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Searching for Life in the Universe

by Mark Pitts, IfA Graduate Student

One of the biggest questions driving modern astronomy is whether life beyond Earth ever existed or still exists today. This search has drawn scientists to look both within our own solar system and at the countless other systems within our Milky Way galaxy for indications of past or present life. At the UH Manoa Art Building Auditorium on July 28, two guest lecturers spoke about different methods of "Searching for Life in the Universe": geological exploration of the solar system and radio searches of the Milky Way for signs of intelligence. IfA and the UH NASA Astrobiology Institute sponsored the Frontiers of Astronomy presentation.

Chris McKay and Seth Shostak
Chris McKay and Seth Shostak

Chris McKay of the NASA Ames Research Center is an expert in forms of life dwelling within extreme Earth environments that act as proxies for conditions on other places in the solar system. He also aids in the design of robotic probes to search for signs of life in hostile extraterrestrial environments. McKay laid out three reasons he feels are the most significant ones for searching for life beyond Earth. The first is to know that life has emerged in other places completely independent of life on Earth. The second is to gain insight into how diverse life can be by analyzing the differences between how terrestrial and alien life forms sustain and reproduce themselves. McKay's third reason is to answer a simple yet important question: How common is life within the Universe? Is the Earth's situation incredibly unique, or is life a likely occurrence given a set of favorable initial conditions? Only a full accounting of the when and where life has emerged within the solar system can begin to answer such a question.

According to McKay, Mars is the best candidate for finding evidence of past or present alien life. Recent robotic exploration has hinted at a warmer and wetter environment in the Red Planet's past compared with what is observed today. On Earth, life seems to have emerged almost as soon as it could, appearing around 700 million years after our planet's formation. If life can develop that quickly, and Mars did indeed contain liquid water on its surface long ago, it is plausible that life also emerged there and thrived for millions, or even billions, of years before the planet cooled and became a frozen desert. McKay recommends excavating the polar regions to find traces of long-deceased martian life, as the deep permafrost may very well have preserved such evidence there better than anywhere else on the planet. To find evidence of life, McKay recommends looking for building blocks similar to those used by terrestrial life: amino acids, nucleotide bases, or an overabundance of either a left- or right-handed geometry in the shapes of organic compounds.

The second speaker, Seth Shostak, spoke about the efforts of the SETI (search for extraterrestrial intelligence) Institute to receive alien-produced radio transmissions from distant star systems. To Shostak, the question of whether there are other intelligent civilizations in our galaxy is a matter of numbers. There are 20-50 billion other Sun-like stars in our galaxy, and many of them are likely to have planetary systems, so the chance that we are the only civilization to emerge and acquire the skills to transmit radio signals into space seems remote. Given the distances and extremely long times associated with space travel using current technology, listening for intelligent life remains the most practical way to search for it. While Shostak doubts we would be able to understand any alien transmission we intercept, he is confident that the exponential increase in computing power over the years will allow us to pick up an alien signal within the next two dozen years.

Both scientists were visiting UH to give talks at the Computational Astrobiology Summer School of the UH/NASA Astrobiology Institute.

www.seti.org/
astrobiology.arc.nasa.gov/
www.ifa.hawaii.edu/UHNAI/