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Using Light's Handedness To Find Alien Life
Rational Egoist writes "Scientists working at the National Institute of Standards and Technology have come up with a novel, easy way to detect life on other planets. Rather than try to measure the composition of atmospheres, they want to look at the chirality of light coming from the planet. From the article: '"If the [planet's] surface had just a collection of random chiral molecules, half would go left, half right," Germer says. "But life's self-assembly means they all would go one way. It's hard to imagine a planet's surface exhibiting handedness without the presence of self assembly, which is an essential component of life."' And they have already built a working model: 'Because chiral molecules reflect light in a way that indicates their handedness, the research team built a device to shine light on plant leaves and bacteria, and then detect the polarized reflections from the organisms' chlorophyll from a short distance away. The device detected chirality from both sources.' The article abstract is available online."
What if the aliens are ambidextrous?
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if you had to google chirality
What 'handedness' is earth? I think that because of the vast amount of life on our planet, the handedness would be (statistically speaking) about the same in both direction
As far as I know, all known life on earth is left handed (i.e. built from left handed amino acids)
What 'handedness' is earth?
I have no idea. But I'm not sure it matters. Even if Earth was perfectly neutral the method still works. If the presumption is true then any planet significantly away from average would indicate life. Even if it wouldn't find planets with life that were average.
Life on earth exhibits a specific "handedness" or chirality. All DNA twists the same way, for example. Apparently the term for this is homochirality.
http://en.wikipedia.org/wiki/Homochirality
CBC's science program Quirks and Quarks had an interesting story about the handedness of molecules that it played last month. (Audio available in Ogg Vorbis) It provides a nice, friendly introduction to this topic.
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The chirality ('handedness') of all known forms of life on earth is the same. Your enzymes can work on certain biomolecules but will not work on their mirror image (a molecule with opposite handedness). Once enzymes are fully formed to do a particular task, there usually isn't much selection pressure to evolve another enzyme to make the same products on mirror image biomolecules. As a result, handedness has been conserved throughout evolution and all organisms share the same handedness with respect to what forms of biomolecules they can process and produce.
So, to sum up the article... Chirality is not dead!
Smells of a "fund me, or PhD me" non-story.
Also possible: "Buy my freaking huge flashlights!"
Anyway, I guess a star would work as a light source to.
This just might work. It'll take incredibly good optics, of course, and the chirality of the light from these distant planets might be lost when the light goes through the earth's atmosphere. Might take a gigantic telescope in outer space.
The whole reason that life produced molecules of fixed chirality is that molecules precursing life are generated in cold gase nebulae that are often effected by radiation from young stars which have a particular chirality. That is to say, the cold nebulae that was the precursor of the Sol system, had light whose chirality precipitated right handed sugars and left handed amino acids.
A planet let's say, made of hydrocarbons and complex organic molecules that formed in such a cold dark nebulae, might have no life, but it's chemistry would in fact have fixed chirality. That is to say, someone needs to point the first instance of this instrument at Titan, a place where we are pretty sure no surface life (as we know it) might exist, but whose surface chemistry may very well have preserve some of the chirality of the nebulae that formed the Sol system. If we receive significant chirality frozen in the Titan surface, it would be a strong indicator that this test is less than optimal for finding earth like planets.
First, for those who are wondering "What the heck is chirality?". So, you have left handed gloves and right handed gloves, and you can't transform one into the other without doing something like flipping it through a fourth spatial dimension (strangely, flipping it through the time dimension will result in an opposite handed glove traveling backwards in time that's made of antimatter) or turning it inside out. Proteins, also being three dimensional objects, are the same way. And there is a convention for deciding whether a given molecule is right or left handed. Chemical processes tend to produce equal numbers of left and right handed versions. Biological processes on earth tend to produce almost exclusively right handed molecules.
I didn't know this before reading the article, but it makes sense... the chirality of a molecule apparently affects the polarity of the light that is reflected from it or transmitted through it.
Now, to talk about what I think of the article...
Scientists make too many assumptions. Life requires self-replication... that's it. It doesn't require water and it doesn't require chirality. It doesn't require a whole host of things that scientists tend to assume it requires simply because it's a characteristic we've observed about life on earth.
But, I will agree that if they can detect the predominance of one particular chirality then that's a strong indicator of some life-like process at work.
That absence of chirality is no indicator that there isn't life. It just won't resemble the life we have here on earth.
It may be possible to prove that self-replication within a given system (like chemistry, for example) is very hard without certain conditions. I'm willing to believe, for example, that non-carbon based life that primarily functions chemically is highly unlikely because carbon is such a fantastically versatile atom chemically speaking.
Of course, there might be life based on nuclear processes or, even farther fetched, life based on gravitational processes. As support for the second, galaxies have a very complex lifecycle in which supernovas and black holes play key roles. They eat the thin gas left over from the big bang, and metabolize it into new stars with supernovas and black holes. I'm not sure where self-replication fits into that picture so galaxies may just be metabolism absent a mechanism for self-replication (i.e. engines) and hence not really alive.
Life based on nuclear processes or gravity is certainly not going to exhibit any chirality signature, nor require water or even carbon.
But, as I said, I will agree that a chirality signature is strong evidence for chemistry based life. I just don't think its absence is strong evidence against life.
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If we can't actually go visit any aliens we detect because they are light years away, it is just going to drive us batty.
And I don't really want the aliens coming to visit us either, because that would mean they were more technologically advanced than humans. And the inferior species always seems to end up as food or raw material. Come on, even Hollywood has figured this out!
Surely this would be a good test to check out Europa?
Even though the ice crust might obfuscate things, if the light was from reflected from the area of a crevice/crack then there would be elements (or the lack thereof) in the frozen water that give some indication.
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You appear to be wrong on a few big things...
-most compounds are not chiral, so even if a dead planet had some pure enantiomers, they would be insignificant compared to one with life, life produces a crazy large amount of them
-no one has quite figured out why life has the handedness it does, some say it could be because of silicon catalyzing a certain handedness, others disagree, there is not an answer to this question yet, but it makes sense that life would evolve to have a specific handedness so all the parts could be interchangeable and we don't have bizzaro ecoli floating around that can exchange DNA with normal ecoli
-since when does polarized light catalyze chiral reactions?? UV light can catalyze reactions, and chiral molecules can cause a reaction to form with a specific handedness, but only chiral MOLECULES can catalyze reactions to cause a more enantiomericly pure product
...is that life forms a kind of amplification process.
If you have some random soup of molecules formed by abiotic processes then apart from some small biases brought about by parity-violating fundamental physics we expect complete symmetry between left- and right-handed molecules.
But life, arguably, forms a kind of amplification process. Competition between molecules with different chirality might serve to increase any initial small difference between one group and another. So what starts as almost exact symmetry results in a planetwide bias one way or the other.
But there are two issues.
(1) Could such a planetwide bias show up strongly enough in the polarisation of light reflected from the planet. It seems very unlikely given how messy a planet is. Let's say you pick a million different types of molecule than come in chiral pairs and for each molecule pick one of the pair, discarding the other. Now jumble up many different copies of each of these molecule types. Your chances of detecting chirality from afar is minimal even though, in some sense, the mixture is perfectly chiral, because of the overall randomness of the mixture.
(2) Could any other physical processes cause such amplification? The answer is yes. For example some kinds of crystal growth can result in homochirality.
So I'm pretty sceptical despite the idea being neat.
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-since when does polarized light catalyze chiral reactions?? UV light can catalyze reactions, and chiral molecules can cause a reaction to form with a specific handedness, but only chiral MOLECULES can catalyze reactions to cause a more enantiomericly pure product
Not quite, IIRC, there are examples of some reactions with polarized light which gives ~1% excess of one enantiomer. It has been hypothesized to be the origin of the handedness of life. But in itself, it will not give enough of a excess to be meassured with this technique.
I requested the full paper but... as we are friday afternoon here in Europe I'll probably get it on Monday ;-)
In the meanwhile, from the abstract I feel this'll be more applicable to say checking remotely life hints in Jupiter's atmosphere here, than getting answers for remote stars tomorrow.
I for one highly doubt, for instance, that just analysing an exoplanet's transit onto its star will bring any measurable polarization. ;-) it'll be very difficult to detect the ppm of added polarization.
Just remember what you see is star light that passed through the planet's *atmosphere*, not reflected onto its ground (and grass/trees).
And as this specific light is moreover buried within the 99,99% of starlight that just didn't cross the planet at all, even with a specifically intense *atmospheric* life (a dense, GREEN atmosphere
Rather, I see this either for
a) a futuristic payload for the (too futuristic) Darwin project from Esa/Nasa ( http://www.esa.int/esaSC/120382_index_0_m.html/ ), when the dozen of years of development (and equal number of euro and dollar billions) will have been invested: if things go well, no more crises, etc., we then will have a way to just switch the starlight off (via destructive interferometry), and see only planet's light.
Then maybe you'll measure polarization. But then you'll also measure specific wavelength absorptions, so get directly to molecules (which is the raison d'être of the Darwin project)
b) as said earlier, maybe in nearer times a way to observe our neighboring planets atmospheres, and suddenly discover they may be polarized (or not, and that check will be quick).
If they were it'd definitely be fun.
In my space factory there is a breadboard of the Darwin nulling interferometric concept. Nifty. Representing maybe 1% of the required development work. But nifty, definitely: capable of switchig off a star light that is millions of times superior to the planet's reflected light and at the same time leave planet's light in, when planet is just the pixel against the star's one. As they say on Esa's site, capable of seeing a candle light stuck against a lighthouse firewindow, from 1000 km away.
Herve S.
This is the basis for creating artificial sweeteners. Sucralose contains mostly dextrose, which is a mirror image of glucose. They have the same chemical formula, but since it's of the opposite chirality of all the other structures in your body it's unable to be metabolized.
The body can metabolize dextrose (d-glucose) just fine (in fact, it's the l-glucose that the body cannot metabolize). Sucralose, on the other hand, is a different molecule since it contains chlorine atoms in some of the places where sucrose contains HO groups. Sucralose is also about 600 times sweeter than sucrose.