* Astronomy

The great search for extraterrestrial life has focused on water at the expense of a crucial element, say geobiologists at the University of Southern California.

Writing in the Perspectives section of the May 5 issue of Science, four University of Southern California (USC) researchers propose searching for organic nitrogen as a direct indicator of the presence of life. Nitrogen is essential to the chemistry of living organisms.
Even if NASA were to find water on Mars, its presence only would indicate the possibility of life, said Kenneth Nealson, Wrigley Professor of earth sciences in the USC College of Letters, Arts and Sciences.

"It's hard to imagine life without water, but it's easy to imagine water without life" - Kenneth Nealson.

The discovery of nitrogen on the Red Planet would be a different story.

"If you found nitrogen in abundance on Mars, you would get extremely excited because it shouldn't be there" - Kenneth Nealson.

The reason has to do with the difference between nitrogen and carbon, the other indispensable organic element.
Unlike carbon, nitrogen is not a major component of rocks and minerals. This means that any substantial organic nitrogen deposits found in the soil of Mars, or of another planet, likely would have resulted from biological activity.
Dimming the hopes of life-on-Mars believers is the makeup of the planet's atmosphere. The abundant nitrogen in Earth's atmosphere is constantly replenished through biological activity. Without the ongoing contribution of living systems, the atmosphere slowly would lose its nitrogen.
The extremely low nitrogen content in the Martian atmosphere suggests that biological nitrogen production is close to zero.
However, the authors write, it is possible that life existed on Mars at some hypothetical time when nitrogen filled the atmosphere.
Co-author Douglas Capone, Wrigley Professor of environmental biology in USC College, said NASA should establish a nitrogen detection program alongside its water- seeking effort. He noted that next-generation spacecraft will have advanced sampling capabilities.

"What we're suggesting here is basically drilling down into geological strata, which they're going to be doing for water anyway." - Douglas Capone.

"The real smoking gun would be organic nitrogen...If your goal is to search for life, it would be wise to include nitrogen."- Kenneth Nealson.

In their acknowledgments, the authors thanked the students of the Spring 2004 Geobiology & Astrobiology course at USC, with whom Nealson and Capone began their discussion on how to search for life outside earth.
The authors also thanked NASA, the Department of Energy and the National Science Foundation for their financial support.
Along with Nealson and Capone, USC graduate student Beverly Flood and former USC Research Professor Radu Popa (now a professor of biology at Portland State University) contributed to the Perspectives paper.

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The components of life may have been under attack in the hostile environments of the universe's first galaxies.

A science team led by graduate student Yanling Wu of Cornell University, Ithaca, N.Y., recently came to this conclusion after studying the formation and destruction of polycyclic aromatic hydrocarbons molecules (PAHs) in more than 50 blue compact dwarf (BCD) galaxies using the Spitzer Space Telescope. These organic molecules, comprised of hydrogen and carbon, are believed by many scientists to be among the building blocks for life.

"One of the outstanding problems in astronomy today is whether complex organic molecules of hydrogen and carbon, similar to those responsible for life on Earth, are present in the early universe" - Yanling Wu.

Mature massive galaxies like our Milky Way formed from the merging of smaller galaxies, probably about the size of nearby BCD galaxies. Since current technology is not sensitive enough to easily identify and study in detail the universe's first galaxies, astronomers must infer the physical properties of the early structures by observing similar nearby galaxies like BCDs.

"We believe that BCD galaxies are similar to the universe's first galaxies because they are infant galaxies, actively forming stars, and are not very chemically polluted" - Yanling Wu.

Because most atomic elements other than hydrogen and helium are born from the death of stars, astronomers suspect that in the first few million years after the big bang galaxies were not "chemically polluted" with elements other than hydrogen and helium. In astronomy, these relatively unpolluted galaxies are said to have low metallicity.
The BCD galaxies' blue colours tell astronomers that these structures are actively forming massive stars. By logically combining the galaxy's blue colour with the fact that it is low in metals, astronomers can infer that this is a young galaxy.
In her research, Wu found that nearby BCD galaxies with lowest metallicity also had little or no PAHs. As the galaxies became more chemically polluted, more traces of PAHs were found.
This phenomenon makes sense because heavy metal elements like carbon are formed from the death of stars, and some of these galaxies may just be too "young" to have produced enough carbon to create PAHs.
However, in some of the BCD galaxies where the conditions allow for the formation of PAHs, Wu found that those molecules were being destroyed by intense ultraviolet radiation from the young massive stars.

"Because BCD galaxies are metal poor and very compact, the intense ultraviolet radiation from young stars will destroy PAH molecules even if they are formed. The threshold for when these PAH molecules stop being destroyed is still uncertain." - Yanling Wu

"This leads to an interesting paradox, where the young stars responsible for the formation of PAHs may also be the main culprit of their destruction" - co-author Dr. Vassilis Charmandaris, University of Greece, Heraklion.

The organic PAHs were detected using Spitzer's Infrared Spectrometer (IRS).

"Yanling has made significant progress in a research area first opened by International Space Observatory. With Spitzer, Yanling is able to extend BCDs observations to a much larger sample; the new results provide a glimpse into the formation of galaxies in the early Universe" - Dr. Jim Houck of Cornell University.

Houck is Wu's academic advisor and a co-author of the paper. He is also the Principal Investigator for Spitzer's IRS instrument and played a vital role in its creation.

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NASA Discovers Life's Building Blocks Are Common In Space

After A team of exobiology researchers revealed today organic chemicals that play a crucial role in the chemistry of life are common in space.

"Our work shows a class of compounds that is critical to biochemistry is prevalent throughout the universe. NASA's Spitzer Space Telescope has shown complex organic molecules called polycyclic aromatic hydrocarbons (PAHs) are found in every nook and cranny of our galaxy. While this is important to astronomers, it has been of little interest to astrobiologists, scientists who search for life beyond Earth. Normal PAHs aren't really important to biology. However, our work shows the lion's share of the PAHs in space also carry nitrogen in their structures. That changes everything" - Douglas Hudgins, astronomer at the Ames Research Centre, Moffett Field, California.

Douglas Hudgins is principal author of a study detailing the team's findings that appears in the October 10 issue of the Astrophysical Journal.

"Much of the chemistry of life, including DNA, requires organic molecules that contain nitrogen . Chlorophyll, the substance that enables photosynthesis in plants, is a good example of this class of compounds, called polycyclic aromatic nitrogen heterocycles, or PANHs. Ironically, PANHs are formed in abundance around dying stars. So even in death, the seeds of life are sewn" - Louis Allamandola, team member, astrochemist at Ames.

The team studied the infrared "fingerprint" of PANHs in laboratory experiments and with computer simulations to learn more about infrared radiation that astronomers have detected coming from space. They used data from the European Space Agency's Infrared Space Observatory satellite.

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