Using Light's Handedness To Find Alien Life 210
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."
Re:How about earth? (Score:5, Informative)
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)
Re:How about earth? (Score:5, Informative)
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 [wikipedia.org]
Quirks and Quarks Had a Good Story about This (Score:5, Informative)
CBC's science program Quirks and Quarks had an interesting story about the handedness of molecules [www.cbc.ca] that it played last month. (Audio available in Ogg Vorbis) It provides a nice, friendly introduction to this topic.
Re:How about earth? (Score:3, Informative)
Life Jim, but not as we know it! (Score:5, Informative)
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 [wikipedia.org] 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.
Re:One problem (Score:4, Informative)
Then this scan won't find them and no preemptive Relativistic Kill Vehicle [wikipedia.org] will be dispatched to their planet.
Re:I'm skeptical.... (Score:5, Informative)
-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
Re:I'm sceptical.... (Score:2, Informative)
According to this article (http://asunews.asu.edu/20080229_pizzarello [asu.edu]), an un-contaminated meteorite was was found to have amino acids with mixed chirality, but with a bias towards the left-handed (up to 15%), not the 50%-50% suggested in the article linked in the submission. So to some extent, this supports what you said.
Even so, the technique described in the submitted article could work. It's all about signal to noise. If some feature of a planet reflects vastly more chiral bias than a rocky moon or asteroid in the same system, that could indicate that it harbors life.
Re:I'm skeptical.... (Score:3, Informative)
-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.
Re:How about earth? (Score:4, Informative)
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.
Re:Define "Short Distance" (Score:3, Informative)
Parent is abrasive, but I think his point is probably correct.
I'm not an astronomer - but I'm a biologist and we do circular dichroism measurements on biological samples (wikipedia article is good enough: http://en.wikipedia.org/wiki/Circular_Dichromism [wikipedia.org]).
The notion that you could detect these signals from an exoplanet lightyears away - given that we can't, at the moment, detect light from such planets at all - strikes me as somewhere between far fetched and complete bullshit.
On the other hand, as a device on a mars rover (or even a satellite probe, maybe, although I doubt this would work through the atmosphere) this makes a lot of sense. So tag this as xenobiology rather than astronomy and we're maybe okay. Can't say more without reading the actual paper.