Posted on 08/24/2005 10:16:24 PM PDT by LibWhacker
Space radiation preferentially destroys specific forms of amino acids, the most realistic laboratory simulation to date has found. The work suggests the molecular building blocks that form the "left-handed" proteins used by life on Earth took shape in space, bolstering the case that they could have seeded life on other planets.
Amino acids are molecules that come in mirror-image right- and left-handed forms. But all the naturally occurring proteins in organisms on Earth use the left-handed forms - a puzzle dubbed the "chirality problem".
"A key question is when this chirality came into play," says Uwe Meierhenrich, a chemist at the University of Nice-Sophia Antipolis in France. One theory is that proteins made of both types of amino acids existed on the early Earth but "somehow only the proteins of left-handed amino acids survived", says Meierhenrich.
Meierhenrich and colleagues have a different theory. "We say the molecular building blocks of life were already created in interstellar conditions," he told New Scientist.
The team believes a special type of "handed" space radiation destroyed more right-handed amino acids on the icy dust from which the solar system formed. This dust, along with the comets it condensed into, then crashed into Earth and other planets, providing them with an overabundance of left-handed amino acids that went on to form proteins.
Magnetic alignment
The radiation is called circularly polarised light because its electric field travels through space like a turning screw, and comes in right- and left-handed forms.
It is thought to be produced when dust grains become aligned in the presence of magnetic fields threading through regions of space much larger than our solar system. Circularly polarised light is estimated to make up as much as 17% of the radiation at any given point in space.
In 2000, an experiment showed that when circularly polarised ultraviolet light of a particular handedness was shone on an equal mix of right- and left-handed amino acids, it produced an excess of 2.5% by preferentially disintegrating one type.
But that experiment was done using amino acids in a liquid solution, which behave differently than those in the solid conditions of icy dust in space. To avoid absorption by water molecules, it was also necessary to use light at a wavelength of 210 nanometres – significantly longer than the peak of 120 nm radiation actually measured in space.
Biased meteorites
Now, Meierhenrich's team has performed a similar experiment. The group shone circularly polarised light at a wavelength of 180 nm on a solid film of both right- and left-handed forms of the amino acid leucine. It found that left-handed light produced an excess of 2.6% left-handed amino acids.
"Going towards greater realism by exploring another wavelength of light and solid samples is definitely a good thing and a logical step forward," says chemist Max Bernstein of NASA's Ames Research Center in California, US, who is not part of the team.
He says the research adds to previous measurements of an excess of left-handed amino acids in two meteorites. "If it is thanks to meteorites that our amino acids are left handed, then the same bias should exist at least across our solar system", he told New Scientist.
Alien life
But other solar systems may harbour right-handed amino acids if they are subjected to the other type of circularly polarised light, says Meierhenrich.
"The chiral amino acids might have been delivered to other planets, to other solar systems," he adds. "The probability that life arose somewhere else is increased with this experimental result."
Meierhenrich will continue to reduce the wavelength of the experimental radiation by using a synchrotron facility, due to begin operating in 2006. But the real test of his theory may come in 2014, when the European Space Agency's Rosetta spacecraft lands a probe on Comet 67P/Churyumov-Gerasimenko.
He designed an instrument for the lander that will measure the handedness of any amino acids it finds. "If we identify left-handed amino acids on the cometary surface, this would underline the hypothesis that the building blocks of proteins were created in interstellar space and were delivered via comets or micrometeorites to early Earth," he says.
placemarker for reading tommorow
Of course, when an experiment can actually be performed to generate actual data, this may then qualify as actual science! As it is, it's just another model, just like all the globaloney models we're supposed to ruin our economy for! Just because a model seems realistic doesn't mean it actually reflects reality. I had a very realistic model of Ultra Man when I was 10.....but sadly, he's not real either.
they are just passing the problem elsewhere, OK so how do they explain why space would choose to have only predominately one sense of polarization to produce only one sense of amino acids?
Still waiting for the basic answer why only one sense of amino aids (or in this case polarized light) in all biological life when in nature there exits two to choose from, there should be 50% diversity between left and right, if the process was truly random ...?
Only one direction of polarised light effect in our area of the galaxy is what I think they are getting at
Yes, that was my thought also. Indeed, I am much more skeptical about postulating chirality of radiation than of chemical compounds, so the problem seems to have been made bigger.
When you boil it down, there are only three natural explanations of a perceived asymmetry: an intrinsic asymmetry in physical law - and that dog fer sure won't hunt - an existing prior asymmetry, and a spontaneous symmetry breaking.
Well, the Earth does have two known asymmetries - its direction of rotation and the polarity of its magnetic field. The former raises an immediate problem - best illustrated by the old "water down the toilet" joke - any asymmetry in the northern hemisphere would surely require the opposite asymmetry in the southern. So maybe, just maybe, the chirality happened at a time when one hemisphere was ocean and the other land, so only the left-handed guys made it. That hypothesis is testable once we have enough evidence about past continental drift.
But the combination of rotation and magnetic polarity creates a true asymmetry. The problem there is that we have no mechanism for how the earth's magnetic field could affect chemical composition.
So for now, I fall back on spontaneous symmetry breaking. Start with a world half full of primitive L critters, and half full of their R mirror images. As we know, L must eat L, and R must eat R. But you can't tell them apart - not if you're a primitive cell.
Now a random event - maybe a tsunami - tips the balance to 51% L and 49% R. The L's are now slightly more successful at eating, because 51% of what they find is useful food. This advantage magnifies over time, until all the Rs have starved.
Again, verifiable in principle if we could find some primitive microfossil with the opposite handedness. Way, way back in time, so not much chance; but not zero chance.
A great puzzle. In fact, it is #2 on the list of puzzles I worry about late at night. (Should you care, #1 is the apparant time asymmetry in the decay modes of the neutral kaon)
Aha, we now have an answer for the Man in the Moon.
In the Beginning God created the Heaven and the Earth...
Unfortunately, that's an Urban Legend.. it's the same direction for north and south of the hemisphere..
As for the magnetic field, I'm just not sure what you're talking about..
Deformity caused by Solar Wind?
That is correct.. It is a "localized" phenomenon, and the article says so quite clearly..
" It is thought to be produced when dust grains become aligned in the presence of magnetic fields threading through regions of space much larger than our solar system. Circularly polarised light is estimated to make up as much as 17% of the radiation at any given point in space."
Yes, I know - that's why I called it a joke!
But on the larger scale - the prevailing winds, for instance - the two hemispheres are antisymmetric. How this would affect living things is, of course, another problem.
On the magnetic field - we know that many living things are sensitive to the Earth's magnetic field - many species of migratory bird, for instance. And any small organism containing a metallic ion can also, in principle, detect the field. Put together the magnetic field (N/S), the gravitational field (up/down) and the Coriolis force (E/W) and we have a classic "right hand / left hand" rule situation - a true asymmetry. This could perhaps preference left-handed over right-handed molecules, though at present we have no idea how.
As I said, a big problem.
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That is the next question. Where does the chiralty of a special type of "handed" space radiation come from? It was shown 1/2 century ago that the universe does not have a net rotation and that was in response to one of Goedel's questions related to a solution of Einstein's theory of relativity. Where else could a chiralty come from? A predominance of existence of particles versus anti-particles?
Left-hand ping
Not starved, been eaten.
Good analysis though.
Humble, thought that you might want to weigh in here.
How do we test for your simple truth?
Thanks. I'm asking for opinions as to whether the list should be pinged for this.
Whenever I am dealing with circularly polarised light I never fail to
consider it's electric field. Regardless of whether it comes in right- or left-handed forms.
I begin to be concerned when it gets all aligned in the presence of
magnetic fields and left-handed amino acids start taking their toll.
To avoid absorption I usually rely on icy dust in space.
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