Did Comets Make Life on Earth Possible?

Stefan Lovgren
for National Geographic News
October 2, 2003

An ambitious new NASA research project aims to answer perhaps the most vexing and profound of scientific mysteries: How did life on Earth begin?

The multimillion-dollar undertaking, led by the NASA Goddard Space Flight Center in Greenbelt, Maryland, brings together an interdisciplinary team of scientists from around the world to study how organic molecules are created in interstellar clouds and delivered to planets as they form.

The research will focus on the role of comets. Many scientists believe there is increasing evidence that comets supplied at least part of the raw material for the origin of life on Earth. The theory is changing the way scientists think about life in the universe and raises the possibility of alien worlds.

"Our mission is to gain a greater understanding of the origin and evolution of organic material on Earth," said Michael Mumma, a comet expert and director of the Goddard Center for Astrobiology, NASA Astrobiology Institute, who is leading the research. "The key question is: Were water and organic molecules delivered to Earth by cometary impact and does [that process] extend to planets elsewhere?"

Dirty Snowballs

Astronomers believe that stars, planets, and comets form in a massive chain reaction that begins when a cloud of interstellar material collapses under its own gravity. Some of the material forms the star—like our sun—and some of it gets spread out in a disk around the nascent star.

Some material in this disk later aggregates and forms planets. Close to the sun, where it's warm, leftover debris (rocky material) turns into asteroids. In the outer regions, where it's cold, icy chunks of rock and dust turn into comets.

It is generally believed that organic molecules, which contain carbon atoms and are present in all life forms known to science, are trapped in large amounts in both interstellar clouds and comets.

"We have extremely definite evidence from our radio observations that there's quite an array of organic molecules in interstellar space," said Bill Irvine, a professor of astronomy at the University of Massachusetts in Amherst, who is measuring radio waves from celestial objects as part of the research effort.

There's other evidence that comets contain organic material. When European spacecraft analyzed dust particles from the Halley comet in 1986, it turned out to be some of the most organic-rich material measured in the solar system. Meteorites that have hit Earth contain a whole suite of molecules, including amino acids, which play an important role in terrestrial biology.

"If such material exists in meteorites, which come from a class of asteroids, there's every reason to think it must also exist in comets," Irvine said.

Panspermia Goes Primordial

Continued on Next Page >>




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