Scientists Give a Hand(edness) to the Search for Alien Life

Scientists Give a Hand(edness) to the Search for Alien Life
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 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 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 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 as we know it.”

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 (news : web)

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Apr 22, 2009

So you look at a planet, and if the light is heavily polarized, it MIGHT mean life. Very cool.

Apr 22, 2009
Yeah but here comes the part in where we have basically never seen another planet outside our solar system directly. Theres not enough light coming from them.

Apr 23, 2009
Detecting the effects chirality has on reflected light will require a BIG telescope... there are some engineering plans for extremely large telescopes, but even those might be pushed beyond their limit. The feasibility will require years of testing before it can be confirmed.

Apr 23, 2009
The thing is they might just look at the light captured from the whole universe not just from a fixed point. We might be able to answer to the question "Is there life in the universe?".

Apr 23, 2009
This is beyond awesome. Even if it'll be a few decades before we can figure out how to do this when looking at worlds many light-years away, this effectively could detect life at nearly any point in a world's history. Even before Earth's great oxidation that effectively planted a "life is here" sign for the Universe to see, this device could detect that the Earth was a living world.

Apr 23, 2009
"As life spreads, the team theorizes, the landscape will eventually have a large amount of molecules that favor one handedness."

So I think that they are saying that any light reflecting off of organic molecules will show the biased chirality caused by ages of developing lifeforms, while non life-related molecules will give a random result. Add it all up and there might be a bias in favor of left or right handedness which can be detected.

Apr 23, 2009
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Apr 24, 2009

Pulsars emit circular polarized light.

Several years ago Dr. Cronin suggested that such light probably separated d- and l-amino acids in the Murchison carbonaceous meteorite - long before the start of life in the solar system.

With kind regards,
Oliver K. Manuel

Apr 26, 2009
In theory all it would take is a really large telescope with the ability to filter out noise and excess light from a nearby star. Most of the telescopes we will be building in 20 years will have a good chance of doing just that. I think chirality will be both a simple and effective way in providing additional evidence of whether a exoplanet has life... after all it won't be the only method at work.

Apr 30, 2009
All of the above comments about big telescopes refer to extra-solar planets, But a sensitive enough test would allow us to examine the oceans of Europa, the surface of Titan, and other possible targets inside our own solar system using spacecraft explorers. This is a VERY big deal.

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