Whether we are alone in the universe is one of the most profound questions that science can address. Discovering remote examples of life would affect our self-image, and further push humanity off the pedastal adopted by the scheme of creationism.
Astronomers are convinced that life beyond Earth will be detected imminently. There is increasing hope that such a discovery will occur within the next decade. There are many reasons to be so optimistic and hopeful. For one, the universe is highly habitable. The major elements required for life, such as carbon, nitrogen and oxygen, were created within the first generation of stars and then ejected into space, where they now form planets such as our own. As the universe ages, and more carbon is produced, it gets more hospitable for life.
A second reason scientists are positive about the existence of life elsewhere is the fact that biology exists in every conceivable part of the Earth. Living creatures, from microbes to mammals, have spread into every ecological niche, including many that required adaptation to extremes of temperature, pressure and toxicity. Life doesn’t necessarily need a star and it might not even need a planet.
In the past few years astronomers have found an increasing number of planets outside our solar system. The Kepler satellite has begun to find Earth-like planets in the habitable zones of their stars. We estimate there are billions of habitable worlds in the galaxy, and many more habitable spots such as the moons of giant planets. The principal of mediocrity tells us that the full number of habitable worlds among all of the galaxies in the observable universe is unimaginably large. It defies belief that all these planets are sterile. Yet logically we have to accept the possibility that biology is exceptionally rare and constantly changing.
Taking the next step-actually proving the existence of life away from Earth-will be difficult. It will take many years and discoveries to reach a point of clarity and certainty. Current and planned missions to Mars can only scratch its surface and life-finding missions to the outer solar system will cost billions of dollars and are decades away. Astronomers are perfecting the techniques needed to detect biomarkers: the chemical imprints of life in planetary atmospheres. The archetypal biomarker is oxygen since it would disappear in less than 10 million years in the absence of life. Such an experiment can probably be carried out within the next decade.
The possibility of detecting life on planets in other systems remains a goal that is tantalizingly close. Such a detection would profoundly change the human race and would force us to re-address our place in the universe.
Stephen Andrew Appleby is from Lichester England where he earned his master’s degree from the University of Manchester in Mathematics and Physics, and completed his doctoral degree at Jodrell Bank Observatory in Theoretical Physics. He is a professor and a postdoctoral research assistant at Ewha’s Institute of the Early Universe.