HKU Bulletin October 2012 (Vol. 14 No.1)

Cover Story We Are Stardust Discovery of complex organic matter in stardust may give clue to origins of life. If Professor Sun Kwok had a dollar for each time someone had asked him “Is there life on Mars?”, he would probably be a very rich man. It is the burden of every astronomer to be asked this question, usually in a not-too-serious way. However, recently, Professor Kwok, who is Dean of the Faculty of Science, has been giving a very serious answer. “I am more optimistic than ever before that there is life elsewhere,” he says. “Not aliens, but bacteria, micro-organisms.” His conviction springs from his discovery – made together with Dr Zhang Yong, Research Assistant Professor in the Department of Physics – that organic compounds of unexpected complexity exist in the stardust that is strewn across the universe by dying stars. “So complex are these compounds,” says Professor Kwok, “that they’re similar to those that make up living organisms.” The findings suggest that complex organic compounds can be synthesised in space and may even have seeded life on Earth and other planets. Professor Kwok has done a great deal of research during his 30-year career into planetary nebulae (dying stars) and has long had a deep interest in stardust – small particles made by stars at the end of their lives and emitted across the universe. Infrared emissions The new findings came about when he and Dr Zhang were studying the well-known but mysterious infrared emissions that are found in stars, interstellar space and galaxies. Collectively known as ‘Unidentified Infrared Emissions’, their existence is nothing new in scientific fields. “When a star dies it ejects atoms, molecules, solids, we have long known about this,” says Professor Kwok. “But in the past we thought it was simple inorganic matter. However, analysis of spectra of stardust – using infrared spectroscopic data – shows that these emissions contain a mixture of aromatic [ring- like] and aliphatic [chain-like] components, with chemical structures resembling those of coal and petroleum.” Understandably, this has sparked huge interest. The highly respected journal Nature reported the findings, and many other publications, both scientific and general interest, have picked up the story. There has also been press coverage around the world, and it has only been fuelled recently by the landing on Mars of the United States’ ‘Curiosity’ rover and the ‘where-do-we-come-from?’ sci-fi movie Prometheus . “Our work has shown that stars have no problem making complex organic compounds under near vacuum conditions. Theoretically this is impossible, but observationally we can see it happening,” says Professor Kwok. The implications of the discovery are vast. Scientists have believed since the 1950s all things on Earth are derived from simple chemicals. The Miller-Urey Experiment (published in 1953 and considered to be the go-to origin of life experiment) simulated hypothetical conditions thought to be present on early Earth and tested for the occurrence of chemical origins of life – thereby showing that it was possible for life to have formed in this way. “But if stars can make such complex compounds, then the ingredients of life may be more common than we thought, and that process of creating life may have been easier than we thought because complex compounds were involved, not just simple ones,” says Professor Kwok. “Life elsewhere” “If stars can make complex compounds, and across the galaxy there are many, many stars ejecting this stuff, so some of it must have spilled into other stellar systems and other planets – so maybe there is life elsewhere.” These ‘ifs’ give rise to even bigger and increasingly intriguing ‘ifs’. Says Professor Kwok: “If we found signs of life elsewhere, it would give us a second example biology – Earth being the first example. And, if so, will these other forms of life be similar to us or very different? If similar, how come? Do we share the same origin?” “Then there is the whole major question of how did this stardust get into the Solar System and how did it reach Earth?” One theory is that as the organic dust is similar to compounds found in meteorites it could have been carried in comets and asteroids that bombarded the Earth four billion years ago. Perhaps when Joni Mitchell sang “We are stardust. Billion year old carbon,” she was nearer to the truth than she knew. Professor Kwok, has recently been elected Vice-President of the International Astronomical Union (IAU)’s Bioastronomy Commission 51, which was held this year in Beijing. The IAU, which has 10,000 members worldwide, was founded in 1919 with the aim of promoting and coordinating the science of astronomy through international cooperation. Professor Kwok was particularly thrilled that a surprise guest attended the event – China’s Vice-President Xi Jinping. “None of us knew the Vice-President would be attending – his presence is a strong signal of China’s commitment. I’m very excited about what’s happening there, they have big plans to spend billions on astronomy – a billion alone on building a telescope in Antarctica. While Europe and the US may be growing more cautious in their spending at the moment, China has the commitment and desire to explore space.” M i j k l j m n o p p k q r s p t u j k s r v v k j w x y z { k | } ~ j v w k p p w y s k j y k y y r u r y q r p k y k s w } y ~ j p o r j m y r r v j v | } u j r v m r y p k s p o r y p r j y p m k y q v p j k y k l m q y m k y } p p o r w l k v m x l k y j n y m p p r j m y w r } o r q m y k y n z k y n m y o r q y r p j y r x q m v s k x y p k r l y x s p x j m y n y r r p m y n k l q r k j n y m v p o m n o j p r o m v m p x j r k s p o r y r x q { v p | r y { m p o p o r x q r w r r q r v k r If stars can make such complex compounds, then the ingredients of life may be more common than we thought. ¡ ¢ £ ¤ ¥ 09 October 2012