Dr Sabrina Dyall, Associate Prof in Biosciences, UOM
‘We started off “combing” beaches to migrate from Africa to the rest of the world and now we are watching the aptly named Curiosity and Perseverance roving around on a planet millions of kilometres away!’
From ancient times humans have looked up at the skies and asked themselves whether they were alone in the universe, and also pondered: What is Life? The answers have ranged from the mythological to the philosophical and the religious, but now it is science that is unravelling the mystery of Life in its multifarious dimensions. One of the frontier fields in this respect is Astrobiology. To tell us about it and how the scientific quest for Life in the universe has potential benefits for mankind, we approached Dr Sabrina Dyall, a Mauritian scientist who has worked for NASA, where she did research in Astrobiology
Following in the footsteps of her parents and her elder sister Veena, Dr Sabrina Dyall became a laureate in 1988. At the Imperial College London, she graduated in Chemistry and Biochemistry and followed up with a PhD. Sabrina undertook postdoctoral studies at the Universities of California, Los Angeles (UCLA), Manchester and Melbourne. Her research focused on unicellular organisms and the evolution of cellular compartments, which led to several seminal publications, including two in the prestigious journals Science and Nature. Dr Dyall returned to Mauritius in 2010, where she is currently Associate Professor in Biosciences at the University of Mauritius. She retains much interest in Astrobiology, although she has now shifted her focus to topics directly relevant to Mauritius. What follows is nothing short of an exhilarating mini-tour of our galaxy…
* Perhaps a good way to start is to ask: How would you define Life? What are the different hypotheses about its origin?
I set the shortest exam question in the Biology undergraduate course at UoM a few years back: “Define Life”. My ex-students, now long graduated, still joke about it but did an excellent job at answering it.
Two words that can trigger a life-long debate. One answer can be obtained by using a biology textbook checklist when observing something suspected of being alive. Another answer could be: Life is made up of cells. Another one would define it as the ability to transfer information from generation to generation.
JBS Haldane wrote a whole book on the topic and concluded with “I know it when I see it”! NASA’s answer is “If it’s Darwinian, it’s alive”. Personally, I prefer the link that Schrodinger made between the Second Law of Thermodynamics and Life: Life is a process that stops your molecules from simply decaying into more stable forms.
Life may have originated on Earth around 3.7 to 3.9 billion years ago when the planet was 500-600 million years old and geologically unstable. Such instability would have given rise to high surface temperatures on land and in the oceans and to an atmosphere without oxygen but consisting of gases such as ammonia, hydrogen, carbon dioxide, hydrogen sulphide, etc. Thus, hypotheses on the origin of Life centre around reactions and molecules that would have been stable under such conditions.
Some hypotheses propose that the first cells formed in the deep ocean, others propose volcanic pumice as the cradle. How did the first cells transmit genetic information to their descendants? Most theories tend to favour RNA as the primordial genetic material. Such theories are fuelled by our advancing knowledge of biochemistry derived from studies of extant organisms. Sometimes I wish I could travel back in a Tardis (a fictional time machine and spacecraft) to that point in time…
* You have worked in Astrobiology. Could you please shed some light on this discipline, and where/how does your work fit into the search for extra-terrestrial Life? Can this kind of study be pursued in Mauritius?
Basically, astrobiology investigates the origin, evolution, distribution and future of Life in the Universe. It is a multidisciplinary field that assembles biology, chemistry, physics, geology, astronomy, planetary sciences as its main disciplines.
The major objectives are (1) to search for habitable environments in or outside the Solar System, (2) to search for evidence of prebiotic chemistry and Life on Mars and other bodies in the Solar System, (3) to investigate the origins and early evolution of Life on Earth, and (4) to investigate the potential for Life to adapt to challenges on Earth and space.
I was involved in NASA’s Astrobiology program when I was an Assistant Researcher at the University of California, Los Angeles (UCLA) in the early 2000s. There, I was part of an Institute that included biologists, chemists and geologists. My project aimed at investigating the origin and evolution of cellular compartments, in line with objectives 3 and 4. Other biologists were studying extremophiles: microorganisms that live at extremes of pH, salinity and/or temperature. Collectively, we were exploring what were the limits for cellular Life on Earth.
These data are now used to redefine “habitable environments” in planetary missions such as those of Curiosity. In parallel, we compared protein and DNA sequences between diverse organisms to model what the common ancestor to all extant living organisms might have looked like.
Life on Earth is made up of three main branches: Bacteria, Archaea and Eukarya. If we superficially observe a dog, a coconut tree, a bacterium, a worm and a carrot, we immediately think that they are very different. However, when we observe their basic metabolic properties and their information pathways, they are quite similar. The similarities strongly suggest that all extant organisms have a single common ancestor, or to put it in another way: all living organisms descend from the same cell.
Thus, DNA sequence analyses allow biologists to formulate hypotheses on the origins and evolution of Life, and to subsequently challenge the hypotheses. Such studies can indeed be pursued in Mauritius. So far, only a minor fraction of microorganisms on Earth has been thoroughly studied. There are several interesting habitats in Mauritius that can be explored for novel microorganisms.
* NASA’s Perseverance Rover has landed on planet Mars about a month ago. Its mission is to search for evidence of ancient life and collect rocks to be brought back to earth. Have there been other similar missions, including by other countries and on other planets that have been sent?
Perseverance is the most sophisticated of rovers sent to Mars, to join Curiosity and InSight. Curiosity has been studying habitable environments on Mars since 2012, and the race to find Life on Mars has erupted from the data generated. InSight is investigating geophysical processes and mapping the rocky planet. It has been getting quite busy around and on Mars with rovers and orbiters sent by China, India and the United Arab Emirates.
Currently, Perseverance is in the 45-km wide Jezero Crater, an ancient, 3.5 billion-year old river delta that was flagged as a potential habitable environment. Perseverance will now collect rocks and sediment from the area and screen for signs of ancient Life. Russia and the European Space Agency (ESA) will launch missions in 2024 to join the search.
Although most of the search for extraterrestrial Life has focused on Mars, missions have been planned to map Mercury and Venus. Europe and Japan launched BepiColombo to reach Mercury in 2025 and India plans to launch Shukrayaan-1 in 2023 to Venus.
* What are the kinds of evidence of life looked for? Have there been any promising hints to date?
Preliminary evidence that such missions look for is water. Life as we know it is dependent on water. The presence of liquid water on a planet or a moon also signifies that the temperature range is permissible for Life. Although Mars is now a frozen desert, NASA’s Curiosity has found evidence that it was once warmer and had flowing water bodies. Once the presence of water is established, one can then search for the presence of organic molecules that are cellular building blocks. Indeed, organic molecules have been detected in several locations on Mars. However, it is unclear whether these molecules were generated by biological as opposed to geochemical processes.
In the 1950s, Miller and Urey mimicked early Earth conditions on a mixture of simple inorganic molecules such as carbon dioxide, nitrogen, ammonia and hydrogen to generate organic compounds such as amino acids in a purely chemical process, without the intervention of living cells. Though promising, the discovery of organic molecules on Mars is not “damning” evidence on its own, but does contribute to the body of evidence.
Other evidence includes discovery of microfossils – these are impregnations of microorganisms in sedimentary rock. Why look for microorganisms? Because microorganisms can thrive under a wide range of temperatures, pH and salinities and are thus more likely to be found in harsh environments such as the Martian one. Carbon-based Life can also be detected through determining the ratio of isotopes 12C to 13C in molecular fossils. From what we know about Life on Earth, cells tend to favour one isotope over another.
* Why this interest in looking for Life elsewhere? How long does it date back to?
Humans are explorers. We started off “combing” beaches to migrate from Africa to the rest of the world and now we are watching the aptly named Curiosity and Perseverance roving around on a planet millions of kilometres away! We want to know what’s out there – are we alone in this immense Universe? This question has been with us for thousands of years. There are depictions of extraterrestrial beings in spaceships on ancient monuments in Mexico and Central America.
The debate over the existence of “other beings” has been around since Ancient Greece and took off after the acceptance that other planets in the Solar System revolved around the Sun, raising the possibility that these planets may harbour Life. In the 19th century, several renowned scientists such as Gauss, Galton and Tesla amongst others devised transmission systems to contact extraterrestrial beings.
* These missions are very expensive. Is there any likely ‘benefit’ for earthlings if ever life is discovered elsewhere in the solar system? What could be the possible impact of such a discovery – on science, on society at large?
From the point of view of science, it would be tremendous. We may encounter a new domain of Life with novel metabolic properties. This would contribute towards a deeper understanding of the origin of Life in the Universe. The novel metabolic and/or cellular properties could be engineered into developing biotechnologies and innovative solutions.
At the level of society at large, such a discovery would first and foremost satisfy our curiosity and settle this longstanding question of whether extraterrestrial Life exists or not. A second impact would be that humans would finally know that we are not alone and would move away from anthropocentric attitudes.
* The dry, forbidding landscape of Mars revealed by the Mars Rover doesn’t suggest that we are likely to see ‘little green men’ a la ET there soon isn’t it?
It is more likely that we find microorganisms because of the harsh conditions. I am sure all these orbiters and rovers would have long detected “little green men” if there were any roaming around!
* What do you make of the setting up of human colonies on Mars, an idea being floated?
I am not supportive of this idea unless it is strictly for scientific research. After what we humans have done to the earth, let us not go out and spoil another planet. The grass certainly does not seem greener on Mars, but I am against considering it a back-up planet to save humanity. Moreover, there is the problem of extremely high radiation exposure to resolve before this idea can even be entertained.
* A parallel endeavour is SETI – the Search for Extra-Terrestrial Intelligence. Who was the brain behind this project, what are the tools used and where has this project reached?
SETI was set up in 1984 by a small group of scientists that later expanded to include Carl Sagan and some Nobel Prize winners. The Institute initially engaged in research and surveillance through telescopes and spectroscopy in real-time. I remember connecting my Mac G5 to provide computing power to SETI remotely in the 2000s, wishfully waiting for that signal to pop up… SETI has pretty much similar objectives to NASA’s Astrobiology program but also widely engages in education and in promoting STEM subjects.
* Given the astronomical distances that have to be scanned, don’t they represent an obstacle? Doesn’t that tend to discourage the scientists?
Not really, telescopes and spectroscopy can retrieve data from the far corners of the Universe. Spectra can be analyzed for signatures indicating organic molecules or pre-biotic molecules relevant to Life. Distant planets resembling Earth both in size and orbit have thus been detected. Of course, these are several light years away and we do not yet have the technology to travel such distances although scientists could launch robotic devices to further explore the outer reaches of the Solar System.
* Again, the same question comes up: what next, especially given the costs?
We wait with baited breath for the outcome of Perseverance’s mission. In the next two weeks, we shall witness the helicopter Ingenuity undertaking reconnaissance flights in the Jezero Crater. Soon Perseverance will analyze the chemical signatures in rocks and sediments. These rocks will then be returned to Earth for more thorough analyses in the early 2030s. Meanwhile, NASA is working on a new rocket propelling system in its aim to send humans to Mars, a perilous 7-month journey. We shall need to be patient on an astronomical scale.
* Finally, how do you see the future unfolding in this search for distant Life and intelligence – what kind of intelligence could it be: of the AI type?
Given the astronomical distances, we could very well encounter AI before we encounter the natural intelligence that created it. Most of my answers have focused on identifying Life loosely resembling that on Earth. We should also keep our minds open to encounters with completely different manifestations of Life à la “I know it when I see it”.
* Published in print edition on 6 April 2021