The daisy world model describes a hypothetical self-regulating planet, maintaining a delicate balance involving its biogeochemical cycles, climate, and feedback loops that keep it habitable. It is associated with the Gaia hypothesis developed by James Lovelock. How can we detect these worlds if they are there?

Looking carefully at the information.

A Daisy World (DW) is inhabited by two types of daisies: white and black. They have different albedos, and blacks absorb more sunlight and warm the planet, while whites reflect more sunlight and cool the planet.

As the DW star brightens, the planet’s temperature rises. At first, black daisies thrive because they absorb more energy. However, as the planet gets hotter, absorbing more energy becomes undesirable, and the white daisies begin to outcompete the black ones and thrive. As they grow, they reflect more sunlight and cool the planet.

The result is a delicate homeostasis where daisies regulate the temperature of the planet and keep it within a habitable range. It can’t get too hot or too cold. The DW model shows how life can influence a planet’s climate and create favorable conditions for its own survival.

Earth isn’t exactly a daisy world, but life on Earth influences the climate. The DW model simply illustrates the concept of basic climate feedback mechanisms.

In new research, scientists from the Department of Physics and Astronomy and the Department of Computer Science at the University of Rochester wanted to find ways to analyze how planetary systems as biospheres and geospheres are coupled. If self-regulating “daisy worlds” exist, how can we detect them?

The research is “Exo-Daisy World: Revisiting Gaia Theory through an Informational Architecture Perspective”. The lead author is Damian Sowinski, a physics researcher and postdoctoral associate in the Department of Physics and Astronomy at the University of Rochester. The research is awaiting publication and not yet peer-reviewed, but it is available on arXiv preprint server.

The idea is to find a way to detect agnostic biosignatures on exoplanets. Common biosignatures are specific chemicals, such as oxygen or methane, that may be byproducts of living organisms. Agnostic biosignatures are indications that life is present, but are not based on identifying the types of organisms that could produce them. Instead, they are like the global planetary patterns that the living worlds produce.

For the authors, finding agnostic biosignatures starts with information and how it flows.

“In this study, we extend the classic daisy world model through the lens of Semantic Information Theory (SIT), with the aim of characterizing information flow between those biosphere and the planetary environment – ​​what we call the information architecture of daisy world systems,” the authors explain.

Semantic information theory has been around since the middle of the 20th century. It tries to define meaning in different contexts, how subjective human interpretation affects it, and related concepts in the same vein. It is taking on a new focus as artificial intelligence and machine learning become more widespread.

There is a desire to understand the atmospheres and environments of exoplanets and have a way to tell the difference between those that might support life and those that don’t. This is a complex issue that depends on agnostic biosignatures.

Agnostic biosignatures are complex patterns and structures that cannot be explained by non-biological processes. There is also an imbalance, a new transfer of energy, unusual levels of organization at different scales, and cyclical or systematic changes that suggest a biological cause.

An agnostic biosignature search may involve complex molecules that need biological synthesis, chemical distributions that require metabolism, unexpected accumulations of specific molecules, and features in an atmosphere or on a planetary surface that require biological maintenance.

Some examples of agnostic biosignatures on Earth are methane and oxygen coexisting in the atmosphere, the “Red Edge” of the Earth’s vegetation spectrum, and daily or seasonal cycles of gas emissions.

“The search for life on exoplanets requires the identification of biosignatures, which are based on the fact that life has significantly altered the spectroscopic properties of a planet. Thus, searches for exoplanetary life focus not on detecting individual organisms, but on identifying the collective effects of life on the planetary system. — what we call exo-biospheres,” the authors explain.

In short, we cannot study biosignatures without studying biospheres. In doing so, it is essential to understand where and how an exo-biosphere reaches a “mature” state where it exerts a strong influence on the atmosphere, hydrosphere, cryosphere and lithosphere, collectively known as the geosphere. Once they are mature and exerting a strong influence, they are in line with the daisy world hypothesis.

The authors’ goal is to study how information flows between a biosphere and the planetary environment. To do this, they modeled the potential conditions on M dwarf exoplanets and came up with equations that describe the co-evolution of daisies on these worlds with their planetary environments. They have created what they call an “informational narrative” for exo-daisy worlds (eDWs).

Typically, homeostatic feedback in DW is based on physical quantities such as radiation fluxes, albedos, and plant life cover fractions. This is the physical narrative. However, researchers have used semantic information theory to derive a complementary narrative based on how information flows. In their work, SITs focus on the correlations between an agent – the biosphere – and an environment and how these correlations benefit the agent.

Their model showed that as stellar luminosity increases, correlations between the biosphere and its environment intensify. Correlations correspond to distinct phases of information exchange between the two. This leads to the idea of ​​bridle control, a control exerted by flora through positive and negative differences in their albedos relative to bare land. This is how the biosphere exerts a regulating influence on a planet’s climate. In their briefing paper, planetary temperatures are narrower “to the cooler and warmer limits of the tolerable temperature range”.

Not all information that flows between the biosphere and the environment is relevant. The biosphere does not use all of them because some of them do not help the biosphere maintain control. The authors say that by analyzing all this information according to information theory, they can determine which information, and when and how, contributes to its own viability.

The daisy world model is instructive, but it is a toy model. For example, it does not include stochastic events such as volcanic eruptions. But the big question is how does it relate to exobiospheres?

The authors say their work shows the potential of using approaches like SIT to understand how exoplanets and their biospheres evolved together, just as they did on Earth. More realistic models will be needed that include more complex networks of interactions between the living and nonliving systems of an exoplanet. The biosphere processes information in ways that nonliving systems do not, so information-centric systems can cover agnostic biosignatures in ways that physical or chemical models cannot.

“As a result, the next step in our research program will involve the application of SIT and other information theoretic approaches to more complex models of coupled planetary systems,” the authors conclude.