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Note: This article first appeared in the Ithaca Times for 8 December 2004. Copyright © 2004 Ithaca Times, used by permission.
Geoffrey W. Marcy is Professor of Astronomy at the University of California at Berkeley. He is also among the first scientists to have discovered planets around Sun-like stars in our galaxy, leading us one step closer to learning whether Earth is the only planet with life or just one of many inhabited worlds in the universe.
Marcy visited the campus of Cornell University last week to participate in the Thomas Gold Lectureship of Astronomy series as the lecturer for 2004-2005.
Marcy's first lecture on November 29, titled "The Properties of Planetary Systems", was a technical look at the work he and colleagues have conducted since 1987 investigating 1,330 Sun-like stars in our region of the Milky Way galaxy for any planets around them.
Trying to observe a planet around a distant star has been compared to attempting to detect a firefly sitting on the edge of a search light very far away. Since it is not possible to detect these worlds from Earth directly, astronomers watch for "wobbles" in a star's movement caused by the gravitational pull of any planets around it.
For comparison, imagine watching a person walking an unseen dog on a leash getting yanked around by their pet while trying to walk in a straight path. You can infer the dog is there by the way the owner is tugged off their course.
Using this method, Marcy and his team have found almost one hundred exoplanets since 1995. Most are as large as or larger than the gas giant planet Jupiter of our solar system, which could hold over one thousand Earths itself.
Since the astronomers can only discover these worlds by their pull on a star, typically only the largest members of those systems can be found at present. Recently, however, exoplanets of sizes closer to Saturn and Neptune have been detected.
"There are more Neptunes than Saturns in the galaxy," stated Marcy, basing this on the number of known exoworlds and projecting the estimate statistically onto the rest of the stars in the Milky Way.
What Marcy and other astronomers are hoping to find eventually are the relatively small, rocky worlds - the ones that may be other Earths which could harbor life. While these celestial bodies are currently too small to detect from the stellar wobble observations, space satellites planned for the coming decades, such as the Terrestrial Planet Finder (TPF), could see Earth-like worlds and even report on their compositions to determine if any life could exist on them.
Professor Marcy's second and final talk in the lecture series came on Dec. 2. Titled "Planets, Yellowstone, and Prospects for Life in the Universe", Marcy delved into the underlying reason for his search for alien worlds: To find out how many stars have their own planetary systems. The more suns that have worlds circling them, the higher are the chances for life existing beyond Earth.
Marcy began his examination of the possibility for alien life by starting with our celestial neighborhood, the worlds of our solar system. He highlighted the recent findings by the Mars Exploration Rovers (MER) Spirit and Opportunity that water once flowed across at least some of the Red Planet in the distant past, increasing the chances for life having been there as well.
Another world that has gotten recent headlines is Saturn's largest moon, Titan. The Cassini probe orbiting that ringed gas giant has also begun to reveal what Titan looks like under its thick veil of orange clouds. It is a truly alien place, and though the moon is seemingly too cold for any Earth-type life, Marcy speculated that some kind of organisms could be there with a chemistry far different from what we know of here, possibly swimming in lakes of liquid ethane.
Marcy then headed the audience out into the wider galaxy to examine some of the strange alien worlds he and his team have found in the past decade.
Since the majority of known exoplanets are around the size of Jupiter or larger, scientists have speculated whether life exists on them. A number of these planets actually orbit very close to their stars and are presumably so hot that it is hard to imagine would kind of organisms could survive on them.
However, for those known globes that do orbit at more "reasonable" distances from their suns, Marcy said that while he "would not bet on life on those worlds as we know it, I could imagine life that floats in their thick air."
Using his seventeen years of data and discoveries, Marcy estimates that perhaps twenty billion planetary systems exist in our Milky Way. Combine that with how hardy life can be on this planet - such as dwelling in hot, acidic geysers and miles under the ocean - and Marcy thinks that simple life forms are "common" in our galaxy and probably most others.
As for intelligent alien life, "we must hunt explicitly for extraterrestrial intelligence to find brethren in the galaxy," said Marcy.
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