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Chris McKay
NASA Ames Research Center



The Greenland ice cap
Liquid water is the sine qua non of life on Earth, and where it doesn't exist, life "checks out." No life form on this planet has yet deduced a method to live in ice, but if it should, it would have the ice environment all to itself, unchallenged, for a bit of time.



Non-terrestrial biochemistries
No matter how an alien biochemistry is constructed, it will almost certainly be composed of a Lego-like "toolkit," made up of a very few commonly repeated building blocks.






April 3, 2006

Part III: Could We Tell Life If We Saw It?

Life in Ice on Mars
Christopher P. McKay
NASA Ames Research Center
28 min. (slideshow requires QCShow Player)
Audio only (mp3 format)
View as a webpage (quicktime, real player) (notes)

In the coming century, we are going to seek out life, if not in the stars, at least on the moons and planets of our solar system.

Water is the sine qua non of life on Earth. Where water is absent, life doesn't exist on this planet. But the presence of water isn't sufficient either. There are broad regions of the Earth where life hasn't been able to make a go of it, and the icecaps of Greenland are one of those places.

Chris McKay points out something that would shock any ecologist: "It's often said that life covers everywhere on this planet. It's not true. There are large places on this planet where no life forms have figured out how to make a go of it. And this is one them: the ice environment."

Is the a priori demand for liquid water a good model for life elsewhere? At the moment we don't know. "Following the water" is the most conservative approach we can take, simply because we know it works.

Where liquid water is absent on this planet, life "checks out," and in this talk, McKay talks about three regions of the planet in which he is conducting his investigations: in the dry valleys of Antarctica, in the Atacama desert of Chile, and the tops of the high tropical mountains in the African rift.

None of these places are perfect analogs of Mars, but they are in many ways similar. Although current evidence suggests that the surface of Mars is inimical to terrestrial life, there remain plausible scenarios for extant microbial life on Mars, but only of very modest plausibility.

The surface of Mars today is far more inhospitable to life than any of these areas on Earth. It's cold, dry, and chemically oxidizing and is exposed to an intense flux of solar ultraviolet radiation. Temperature is of interest, not only because of its controlling influence on metabolic rates but also because of its influence on the stability of liquid water.

Liquid water is essential for life. All known terrestrial life is built on an aqueous chemistry. That statement is not based on any theory. It's merely an observation, but given our current state of knowledge of chemistry and biology, it is hard for us to imagine the existence of life independent of liquid water.

In the last few slides of his talk, McKay presents another of his ideas: No matter what biochemical pathways life may adopt in alien environments, it will almost certainly not exhibit a broad, continuous range of molecular constructions. Almost certainly, it will appear as if it were a Lego-like toolkit, composed of only a few dozen fundamental molecules. Recognizing this fact provides us the opportunity to potentially observe the biomarkers of life, even if its adopted biochemistry is wholly foreign to us.

— Wirt Atmar


About the Speaker

Chris McKay is a planetary scientist with the Space Science Division of NASA Ames Research Center. He received his Ph.D. in AstroGeophysics from the University of Colorado in 1982 and has been a research scientist with the NASA Ames since that time.

Dr. McKay is one of the world's leading researchers studying Titan, and has been involved in numerical modeling of planetary atmospheres for many years. He is currently working on models of Titan's thick atmosphere in support of the joint NASA/ESA mission to the Saturn system. Dr. McKay is co-Investigator on the Titan probe atmospheric structure experiment (HASI). His broader interests focus on understanding the relationship between the chemical and physical evolution of the solar system and the origin of life.

He has been actively involved in planning for future Mars missions including human settlements. Chris has also been involved with polar research since 1980, traveling to the Antarctic dry valleys and more recently to the Siberian Arctic to conduct research in these Mars-like environments.

All of his work centers around his primary research interests: the origin of life on Earth and the possibility that life might have originated on other planets as well.

Dr. McKay is a recipient of the prestigious Kuiper Award from the Division of Planetary Sciences of the American Astronomical Society for his contributions.


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