21 September 2009

Cosmic Matters

A month ago astronomers announced that the amino acid glycine was detected in a comet. The discovery was made while analyzing samples brought back to Earth by the Stardust spacecraft, which flew through Comet Wild 2 in 2004.

My immediate reaction upon reading this news in the paper was, “How far we have come!” For most of history, astronomers could not be sure that the stuff of the heavens was the same as the stuff on Earth. And they figured an answer would be forever out of their reach. That is, until 150 years ago when Gustav Kirchhoff (left in picture), a professor of physics at the University of Heidelberg, and chemist Robert Bunsen (on the right), creator of the famous laboratory burner, showed us how to identify substances by the specific colors of light they emitted during chemical reactions or when burning. And since light knows no distance in space, electromagnetic waves can be effectively studied whether the light originates from a distance of one foot within a laboratory or from one million light-years away.

Kirchhoff eventually turned his attention to the heavens and with his spectroscope identified a number of elements in the Sun’s atmosphere, including sodium, iron, calcium, magnesium, chromium, barium, copper, zinc, and nickel. Here was definitive proof that the chemistry of the Earth was indeed identical to the chemistry of space. Within a few years, other astronomers reported finding similar elements in the stars. The long-standing Aristotelian belief that cosmic matters differed from the terrrestrial elements was finally abolished.

A century later, astronomers became even more ambitious. In 1955 physicist Charles Townes, who would go on to win a Nobel prize for his invention of the maser, gave a talk suggesting that celestial elements were likely linking up and forming actual molecules out in space. Among his candidates were carbon monoxide (CO, the stuff of car exhaust), ammonia (NH3), water (H2O), and the hydroxyl radical OH, the oxygen-hydrogen combination that distinguishes all alcohols. But most astronomers at the time were convinced that such molecules were quickly destroyed and hence too rare to seek out.

Fortunately a few MIT radio astronomers didn’t heed those warnings and looked anyway. In 1963 they found OH screaming out at 1,667 megahertz in the supernova remnant Cassiopeia A. A few years later, Townes himself, along with colleagues at the University of California at Berkeley, recorded the radio cries of ammonia and water from space. A race quickly ensued to snare the next new molecules. By 1973 nearly thirty cosmic molecules were identified; by the end of the 20th century, the total was more than a hundred—from ethyl alcohol and hydrogen cyanide to methane, formaldehyde, and nitrous oxide (or laughing gas).

And now the list includes an amino acid, one of the vital building blocks for life. The foundations for life on Earth may have been laid down before our planet even formed nearly five billion years ago.

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