter. Not very pristine.
In contrast, asteroids are known to have a reddish hue. So the two populations are visually pretty easy to distinguish.
Of course the real trick was how to do the centaur.
It was easy enough for Tim to find a 3D horse mesh to work with, but we all thought it would be less cartoony and more engaging if we could use a real human for the graphic. Fortunately I had a friend training for a triathlon who was happy to help out the cause of science (thanks CB!). I set up a quick photo shoot to match the layout of the graphic and Tim blended it seamlessly onto the digital horse.
Shooting a real horse would have been nice too… but the logistics of that were a bit too complex to imagine!
We made sure our centaur was looking right at a comet, to connect to the overall result, then celestialized it all a bit to make it look more etherial. And the result is (hopefully) a memorable piece of science-inspired art that makes you want to know more!
PS – Bringing NEOWISE Back to Life
In a fortunate turn of events, NASA has just announced plans to reactivate the WISE spacecraft (which has been in a dormant stand-by mode since 17 Feb 2011) in order to continue its NEOWISE mission. Early feedback from the sleepy spacecraft look promising for a full return to duty.
Look for a better understanding of asteroids and centaurs in the coming years!