Scientists Give a Hand(edness) to the Search for Alien Life
(麻豆淫院Org.com) -- Visiting aliens may be the stuff of legend, but if a scientific team working at the National Institute of Standards and Technology is right, we may be able to find extraterrestrial life even before it leaves its home planet鈥攂y looking for left- (or right-) handed light.
The technique the team has developed for detecting life elsewhere in the universe will not spot aliens directly. Rather, it could allow spaceborne instruments to see a telltale sign that life may have influenced a landscape: a preponderance of molecules that have a certain 鈥渃hirality,鈥� or handedness. A right-handed molecule has the same composition as its left-handed cousin, but their chemical behavior differs. Because many substances critical to life favor a particular handedness, Thom Germer and his colleagues think chirality might reveal life鈥檚 presence at great distances, and have built a device to detect it.
鈥淵ou don鈥檛 want to limit yourself to looking for specific materials like oxygen that Earth creatures use, because that makes assumptions about what life is,鈥� says Germer, a physicist at NIST. 鈥淏ut amino acids, sugars, DNA鈥攅ach of these substances is either right- or left-handed in every living thing.鈥�
Many molecules not associated with life exhibit handedness as well. But when organisms reproduce, their offspring possess chiral molecules that have the same handedness as those in their parents鈥� bodies. As life spreads, the team theorizes, the landscape will eventually have a large amount of molecules that favor one handedness.
鈥淚f the surface had just a collection of random chiral molecules, half would go left, half right,鈥� Germer says. 鈥淏ut life鈥檚 self-assembly means they all would go one way. It鈥檚 hard to imagine a planet鈥檚 surface exhibiting handedness without the presence of self assembly, which is an essential component of life.鈥�
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鈥� chlorophyll from a short distance away. The device detected chirality from both sources.
The team intends to improve its detector so it can look at pond surfaces and then landscape-sized regions on Earth. Provided the team continues to get good results, Germer says, they will propose that it be built into a large telescope or mounted on a space probe.
鈥淲e need to be sure we get a signal from our own planet before we can look at others,鈥� he says. 鈥淏ut what鈥檚 neat about the concept is that it is sensitive to something that comes from the process behind organic self-assembly, but not necessarily life as we know it.鈥�
More information: W.B. Sparks, J. Hough, T.A. Germer, F. Chen, S. DasSarma, P. DasSarma, F.T. Robb, N. Manset, L. Kolokolova, N. Reid, F.D. Macchetto and W. Martin. Detection of circular polarization in light scattered from photosynthetic microbes. Proceedings of the National Academy of Sciences, April 20, 2009.
Provided by National Institute of Standards and Technology ( : )
