life on other planets

NASA researchers have found that many of the basic building blocks for life here on Earth are common throughout the Universe. Using the Spitzer Space Telescope, the researchers observed that complex organic molecules called polycyclic aromatic hydrocarbons (PAHs) are everywhere they looked: in the Milky Way and in the most distant observable galaxies. Most of these molecules contain nitrogen, which is the key requirement for life.

Duplicating the harsh conditions of cold interstellar space, scientists from NASA's Ames Research Center have shown that nitrogen containing aromatic molecules, chemical compounds that could be important for life's origin, are widespread throughout space.

Combining laboratory experiments with computer simulations, this team had earlier shown that complex organic molecules known as polycyclic aromatic hydrocarbons (PAHs) are widespread throughout space. PAHs, large, flat, chicken-wire shaped molecules made up of hydrogen and carbon are extremely stable and can withstand the hostile radiation environment of interstellar space. The Ames team showed that PAHs are responsible for the mysterious infrared radiation that astronomers first called the Unidentified Infrared Emission. NASA's Spitzer Space Telescope, an instrument of unprecedented sensitivity, has now detected the PAH tell-tale signature throughout our galaxy the Milky Way and in galaxies very far away, galaxies nearly as old as the Universe itself. Now the Ames team has found that these PAHs contain nitrogen, a key biochemical element (Figure 1). Doug Hudgins, the lead author of the study, points out "Not only are nitrogen containing aromatic hydrocarbons the information carrying molecules in the DNA and RNA that make up all living matter as we know it, they are found in many biologically important species. For example, caffeine and the main ingredient in chocolate are among these kinds of molecule (Figure 2). Seeing their signature across the Universe tells us they are accessible to young, habitable planets just about everywhere."

This is the first direct evidence for the presence of complex, prebiotically important, biogenic compounds in space and brings us a step closer to assessing if life's origin on Earth may have had a helping hand from infalling stardust. The bulk of the astronomical evidence points to the formation of these nitrogen containing PAHs in the winds of dying stars which inject them into interstellar space. Eventually they become incorporated into the clouds of material that give birth to stars and planets. Freshly formed planets continue to collect infalling material (dust, asteroids, meteorites, and comets) from the star formation process and life on Earth is thought to have emerged from this primordial chemical soup.

This discovery is profound at several levels. "First, this resolves part of a longstanding mystery about the distribution of nitrogen in space, second, PANHs have signatures in the optical and radio wavelengths that can account for unexplained astronomical phenomena and third, these compounds are of biogenic interest" summed Hudgins. "Most people will take notice of their possible role in the origin of life, the point in our history when chemistry became biology, but there are other serious implications as well" he continued.

There are hundreds if not thousands of these species in space and it is beginning to look like these types of compounds are strikingly similar to many of those brought to Earth today by infalling meteorites and their smaller cousins, the interplanetary dust particles. Every year more than a hundred tons of extraterrestrial stuff falls on the Earth, and much of it is in the form of organic material. In the early life of our Solar System, before the debris from its formation was fully cleared away, these materials were deposited on the Earth in far greater quantities than we see today. Thus, much of the organic material found on the primordial Earth likely included a strong dose of interstellar PANHs.

These results are published in the current, issue of the Astrophysical Journal. The authors and team members include Drs. Hudgins, Bauschlicher, Mattioda, Peeters, and Allamandola of NASA's Ames Research Center.