Life elsewhere in Solar System could be different from life as we know it

WASHINGTON — The search for life elsewhere in the solar system and beyond should include efforts to detect what scientists sometimes refer to as “weird” life — that is, life with an alternative biochemistry to that of life on Earth — says a new report from the National Research Council. The committee that wrote the report found that the fundamental requirements for life as we generally know it — a liquid water biosolvent, carbon-based metabolism, molecular system capable of evolution, and the ability to exchange energy with the environment — are not the only ways to support phenomena recognized as life. “Our investigation made clear that life is possible in forms different than those on Earth,” said committee chair John Baross, professor of oceanography at the University of Washington, Seattle.

The report emphasizes that “no discovery that we can make in our exploration of the solar system would have greater impact on our view of our position in the cosmos, or be more inspiring, than the discovery of an alien life form, even a primitive one. At the same time, it is clear that nothing would be more tragic in the American exploration of space than to encounter alien life without recognizing it.”

The tacit assumption that alien life would utilize the same biochemical architecture as life on Earth does means that scientists have artificially limited the scope of their thinking as to where extraterrestrial life might be found, the report says. The assumption that life requires water, for example, has limited thinking about likely habitats on Mars to those places where liquid water is thought to be present or have once flowed, such as the deep subsurface. However, according to the committee, liquids such as ammonia or formamide could also work as biosolvents — liquids that dissolve substances within an organism — albeit through a different biochemistry. The recent evidence that liquid water-ammonia mixtures may exist in the interior of Saturn’s moon Titan suggests that increased priority be given to a follow-on mission to probe Titan, a locale the committee considers the solar system’s most likely home for weird life.

“It is critical to know what to look for in the search for life in the solar system,” said Baross. “The search so far has focused on Earth-like life because that’s all we know, but life that may have originated elsewhere could be unrecognizable compared with life here. Advances throughout the last decade in biology and biochemistry show that the basic requirements for life might not be as concrete as we thought.”

Besides the possibility of alternative biosolvents, studies show that variations on some of the other basic tenets for life also might be able to support weird life. DNA on Earth works through the pairing of four chemical compounds called nucleotides, but experiments in synthetic biology have created structures with six or more nucleotides that can also encode genetic information and, potentially, support Darwinian evolution. Additionally, studies in chemistry show that an organism could utilize energy from alternative sources, such as through a reaction of sodium hydroxide and hydrochloric acid, meaning that such an organism could have an entirely non-carbon-based metabolism.

Researchers need to further explore variations of the requirements for life with particular emphasis on origin-of-life studies, which will help determine if life can exist without water or in environments where water is only present under extreme conditions, the report says. Most planets and moons in this solar system fall into one of these categories. Research should also focus on how organisms break down key elements, as even non-carbon-based life would need elements for energy, structure, and chemical reactions.

The report also stresses that the future search for alien life should not exclude additional research into terrestrial life. Through examination of extreme environments, such as deserts and deep under the oceans, studies have determined that life exists essentially anywhere water and a source of energy are found together on Earth. Field researchers should therefore seek out organisms with novel biochemistries and those that exist in areas where vital resources are scarce to better understand how life on Earth truly operates, the committee said. This improved understanding will contribute greatly toward seeking Earth-like life where the conditions necessary for its existence might be met, as in the case of subsurface Mars.

Space missions will need adjustment to increase the breadth of their search for life. Planned Mars missions, for example, should include instruments that detect components of light elements — especially carbon, hydrogen, oxygen, phosphorous, and sulfur — as well as simple organic functional groups and organic carbon. Recent evidence indicates that another moon of Saturn, Enceladus, has active water geysers, raising the prospect that habitable environments may exist there and greatly increasing the priority of additional studies of this body.

NASA sponsored the report. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies. They are private, nonprofit institutions that provide science, technology, and health policy advice under a congressional charter. The Research Council is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering. A committee roster follows.

Copies of THE LIMITS OF ORGANIC LIFE IN PLANETARY SYSTEMS will be available from the National Academies Press; tel. 202-334-3313 or 1-800-624-6242 or on the Internet at http://www.nap.edu. The cost of the report is $27.50 (prepaid) plus shipping charges of $4.50 for the first copy and $.95 for each additional copy. Reporters may obtain a pre-publication copy from the Office of News and Public Information (contacts listed above).

[ This news release and report are available at HTTP://NATIONAL-ACADEMIES.ORG ]

NATIONAL RESEARCH COUNCIL

Division on Engineering and Physical Sciences

Space Studies Board

COMMITTEE ON THE LIMITS OF ORGANIC LIFE IN PLANETARY SYSTEMS

JOHN A. BAROSS (CHAIR)

Professor of Biological Oceanography

University of Washington

Seattle

STEVEN A. BENNER

Distinguished Fellow

Foundation for Applied Molecular Evolution

Gainesville, Fla.

GEORGE D. CODY

Geologist and Member of Senior Research Staff

Geophysical Laboratory

Carnegie Institution of Washington

Washington, D.C.

SHELLEY D. COPLEY

Professor

Department of Molecular, Cellular, and Developmental Biology

University of Colorado

Boulder

NORMAN R. PACE*

Professor

Department of Molecular, Cellular, and Developmental Biology

University of Colorado

Boulder

JAMES H. SCOTT

Leader of the Geobiology Group

Department of Earth Sciences

Dartmouth College

Hanover, N.H.

ROBERT SHAPIRO

Professor Emeritus and Senior Research Scientist

Department of Chemistry

New York University

New York City

MITCHELL L. SOGIN

Director

Bay Paul Center for Comparative Molecular Biology and Evolution

Marine Biological Laboratory

Woods Hole, Mass.

JEFFREY L. STEIN

Kauffman Fellow

Sofinnova Ventures

San Francisco

ROGER SUMMONS

Professor

Department of Earth, Atmospheric, and Planetary Sciences

Massachusetts Institute of Technology

Cambridge

JACK W. SZOSTAK*

Alexander Rich Distinguished Investigator

Massachusetts General Hospital, and

Professor of Genetics

Harvard Medical School

Boston

RESEARCH COUNCIL STAFF

DAVID H. SMITH

Study Director

* Member, National Academy of Sciences