Alien Biochemistry

Biochemistry is a broad scientific field concerning the chemical makeup and behavior of living organisms and their environments. Life from Home is carbon-based and requires liquid water, but has an array of other chemical features that may not necessarily be shared with other water-solvent carbon-based organisms. Alien life is extremely diverse, as each homeworld poses its own elements, opportunities, and challenges that drive its inhabitant’s evolution.

Most known life requires several fundamental chemical building blocks in order to develop and function, around which the entire domain of organisms is based; however, these essential components vary. Alternate biochemistry is a scientific branch that seeks to catalog and study the variety of ways in which alien life has developed.

Currently, the vast majority of alien life discovered is simple cellular life. Macroscopic organisms, though relatively rare, can still be presumed to be abundantly common throughout the galaxy and universe.

Bases

Carbon atoms are an excellent building block for life. Carbon by itself is a relatively abundant atom throughout the universe and is able to form four simultaneous valence bonds with other atoms, permitting an enormous number of potential chemical compounds for life to build upon. The strength of the bonds themselves are of a relative median allowing them to form into large complex compounds which remain stable under some natural conditions and react under others, making them effective in biological processes. Carbon atoms can also form long chains with themselves and other atoms, a characteristic fundamental to biological structures such as proteins and DNA.

Carbon-based life is as such the most common known form of life, based on current discoveries. However silicon-based life is known to exist, found generally on hotter worlds due to the nature of silicons properties. Carbon is also more likely to be pulled into a world’s core of hotter and denser worlds, making it less abundant for surface life. Silicon-based life is often anaerobic as silicon tends to form silicon dioxide in the presence of oxygen (rather than carbon dioxide in carbon environments). Silicon dioxide is a solid and inhibits the development of life.

Other bases are thought possible under rare but not impossible conditions, such as boron and sulfur. Numerous metals such as iron, titanium, and tungsten are also able to form their own complex compounds when combined with oxygen into their respective oxides, and life based on these elements is theorized to occur on extremely hot worlds where carbon-based and even silicon-based life could never survive.

Solvents

Water

Water is a critical component of Home-based life. Water possesses an asymmetrical electric charge in its atoms, making it a polar molecule; this property gives it the tendency to pull apart the bonds of various other common compounds that are also polar, dissolving them and carrying them elsewhere. For the origin of life, water has the tendency to create a “primordial soup” that allows ample potential for the creation of biological building blocks, as well as an environment for any life that develops to perform biological functions.

Before humanity left Home, it was often presumed that alien life would most commonly utilize water since it’s such an effective solvent and so abundant throughout the universe. Current research shows this to be the case, but a variety of other solvents have been found to host native life as well, with other solvents theorized to host rare exotic lifeforms. Many of these alternate solvents are not stable within oxygen atmospheres, and so their life is likely to be anaerobic.

Ammonia

Ammonia possesses many of the characteristics needed to be an effective solvent. It shares many similarities with water, and has its own set of chemical groups analogous to water-based biochemical groups. The range of temperatures that support liquid ammonia varies with pressure; at a pressure of 1 atm, the range is -78°C to -33°C, but at 50 atmospheres the boiling point is 88°C with almost the same freezing point.

Hydrocarbons

Hydrocarbons constitute a group of solvents applicable on lower temperature worlds. Hydrocarbons are a less effective solvent than water, but are also less disruptive to biochemical bonds. Regardless, worlds that possess liquid hydrocarbons are typically too cold to support liquid water.

Methane is the most common hydrocarbon able to act as a solvent, and relative to water is liquid at extremely low temperature ranges. Methanol is another hydrocarbon, with a liquid temperature range higher than methane. Both liquid methane and liquid methanol have been found to host life.

Supercritical Fluids

Supercritical fluids are substances at a temperature and pressure above their critical point where there is no distinction between liquid and gas. Supercritical fluids are common in high-pressure and/or high-temperature atmospheres, particularly those of gas giants. Supercritical hydrogen and supercritical carbon dioxide have both been shown to be effective solvents, and are found in many planetary environments. Water is also somewhat commonly found as a supercritical fluid, not only within gas giants but even as familiar as billowing from thermal vents in the oceans of Home. Only supercritical water has been found to host life.

Formamide

Formamide is an excellent solvent and possesses a liquid temperature range comparable to water. It has been theorized that formamide is in fact more effective than water at accommodating the development of life, but in primordial conditions formamide itself requires water combined with exceptional heat circumstances in order to form, making it unlikely for life to develop within it rather than the inherently far more abundant water.

The moon QY-Devonias-IIId is home to the only known example of naturally occurring formamide-solvent life.

Sulfuric Acid

Perhaps too effective of a solvent, sulfuric acid has been found to harbor very simple life on various hot worlds. Highly reactive with the ability to dissolve a diverse range of compounds, sulfuric acid is the only common high-temperature solvent, remaining in a liquid state at temperatures far higher than water. The abundance of hot planets where sulfuric acid can pool under the same conditions that boil or destroy other potential solvents afford the acid many chances to develop life free of solvent competition, pushing new and exotic lifeforms (albeit often very simple) into existence.

Other Alternates

Arsenic and Phosphorus

Phosphorus is an important element in Home life, being one of the key constituents in DNA and other biomolecules. Arsenic is also an element, near phosphorus on the periodic table, but in contrast is very toxic to most natural life from Home for which it interferes with biochemical processes. Arsenic and phosphorus are however very chemically similar, and throughout the universe arsenic is actually more abundant than phosphorus. Compounds that do utilize arsenic instead of phosphorus are less stable in water, making them less likely to be widely incorporated into water-soluble biochemistry. Despite this trait there are numerous examples of life known to exhibit a phosphorus-arsenic reversal, where arsenic forms a key component for their biological structure and phosphorus is the toxic component.

Multi-Colored Photosynthesis

Plant life from Home is green because the photosynthesizing cells absorb the sun’s red and blue light, but not all of it’s green light, which is reflected and gives plants their color. However, the sun emits light predominantly on the green spectrum, thus creating an abundance of energy at this wavelength. Plants evolved to reflect some of this green light, as the energy fluctuations between the peak intensity of day and the darkness of night proved too intense for photosynthesizing cells to handle.

These particular circumstances are specific to Home. The integrity of the cells, the properties of the sun’s emitted light, the length of Home’s day, and the distance from Home to the sun are just some of the deterministic factors that led to plants developing their predominantly green color. Across known space, different circumstances have led to photosynthesizing life developing a wide range of color schemes dependent on their own unique circumstances.

Chirality

In chemistry, chirality is a geometric property of chemical compounds that can prevent two otherwise identical molecules from being able to interact with one another. A molecule is considered chiral if its component atoms can be arranged in more than one configuration such that two otherwise identical molecules cannot interact with one another. Typically, chiral compounds have a “handedness”, a left and a right. The molecules are otherwise identical in almost all ways related to their properties.

Home-based life is carbon-based, composed of amino acids and other compounds like sugars. Many of these compounds are chiral, but the orientation was set in the earliest stages of evolution, and as such all proceding life has used the same chirality for a given compound. The orientation however does not appear to have any benefit one way or the other, and as such is seemingly determined randomly.

Some alien lifeforms have been found to utilize some of the same building blocks as life from Home, both of the same and opposite chiral orientation. When two lifeforms are composed of matching chiral compounds, even if from different life domains, they may be able to interact with one another such as through consumption and digestion. However, two lifeforms that utilize the same chiral compounds of opposite configuration may exhibit identical properties, but simply cannot interact in a normal fashion as the mirrored compounds are incapable of bonding.

Many of the building blocks of life, even those beyond carbon, are chiral. A multitude of alien lifeforms have been found that share some of their fundamental compounds with life from other worlds, often sharing a compound that life from Home does not use. The chiral configurations are, in most cases, deemed to be mathematically random; where data is sufficient, catalogs show an equal share of handedness between life of different origins.

Non-Chemical Life

Life discussed in almost all contexts relates to biological life based on chemical interactions between atoms and compounds. But an extremely exotic form of life is believed to exist based on standard plasma, in which charged particles exhibit partitioning similar to how cells create cell walls to isolate their internal structure from their environment. In the single example known, plasmas found in the upper atmosphere of a gas world had naturally formed a basic ecosystem.

Assumptions and Future Developments

Based on all discoveries so far, it is well presumed that basic life in the universe is extremely common and diverse. Many theories propose additional forms of life exotic and unlike anything discovered thus far, possible under rare conditions. Humanity has thus far explored barely a speck of the galaxy, only around 0.000003% of its star systems; there are undoubtedly rarer and more exotic discoveries yet to be made, far beyond the imagination.

Numerous alternate biochemical concepts not yet discovered in nature have been proposed as distinct possibilities, based on current astronomical and biochemical analysis.

Alternate Solvents

Many compounds related to water that consist of a hydrogen atom bonded with two other atoms have been proposed as alternate solvents, such as hydrogen fluoride, sulfide, and chloride. These compounds are all found to be lacking in some important properties that inhibits them from being a competitive solvent on their own.

Liquid nitrogen and liquid hydrogen have been proposed as potential solvents on extremely cold worlds. While worlds have been found with these liquids on or under their surface, no life has yet been found to utilize it.

Sulfur-based and borane-based life is thought to be possible. They exhibit some of the properties that make carbon effective, but have a multitude of inhibiting properties that would pose significant challenges to developing life.