Is It All About Aliens? An Astrobiological Review

This artist's concept of Kepler-452b, which is about 60 percent larger in diameter than Earth.

Credits: NASA/JPL-Caltech/T. Pyle

Is It All About Aliens? An Astrobiological Review

By Nathan Hadland

Astrobiology is an emerging and continually evolving science that seeks a comprehensive and encompassing definition. Indeed, the principles of the field have fundamentally existed since humans developed the ability to form conscious, inquisitive thought. The questions that form the basis of scientific pursuit include, most primitively, “are we alone” and “where did we come from?” In its basic form, astrobiology is the study of the origin, evolution, and distribution of life on Earth and in the universe. It is a survey of the broad processes that encompass all scientific disciplines from astrophysics to molecular biology. Commonly, when I am asked what I study at university, I get a blank expression of incomprehension in response. Not surprisingly, the pervasive perception of astrobiology is that it is the study of aliens. It seems that the public views the field as a pseudo-scientific speculation of extraterrestrial civilizations. Of course, if you are reading this you are likely aware that this is not the case. The field requires an understanding that surpasses any singular field of study and therein lies the difficulty. An astrobiologist must understand a large array of processes that govern the universe in order pursue extremely complex questions. However, taken at face value, the wide scope and complexity of the field can seem to the public as horrendously narrow and therefore unreasonable to pursue as a field of scientific inquiry.

Life appeared quickly after the heavy bombardment, early in Earth’s history.

So what are the questions that an actually astrobiologist pursues? Perhaps most significantly, the origin of life. At a glance, the question of abiogenesis, or the evolution of living organisms from an inorganic source, seems like a simplistic idea. However, astrobiologists have been unable to correctly replicate the conditions under which life arose. The famous Miller-Urey experiment used a mixture of primitive gases (ammonia, methane, and hydrogen) that were thought to be present in the “primordial soup” and generated organic compounds, a key component in the jump from abiotic to biotic material. One prevailing idea is that hydrothermal vents allowed the formation of these reduced organic compounds, and thus, the ancient chemosynthetic microorganisms currently living in these environments may hold the key to the origin of life (2). Another popular idea that allows the jump from these basic amino acids to replicating and evolving microbial life is the RNA World Theory. The theory postulates that ribonucleic acid (RNA) arose as a biotic catalase and became the first dominant genetic material as opposed to deoxyribonucleic acid (DNA). Much of the current conversation centers around whether genes or metabolism arose first (1). Any model that attempts to demonstrate an abiogenesis mechanism must show the step from organic monomers and polymers to some sort of collection of these molecules with genetic hardware. Yet another theory of the origin of life on Earth is called “panspermia”, which states that the biology on Earth was seeded from another source such as Mars, Europa, or another planetary system using comets and asteroids, so long as the bactericidal effects of UV radiation were appropriately managed through shielding in rock (3). However, regardless if this postulation is correct, this mechanism is ultimately unsatisfying because it transfers the problem of life’s origin to another source.

The study of exoplanets will reveal what makes a planet habitable.  

A major aspect of astrobiology is the field of planetary science, including astrogeology, biogeology, astroecology, and the study of exoplanets. The question of what makes a planet habitable is perhaps the most interesting. The largest effort in this area is the exploration of our own solar system. The smaller bodies that are the most promising for extant life include Mars, Europa, and Titan. The discovery of microbial life within our solar system that has distinct biochemistry apart from life on Earth would be a clear indication that abiogenesis occurred independently several times in a single planetary system and would therefore imply that it is a relatively easy jump from simple collections of organic molecules to cellular life. Indeed, such study of these bodies as well as extrasolar terrestrial planets and their respective atmospheric composition, raises interesting questions with regards to the minimum necessary requirements for the rise of microbial life and further, for multicellular life (4). Determining the habitable zone (HZ) around a star is an interesting point of research. The HZ cannot be too close to the star, as is the case for red dwarfs, for fear of tidal locking. The HZ around a larger star is highly unstable because of the violent behavior inherent in supergiants and their relatively short lifespans. Additionally, the presence of a large jovian planet may be necessary to mitigate the number of comets and asteroid impacts and consequently reduce the potential number of mass extinctions (5). Astrobiologists answer these questions by investigating the history of Earth, including the formation of the solar system, climate evolution, paleontology and mass extinctions, and the interaction between Earth’s geology and biosphere.

Human exploration of the cosmos, a topic that ARES is extremely interested in, is a major aspect of astrobiology. Building effective life support systems for humans to live in the harshest environments our species has ever explored is an extraordinarily difficult issue. With our Research to Advance the Development of Interstellar Horticulture (RADISH), we tackle the problem of creating a sustainable, in situ food production method on Mars. Experimentation with elevated light levels, hydroponics, and controlled environmental parameters may hold the solution (6). Remediation of perchlorates within Martian regolith is a major issue and also very interesting topic of research. The medical effects of weightlessness, the psychological aspects of extended space flight, protection from radiation, and creating effective habitats are all being heavily researched in industry, in governments, and in academia.

Astronomers use radio telescopes to survey the skies for extraterrestrial signals.

The aspect of astrobiology that the layman thinks of when encountering the field is the Search for Extraterrestrial Intelligence (SETI). The most effective method for this effort is the use of radio telescopes to survey the universe for signals from another intelligent civilization within our galaxy. Astrobiologists and astronomers working in this field utilize the Drake Equation which is:

N =R*f_g f_p n_e f_l f_i f_c L

Where N=the number of galactic civilizations where communication is possible; R*= the rate of star formation in the Milky Way; f_g=the fraction of stars capable of supporting life; f_p = the fraction of stars with planets; n_e = number of planets per system with ecologically suitable conditions; f_l = fraction of planets where life originates and evolves into complexity; f_c = the fraction of planets with intelligence (measured by ability to build a radio telescope); and L= mean lifetime of the technological civilization (7). Notice that if any one the values approaches zero, the number of civilizations within our galaxy approach zero as well. The discovery of another intelligent civilization would be perhaps the most momentous and altering event in human history and thus the search continues.

Astrobiology is one of the most exciting and prevalent scientific fields in contemporary society. The pursuit of astrobiological questions involves the integration of knowledge spanning from physics to planetary science to molecular biology and beyond. To be an astrobiologist means to avoid viewing these fields in isolation, but rather view the biosphere and the universe as a whole, and use reductionist thinking to find answers. Indeed, the most prevalent and perplexing questions facing humanity employ aspects of astrobiology, such as anthropogenic climate change and exploration of the solar system. As Carl Sagan said “Somewhere, something incredible is waiting to be known.” We intend to find out.

Nathan Hadland is an astrobiology student at Florida Institute of Technology where he studies the atmospheric dynamics on ice giants such as Neptune and Uranus. Nathan is also a member of the RADISH research group at Florida Tech and on the Farmbot team. He has been an active member of ARES since its inception in the fall of 2016. 

References:

1.  Copley, Shelly D., Smith, Eric, Morowitz, Harold J. The origin of the RNA world: Co-evolution of genes and metabolism. Bioorganic Chemistry 35-6, 430-443 (December 2007) 
2. Martin, William, Baross, John, Deborah, Kelley, Deborah. Hydrothermal vents and the origin of life. Nature Reviews Microbiology 6, 805-814 (November 2008).
3. Mastrapa, R.M.E., Glanzberg, H., Head, J.N., Melosh, H.J., Nicholson, W.L. Survival of bacteria exposed to extreme acceleration: implications for panspermia. Earth and Planetary Science Letters 189-1, 1-8 (June 2001).
4. Shapiro, Robert, Schulze-Makuch, Dirk. The search for alien life in our solar system: strategies and priorities. Astrobiology, 9-4, (2009).
5. Franck, S., Block, A., Bloh, W., Bounama, C., Garrido, I., Schellnhuber, H.J. Planetary habitability: is Earth commonplace in the Milky Way? Naturwissenschaften, 88-10, 416-426, (October 2001).
6. Nelson, M., Dempster, W.F., Allen, J.P. Integration of lessons from recent research for “Earth to Mars” life support systems. Advances in Space Research, 41-5, 675-683, (2008)
7. Cirkovic, Milan M. The temporal aspect of the Drake Equation and SETI. Astrobiology, 4-2, (2004).