Worlds Beyond: The Search For Other Life In The Cosmos

 

Astrobiology, Geobiology, and Life Beyond 

The field of Astrobiology is concerned with finding biology on other planets or other solid bodies in space.  Geobiology is the study of the interactions between living organisms and their geological environment. It explores how life influences geological processes and how geological factors, such as minerals and rocks, shape and affect life forms. The two fields of course overlap in many ways, as emergence of life throughout the cosmos is greatly dependent on geochemical conditions.  Besides a solid surface with minerals, whether in the form of a rocky planet, dwarf planet, or meteorite, other predictors of life are gaseous atmospheres and water. Chemical reactions are the kick starter for chemistry to turn into biochemistry. These reactions could come about through meteor impacts, volcanic activity, solar rays, hydrothermal vents, and more (or a combination of things). We know that one or a combination of these things led to life emerging on our wet rocky planet of Earth, but how can we detect life on solid surfaces that are beyond our reach? Read on. 

The Pool Of Possibility 

What pool do we have to work with in terms of our options we have to work with? In an (observable) universe that may contain 100 billion to 200 billion galaxies, tens of billions to hundreds of billions of solar systems in each galaxy, and about 10^22 planets, the possibilities may seem endless, but when we go back to the requirements, we need to be more cautious and specific in what we're looking for.  For examples, many planets in the universe are (like Neptune and Saturn in our solar system) gaseous, and therefore highly unlikely to contain life. Other planets may be solid and rocky, but lack the other necessary components such as water and gaseous atmospheres. We can even get more detailed than that, and say that some wet rocky planets may have all the necessary ingredients except carbon, which is crucial for life on Earth because of its unique ability to form complex molecules through chemical bonding. Is non carbon-based life a possibility? Yes, but there's a lot of extraterrestrial chemistry that we know nothing about that would have to be studied in order to even begin to find out. The point is, the problem complexifies with the more (necessary) questions that we ask, and since astrobiology is a multidisciplinary field that incorporates astronomy, biology, chemistry, geology, physics, and more, we need to examine these problems through a systems-approach instead of a singular approach, meaning that we need to tackle each problem within the context of other factors instead of on its own. 

Life Detection Methods

In order to improve and expand our search for extraterrestrial life, we need to employ the most high-quality and cutting edge technology. Spectroscopy as a generalized technique in science is a scientific method of studying objects and materials based on color.  As applied to astrobiology, it's a technique that entails examining the light released or captured by a planet's atmosphere or surface. Researchers search for distinctive patterns, like indications of water, organic compounds, or gases such as oxygen and methane, which might indicate potential biological processes. Chromatography in astrobiology is achieved through simulation experiments and analyses conducted in laboratories using Earth-based analogs or synthetic environments designed to mimic extraterrestrial conditions.  Types of chromatography include gas, liquid, and ion. Gas chromatography is extensively used in astrobiology for analyzing volatile and semi-volatile organic compounds in samples related to extraterrestrial environments or analogs. Liquid chromatography is used in order to separate non-volatile and polar compounds, including biomolecules. Ion chromatography is employed to analyze ionic compounds, including inorganic ions and organic acids. Of course, direct imaging through telescopes is also employed,

but is subject to challenges because stars emit significantly brighter light than the faint reflections from planets. Methods such as coronagraphs, starshades, and interferometry are employed to obstruct or reduce starlight, thereby enhancing the detectability of exoplanets. Capturing images of distant exoplanets in our galaxy or neighboring galaxies necessitates the use of high-powered telescopes equipped with sophisticated adaptive optics technology in order to minimize atmospheric distortions.  Advanced telescopes like the Hubble Space Telescope (HST), the James Webb Space Telescope (JWST), and future space observatories are capable of high-resolution imaging. They can capture detailed images of planetary surfaces, including features like mountains, craters, valleys, and atmospheres.  Space probes and rovers have delivered detailed images of planets and moons within our solar system, revealing their geological characteristics and surface environments. Hopefully sooner than later, advancements in aerospace engineering and long distance space travel can put more rovers, probes, and astronauts deeper into space. We have already observed nucleobase formation in various meteorites, showing that spontaneous formation of genetic building blocks happens elsewhere.

Life Beyond Us: Conclusion 

Some scientists, like biochemist and molecular biologist Dr. Steven Benner think that microscopic microbial life is common on wet rocky planets. Dr. Benner has said that he thinks about 90% of wet rocky planets will have microbial life on them. Other scientists who work (in some way) in astrobiology are less optimistic in terms of the figures they cite. In terms of intelligent life, it largely depends on evolutionary biology and processes in evolution that would produce an intelligent organism. The fascinating endeavor of space exploration and life detection will be an evolving puzzle throughout the 21st century and beyond, and you can contribute to it by pursuing research in one of the many relevant scientific fields that make up astrobiology. 

Sources:

Astrobiology At NASA - Life Detection

Search for Life outside the Solar System

Life: What It Is And How It Forms

 

Biology emerged from biochemistry which emerged from chemistry which emerged from physics. Sounds simple, no? Not quite. How the first protocell emerged on the early Earth to give way to humans, reptiles, insects, and all other forms of life is a complex and interesting problem that requires various areas of science, from astrobiology to biochemistry to physics in order to answer. But did life actually predate this protocell? According to NASA, life is a "self-sustaining chemical system capable of Darwinian evolution." Let's learn more about such systems. 

Origin Of Life 

It was once thought that chemical systems were disorganized and random. As chemistry and biochemistry in particular advanced, we realized that chemical and molecular systems exhibit features of Darwinian selection. Some molecules gravitate toward self-assembly and eventually form membrane-like structures or other biologically important constructs. Selection predated biology. The subfield of Chemistry that studies selection on a chemical and molecular level is called Systems Chemistry. This subfield is essential for studying the origin of life on Earth and other planets because it can help us discover how these systems generated the first protocell on Earth about 3.8 billion years ago, which then evolved and complexified. 

Dr. Gerald Joyce, a prominent figure in the origin of life research, conducted an experiment that made significant strides in elucidating chemical evolution. The experiment centered on the in vitro evolution of RNA enzymes, also termed ribozymes, which have the capacity to catalyze RNA replication.

Joyce and his research team commenced with a diverse pool of random RNA sequences. They subjected these sequences to a process known as in vitro selection or systematic evolution of ligands by exponential enrichment (SELEX). During SELEX, RNA molecules demonstrating even rudimentary abilities to catalyze self-replication were preferentially amplified and isolated. Subsequent rounds of mutation and selection were applied to these chosen molecules, progressively enhancing RNA replicase activity over time. By showing that RNA molecules could evolve in the laboratory to perform a function as complex as self-replication, Joyce provided experimental evidence for the plausibility of chemical evolution. 

Along with this (and other) experimental support, the RNA world hypothesis for the origin of life on Earth is most prominent compared to others (such as metabolism first and protein first) because RNA uniquely contains catalytic as well as informational functions. It is able to catalyze a variety of biochemical interactions as well as store genetic information.

Geochemistry On The Early Earth 

In order to begin understanding the complex process by which this occurred, we must understand the geochemistry. The early Earth was very different than our current beautiful planet. Billions of years ago, Earth had very low levels of oxygen (less than one part per billion) while having carbon dioxide levels likely exceeding 70%. 

In order to replicate conditions on the early Earth and hopefully generate genetic material, Stanley Miller and Harold Urey conducted an experiment simulating early Earth conditions to demonstrate the synthesis of organic compounds from inorganic constituents. They used methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O) in a ratio of 2:2:1, along with an electric arc to simulate lightning. They were able to produce simple organic compounds, including amino acids, which are the building blocks of proteins and other macromolecules. Although this experiment was an exciting leap for the study of the origin of life, it wasn't without it's inaccuracies. Later research suggests that the Earth's early atmosphere likely consisted of about 97% carbon dioxide (CO2) and 3% nitrogen (N).  In addition, the type of glassware they used, borosilicate glass, was crucial in catalyzing organic compound synthesis. This may not be a major issue, because the first protocell on Earth was generated through mineral and geochemical interactions. 

The most likely settings for where life got started on Earth are hydrothermal vents, tidal pools, and hot springs. There are multiple reasons for this, including them being a rich source of chemical energy, serving as mineral catalysts, and being able to concentrate a high volume of organic (carbon-based) molecules. Another theory is Panspermia, which posits that life emerged on Earth through extraterrestrial delivery (through a meteorite or similar object). Panspermia was more popular among origin of life scientists in years past, but seems to have gone down in popularity, probably because many settings on early Earth were seemingly great for abiogenesis (formation of life from inorganic material) to occur. 

Sources:

The antiquity of RNA-based evolution | Nature

RNA-catalyzed evolution of catalytic RNA - PubMed (nih.gov)

Geochemistry and the Origin of Life: From Extraterrestrial Processes, Chemical Evolution on Earth, Fossilized Life’s Records, to Natures of the Extant Life - PMC (nih.gov)