Beneath Alien Skies, Part Two: Charting Our Course
Beneath Alien Skies, Part Two: Charting Our Course
Preksha Sanjay Madhva, Robotics Engineer
8.2 minute read
Fellow Xenologists, the universe beckons! Vast and filled with secrets waiting to be unearthed, the uncharted expanse of planets before us holds the promise of astounding lifeforms. But what factors must we consider as we chart our course and select our expedition’s destinations? Join me as I ponder over what planetary factors could affect the kinds of lifeforms we’d find and how they play a hand in shaping the local ecosystems.
The Unseen Hand of Gravity
Gravity, the fundamental force that binds celestial bodies, exerts a pervasive influence on the evolution of life. On Earth, we see its effects in the sturdy limbs of terrestrial animals, the intricate circulatory systems that pump fluids against its pull, and the limitations it imposes on the size and scale of flying creatures. Now, imagine a planet with significantly stronger gravity. Life on such a world might be characterized by compact, low-slung forms, perhaps with multiple limbs to provide stability and distribute weight. Skeletons would likely be far denser and more robust than creatures of Earth, capable of withstanding the immense gravitational forces. The very act of movement could be a more energy-intensive endeavor, possibly leading to slower metabolisms or highly efficient musculature. Furthermore, the challenges of circulating fluids against a powerful gravitational gradient could drive the evolution of complex, multi-chambered hearts or entirely novel circulatory systems to allow the transportation of resources in multicellular organisms. Flight for larger organisms might be an insurmountable obstacle, potentially leading to a dominance of ground-dwelling or aquatic life. Even the structure of plant-like organisms could be affected, perhaps evolving to be shorter and sturdier to avoid collapsing under their own weight.
Pelorocephalus. Visual of a compact, low slung form. (Nobu Tamura)
Conversely, a planet with weaker gravity would present a dramatically different evolutionary landscape. Here, life might reach colossal sizes with delicate, lightweight structures. Imagine towering organisms with thin, elongated limbs or even buoyant forms that float effortlessly through the atmosphere or oceans. Skeletons, if present at all, might be minimal, providing only basic support. Circulatory systems would face less resistance, thus leading to simpler designs. Flight could become a much more accessible evolutionary pathway, which could give rise to enormous aerial creatures with vast wingspans. Even the fundamental processes of growth and reproduction could be influenced, potentially allowing for faster growth rates or different methods of dispersal. The very physics of such a low-gravity environment could open up possibilities for locomotion and body plans that seem fantastical from our Earth-bound perspective.
Diplocaulus. Visual of a compact, low slung form. (Entelognathus)
The Influence of Stellar Proximity and Orbital Paths
A planet's position relative to its star and the path it traces in its orbit dictate the amount and intensity of stellar radiation it receives, a crucial factor in shaping the energy landscape for potential life. On Earth, our comfortable distance allows for liquid water to exist across vast regions, and the steady influx of sunlight drives photosynthesis, the foundation of our food web. However, venture closer to a star, and the environment transforms dramatically. Planets bathed in intense stellar radiation might be scorching hot, rendering liquid water unstable on the surface. Life in such extreme conditions would necessitate remarkable adaptations to survive the heat. Their biochemistry might be based on entirely different sets of reactions that thrive at high temperatures, and they could possess sophisticated mechanisms for dissipating heat, such as highly reflective outer layers or internal cooling systems. Perhaps life would retreat to subsurface environments where temperatures are more stable, drawing energy from geothermal sources or chemosynthesis.
On the other hand, a planet orbiting far from its star would be a frigid realm, receiving only a faint trickle of light and heat. Here, liquid water might be locked away as ice, and life, if it exists, would need to contend with extremely low temperatures. Organisms living in this environment may prefer endothermic processes to allow them to survive extreme cold by absorbing heat and thus avoiding heat loss from something as basic as digesting food. These endothermic organisms might even evolve antifreeze-like compounds in their cells or circulatory systems to prevent freezing or possess incredibly slow metabolisms to conserve energy.
Scotia Sea Icefishes, like Chaenocephalus aceratus (Blackfin Icefish), have anti-freeze proteins that prevent their bodily fluids from freezing. (Uwe kils)
To such endothermic creatures, heat would quite literally be a death sentence, and as such would need to develop methods of survival with minimal heat generation due to basic actions of life like metabolism or locomotion. Subsurface oceans, however, warmed by internal geological activity, could become havens for exothermic life. Photosynthesis, if it occurs, would need to be incredibly efficient at capturing the meager available light, potentially leading to the evolution of novel photosynthetic pigments and light-harvesting structures, as green chlorophyll would no longer be the optimal method to capture the maximum energy from light.
The shape of a planet's orbit around its star adds another layer of complexity. Earth's relatively circular orbit results in fairly predictable seasonal changes. However, a planet with a highly elliptical orbit would experience dramatic swings in temperature and light intensity as it journeys closer and farther away from its star. Life on such a planet would need to be extraordinarily adaptable, capable of surviving both scorching summers and frigid winters. This could lead to the development of physiological mechanisms that enable rapid acclimatization to extreme temperature changes or the evolution of dormant states, similar to hibernation or aestivation on Earth, allowing organisms to survive unfavorable periods. Vast migrations to follow habitable zones as the planet orbits its star could also be a key survival strategy.
The Rhythms of Alien Days and Nights
The duration and intensity of a planet's day-night cycle, determined by its rotational period, can profoundly influence the biological rhythms and behaviors of its inhabitants. Earth's roughly 24-hour cycle has ingrained circadian rhythms into almost all forms of life, regulating sleep-wake patterns, metabolic processes, and even gene expression. Imagine a planet that rotates much slower, resulting in days and nights that stretch for weeks or even months in the equivalent Earth-time. Creatures from such a planet would need to adapt to these extended periods of light and darkness. Organisms might evolve highly efficient energy storage mechanisms to survive the long nights and develop specialized sensory systems that function optimally in either (and rarely both) prolonged light or darkness. Behavioral patterns could be drastically different, with extended periods of activity or dormancy tied to the slow cycle of light and dark.
Alternatively, a planet with a very rapid rotation would experience extremely short days and nights. Life here might evolve with fast metabolic rates and rapid behavioral responses to the quick transitions between light and dark. Sensory systems would need to be highly adaptable, capable of adjusting quickly to the changing light levels. The constant flux might also influence patterns of activity and rest, potentially leading to fragmented periods of both rather than the consolidated circadian rhythm blocks we see with humans on Earth.
How Chemical Composition Shapes Life's Blueprint
The fundamental chemical makeup of a planet provides the raw materials for life and dictates the types of biochemical reactions that are possible. Earth's abundance of carbon, oxygen, nitrogen, and hydrogen has provided the foundation for our carbon-based, water-dependent life. However, the universe is a vast repository of elements, and planets with different compositions could potentially give rise to life with entirely different biochemistries. Silicon, as explained earlier in Beneath Alien Skies: Part One, shares some chemical similarities with carbon and has been proposed as a potential alternative backbone for complex molecules.
Comb Jelly (Cydippida) have photo-proteins that react with the presence of calcium (which could also be dissolved in alternative solvents to water like liquid ammonia) to give its ethereal glow and is an example of how the chemical make up of the creature's surroundings can influence their evolution. (Ribeirodos Santos)
Furthermore, the availability of different solvents could drastically alter the nature of life. While water is a versatile solvent, other liquids like methane or ammonia can exist under certain planetary conditions and could potentially serve as the medium for biochemical reactions. Life in a methane ocean on a cold moon would likely have a biochemistry and set of adaptations utterly unlike our own. The presence or absence of specific elements could also influence the structural components of life. Imagine organisms with exoskeletons made of different minerals and metals or internal frameworks based on elements less common on Earth. The very nature of metabolism, energy acquisition, and reproduction could be fundamentally different depending on the available chemical building blocks.
A Fresh Breath of Alien Air
A planet's atmosphere plays a crucial role in regulating temperature, shielding against harmful radiation, and providing the gases necessary for respiration (for Earth life, at least). An atmosphere with a different composition of gases would necessitate radically different respiratory systems or even the evolution of non-respiratory metabolisms. For example, on a planet with a methane-rich atmosphere, life might have evolved to utilize methane as an energy source, perhaps through chemosynthetic pathways. The absence of oxygen, so vital for most complex life on Earth, would not preclude the existence of life. Anaerobic organisms, one amongst the many denizens of Earth, thrive in oxygen-poor environments and have, in fact, been the dominating form of life on Earth before organisms like algal blooms vastly altered the oxygen concentration in our atmosphere.
Thermophilic bacteria like Methanopyrus kandleri found in deep sea thermal vents are rod-shaped obligate anaerobic organisms and use hydrogen and carbon dioxide for respiration in a process called methanogenesis.(Photo byfkfkrErbe, digital colorization by Christopher Pooley, both of USDA, ARS, EMU)
The density and pressure of an atmosphere can also exert significant evolutionary pressures. High atmospheric pressure might favor smaller, more compact organisms to withstand the crushing forces, while low pressure could lead to larger, more expansive forms. The presence or absence of an ozone layer, or its equivalent for other types of radiation, would influence the amount of harmful ultraviolet or other high-energy radiation reaching the surface, driving the evolution of protective pigments, shells, or nocturnal habits. The very dynamics of the atmosphere, such as wind patterns and cloud cover, could also shape the distribution and evolution of life.
How Temperature Defines Habitable Niches
The overall temperature of a planetary environment is a fundamental determinant of the types of biochemical reactions that can occur and the physical states of essential molecules like water. Earth's diverse temperature zones have fostered an incredible array of life adapted to different thermal niches, from the icy poles to scorching deserts and deep-sea hydrothermal vents. On other planets, the prevailing temperatures could be far outside the range that Earth life can tolerate.
Extremely hot planets might harbor thermophilic or hyperthermophilic organisms with enzymes and cellular structures that remain stable and functional at high temperatures. They might thrive in volcanic regions or deep subsurface environments where heat is abundant. Conversely, frigid planets could be home to psychrophilic (or cold-loving) organisms with adaptations to survive and even thrive in sub-zero temperatures, perhaps with specialized proteins that maintain flexibility at low temperatures or antifreeze compounds that prevent ice crystal formation. Life on such worlds might be confined to specific microclimates, such as geothermal vents in icy oceans, where liquid water can exist. The overall global temperature of a planet, therefore, dictates the fundamental constraints on the types of life that can arise and the strategies they must employ to survive and reproduce.
Xanthoria Elegans, a lichen that can continue photosynthetic processes at -24C and can even survive in space for 16 hours. (Richard Droker, CC BY-NC-ND)
In conclusion, each of these planetary factors, acting in concert, creates a unique set of environmental pressures that would guide the adaptation of traits and the trajectory of evolution on other star systems. The sheer diversity of potential planetary conditions suggests that the life that might exist beyond Earth could be far more varied and wondrous than we can currently imagine, pushing the boundaries of our understanding of biology and the very nature of the way life would blossom under different suns.
Having investigated my exoplanetary survey records, I, the expedition’s Xenologist, have narrowed down our list of contenders to four planets. Come and take a look at my navigation systems! The first planet on our expedition is a seemingly barren, grey world designated Cryptos. Its surface appears desolate, scarred by ancient impacts and devoid of any visible flora or fauna. Yet, I have spectroscopic analysis that hints at vast subsurface caverns teeming with unique life forms shielded from the harsh exterior. I believe we can find a variety of life there, though perhaps too small to be visible to the naked eye. The second hologram shimmers with the familiar deep blue of Neptune. Advanced scans indicate thriving ecosystems within its icy, ammonia-rich oceans, adapted to extreme pressures and frigid temperatures. The third planet pulses with highly anomalous thermal signatures in the holographic display. Designated Ignis, its surface is a riot of vibrant purple and fiery red vegetation, hinting at extremophile life forms thriving in the scorching conditions under an alien sun. Finally, the fourth projection swirls with the thick, yellowish clouds of Venus. High fidelity optic arrays, however, reveal colossal life forms, dubbed "sky whales," gracefully navigating the sulfuric acid atmosphere, their buoyant bodies adapted to the dense environment. So quick, pack your bags and double-check your atmospheric processors. Let’s ignite our engines and forge a path to discovery!
Recommended column to read next: Beneath Alien Skies, Part One