Kurzgesagt – In a Nutshell
Kurzgesagt – In a Nutshell
Embedded Files
Sources – Perfect Planet
Sources – Perfect Planet
We thank the following experts for their critical reading, feedback, and corrections:
René Heller
Team Lead for PLATO Research & Development, Max Planck Institute for Solar System Research
Andrés Moya Bedón
Senior Researcher at the School of Physics, University of València
Sofia J. van Moorsel
Group Leader, Department of Geography, University of Zurich
The star systems, planets, and species in this video, with the exception of those on the Solar System and Earth, are fictional.
—Big parts of it are covered by deadly deserts of ice, fire, rock or darkness where life struggles or is barely present.
#Heller, René (2015): “Better than Earth”, Scientific American
https://www.scientificamerican.com/article/planets-more-habitable-than-earth-may-be-common-in-our-galaxy/
https://personal.tcu.edu/dingram/better.pdf
Quote: “These days habitability varies widely across Earth, so that large portions of its surface are relatively devoid of life—think of arid deserts, the nutrient-poor open ocean and frigid polar regions.”
—As we have begun to look deep into our galaxy we’ve found a new and weird type of planet: Super-Earths, planets larger than Earth that have the potential to not only host life but to be superhabitable.
#Heller, René (2015): “Better than Earth”, Scientific American
https://www.scientificamerican.com/article/planets-more-habitable-than-earth-may-be-common-in-our-galaxy/
https://personal.tcu.edu/dingram/better.pdf
Quote: “In fact, some exoplanets, quite different from our own, could have much higher chances of forming and maintaining stable biospheres. These “superhabitable worlds” may be the optimal targets in the search for extraterrestrial, extrasolar life.
[...]
Most of the planets discovered over the past few years are so-called super-Earths, planets larger than Earth by up to 10 Earth masses, with radii between that of Earth and Neptune. These planets have proved to be extremely common around other stars, yet we have nothing like them orbiting the sun, making our own solar system appear to be a somewhat atypical outlier.
Many of the bigger, more massive super-Earths have radii suggestive of thick, puffy atmospheres, making them more likely to be “mini Neptunes” than super-sized versions of Earth. But some of the smaller ones, worlds perhaps up to twice the size of Earth, probably do have Earth-like compositions of iron and rock and could have abundant liquid water on their surfaces if they orbit within their stars’ habitable zones.”
—The perfect world needs a perfect star – but that may not be a yellow dwarf like our sun because they die in under 10 billion years and keep getting hotter as they age.
By “yellow dwarf” we mean main-sequence G-type stars like the Sun. By “dying” we mean exiting the main sequence. Though the star surface does not become hotter, it gets hotter around the star, because the star expands as it ages.
#Glozman, Igor: “Star classification” (retrieved 2026)
https://people.highline.edu/iglozman/classes/astronotes/hr_diagram.htm
#Heller, René (2015): “Better than Earth”, Scientific American
https://www.scientificamerican.com/article/planets-more-habitable-than-earth-may-be-common-in-our-galaxy/
https://personal.tcu.edu/dingram/better.pdf
Quote: “About five billion years from now, our sun will have largely exhausted its hydrogen fuel and begun fusing more energetic helium in its core, causing it to swell to become a “red giant” star that will scorch Earth to a cinder.”
We thank our expert René Heller for the following comment:
Quote: “Sun-like stars don't get hotter as they age. In fact, they get cooler at the surface. But their radii increase so dramatically that the net result is still an increase in luminosity. In other words, they cool and inflate at the same time.”
—70% of the window for life on earth has already passed. Earth has a mere couple billion years left before the sun ends it all.
#Marris, Emma (2013): “Earth's Days Are Numbered” Scientific American
https://www.scientificamerican.com/article/earths-days-are-numbered/
Quote: ”The inner edge of the Sun’s habitable zone is moving outwards at a rate of about 1 meter per year. The latest model predicts a total habitable zone lifetime for Earth of 6.3 billion–7.8 billion years, suggesting that life on the planet is already about 70% of the way through its run.”
—70% of stars are red dwarfs. Pretty small and alive for trillions of years, basically forever. Since they’re not that bright and hot, their habitable zones, where water can be liquid, are pretty close to them.
Here and in the rest of this script we use “red-dwarfs” in the narrow sense, to describe M-class dwarf stars. K-class dwarfs are referred to as “orange dwarfs”
#Dieterich, S.(2020): “How Well Do We Understand M Dwarfs?”, Space Telescope Science Institute Newsletter
Quote: “[Red dwarves] comprise about seventy percent of the stars in our galaxy (Henry et al. 2006, 2018), and yet they are arguably the least understood type of star.”
#Engle, Scott G.; Guinan, Edward F. (2023): “Living with a Red Dwarf: The Rotation–Age Relationships of M Dwarfs”, The Astrophysical Journal Letters, vol. 954, 2
https://iopscience.iop.org/article/10.3847/2041-8213/acf472
https://arxiv.org/abs/2307.01136
Quote: “More massive M dwarfs can live on the main sequence for over 100 Gyr while those of lower mass (M < 0.2 M⊙) can live as long as ∼1 trillion (∼1012) years (Choi et al. 2016)”
#Heller, René (2015): “Better than Earth”, Scientific American
https://www.scientificamerican.com/article/planets-more-habitable-than-earth-may-be-common-in-our-galaxy/
https://personal.tcu.edu/dingram/better.pdf
Quote: “M dwarf stars are smaller and more parsimonious still and can steadily shine for hundreds of billions of years, but they shine so dimly that their habitable zones are very close-in, potentially subjecting planets there to powerful stellar flares and other dangerous effects.”
—Which makes it very likely that their planets are tidally locked, one hemisphere a hot desert and the other an icy hell.
We thank expert René Heller for suggesting this scenario.
—Also young red dwarfs tend to vomit deadly radiation that sterilizes their planets or boils their oceans away.
#Heller, René; Armstrong, John (2014): “Superhabitable Worlds”, Astrobiology, vol.14, 1
https://journals.sagepub.com/doi/full/10.1089/ast.2013.1088
Quote: “M stars remain very active and emit a lot of X-ray and UV radiation during about the first billion years of their lifetime (Scalo et al., 2007). The activity-driven XUV flux of G stars, such as the Sun, falls off much more rapidly, but their quiescent UV flux is enhanced with respect to K and M dwarfs. What is more, while the UV flux of young M stars is generally much stronger than that of young Sun-like stars, quiescent UV radiation from evolved M dwarfs may be too weak for some essential biochemical compounds to be synthesized (Guo et al., 2010). Thus, they do not seem to offer superhabitable primordial environments.“
—The perfect stars for life might be orange dwarfs. In the goldilocks zone between red and yellow dwarf, their energy output is incredibly stable, radiation tends to be less aggressive and most importantly: They live up to 70 billion years, giving life plenty of time to emerge, evolve and thrive.
By “orange dwarf” here and in the rest of this script, we refer to K-type dwarf stars in contrast to M-type dwarfs, which we call red dwarfs.
#Heller, René (2015): “Better than Earth”, Scientific American
https://www.scientificamerican.com/article/planets-more-habitable-than-earth-may-be-common-in-our-galaxy/
https://personal.tcu.edu/dingram/better.pdf
Quote: “Our sun is 4.6 billion years old, approximately halfway through its estimated 10-billionyear lifetime. If it were slightly smaller, however, it would be a much longer-lived K dwarf star. K dwarfs have less total nuclear fuel to burn than more massive stars, but they use their fuel more efficiently, increasing their longevity. The middle-aged K dwarfs we observe today are billions of years older than the sun and will still be shining billions of years after our star has expired. Any potential biospheres on their planets would have much more time in which to evolve and diversify. [...]
Being longer-lived than our sun yet not treacherously dim, K dwarfs appear to reside in the sweet spot of stellar superhabitability”
#Heller, René; Armstrong, John (2014): “Superhabitable Worlds”, Astrobiology, vol.14, 1
https://journals.sagepub.com/doi/full/10.1089/ast.2013.1088
Quote: “Stellar UV radiation can damage deoxyribonucleic acid (DNA) and thus impede the emergence of life. Today, Earth has a substantial stratospheric ozone column that absorbs solar irradiation almost completely between 200 and 285 nm (UVC) and most of the radiation between 280 and 315 nm (UVB). During the Archean (3.8–2.5 Gyr ago), this ozone shield did not exist, yet life managed to form. We can assume that terrestrial planets with anoxic primordial atmospheres would be more habitable than early Earth if they received less hazardous UV irradiation.
M stars remain very active and emit a lot of X-ray and UV radiation during about the first billion years of their lifetime (Scalo et al., 2007). The activity-driven XUV flux of G stars, such as the Sun, falls off much more rapidly, but their quiescent UV flux is enhanced with respect to K and M dwarfs. What is more, while the UV flux of young M stars is generally much stronger than that of young Sun-like stars, quiescent UV radiation from evolved M dwarfs may be too weak for some essential biochemical compounds to be synthesized (Guo et al., 2010). Thus, they do not seem to offer superhabitable primordial environments. K stars offer a convenient compromise between moderate initial and long-term high-energy radiation. This is supported by considerations of the weighted irradiance spectrum of complex carbon-based molecules, indicating that planets in the HZs of K main sequence stars experience particularly favorable UV environments (Cockell, 1999). This indicates that K dwarf stars are favorable host stars for superhabitable planets.”
#Vilović, Iva et al. (2025): “Superhabitable Planets Around Mid-Type K Dwarf Stars Enhance Simulated JWST Observability and Surface Habitability”, Astronomical Notes (Astronomische Nachrichten), vol. 346, 2
https://onlinelibrary.wiley.com/doi/10.1002/asna.20240081
Quote: “K dwarfs are also more abundant than G-type stars, representing about 12% of the total stellar population compared with 8% for G stars (Arney 2019), and their expected life spans of between 17 and 70 billion years are comparable to, longer or much longer than the age of the Universe.”
However, the amount of UV radiation emitted by K-type stars and for how long they emit high amounts of radiation is contested:
#Richey-Yowell, Tyler et al. (2022): “HAZMAT. VIII. A Spectroscopic Analysis of the Ultraviolet Evolution of K Stars: Additional Evidence for K Dwarf Rotational Stalling in the First Gigayear”, The Astrophysical Journal, vol. 929, 2
https://iopscience.iop.org/article/10.3847/1538-4357/ac5f48
Quote: “K dwarfs have recently garnered attention for providing such a hospitable environment as to host potentially “superhabitable” planets (e.g., Heller & Armstrong 2014; Cuntz & Guinan 2016; Arney 2019); yet, a prolonged period of saturated flux weakens this case. Further observations of open cluster members between 650 Myr and 3 Gyr will be required to resolve at what age K dwarf rotational spin-down resumes. The delayed time evolution of K stars would increase the accumulated UV flux incident on their planets if the saturated period lasts for multiple gigayears. Additionally, a comparison of the flare evolution between these two types of stars will contribute to understanding the atmospheres of planets around these types of stars.”
We thank expert Sofia van Moorsel for the following comment:
Quote: “However, diversity increases and decreases constantly. It is not a linear process. So having more time doesn't necessarily lead to more diversity at the "end" nor at any given time point. Evolution doesn't really need that long....a few generations of any given species is generally enough to create innovation.”
—Hestia’s radius is 1.3 times Earth’s, so it has 70% more surface area – a lot more space for life. With almost twice earth’s mass and 20% more surface gravity, walking on it you’d feel 20% heavier. Unfortunately it's a hot dead desert.
There is considerable variability in the mass-radius relationship of exoplanets, so the radius and mass of Hestia are chosen to approximate those of a rocky exoplanet with high habitability.
They have been double-checked by expert René Heller.
#Heller, René (2015): “Better than Earth”, Scientific American
https://www.scientificamerican.com/article/planets-more-habitable-than-earth-may-be-common-in-our-galaxy/
https://personal.tcu.edu/dingram/better.pdf
Quote: “Astronomers searching for life around other stars increasingly focus on super-Earths: planets larger than our own, by up to 10 Earth masses yet smaller than gas giants and thus potentially rocky. Super-Earths of about two Earth masses are particularly promising targets because they possess certain properties ( below ) that could render them “superhabitable”—friendlier to life than our own planet is.”
Given a radius for Hestia of 1.3 times the radius of Earth, the surface of Hestia is:
rHestia=1.3rEath
AHestia= (rHestia/rEath)2AEath=(1.3/1)2AEath=1.69 AEath
The acceleration of gravity g on the surface of a planet of mass M and radius r is:
g= GM/r2,
where G is the Universal Gravitational Constant. Then, the difference in the surface gravity acceleration between Earth and Hestia is:
gHestia=(MHestia/MEath) / (rHestia/rEath)2 gEath=1.18 gEath,
That is, around 20% higher, so you would feel 20% heavier.
—Like Mars and Venus today, it’s still missing two things : Firstly, a magnetic field that protects Hestia from solar storms and cosmic radiation that sterilize its surface and blow its atmosphere away like poor Mars.
#Heller, René; Armstrong, John (2014): “Superhabitable Worlds”, Astrobiology, vol.14, 1
https://journals.sagepub.com/doi/full/10.1089/ast.2013.1088
Quote: “To allow for surface life, a world must be shielded against high-energy radiation from interstellar space (termed “cosmic radiation”) and from the host star (Baumstark-Khan and Facius, 2002). Too strong an irradiation could destroy molecules relevant for life, or it could strip off the world's atmosphere, an effect to which low-mass terrestrial worlds are particularly prone (Luhmann et al., 1992). Protection can be achieved by a global magnetic field, whether it is intrinsic as on Earth or extrinsic as may be the case on moons (Heller and Zuluaga, 2013), and by the atmosphere. [...]
To sustain an intrinsic magnetic field strong enough for protection over billions of years, a terrestrial world needs to have a liquid, rotating, and convecting core. Within Earth, this liquid is composed of molten iron alloys in the outer core, that is, between 800 and 3000 km from its center.”
The role that global magnetic fields play in the preservation of a planet’s atmosphere in general, and in particular in the case of Mars, is disputed:
#Egan, Hilary et al. (2019): “Do Magnetic Fields Prevent Atmospheric Escape?“, Bulletin of the American Astronomical Society, vol. 51, 6
https://ui.adsabs.harvard.edu/abs/2019ESS.....432904E/abstract
#Siegel, Ethan (2024): “Mars could have lived, even without a magnetic field”, BigThink
https://bigthink.com/starts-with-a-bang/mars-live-magnetic-field/
— Venus turned into a 470 degree hell, because without tectonic plates breaking and mixing, the tension and heat below its surface unloads in apocalyptic volcanic eruptions.
#The Planetary Society (2023): “Life on Venus: Your Questions Answered”
https://www.planetary.org/articles/life-on-venus-your-questions-answered
Quote: “At the surface, Venus has average temperatures of 470 degrees Celsius (878 degrees Fahrenheit) — hot enough to melt lead.”
#The Planetary Society (2018): “The Venus controversy”
https://www.planetary.org/articles/the-venus-controversy
Quote: “Plate tectonics plays a crucial role in Earth's geology. The churning of the solid rocky mantle, with hot material rising from deep in the interior and causing volcanic eruptions at the surface, efficiently moves heat from deep within Earth out of the planet and into space. On Venus, without plate tectonics, heat has no quick route out of the interior. The planet generates internal heat in the same ways that Earth does: by freezing of the core and radioactive decay. But the heat has nowhere to go. It builds up, and the overheating mantle starts to melt. If there continues to be no heat release, it’s possible for large sections of the mantle to melt relatively quickly, generating a massive reservoir of magma at the crust-mantle boundary that then erupts”
This increased vulcanism liberates great quantities of CO2 in the atmosphere that keep heat inside the planet’s atmosphere through the greenhouse effect.
Here we describe the “catastrophic resurfacing” model of Venus`vulcanism, but there are other models of how vulcanism on Venus works, and the reality could be a middle ground between different models.
#The Planetary Society (2018): “The Venus controversy”
https://www.planetary.org/articles/the-venus-controversy
Quote: “The catastrophic resurfacing model is loud, flashy, and exciting. However, scientists are prone to asking: what if? What if things were a bit more stable? Proposers of the steady-state hypothesis questioned the necessity of catastrophe, given the diversity of volcanism on Earth. The steady-state approach hinges on a Venus that is more compatible with Earth on the inside and the outside, in which volcanism is produced intermittently in discrete locations.”
—Continental plates moving into the depths also remove CO2 from the surface, which is great, because excess CO2 makes the atmosphere heat up too much.
#Heller, René; Armstrong, John (2014): “Superhabitable Worlds”, Astrobiology, vol.14, 1
https://journals.sagepub.com/doi/full/10.1089/ast.2013.1088
Quote: “On Earth, plate tectonics drive the carbon-silicate cycle. In this planet-wide geochemical reaction, near-surface weathering of calcium silicate (CaSiO3) rocks leads to the formation of quartz-like minerals, that is, silicon dioxide (SiO2). At the same time, carbon dioxide (CO2, e.g., from the atmosphere) combines with the residual carbon atoms to form calcium carbonate (CaCO3). When subducted to deeper sediments, elevated pressures and temperatures reverse this reaction, ultimately leading to volcanic outgassing of CO2. If this cycle stopped or if it never started on a hypothetical terrestrial, water-rich planet, then silicate weathering would draw down atmospheric CO2, which could lead to a global snowball state.”
—And they also bring up a vital mix of water, minerals and elements that life can feast on.
#Boyle, Rebecca (2018): “Why Earth’s Cracked Crust May Be Essential for Life”, Quanta Magazine
https://www.quantamagazine.org/why-earths-cracked-crust-may-be-essential-for-life-20180607/
Quote: “As the Pacific plate is dragged down into Earth’s mantle, it warms up and releases water trapped within the rock. In a process called serpentinization, the water bubbles out of the plate and transforms the physical properties of the upper mantle. This transformation allows methane and other compounds to percolate out of the mantle through hot springs on the otherwise frigid ocean floor.
Similar processes on early Earth could have supplied the raw ingredients for metabolism, which may have given rise to the first replicating cells.”
—Moons are crucial because with the right resonance, they create stability, avoiding overly punishing disruptions.
The right setup of moons may help stabilize the axial tilt of the planet. They would keep the axis with the “gentle tilt” we have given it to guarantee gentle seasons across tens of thousands of years.
#Lunar and Planetary Institute Learning: “Explore Marvel Moon: The Moon's Influence on Us“
https://www.lpi.usra.edu/education/explore/marvelMoon/background/moon-influence/
Quote: “The Moon's gravitational pull acts like training wheels for Earth on its journey around the Sun. It keeps Earth’s axis pointed at a consistent angle of about 23.5°. Without the Moon, this angle could vary wildly over eons, from a much smaller tilt that would largely eliminate seasons, to a larger tilt that would alternately burn and freeze large portions of the Earth’s surface.”
However, moons may not be necessary to stabilize the axial tilt:
#Schiling, Gobert (2011): “Who Needs a Moon?”, Science
https://www.science.org/content/article/who-needs-moon
#Whaltman, Dave (2013): “Our Large Moon Does Not Stabilize Earth's Axis”, European Planetary Science Congress
https://ui.adsabs.harvard.edu/abs/2013EPSC....8...37W/abstract
—Earth has a huge downside for life: most of its land is bound in large continents whose central areas are very far away from water, creating deserts with scarce resources and hostile environments.
Continentality is a major factor that leads to the formation of deserts.
#Wikle, Thomas A. (2017): “Arid Climates and Desertification”, International Encyclopedia of Geography: People, the Earth, Environment and Technology (eds D. Richardson, N. Castree, M.F. Goodchild, A. Kobayashi, W. Liu and R.A. Marston).
https://onlinelibrary.wiley.com/doi/10.1002/9781118786352.wbieg0243
Quote: “Covering nearly half of the earth's land surface, dry climates are extremely diverse in terms of temperature, patterns of precipitation, and physical appearance. A common attribute to all arid regions is low precipitation. Factors contributing to aridity include persistent high surpressure, continentality, and location relative to either mountain ranges that block moisture-laden winds or cool ocean waters that inhibit rainfall. Using Köppen's Climate Classification System, arid climates are designated as hot or cold deserts or as semiarid steppes. Arid and semiarid areas are susceptible to the impacts of drought but also to human degradation harmful to the productivity of vegetation called desertification.”
— We’ll give it many, fragmented continental plates, creating a geology that is ideal for producing long island arcs.
#Encyclopedia Britannica: “Island Arc” (retrieved 2026)
https://www.britannica.com/science/island-arc
Quote: “The majority of island arcs occur along the western margin of the Pacific Basin. The few exceptions are the East Indian and the West Indian arcs and the Scotia Arc in the South Atlantic. According to prevailing theory, island arcs are formed where two lithospheric plates (enormous rigid slabs that constitute segments of the Earth’s surface) converge. Upon colliding, one of the plates—that bearing heavy, oceanic crust—buckles downward and is forced into the partially molten lower mantle beneath the second plate with lighter, continental crust. An island arc is built up from the surface of the overriding plate by the extrusion of basalts and andesites.”
—creating the maximum land surface area for life.
We mean for life both on land and in the ocean. The fact that there is less land surface may result in less land life, but as we will see, the planet could also have rich marine ecosystems.
—Hestia’s biomass on land is also supercharged because our planet is 5°C warmer than earth.
Note that this “+5°C” temperature is a stable feature of Hestia’s climate. An increase of +5°C degrees on Earth’s temperature taking place over geologically short periods (like those of anthropogenic climate change) would be catastrophic for all life on Earth:
#Heller, René; Armstrong, John (2014): “Superhabitable Worlds”, Astrobiology, vol.14, 1
https://journals.sagepub.com/doi/full/10.1089/ast.2013.1088
Quote: “On worlds with substantial atmospheres, in other words with surface pressures P at least as high as those on Mars (where 1 mb≲P≲10 mb), surface temperatures will generally be different from the thermal equilibrium temperature given by stellar irradiation and planetary albedo alone (Selsis et al., 2007; Leconte et al., 2013). The biodiversity, or the richness of families and genera, seems to have multiplied during warmer epochs on Earth (Mayhew et al., 2012), indicating that worlds warmer than Earth could be more habitable.[...]
However, warming Earth does not necessarily yield increased biodiversity. Warming on short timescales causes mass extinction, which can currently be witnessed on Earth. Only a planet that is warm compared to Earth on a billion-year timescale or a world that warms gently over millions and billions of years could have more extended surface regions suitable for liquid water and biodiversity.
On the downside, with fewer temperate zones and no arctic regions, an enormous range of life-forms known from Earth could not exist. Above all, a world that is substantially warmer than Earth might have anoxic oceans. On Earth, oceanic anoxic events occurred in periods of warm climate, with average surface temperatures above 25°C compared to pre-industrial 14°C (GRID-Arendal, 1995), and resulted in extensive extinctions like the Permian/Triassic around 250 Myr ago (Wignall and Twitchett, 1996). While the concatenation of circumstances that led to extinctions during hot periods is complicated and may reflect problems of Earth's ecosystem, it cannot be excluded that a world moderately warmer than Earth could be superhabitable. A colder planet, however, can be assumed to be less habitable, as less energy input would slow down chemical reactions and metabolism on a global scale.”
—Tropical rainforests have ideal conditions for life. On Earth they hold more biomass than any other land ecosystem, and Hestia is nothing but tropical forests, and ice free polar regions.
#Phillips, Oliver L. et al. (2019): “Species Matter: Wood Density Influences Tropical Forest Biomass at Multiple Scales”, Surveys in geophysics vol. 40,4
https://pmc.ncbi.nlm.nih.gov/articles/PMC6647473/
Quote: “Tropical forests contain more species and biomass than any other biome on Earth. While they are being rapidly degraded and deforested, large areas of relatively intact tropical forest still exist, particularly in the Amazon and Congo basins. Wherever they persist, tropical forests contribute hugely to societies, economies, and human well-being, providing vital services that sustain people and nations”
The data of the graph is taken from:
#Pan, Yude et al. (2013): “The Structure, Distribution, and Biomass of the World’s Forests”, Annual Review of Ecology, Evolution, and Systematics, vol. 44, 593-622
https://forestplots.net/upload/publication-store/2013/Pan/AnnRevEcolEvoSyst_Pan_et_al_2013_World_Forests.pdf
—On Earth tropical forests like the ones in these islands house 50% of all species on just 10% of its land.
#Lewis, Simon L. (2006): “Tropical forests and the changing earth system”, Philosophical transactions of the Royal Society of London, Series B, Biological sciences, vol. 361, 1465
https://pmc.ncbi.nlm.nih.gov/articles/PMC1626535/
Quote: “Tropical forests cover only ca. 10% of the Earth's land surface, but are of global importance, as they store and process large quantities of carbon—processing, via photosynthesis and respiration, approximately six times as much carbon as humans release into the atmosphere through fossil fuel use—and house between one-half and two-thirds of the world's species.”
—On earth, plants are green to best catch energy from the sun – but with Hestia’s orange dwarf, they take on darker shades to hoard the fainter light.
#Kiang, Nancy Y. (2008): “The Color of Plants on Other Worlds”, Scientific American
https://www.scientificamerican.com/article/the-color-of-plants-on-other-worlds/
Quote: “Around cooler stars such as red dwarfs, planets receive less visible light, so plants might try to absorb as much of it as possible, making them look black. [...]
We found that the photons reaching the surface of planets around F stars tend to be blue, with the greatest abundance at 451 nm. Around K stars, the peak is in the red at 667 nm, nearly the same as on Earth. Ozone plays a strong role, making the F starlight bluer than it otherwise would be and the K starlight redder. The useful radiation for photosynthesis would be in the visible range, as on Earth.”
We choose darker green as a middle ground to represent both the fact that the star Rhea is dimmer and therefore plants would tend to be darker, and that ot is still similar enough to the Sun that the plants on Hestia may reasonably resemble Earth’s. We thank expert René Heller for the following comment:
Quote: “The Sun emits most of its light in the green part of the spectrum. If a plant appears green, then it's because the plant absorbs the blue and red light, while it reflects the green light. They do this because they would overheat if they would also absorb the green light. So saying: "plants are green because this is ideal to catch energy from the sun" is correct (because absorbing blue and red works well) but somewhat misleading (because they don't actually need the green light to catch the energy).”
—Hestia’s large mass holds gases much firmer than Earth, so its atmosphere is much thicker, with one and a half times the pressure – but much richer in oxygen and CO2.
#Vilović, Iva et al. (2025): “Superhabitable Planets Around Mid-Type K Dwarf Stars Enhance Simulated JWST Observability and Surface Habitability”, Astronomical Notes (Astronomische Nachrichten), vol. 346, 2
https://arxiv.org/pdf/2501.03214
Quote: “Motivated astrophysically, a superhabitable planet would be slightly larger and more massive than Earth to retain a thicker atmosphere–providing the necessary mass and energy to support a more extensive biosphere–and support plate tectonics (Schulze-Makuch et al. 2020). Additionally, a strong magnetic field would protect the planet from harmful radiation, preserving its atmosphere and potential life forms (Lammer et al. 2009).”
#Heller, René (2015): “Better than Earth”, Scientific American
https://www.scientificamerican.com/article/planets-more-habitable-than-earth-may-be-common-in-our-galaxy/
https://personal.tcu.edu/dingram/better.pdf
Quote: “What would a superhabitable planet look like? Higher surface gravity would tend to give a middling super-Earth planet a slightly more substantial atmosphere than Earth’s, and its mountains would erode at a faster rate. In other words, such a planet would have relatively thicker air and a flatter surface.”
#McIntyre, Sarah R. N.; King, Penelope L.; Mills, Franklin P. (2023): “A rocky exoplanet classification method and its application to calculating surface pressure and surface temperature”, Monthly Notices of the Royal Astronomical Society, vol. 519, 4, 6210–6221
https://academic.oup.com/mnras/article/519/4/6210/6986274
Quote: “An initial estimate of an exoplanet’s surface pressure (Psurf) can be obtained from a simple model based on hydrostatic equilibrium (e.g. Kippenhahn, Weigert & Weiss 1990; Mordasini et al. 2012; Kopparapu et al. 2014; Silva et al. 2017; Hall 2020), using available observational data on an exoplanet’s mass (Mp) and radius (Rp):
"
As explained in a previous section of this document, we have chosen the parameters:
rHestia=1.3rEarth
MHestia=2 MEarth
Using the formula above:
PHestia=(MHestia/MEarth)2(rEarth/rHestia)4 PEarth ~1.4 PEarth
Which means that the surface pressure on Hestia is approximately one and a half times that of Earth.
The higher oxygen and CO2 concentrations are chosen to accommodate higher biomass and higher temperatures.
—This could be catastrophic for life because high oxygen makes wildfires easier to start and more devastating– but since Hestia is so warm and humid, evaporation produces so much rain that wildfires never get powerful enough to wipe out ecosystems.
#Vitali, Rayanne et al. (2022): “Increased fire activity under high atmospheric oxygen concentrations is compatible with the presence of forests”, Nature Communications, vol. 13, 7285
https://www.nature.com/articles/s41467-022-35081-z
Quote: “Early calculations from Watson et al.29 concluded that with 25% vol. O2 forest regeneration would be prevented by continuous fire, even at elevated moisture levels. Others have suggested that forests with higher moisture content and rapidly reproducing trees would be more tolerant to rising oxygen concentrations, arguing for a higher upper limit of 30% vol. O25,12,38. Whilst it is generally agreed that fires are more likely to ignite under high oxygen concentrations, it has been argued that rate of fire spread is strongly dependent on fuel moisture10,39. Experiments by Wildman et al.10 found that vegetation-based fuels with high fuel moisture were unable to burn, even in high oxygen concentrations of 35% vol. O2, suggesting that atmospheric oxygen concentrations of this level and above could be compatible with the existence of forests10,39. Therefore, the upper limit of the fire window is still largely unknown and could be between 25–35% vol. or potentially higher. Yet, to date, no study has thoroughly examined the hypothesis of the upper limit of the fire window: that high atmospheric oxygen concentrations could have led to widespread wildfires that may have inhibited the growth of forest and potentially the formation of forest biomes, and whether fuel moisture might mitigate such effects.”
—The upsides are clearly worth it: On earth the size of animals like insects that rely on breathing by diffusion is limited
#Fisher, Susan; Meuti, Megan; Klooster, Wendy: “Insects & Human Affairs: Pests, Plagues, Pollinators and Poisons”, Ohio State University Pressbooks (retrieved 2026)
https://ohiostate.pressbooks.pub/ent2101/chapter/chapter2/
Quote: “In small insects, simple diffusion is generally sufficient to oxygenate every cell in the insect body. However, this is one of the factors that limits the size of insects. There is a limit, after all, to how much biomass can be efficiently and reliably oxygenated using diffusion. This is not to say that large insects don’t have a few tricks. Indeed, large insects can augment the activity of diffusion by actively pumping air into their bodies. This is done by strategically opening some spiracles while closing others. At the same time, the insect uses abdominal muscles to alternately expand and contract the abdomen. The combination creates a sort of wave of air that flushes oxygen through the entire tracheal system. Still, unlike vertebrates, insects do not have any means to concentrate oxygen within their bodies, and the larger the insect, the greater the distance oxygen must diffuse before reaching an individual cell. These two factors (i.e. the inability to concentrate oxygen and the reliance on simple diffusion to distribute oxygen to each cell) ultimately limit the size of creatures who must conduct respiratory activities without the assistance of a circulatory system.”
#Harrison, Jon F.; Kaiser, Alexander; VandenBrooks, John M.(2010): “Atmospheric oxygen level and the evolution of insect body size”,Proceedings of the Royal Society B: Biological Sciences, vol. 277, 1690,1937–1946
Quote: “Insects are small relative to vertebrates, possibly owing to limitations or costs associated with their blind-ended tracheal respiratory system. The giant insects of the late Palaeozoic occurred when atmospheric PO2 (aPO2) was hyperoxic, supporting a role for oxygen in the evolution of insect body size. The paucity of the insect fossil record and the complex interactions between atmospheric oxygen level, organisms and their communities makes it impossible to definitively accept or reject the historical oxygen-size link, and multiple alternative hypotheses exist. However, a variety of recent empirical findings support a link between oxygen and insect size, including: (i) most insects develop smaller body sizes in hypoxia, and some develop and evolve larger sizes in hyperoxia; (ii) insects developmentally and evolutionarily reduce their proportional investment in the tracheal system when living in higher aPO2, suggesting that there are significant costs associated with tracheal system structure and function; and (iii) larger insects invest more of their body in the tracheal system, potentially leading to greater effects of aPO2 on larger insects. Together, these provide a wealth of plausible mechanisms by which tracheal oxygen delivery may be centrally involved in setting the relatively small size of insects and for hyperoxia-enabled Palaeozoic gigantism.”
—All that oxygen also enables animals to have a faster metabolism, so animals can sustain higher activity levels. Predators hunt more actively, prey can flee more dynamically.
#Seibel, Brad A.; Deutsch, Curtis (2020): “Oxygen supply capacity in animals evolves to meet maximum demand at the current oxygen partial pressure regardless of size or temperature”, The Journal of experimental biology, vol. 223, 12
https://pubmed.ncbi.nlm.nih.gov/32376709/
Quote: “The capacity to extract oxygen from the environment and transport it to respiring tissues in support of metabolic demand reportedly has implications for species' thermal tolerance, body size, diversity and biogeography. Here, we derived a quantifiable linkage between maximum and basal metabolic rate and their oxygen, temperature and size dependencies. We show that, regardless of size or temperature, the physiological capacity for oxygen supply precisely matches the maximum evolved demand at the highest persistently available oxygen pressure and this is the critical PO2 for the maximum metabolic rate, Pcrit-max For most terrestrial and shallow-living marine species, Pcrit-max is the current atmospheric pressure, 21 kPa.”
—In Earth’s thin atmosphere flight costs a lot of energy – but in Hestia’s super dense air, it’s super cheap. Despite the higher surface gravity, animals need much smaller wings to fly and less energy to stay afloat.
#Pajusalu, Mihkel et al. (2024) “A qualitative assessment of limits of active flight in low density atmospheres”, Scientific Reports, vol. 14, 13823
https://www.nature.com/articles/s41598-024-64114-4
Quote: “Based on the variation of conditions supporting flight on Earth, the main limitation seems to be the atmospheric density. As all forms of powered flight require thrust to be generated and for covering significant distances this thrust has to come from changing the velocity of air around the flying organism. Moreover, the lower the atmospheric density, the larger volume of air that needs to be moved or it would need to be moved at a larger velocity.
As can be seen on Earth, long duration flight also requires lift to be generated, and successful lift generation allows birds to achieve very long flight paths. For shorter duration, however, lift is not a requirement and insects can fly mainly by generating vectorized thrust that has to overcome the force of their weight. We propose that active flight is possible if there is a sufficient atmospheric density present (in an atmosphere suitable for life).”
#Schulze-Makuch, Dirk; Heller, Renée; Guinan, Edward (2020): “In Search for a Planet Better than Earth: Top Contenders for a Superhabitable World”, Astrobiology, vol. 20,12
https://pmc.ncbi.nlm.nih.gov/articles/PMC7757576/
Quote: “A larger mass planet with higher gravity would also retain a thicker atmosphere, which would make flight the preferred way of locomotion. On Earth, flight is used by many species as a preferred manner of locomotion, and on a planet with an even thicker atmosphere, that would be even more befitting. This would have advantages for the distribution of species and settlements of islands and continents. However, this relationship would only hold to a certain extent, because if planetary mass becomes too large, the planet might evolve into a gas giant or mini-Neptune retaining the light gases such as hydrogen or being an undifferentiated iron-rich body.”
—This created super weird adaptations like hunters not trying to sneak up but masking their direction of attack with disturbing and distracting noises.
Producing a sound to hide another is called “auditory masking” and it is used to reduce the sensation of noise or make some sounds harder to notice, for example in tinnitus maskers.
#ANSYS (2023): “Auditory Masking: Using Sound to Control Sound”
—Earth’s oceans are on average 3700 meters deep and make up the majority of the surface of our planet.
#NOAA (2024): “How deep is the ocean?”
https://oceanservice.noaa.gov/facts/oceandepth.html
Quote: “The average depth of the ocean is about 3,682 meters (12,080 feet).”
#NOAA (2026): “How much of the ocean has been explored?”
https://oceanexplorer.noaa.gov/ocean-fact/explored/
Quote: “The ocean covers approximately 70% of Earth’s surface.”
—But sunlight can only reach 200 meters deep. This sunlight zone is the only place plankton, the basis for the food web, can turn sunlight into sugar – so this is where 90% of our marine species live. 95% of the sea is in permanent darkness, much of it is actually an abyssal desert.
#Woods Hole Oceanographic Institution Ocean Learning Hub: “Sunlit Zone” (retrieved 2026)
https://www.whoi.edu/ocean-learning-hub/ocean-topics/how-the-ocean-works/ocean-zones/sunlit-zone/
#Davies, Thomas W.; Smyth, Tim (2025): “Darkening of the Global Ocean”, Global Change Biology, vol. 31, 5
https://onlinelibrary.wiley.com/doi/10.1111/gcb.70227
Quote: “Ninety per cent of all marine life lives in the photic zone of the oceans, where sufficient light penetrates to stimulate photobiological processes.”
#U.S. National Oceanic and Atmospheric Administration: “Layers of the Ocean” (retrieved 2026)
https://www.noaa.gov/jetstream/ocean/layers-of-ocean
Quote: “Abyssopelagic Zone: The Abyssopelagic Zone (or abyssal zone) extends from 4,000 meters (13,100 feet) to 6,000 meters (19,700 feet). It is the pitch-black bottom layer of the ocean. The water temperature is constantly near freezing, and only a few creatures can be found at these crushing depths.”
#National Science Foundation (2024): “Dive into research on world's ocean”
https://www.nsf.gov/science-matters/dive-research-worlds-ocean
Quote: “The sunlit zone makes up just about 3% of the ocean by volume but hosts the foundation of the ocean's food web, phytoplankton, which converts sunlight to energy using photosynthesis.”
#Cook Islands Seabed Minerals Authority (2024): “All creatures great and small—life in the abyss”
https://www.sbma.gov.ck/news-3/article-179
Quote: “Life on the abyssal plains is very different to the life we see when swimming along our reefs. Sunlight stops at about 200m depth, and most of the fish and other marine species we’re familiar with don’t dive much deeper than 1,000 m. Animals at 5,000 m have had to adapt to the extreme conditions: dark, cold, and intense pressure.
Deserts are usually defined as areas of land that receive little rainfall (or snow) and thus have small amount of life (usually called biomass) e.g. [1]. The abyssal plains are clearly a lot wetter than your typical desert but are thought to have even less life e.g. [2], [3]. One reason is that there are no plants on the seabed. On land they make up as much as ~80% of the biomass [4].”
—Corals form living megacities stretching over thousands of kilometers, home to trillions of animals competing for real estate and forming complex relationships.
These coral-like creatures are alien species that resemble Earth corals. The notion that corals could be prolific under stable conditions and higher temperatures is based on the observation that during the warmer Carboniferous period corals thrived on Earth:
#Heller, René (2015): “Better than Earth”, Scientific American
https://personal.tcu.edu/dingram/better.pdf
Quote: “[D]uring much of the Carboniferous period, from roughly 350 million to 300 million years ago, the planet’s atmosphere was warmer, wetter and far more oxygen-rich than it is now. Crustaceans, fish and reef-building corals flourished in the seas, great forests blanketed the continents, and insects and other terrestrial creatures grew to gigantic sizes.”
#Yorkshire Dales National Park: “Carboniferous Layers of the Landscape” (retrieved 2025)
https://dalesrocks.org.uk/swaledale/carboniferous-layers-of-the-landscape/signs-of-life-2/
However, corals on Earth are vulnerable to sudden changes in temperature and threatened by anthropogenic climate change:
#U.S. National Ocean Service: “How does climate change affect coral reefs?” (retrieved 2026)
https://oceanservice.noaa.gov/facts/coralreef-climate.html
Quote: “Climate change is the greatest global threat to coral reef ecosystems. Scientific evidence now clearly indicates that the Earth's atmosphere and ocean are warming, and that these changes are primarily due to greenhouse gases derived from human activities.
As temperatures rise, mass coral bleaching events and infectious disease outbreaks are becoming more frequent. Additionally, carbon dioxide absorbed into the ocean from the atmosphere has already begun to reduce calcification rates in reef-building and reef-associated organisms by altering seawater chemistry through decreases in pH. This process is called ocean acidification.
Climate change will affect coral reef ecosystems, through sea level rise, changes to the frequency and intensity of tropical storms, and altered ocean circulation patterns. When combined, all of these impacts dramatically alter ecosystem function, as well as the goods and services coral reef ecosystems provide to people around the globe.”
#University of Queensland (2012): ”Two degrees is too much for most coral reefs”
https://news.uq.edu.au/2012-09-16-two-degrees-too-much-most-coral-reefs
Quote: “A modelling study from an international collaboration involving German, Canadian and Australian scientists has concluded that increasing global temperatures to 2 degrees above pre-industrial global temperatures will be too hot for two thirds of the world’s corals and hence coral reefs.
The study published in international journal Nature Climate Change today reveals that only strong action to mitigate greenhouse-gas emissions plus an assumed ability to rapidly evolve will save some coral reefs.[...]
Our findings show that under current assumptions regarding thermal sensitivity, coral reefs will no longer be prominent coastal ecosystems if global mean temperatures reach 2°C above the pre-industrial temperatures,” lead author Dr Katja Frieler from the Potsdam Institute for Climate Impact Research, said.”
#U.S. National Ocean Service: “In what types of water do corals live?” (retrieved 2026)
—Bordering the megacities are underwater kelp and algae colonies as dense and filled with life as any tropical rainforests.
Kelp forests are found frequently in shallow waters. They are a type of macroalgae:
#NOAA: “What is a kelp forest?” (retrieved 2024)
https://oceanservice.noaa.gov/facts/kelp.html
#NASA Earth Observatory (2015): “Floating Forests Revealed”
https://earthobservatory.nasa.gov/images/85023/floating-forests-revealed
—Even if they occupy only 7% of the total marine area, they are home to more than half of marine life.
#Habitats: “Coastal habitats” (retrieved 2026)
https://habitatsconservation.org/habitat/coastal/
Quote: “Coastal habitats are found along the edges of land and sea, and include beaches and estuaries. Most marine life can be found in coastal habitats, even if this area occupies only 7% of the total marine area. Coastal habitats are important for a variety of reasons, including providing habitat for a wide range of species, regulating water quality, protecting against storms and floods, and supporting paramount human activities such as fishing.”
—A pretty mid planet like Earth hosts an estimated 9 million complex species
#Mora, Camilo et al. (2011): “How Many Species Are There on Earth and in the Ocean?”, PLOS Biology, vol. 9, 8, e1001127.
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001127
Quote: “Knowing the number of species on Earth is one of the most basic yet elusive questions in science. Unfortunately, obtaining an accurate number is constrained by the fact that most species remain to be described and because indirect attempts to answer this question have been highly controversial. Here, we document that the taxonomic classification of species into higher taxonomic groups (from genera to phyla) follows a consistent pattern from which the total number of species in any taxonomic group can be predicted. Assessment of this pattern for all kingdoms of life on Earth predicts ∼8.7 million (±1.3 million SE) species globally, of which ∼2.2 million (±0.18 million SE) are marine. Our results suggest that some 86% of the species on Earth, and 91% in the ocean, still await description. Closing this knowledge gap will require a renewed interest in exploration and taxonomy, and a continuing effort to catalogue existing biodiversity data in publicly available databases.”
The total number of species may be even bigger:
#Wiens, John J. (2023): “How many species are there on Earth? Progress and problems”, PLOS Biology, vol. 21, 11, e3002388
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3002388
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