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."
Scanning for lifesigns (Score:2, Interesting)
One more trek concept brought to real-life, yay! (The other one being the communicators on TOS)
- AC, patiently waiting for warp drives
I'm sceptical.... (Score:5, Interesting)
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.
This is all well and good, but... (Score:4, Interesting)
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!
A sufficient, but not necessary condition for life (Score:3, Interesting)
I suppose that if you were to detect chirality bias in the light coming from a particular planet, that would probably be sufficient to conclude that there might be some form of life on that planet that was causing that particular bias. However, it doesn't seem that it's a necessary condition, i.e. not detecting chiral bias might mean that there might after all be some very strange life form on the planet whose chemistry made use of both left and right handed molecules. In fact, there are some strange life forms on Earth, notably archaea [wikipedia.org], that actually use right-handed proteins in some aspects of their biochemistry, quite unlike all other life forms found on earth, which use left-handed proteins exclusively.
Re:How about earth? (Score:1, Interesting)
>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.
The fact that all life on earth comprises molecules of the same handedness is one of the myriad of strong pieces of evidence that the theory of evolution is correct in its prediction that all species evolved from common ancestors. The chirality of the basic molecules of life just has to be THE most fundamental characteristic that any lifeform can have. The fact that all life on earth is composed of molecules of the same chirality is a reasonable indicator that all life on earth is descendent from a common set of primodorial self-replicating molecules ... possibly even just the one molecule that started it all off.
Re:One problem (Score:1, Interesting)
You know that's a terrible idea, right? The only situation in which a "pre-emptive" RKV would ever make sense is if you know there's only one other civilization in your segment of the galaxy, and that this civilization is not significantly advanced beyond you.
Asimov's "angels and apes" observation ruins the latter. Just by probability alone, virtually any species we encounter will be either millions of years behind us, and thus no threat during our species' lifetime, or millions of years ahead of us, in which case their civilization will most likely not be entirely planet-based, and retribution would soon be at hand.
It's even worse if there are other civilizations out there, undetected. Virtually any RKV is going to be detectable over great distances due to EM radiation, especially infrared. This means that other civs will see the red-hot launch, and see the kinetic effects of the impact, and they will know what we have done. Even if we hide the launch, plain old Newtownian measurements will give them a good line towards the launch point.
They may decide that such a vicious little species is too dangerous to live, and prepare to wipe us out in a more untraceable, or even more unsurvivable fashion.
As soon as we launched an RKV, we'd have to start evacuating Earth, and we'd have to spend the rest of our existence running and hiding, digging into the asteroid belts and trying not to emit detectable heat signatures, lest some civ millions of years beyond our own decides to launch hundreds of RKVs, or worse.
- mantar
The assumption here... (Score:4, Interesting)
...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.
Re:I'm skeptical.... (Score:3, Interesting)
-no one has quite figured out why life has the handedness it does
I recall a theory that it is due to the slight asymmetry in weak interaction, but I've forgotten the exact mechanism. This asymmetry exists basically everywhere in the universe, but as life is self-replicating, it can amplify the effect to a great extent. Here's the first reference found via quick googling:
http://www.springerlink.com/content/0743577n4716u23j/ [springerlink.com]
Re:One problem (Score:3, Interesting)
The problem is that anything above a certain cross-sectional are will probably just disintegrate at 0.99c. At a velocity like that, even the vaccuum of space suddenly becomes quite dense. Heck, you might even run into problems with vacuum energy.
Re:I'm skeptical.... (Score:3, Interesting)
Also, don't forget racemization (http://en.wikipedia.org/wiki/Racemization) - a lot of enantiomeric compounds can spontaneously switch chirality (it's actually a big problem for some extremophile bacteria - they replicate so slowly because they have to expend energy to repair damage from racemization).
Re:One problem (Score:2, Interesting)
You then launch a Bussard Ramjet to nuke the planet. The spacsehip builds a Krasnikov Tube as it goes.
Whoa, hold on for a minute. The energy required to distort space enough to form a Krasnikov Tube is _huge_. There's no way to accelerate something to 0.99c _and_ form a Krasnikov tube behind it using just a Bussard ramscoop. In fact, it might be impossible just to accelerate to 0.99c without a supplementary power source.
I think this is far too ruthless for humans to do and in any case the technology involved is highly speculative and some parts of it are probably not possible, but who says we're the nastiest species out there? Maybe there are much nasier civilisations with the requisite technology.
Why should a species with access to technology like this limit itself to colonizing previously-inhabited planets? They don't have to care about less-developed civilizations - they could simply pwn the whole galaxy within a few million years or so.
Actually you'd don't need the Krasnikov tube. The whole civilisation could travel in Bussard Ramjets. Why do it? Why invade countries for gold, oil or slaves when you could stay home and live sustainably?
Everything is about resources. In my hypothetical planet hopping civilisation planets provide the resources to build more ramjets. You'd send down engineers and machines, they'd strip the planet and turn it into another ships. The reason you target planets with technically advanced civilisations is that they by definition have the resources you need. Maybe you need to fight wars for ideological reasons too or the people in power might want the glory of 'civilizing the barbarians' or making them worship the right god.
It's not like human civilisations have never done this on Earth. In fact pretty much every famous civilisation was to some extend imperialist and didn't just stay home and live sustainably. Maybe there are predator civilisations and prey ones and the predatory ones more fit in Darwinian terms - i.e. they spread more widely, consume the prey and end up writing the history books and portraying themselves as superior.
Certainly the Europeans and Americans have historically been highly predatory and have obliterated scores of more peaceful but 'inferior' civilisations here on Earth. Why is a stretch to think that you couldn't do this on a bigger scale?
Something else occurs to me - you could build lots of Orion type craft to get the loot into orbit since you don't care about the biosphere after you leave. Once in orbit you build a ramjet and head off with lots of new ships plus anything of value (resources or slave labour) from the planet you sacked.
Maybe on Nasa/Esa Darwin project? (Score:5, Interesting)
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/ [esa.int] ), 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.
Re:One problem (Score:3, Interesting)
Why do it? Why invade countries for gold, oil or slaves when you could stay home and live sustainably?
The question is reversed in our case. Why go through all the trouble of exterminating less advanced civilizations, when the planet they're on only contains a tiny fraction of the "resources" in their solar system?
In my hypothetical planet hopping civilisation planets provide the resources to build more ramjets. You'd send down engineers and machines, they'd strip the planet and turn it into another ships. The reason you target planets with technically advanced civilisations is that they by definition have the resources you need.
The rest of their solar systems contains a couple of orders of magnitude more resources. Why ignore them?
It's not like human civilisations have never done this on Earth. In fact pretty much every famous civilisation was to some extend imperialist and didn't just stay home and live sustainably.
It's not about living sustainable. The approach I suggest is far from that, it's about colonizing the whole galaxy (exponential growth is, by definition, not sustainable in the long term).
Certainly the Europeans and Americans have historically been highly predatory and have obliterated scores of more peaceful but 'inferior' civilisations here on Earth. Why is a stretch to think that you couldn't do this on a bigger scale?
Because on Earth, 'inferior' civilizations were densely packed. In the galaxy, you'd have to spend way too much time and effort to track them down. Just start colonizing everything and quarantine every inhabited planet you find (make it a big zoo or something). You'll end up with a couple of orders of magnitude more resources than if you focus on plundering inhabited planets.
Something else occurs to me - you could build lots of Orion type craft to get the loot into orbit since you don't care about the biosphere after you leave.
If you stick with uninhabited planets, you won't even have a biosphere to deal with (so no risk at all of any kind of contamination). In fact, if you stay away from large gravity wells, sending more stuff into space will get even easier.
Re:How about earth? (Score:3, Interesting)
Why is that obvious? It seems obvious that left and right handed molecules should be useful for different things like the Z and S blocks in Tetris, but why should one be discarded entirely?