Somewhere, over the rainbow, far far away
November 7, 2012 2:49 AM   Subscribe

The light from a primary rainbow is partially polarised. Now, in a paper accepted by the journal Astronomy and Astrophysics, the authors show how to use the weak signal from rainbows in starlight reflected by exoplanets to detect the presence of liquid water clouds. [arXiv preprint link]
In particular, liquid water clouds covering as little as 10%-20% of the planetary surface, with more than half of these covered by ice clouds, still create a polarized rainbow feature in the planetary signal. Indeed, calculations of flux and polarization signals of an exoplanet with a realistic Earth-like cloud coverage, show a strong polarized rainbow feature.
posted by Talkie Toaster (21 comments total) 22 users marked this as a favorite
Bloody hell, that's good.

In old skool science fiction it was always assumed that visiting planets around other stars would be easy, because of hyperspace and you had 2-3 men (girls can't be astronauts, don't be silly) exploration teams pootling around in souped up V-2s, but knowing where to look for them would be hard.

Instead now we're getting closer and closer to the point where we can accurately show what a planet around a foreing star looks like, but will likely never be able to visit it...
posted by MartinWisse at 3:07 AM on November 7, 2012 [1 favorite]

Maybe it's aliens watching 3D movies?
posted by iotic at 3:44 AM on November 7, 2012

That's a stroke of genius right there.

Somebody needs to write about how that particular idea came into being.
posted by flippant at 3:45 AM on November 7, 2012 [2 favorites]

ATTENTION SCIENTISTS, please confirm life on exoplanets before I die. I'm planning on living for a long time, so you've really got no excuse. Thanks in advance <3
posted by anaximander at 3:58 AM on November 7, 2012 [2 favorites]

The U.S. election season is over already. Can we stop it with these polarizing posts based on light substances?
posted by ardgedee at 4:19 AM on November 7, 2012 [10 favorites]

Obviously, THIS is why there are so many songs about rainbows.

Because alien songwriters are right there pitching in.
posted by jfwlucy at 4:46 AM on November 7, 2012

We didn't know about any exoplanets when I was a kid, and now we have 843. I'm pretty chuffed about this. Now onwards to extraterrestrial life!
posted by Harald74 at 4:47 AM on November 7, 2012 [2 favorites]

The special rays of starlight rainbows bring messages from the snowflake clouds on faraway worlds where new friends may be hiding.

That's nice.
posted by Segundus at 5:17 AM on November 7, 2012 [2 favorites]

The Melnorme will be pleased to learn the locations of all these Rainbow Worlds
posted by qxntpqbbbqxl at 6:54 AM on November 7, 2012 [3 favorites]

Don't forget the LinksToTheDamnPaper tag!
posted by Blasdelb at 7:19 AM on November 7, 2012

I'm feeling amazed and humbled that someone conceived the idea and flabbergasted that they could quantify the polarity of the rainbows in starlight.
posted by bonobothegreat at 7:36 AM on November 7, 2012 [1 favorite]

Don't forget the LinksToTheDamnPaper tag!

Done. I merely forgot to remember...
posted by Talkie Toaster at 7:48 AM on November 7, 2012 [1 favorite]

Hmm.. I recall a vaguely similar recent effort, during the transit of Venus. Some clever astrophysicists observed the thin atmospheric layer of Venus as it passed over the limb of the Sun. They measured the spectra and the refraction of the limb as it passed behind the atmosphere. I was impressed at the whole idea, but I haven't heard any results yet. I think Bad Astronomer published the report I saw.
posted by charlie don't surf at 8:09 AM on November 7, 2012

We will get to and explore the exoplanets - if by we, we include "AIs in century probes with deep sleep in cruise". Scant comfort for this generation of short-lived, high-maintenance planet dwellers, but we shouldn't begrudge future generations the chance to take what we give them but they cannot get for themselves.

Meanwhile: chasing rainbows across the universe? Astronomy, will you stop being so massively awesome, just for a bit?
posted by Devonian at 8:25 AM on November 7, 2012

You're just a picture
You're an image caught in time
We're a lie, you and I
We're words without a rhyme

There's no sign of the mornin' comin'
You've been left on your own
Like a rainbow in the dark
Just a rainbow in the dark
posted by cmoj at 8:33 AM on November 7, 2012

The idea is awesome, that sounds so minimizing, the idea is so crazy, but in some measure what impresses me the most is that they have equipment that can register and distinguish on this scale (which I imagine to be pretty damn minute).

I swear there's an acceleration of smarts these days, like when they first realized that distributing the computing across many different processors running in parallel increased the amount of calculating that could get done at any one time. I swear it is getting to the point that when they come up with 'ok, we figured out how to build a wormhole hole and use that to look at the other side of the universe' I'm going to be less gob-smacked than I would have been ten years ago.
posted by From Bklyn at 8:50 AM on November 7, 2012

Auguste Comte, 19th century philosopher and arguably the first true philosopher of science (coiner of 'altruism' and God(less)father of secular humanism, interestingly), mentioned the composition of the stars as a thing humans could never know [not included in link].

I find it hard not to sympathize with him given the state of understanding at the time, but the triumphs of astronomy continue to drive me to my knees in abject amazement every other week.
posted by jamjam at 9:32 AM on November 7, 2012 [1 favorite]

That might be a useful tool for the trick bag ... the hairy part might be proving that the light isn't being polarized by some other phenomenon.
posted by Twang at 3:39 PM on November 7, 2012

I learned this when trying to snap a photo of a rainbow with a circular polarizer on my camera. At certain axes, the polarizer made the rainbow disappear. (In the viewfinder. It remained apparent in the sky.)
posted by gjc at 7:26 PM on November 7, 2012

Yeah gjc, there are great tricks you can do with a polarizer, I used to always keep one on my camera, even though it would cost you 2 f stops. Back in the pre-Photoshop days, I would always shoot landscapes with a polarizing filter. Diffuse light from blue sky is slightly polarized, just give a little twist to the polarizer and the blue sky darkens slightly and intensifies a bit. People used to ask me how I got the skies such a perfect shade of blue. Later in my career, as a digital photo retoucher, I was known as the "sky guy" who could take your washed out, smoggy grey Los Angeles skies and make them look natural.
posted by charlie don't surf at 11:33 AM on November 8, 2012

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