It’s Not All Black And White

“So what you guys are telling me is that all those pretty astro‑pictures are faked by being gray‑scale to start with and someone comes along to say ‘This is red‘ and ‘That’s blue.’ Why should we believe any of it?”

“Because those decisions aren’t arbitrary, Mr Feder. Well, most of them. Do you remember one of Al’s Crazy Theories events when you asked about the color of Mars?”

“Yeah, the guy said it’s brown except for the rusty bits floating in the atmosphere. So what?”

“So have you seen Matt Damon’s movie The Martian?”

“Sure. I can’t see a potato without gagging a little.”

“Remember how red the exterior views were? When Watney was driving his rover across Mars, the color scheme was downright crimson, wasn’t it? Does that match the pictures we’ve seen from our real Mars rovers?”

“Sure not. So which one’s right?”

“I hate to say this, but it depends on who’s using the word ‘right’ and in what context The science says ‘shades of brown,’ loud and clear with data to back that up. Camera‑equipped Mars rovers carry color‑calibration patches so we can produce accurate renditions of what the rovers saw — shades of brown. Spectroscopy from satellites in space and analytical tests by rovers on the surface agree that rocks up there chemically match rocks down here. We know what our rocks look like — shades of brown.”

“You say that like there’s a ‘but‘ coming.”

“Mm-hm. It’s called ‘artistic license.’ When The Martian was being filmed consulting scientists said the Mars scenes needed to be brown. The director insisted on red because it ‘looked right’ for the mood he was trying to get across. Besides, after a century of Mars‑based science fiction the public expects red.”

“It’s worse than that, Catherine.”

“Why’s that, Sy?”

“It’s not just the public. Initial prints of Viking‑1‘s first‑ever in‑color Mars surface views had a reddish cast. They looked fine to NASA’s leadership who expected red anyway. The PR team distributed the prints before the image‑processing team completed their signal checks against the calibration patches. Turned out that the red signal channel had been over‑weighted. The trued‑up images show brownish dirt and rocks under a purplish sky. You can find both versions on the internet if you look around enough. A properly color‑balanced Martian sunset looks blue where Earth’s are red.”

“Well, what about pictures we got from other places, like that poster of Jupiter Al had up with the poles all nasty red?”

“That’s where the colors can really get arbitrary. It’s considered bad form to tinker with the underlying gray‑scale data, but the bridge from there to a colored‑in visual image is a matter of taste, judgement and what the researcher is interested in. IF it’s a researcher — some gorgeous amateur‑created images have been done simply for the sake of beauty and that’s OK so long as the intent is made clear. For research purposes there’s basically two ways to go. OK, three. One is if you’ve got just one image, let it alone or maybe enhance the contrast. We astronomers rarely stop at one, though. We use filters or other wavelength selection gadgets to create multiple tailor‑made gray‑scale images.”

“What’s that get you?”

Jupiter’s poles in IR — images credit
NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM

“A temperature scale, for one. Thanks to the Planck curve we have a straightforward relationship between an object’s continuous spectrum and how hot it is. The Juno mission carries a mapping spectrometer, JIRAM, that can capture a near‑infrared spectrum from each pixel in its field of view. That’s the data that NASA’s people used to calculate the heat maps in Al’s poster.”

“What else?”

“Each kind of atom has a unique spectrum in the visible and UV. If a vis-UV mapping spectrometer shows pixels with sulfur spectra, you know where the sulfur is. I’ve seen lovely maps of different atomic species that have been expelled by supernovas.”

“That’s what we’re gonna get from the Webb?”

“Not quite. Atoms don’t do much in the infrared range that JWST is instrumented for. That’s where molecules absorb and emit. There’s a lot of exotic chemistry out there and we’re finally going to be able to see it.”

~~ Rich Olcott

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