Why car exhaust and exploded star N132D may help explain origins of life

William Atkins
Saturday, 01 September 2007 21:19

Science - Space

Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants found in car exhaust and cigarette smoke. They are also found in supernova remnant N132D, the material left over after an old star exploded. Scientists theorize that PAHs play an essential role in the development of life.

N132D is the material left over after a star exploded within the Large Magellanic Cloud. The material, called a supernova remnant, is about 80 light-years in diameter, about 3,000 years old, and has temperatures that range in the tens of million of degrees. The Large Magellanic Cloud, a companion galaxy to the Milky Way galaxy, is about 160,000 light-years from the Earth.

Scientists already knew that PAHs were ring-shaped molecules made of carbon and hydrogen. They are formed by the incomplete combustion of fuels and materials made from carbon such as coal, diesel, tobacco, tar, and wood.

Several PAH compounds are classified by the U.S. Environmental Protection Agency (EPA) as human carcinogens, or cancer causing substance—being found within automobile exhaust, cigarette smoke, and oil spills, to name a few.

Other compounds of PAHS are suspected as being carcinogenic, thus, possibly posing significant health risks to humans and other animals. PAHs are one of the most prevalent organic pollutants within industrialized countries such as the United States.
 

On the other hand, scientists have discovered that PAHs were present between 2.7 and 4.4 billion years ago when the precursors to life on Earth were first thought to appear. Scientists conjecture that PAHs are used as building blocks for larger molecules and, thus, are critical for the chemical processes that ultimately created life.

Recently, astronomers found something interesting. A massive star within the Large Magellanic had exploded and released enough energy to power the Sun for ten billion years. This result, in and of itself, is not unusual for such an explosion. However, the expanding shell of the destroyed star, called supernova remnant N132D, was observed by astronomers--with the use of the Spitzer Space Telescop--to contain PAHs.

The astronomers used an infrared (IR) instrument on board Spitzer that can detect IR emissions from PAHs. They were amazed that the PAHs were able to survive the gigantic blast from the destroyed star.

PAHs were already known to exist on the Earth, and throughout the universe within comets, meteoroids, and interstellar clouds. In fact, scientists at NASA and Stanford University theorize that primitive life may have existed millions of years ago on Mars partially based on the presence of PAHs. However, scientists, before the discovery of N132D, did not realize that PAHs could withstand the devastating conditions within the supernova blast. This event is the first direct proof that PAHS could survive.

Based on this observation, astronomers are contending that a similar star exploded in our corner of the universe at about the same time that the solar system was forming from interstellar gases, at a time estimated to be about four to five billion years ago.

Whether scientists are correct in this conjecture is still to be proven. Additional experiments and observations will be necessary in order to find out more  specifics on the PAHs such as the evolution of PAHs within the supernova remnant N132D, the percentage of PAHs that died and survived within the blast, and the concentration and distribution of PAHs.

The article was based on the NASA article “Cosmic Cockroaches” at website: http://science.nasa.gov/headlines/y2007/31aug_cockroaches.htm.