Instellation

In Astronomy the term instellation refers to the amount of light that shines on astronomical objects, like planets, comets and asteroids, from the star(s) they orbit.^[1]^[2]^[3] In our Solar system the term "insolation" refers to the amount of light received by objects orbiting Sol, our sun. Astronomers realized they needed a more general term, suitable for referring to the light received by objects orbiting stars other than Sol.

References

↑ Evan Gough (2026-01-14). "Two New Exoplanets And The Need For New Habitable Zone Definitions". Universe Today. Archived from the original on May 10, 2026. Retrieved 2026-06-24. An exoplanet's instellation flux, or insolation flux, describes the amount of solar energy that reaches the exoplanet's surface. It's measured in watts per square meter (W/m²). In the paper, the expression 0.1 < 𝑆/S⊕ < 5 defines a range of insolation flux relative to Earth's solar constant. So it translates to a range between about 136 W/m² and about 6805 W/m². Earth's solar constant is around 1361 W/m² at the top of the atmosphere, so that gives an idea of what the term is describing.
↑ Lewis Dartnell (2025-11-08). "Bare, hostile alien worlds may be able to host life after all, after astronomers made one key change". BBC Sky at Night Magazine. Archived from the original on 2025-12-17. Retrieved 2026-06-24. In an influential 2017 paper, Kevin Zahnle and David Catling plotted known exoplanets, as well as the planets and moons in our Solar System, on axes of escape velocity versus instellation.
↑ Keith Cowing (2025-04-28). "Near-circular orbits for planets with Earth-like sizes and instellations around M and K dwarf stars - Nature Astronomy". Nature magazine. Retrieved 2026-06-24.

[universetoday2026-01-14-1] Evan Gough (2026-01-14). "Two New Exoplanets And The Need For New Habitable Zone Definitions". Universe Today. Archived from the original on May 10, 2026. Retrieved 2026-06-24. An exoplanet's instellation flux, or insolation flux, describes the amount of solar energy that reaches the exoplanet's surface. It's measured in watts per square meter (W/m²). In the paper, the expression 0.1 < 𝑆/S⊕ < 5 defines a range of insolation flux relative to Earth's solar constant. So it translates to a range between about 136 W/m² and about 6805 W/m². Earth's solar constant is around 1361 W/m² at the top of the atmosphere, so that gives an idea of what the term is describing.

[Bbc2025-11-08-2] Lewis Dartnell (2025-11-08). "Bare, hostile alien worlds may be able to host life after all, after astronomers made one key change". BBC Sky at Night Magazine. Archived from the original on 2025-12-17. Retrieved 2026-06-24. In an influential 2017 paper, Kevin Zahnle and David Catling plotted known exoplanets, as well as the planets and moons in our Solar System, on axes of escape velocity versus instellation.

[nature2025-04-28-3] Keith Cowing (2025-04-28). "Near-circular orbits for planets with Earth-like sizes and instellations around M and K dwarf stars - Nature Astronomy". Nature magazine. Retrieved 2026-06-24.

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