Habitable Worlds Lab

Incoming starlight scales with stellar luminosity divided by orbital distance squared. The model uses reflected light and uniform heat redistribution to estimate an equilibrium temperature, then adds the greenhouse warming you choose. The surface-water check assumes water is available. It estimates surface pressure from your starting pressure and the remaining atmosphere, with 0.10 bar as a simplified screening threshold. It uses a broad 0–100 °C (32–212 °F) temperature screen and omits pressure-dependent boiling. The colored surface illustrates the temperature and atmospheric inventory. Real climates also depend on circulation, clouds and local conditions.

The model estimates rocky-planet radius from mass (radius in Earth units = mass in Earth units raised to 0.27), then compares escape speed with the selected gas’s root-mean-square thermal speed. The illustrative upper-atmosphere temperature rises with high-energy exposure. Thermal retention is favored when escape speed exceeds six times that thermal speed in this classroom screen. The gas selection tests a representative molecule. Real atmospheres have mixtures, can lose light dissociation products and can replenish gases.

Distance controls how much radiation reaches the planet. Stellar activity controls how much high-energy radiation the star emits. In the illustrative index, a flare-active star emits 12 times the high-energy radiation of its quiet setting at the same orbit. The model flags exposure above six times the quiet Earth reference. A tail visualizes escape stress. Its size, visibility and color are artistic. Atmospheric loss over time also depends on stellar history, atmospheric chemistry, heating, winds and replenishment.

The timeline is a teaching scenario. It starts with one unit of atmosphere and removes a fixed fraction of what remains each simulated year. High exposure and weak thermal retention increase that fraction. The model holds the orbit and stellar activity fixed and scales greenhouse warming with the remaining atmosphere. Its chosen rates illustrate different outcomes over five billion years. Actual loss rates require planet-specific observations and models.

Earth’s dry air is about 21% oxygen. Oxygen partial pressure is the oxygen share multiplied by total pressure. A thin atmosphere can contain 21% oxygen and still fall short of the lab’s Earth-like air target. The steady-source setting holds the oxygen share constant as the atmosphere thins. Without a source, this teaching model lets oxygen react away at a prescribed rate. Earth’s atmospheric oxygen is sustained largely by photosynthesis. The model omits many conditions needed for human survival, including local weather, radiation exposure and trace gas toxicity.

A terrestrial planet is primarily rocky or metallic. Some larger planets are called super-Earths because of their size or mass. That name alone gives us little information about the surface. Ice, desert and global-ocean worlds are surface outcomes in this lab. A gas giant such as Jupiter has a deep hydrogen–helium envelope with no accessible solid surface. Neptune-like worlds form another broad class and can have hydrogen, helium and methane in their outer atmospheres. The lab illustrates a rocky example of a super-Earth once a temperate rocky planet reaches twice Earth’s mass. Choose a different planet type to compare its appearance and light signature. The atmospheric time-lapse applies to rocky worlds.

Some communities around Earth’s deep-sea vents use chemical energy without sunlight. On Enceladus, Cassini detected molecular hydrogen in plumes from a moon with an ocean beneath its ice. That hydrogen is evidence consistent with water–rock reactions and a potential chemical energy source. Earth remains the only world with confirmed life. Explore Oceans Beyond Earth.