The search for alien life is real science, and we’re getting close
Sun Kwok says research in recent years points to the real possibility of a discovery in the near future – an awe-inspiring thought for many of us, especially the young
To most people, extraterrestrial life is science fiction. However, research over the past 25 years has turned this topic into a real area of scientific inquiry. For the first time, scientists are optimistic that extraterrestrial life will be detected in the near future, probably within the next 20 to 30 years.
No, I am not talking about the possibility that we will be visited by humanoid aliens like those in the movies ET or Close Encounters of the Third Kind. Instead, I am talking about lower life forms similar to the most common and oldest organisms on Earth: bacteria. Although we tend to associate life with animals and plants, in fact much of the living biomass on Earth is in the form of microorganisms.
Humans need to consume water and breathe in oxygen, and we can only survive within a narrow range of temperatures. Bacteria are much more resilient. They can flourish in high temperatures, high acidity and extreme dryness. Bacteria have been found in the driest deserts of Chile, frozen lands of Antarctica, highly acidic water bodies, and hot thermal vents deep under the sea.
Right now, the only examples of life we have are on Earth. However, there is really nothing special about Earth. We are one of four rocky planets in our solar system, with a structure that is similar to those of our closest neighbours, Venus and Mars. The source of our energy is the Sun, an ordinary star – one of more than 100 billion stars in our Milky Way galaxy. In the past 20 years, astronomers have discovered several thousand other planets in our galaxy, and many of them are “Earth-like”. So the Earth is far from unique.
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We know from fossil records that life has been present on Earth for at least 3.7 billion years, but we are not sure exactly how it emerged. Life probably began in a “primordial soup” where suitable ingredients in a favourable environment gathered into self-replicating organisms. Until recently, many scientists believed that life developed on Earth in isolation, beginning with ingredients such as ammonia, methane and water. Over the past 20 years, we have learned that old stars produce complex organic compounds in abundance, and these products have been distributed all over the galaxy, including our early solar system. Between 4 and 4.5 billion years ago, our Earth was bombarded by debris from the early solar system. This brought heavy doses of organic matter, which probably facilitated the origin of life.
If external bombardments brought ingredients favourable to the formation of life to Earth, they probably did the same to Mars. From pictures taken by rovers that have been roaming Mars, we know that its landscape is very similar to deserts on Earth. Mars has a thin atmosphere and used to have water flowing on its surface. If life could develop on Earth, it could have done the same on Mars.
The search for signs of life was one of the motivations for the many space missions to Mars. These missions have analysed the contents of Mars’ atmosphere, sampled the soil on the surface, and drilled underground for signs of life. They have revealed evidence for liquid water 3.5 billion years ago and the presence of organic matter on the surface. These findings show that Mars had conditions suitable for the emergence of life.
If life is indeed discovered on Mars, what would be the potential significance? We would know that life is not unique, and Earth is not special. If extraterrestrial life is different from organisms on Earth or operates under different rules of biochemistry, our appreciation of life itself would widen. Among humans, groups of different races are more similar than different.
The detection of extraterrestrial life would also bring home the message that the rise of humans is a result of opportune events, and life could be quite common in the universe. Hopefully, this discovery would give us a new sense of community. We are a class of living organisms who, through incidental evolution, are presently cohabitating on a small, fragile planet. If life existed on Mars in the past but is now gone, why did life go extinct? What circumstances led to the demise of life on Mars but allowed life on Earth to thrive? What lessons can we learn from Mars to ensure the continued survival of organisms on Earth?
As an astrobiologist, I have never been so optimistic about the search for extraterrestrial life. I hope a discovery will come within my lifetime. But in any case, I want to encourage young people all over the world to enter this fascinating area of science. Closer to home, China is expanding rapidly in its space activities and has big plans to explore Mars. Youths in Hong Kong can have an opportunity to contribute towards these efforts. Your work may have a lasting influence on society for generations to come.
Sun Kwok is a chair professor of space science at the University of Hong Kong and president of the Astrobiology Commission of the International Astronomical Union. He has two recent books on this subject, Organic Matter in the Universe, and Stardust: the cosmic seeds of life