Competitions

The UK Centre for Astrobiology at the University of Edinburgh is pleased to announce that Ruby Allen-Brown is this year's winner!

Read her essay below:

Astrobiology’s Blind Spot: Does Starless Necessarily Mean Lifeless?

Traditionally, the habitable zone was a pivotal tool astrobiologists used to determine an exoplanet’s habitability: a conditional region encircling a star in which the temperature allows for liquid water to exist long-term on a planet’s surface. Accordingly, the existence of life on rogue, starless planets was not considered until decades later when scientists realized habitability is more complex. Even today, rogue planets are still overshadowed with discussions of life on glacial moons such as Europa dominating astrobiological speculations. Yet beneath their surfaces, the two share a perhaps surprising number of similarities; both may host subsurface oceans beneath kilometers of ice; both are driven by internal sources of heat rather than stellar; and they could both potentially support life in complete darkness under extreme pressures. Such parallels criticize the deeply rooted assumption that declares sunlight essential for life, setting the scene for a broader, more inclusive definition of habitability itself.

Rogue, or free-floating planets (FFPs) are defined as celestial bodies travelling through space without being gravitationally bound to a star. Like traditional planets, rogue planets are formed through gravitational accretion. Some are thought to have formed independently as failed stars that were unsuccessful in achieving nuclear ignition. Others may have formed as part of planetary systems and were then later ejected, either due to gravitational instabilities in the system or the parent star going supernova. FFPs are surprisingly abundant in the universe: they outnumber stars in the milky way at a ratio of around twenty to one according to current estimates. Furthermore, a significant number of these planets are believed to be Earth-sized. NASA’s Nancy Grace Roman Telescope could find up to 400 FFPs with Earth-like masses when it is set to launch in 2027.

Outwardly, rogue planets may seem utterly uninhabitable; their lack of a nearby star assures they receive no light or heat, leaving their surfaces bleak and frigid. Despite this, many rogue planets may still harbour subsurface oceans beneath a thick layer of ice as a result of several factors. To begin with, FFPs could maintain hydrogenrich atmospheres as they drift through the universe, trapping any internal heat generated and thus providing stable conditions within the planet’s oceans. If this heat is great enough to keep water in its liquid form, an environment suitable for life may be achievable for the rogue planet. Numerous sources could provide this heat including radioactive decay of isotopes such as uranium and thorium in the planet’s core; residual heat left behind from planetary formation; and even tidal heating if the rogue planet has its own moons. In 2011, researchers at the University of Chicago confirmed that rogue planets of Earth-like composition could maintain subglacial oceans if certain conditions are met and therefore may be considered habitable.

Even in total darkness on the ocean’s floor, hydrothermal vent systems on Earth allow life to exist. In the absence of sunlight, ecosystems cannot rely on photosynthesis to flourish but rather the conversion of minerals and chemicals into energy. Chemosynthetic communities like these could also exist on rogue planets if similar hydrothermal vent systems were to exist. It is unlikely that multi-cell organisms would ever develop in this environment with the absence of an oxygenrich atmosphere, however bacteria and archaea like those in Earth’s early history could thrive in the outlined conditions. Another important possibility to consider is that life in this subglacial environment could be fundamentally different from anything we have observed on Earth, challenging all previous anthropocentric assumptions made. If solvents such as ammonia or hydrocarbons were to exist, biochemistry itself as we know it could be completely redefined. As we have discovered from extremophiles on our own planet, life typically finds a way to exist even in the most inhospitable places – why couldn’t the same be true for FFPs?

The fundamental obstacle with the above hypothesis relates to the limited detection methods available: we cannot simply look for transits in front of a host star or detect atmospheric biosignatures if there is no light to analyse. Instead, gravitational microlensing is the leading tool. If a rogue planet happens to pass between Earth and a background star, its gravity will act as a lens, bending the star’s light as it curves around the planet. This magnified light acts as a telltale flare which astronomers can then detect and use to determine more information about the planet’s mass. Infrared surveys with instruments like JWST or WISE are another method of detecting FFPs. In particular, these surveys primarily discover younger planets that are still warm from their initial formation. The issue with these two techniques is that they both rely on specific circumstances to be met in order for detection to be made possible: in reality, the vast majority of rogue planets are already far too cold and ancient for infrared surveys, and microlensing events are not only rare, but also incredibly short-lived. Moreover, without light spectra we cannot discern any information about atmospheric composition, meaning potential biosignatures including oxygen or methane gases remain invisible with our current technology. 

The existence of life on rogue planets would not only provoke scientific interest, but also a large philosophical discussion. For example, would such beings have any concept of time, light or the vast universe laying beyond the ice? Would they ever guess that their icy ceiling is not just ice, but entire galaxies waiting to be discovered? Or would they, like life in Earth’s own hydrothermal vents remain oblivious to the cosmos beyond? Such questions stretch both our scientific and philosophical boundaries, serving as a reminder that life may exist in ways completely unfamiliar to us. This is an important fact to remember as the astrobiology field continues to expand: in the past, anthropocentric expectations have only limited our capabilities. Going forward, it is vital we consider life in all its possible forms as the search continues.

Habitability has long been associated with the warmth of stars, exposing humanity’s bias in our search for extraterrestrial life. But the universe is not made in Earth’s image, and so we have no right to assume life should be either. Rogue planets’ exclusion in mainstream astrobiology is not a consequence of their lack of potential, but rather our lack of familiarity. If one were to pass through our solar system, it could offer a unique chance for exploration that is no longer distant and theoretical, but close, reachable and perhaps even revolutionary. Ultimately, starless does not have to mean lifeless - but only if we choose to see what astrobiology has long left underexplored.

Any queries: UKCA-info@ed.ac.uk

The UK Centre for Astrobiology at the University of Edinburgh invites essays on any topic in astrobiology relevant to this year’s theme.

ICE, ICE, MAYBE? LIFE IN THE COLD UNIVERSE

To enter, you must be 18 or over and enrolled on an undergraduate or postgraduate degree at a UK university. Previous winners excluded.

Email your essay of up to 1500 words from your ...ac.uk email address to UKCA-info@ed.ac.uk using the subject line: “Essay Submission [your name]”.

Submissions will be reviewed by Dr Julie Castillo-Rogez from NASA’s JPL alongside UKCA scientists in Edinburgh with broad expertise across the themes in astrobiology. We are looking for accurate, compelling, and thought-provoking writing from students of any background. Shortlisted essays will feature on the UKCA website and social media. The best submission will earn a £500 prize.

Any queries: UKCA-info@ed.ac.uk

Biological mechanisms to interact with electromagnetic radiation, also known as light, have evolved in almost every living creature. A major application of this is in distinguishing different objects: incident light makes contact with a surface and is altered upon reflection. Sunlight strikes the rings of the blue-ringed octopus and interacts with its compounds, which absorb all wavelengths except blue, imparting a blue tint. Blue is often a hue associated in nature with poisonous material; this serves a dual purpose: animals can avoid potential food items like berries that exhibit a blue tint to prevent their toxic effects, and the prey can improve survivability by deterring predators. Pigmentation also serves a purpose in concealing animals from predators and threats by blending into their surroundings, or mimicking patterns observed on more threatening animals Similarly, the ripeness of fruit, the health of an animal, the quality of a water supply and an object’s temperature are some traits often communicated by the colour of an object which results from its interaction with incident light. The tendency of light to permeate out from its source coupled with the incredible speed with which it reaches distances makes it an invaluable means for a living organism to scope out their surroundings. The visible spectrum of light passes through water largely unfettered which makes it suitable to use as a scanning tool underwater where life initially evolved. Electromagnetic radiation (EMR) emanates large amounts of energy away from an object and into its surroundings. Light can voyage across the vacuum of space since it doesn’t require any medium to travel across. This property enables dissipation of energy from a disproportionally excited, energetic object like a star to its colder surroundings which includes the surfaces of planets where life tends to exist. Light, through the energy it carries, is indispensable to life through keeping water liquid. This prevents the destruction of biological molecules which can largely only exist and perform their designated functions if their surrounding medium is aqueous.

Light produced by the Sun is at the base of every food-chain on Earth. Every lifeform derives energy from light, either by direct photosynthesis, or indirectly via the consumption of these photoautotrophs. Living things need to conform to the conservation of energy and entropic principles which means they cannot generate energy from nothingness, they must procure it from their surroundings in some form. Chemical means of energy generation exist on Earth in chemoautotrophs, harnessing the breaking and reforming of chemical bonds in compounds present in the environment to produce usable energy. However, there are limited compounds that are present in a habitat that can be utilised which becomes a limiting factor when the number of feeders increases. Light from a star is an effectively infinite resource that is available in every exposed part of the Earth for several hours on end. Thus, very sophisticated cellular machinery has evolved to optimally harvest this source of energy. More archaic autotrophs like cyanobacteria and certain algae adapted by producing pigments that absorb wavelengths of light. Dedicated organelles formed from one of the rarest biological phenomena – endosymbiosis, have several functional units involved in capturing and garnering energy from sunlight in plant cells. Complex, multi-layered structures called thylakoids are suspended in a specialised stromal matrix in the chloroplast for the sole purpose of siphoning energy from light. A sophisticated electron transport chain akin to that involved in aerobic respiration evolved to channelise this energy and entrap it in a biologically accessible form – through simple and complex sugars that can be catabolised to release energy in any cell. This process essentially reverses the chemical reaction that occurs during elementary, aerobic respiration (glucose + oxygen -> carbon dioxide + water) with the use of the energy from light and forming glucose as well oxygen. These two products are crucial to the cycle of life, the light-driven process of photosynthesis effectively replenishes their amounts in nature allowing non-autotrophic organisms to utilise them for their bodily processes. Life’s dependence on light is illustrated by the heightened population densities of individual species and higher species variety viewed in the tropics where there is more direct sunlight. Civilisations also tend to cluster close to the tropics due to higher farming potential, longer days, greater rainfall and more tolerable temperatures. Most organisms, even non-photosynthetic ones, have evolved to depend on or harness light in different aspects. Humans, for instance, synthesize vitamin D through a pathway that requires sunlight for one of the steps. Sunlight regulates melatonin production which is instrumental in the sleep cycle, metabolism and stress management. Intense sunlight, on the contrary, causes DNA damage to exposed cells and is carcinogenic upon chronic exposure. Organisms thus evolve pigments like melanin to capture some of this light and prevent it from tampering with their genetic code. Lives of animals are structured by light availability: most animals are diurnal, they function during the day using the ample illumination to find their way around the habitat, hunting, foraging and mating. Nocturnal animals capitalise on the rest period that diurnal animals undergo in periods of low light intensity during the night, they have evolved specialised senses to bypass – such as higher rod cell density in their eyes, to take advantage of the lower visibility from the lack of light to prey on other animals.

Although its effect is less apparent, distance is another key driver of evolution. Allopatric speciation is a facet of evolution that directly results from distance being introduced between members of a species. Should a barrier form between two sects of species, different selection pressures tend to take over each half of the habitat leading to different adaptations, offering a survival advantage, and consequently differing traits being seen in following generations of each half. Minor deviations may instill notable differentiation in species, for example plant height for grazing animals, predator type and abundance which lead to natural selection of diverging characteristics. This would be even more exacerbated when looking at the prospect of interplanetary travel wherein humans residing in civilisations harboured on different planets will have vastly different stresses in their environment. Lowered gravity, for instance, can down-regulate bone density and muscle thickness as the body needs to resist lower gravitational forces acting on its skeleton and joints. This can be viewed in astronauts aboard the International Space Station who need to exercise more rigorously to maintain their previous level of muscle mass. Similarly, other potential differences like duration and intensity of light on the other planets, atmospheric composition can factor in as selection pressures that induce adaptations out of the subset of residing humans. These traits get magnified in every generation as two adapted individuals breed. An accumulation of enough of these adaptive traits leads to splitting off that branch of human into a separate species that is no longer compatible to reproduce with earthly humans.

For more complex creatures, distance also dictates group formation, as proximal individuals tend to bunch into a tribe to maximize survival chances. Proximity ensures effective communication, sharing of resources and surveillance by other members of the tribe. In most social animals like chimpanzees, gorillas and even humans, members of one’s own group are looked upon favourably while those belonging to other groups are often competition for one or the other reason. Whether another member of your species is an ally, or an adversary is often only dictated by the distance between the point of origin of the two. Organisms belonging to the same region and bearing matching physical properties are more likely to be genetic relatives, therefore it makes less evolutionary sense to exhibit hostility towards each other as it endangers the proliferation of their own set of genes. Distance from resources is a crucial determining factor for living things, a habitat located close to the equator is also closer to the Sun almost perennially due to the earth’s geoid shape and receives more light and heat for most of the year. This has numerous implications including denser plant life due to greater light availability, higher species density and larger populations. At a higher order, tribes closer to flowing rivers have access to more fertile soil present along the banks carried downstream from hills, clean, running water and fresh-water fauna. These benefits culminate in riverside locales being the most suitable for the advent of complex civilisation as shown by early settlements like those along the Indus River or the Nile. On a larger scale, this might be reflected in planets naturally located in the Goldilocks Zone having liquid water seeing life develop sooner than their counterparts due to fewer stages of evolution being necessary for life to become viable. Consequently, they would have more time to develop and create technology, becoming more advanced solely based on their distance from their star. Another manifestation of distance would be between multiple inhabited planets: this would play into the tribe-forming aspect discussed previously, possibly leading to interplanetary alliances or warfare which changes the course of life on those planets indelibly.