Astronomers have a new take on what they once considered lifeless outer space. They now think of our galaxy as a vast reactor for biologically significant organic chemistry.
Materials that could jump-start organic evolution have shown up in interstellar dust clouds and dusty planet-forming discs around many stars. These findings fuel an increasingly strong suspicion that the raw material of planet Earth was primed for life.
The infrared-sensing eyes of NASA's Spitzer Space Telescope made the latest discovery. As NASA recently announced, Dan Watson and William Forrest at the University of Rochester in New York found "significant amounts of icy organic materials" around five young stars in Spitzer data.
Water, methanol, and carbon dioxide coat dust particles around these stars located 420 light-years away in the constellation Taurus. NASA notes that, while such materials have been found elsewhere, "this is the first time they were seen unambiguously in the dust making up planet-forming gases."
Such discs appear to be common in our galaxy. Infrared light penetrates dust, allowing astronomers to see into dusty areas. Spitzer - launched last August - can image these areas with unprecedented clarity and detail.
The telescope has been observing the nebula RCW 49, a stellar nursery some 13,700 light-years away in the constellation Centaurus. So far, it has provided early detailed data of discs around two of more than 300 young stars.
The early data suggest all those stars have protoplanetary discs, says Spitzer scientist Ed Churchwell from the University of Wisconsin in Madison. "Spitzer has shown us that star and planet formation is a very active process in our galaxy."
As data on interstellar chemicals have poured in over the past decade, astronomers have abandoned their long-held prejudice against such chemistry. They had thought that ultraviolet radiation from stars, and other harsh conditions, would tear apart organic molecules even if they did form.
However, dust can shield that chemistry. Many reactions occur within protective icy coatings on dust particles. Some 130 organic molecules have revealed themselves so far. They include such interesting species as glycine, an amino acid; and ethylene glycol, the antifreeze in your radiator.
Ethylene glycol is associated with formation of sugar molecules necessary for life. It is what chemists call a reduced form of the sugar glycolaldehyde. The research team that found the antifreeze also detected this sugar in interstellar clouds.
"The discovery further demonstrates how important interstellar chemistry may be in understanding the creation of biological molecules on the Earth," said researcher Phillip R. Jewell when these discoveries were reported in 2002. "Some scientists have even speculated that the Earth could have been 'seeded' with complex molecules from passing comets, which formed from the condensing gas nebula that produced our solar system."
Discoveries since then have inspired some astrobiologists to move from suspicion and speculation to at least mild conviction on this point.
There is no consensus yet. But even skeptics find it interesting that an interplanetary dust particle - snagged in the atmosphere by a NASA aircraft - contains organic molecules that predate Earth.
Meanwhile, scientists are looking forward to the return in January 2006 of the Stardust spacecraft, which has captured dust from Comet Wild 2. Its sample containers may hold more decisive data.