Scientists give a
hand(edness) to the search for alien life
Thursday, April 23,
2009
Light becomes polarized in detectable ways when reflected from
chlorophyll and other chiral molecules necessary to life, so
scientists working at NIST have built a device that can detect this
polarization - potentially offering a way to find extraterrestrial
life from great distances. Their device has already proved itself
able to discern the polarized light scattered from the chlorophyll
in leaves and also cyanobacteria (below), one-celled organisms that
evolved early in the history of life on Earth. Credit (top image):
Shutterstock Credit (bottom image): Roger Burks (University of
California at Riverside), Mark Schneegurt (Wichita State
University), and Cyanosite
Visiting aliens may be the stuff
of legend, but if a scientific team working at the National
Institute of Standards and Technology (NIST) is right, we may be
able to find extraterrestrial life even before it leaves its home
planet—by 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 “chirality,” 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’s presence at great distances, and have
built a device to detect it.
“You don’t want to limit yourself to looking for specific materials
like oxygen that Earth creatures use, because that makes
assumptions about what life is,” says Germer, a physicist at NIST.
“But amino acids, sugars, DNA—each of these substances is either
right- or left-handed in every living thing.”
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’
bodies. As life spreads, the team theorizes, the landscape will
eventually have a large amount of molecules that favor one
handedness.
“If the 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.”
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 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.
“We need to be sure we get a signal from our own planet before we
can look at others,” he says. “But what’s 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.”
###
National Institute of Standards and Technology (NIST)
Thanks to National Institute of
Standards and Technology (NIST) for this article.
