Assuming the skies are clear of suspended particles, what color should they be at mid-day if viewed with human eyes?
The planet is larger and twice as massive as Earth, with a nearly identical atmosphere composition but a far higher surface pressure. This implies a thicker atmosphere with more scattering, which could produce light, warm-toned skies rather than blue ones. I watched some videos by Artifexian on the subject, and used the spreadsheets and sources he had provided to determine what color they should be. However, I wasn't able to come to a solid conclusion based on some gaps and conflicting info:
- The two calculators generally point towards a light, warm-colored sky. This is based on two things: first, the approximate height of the tropopause. This isn't provided in the first calculator, but I roughly extrapolated it from the height at which air pressure is between 70-400hpa (~15591.61-30545km.) This probably isn't the best way of estimating it, and the margin is wide enough to go either way in terms of color.
- Next, I compared this and the planet's actual surface pressure (2.43atm) to the results from the second sheet; it calculates the required properties for a sky, with 1atm of surface pressure and the same scale height, to become warm-toned (tropopause at 21453.68m, ~2.36atm.) The tropopause is based on the scale height and angle of twilight. I was unable to calculate this based on my planet's radius, making the results somewhat inaccurate. It also does not take into account the density of the atmosphere, which would increase scattering at the surface.
- These results conflict with a source he cites in another spreadsheet. This guide suggests my skies will have a bluish tone at 3atm and even 10atm, given the spectral type of the parent star. It mentions that planets with higher gravity can achieve more surface pressure with a thinner atmosphere, and will appear thinner than they actually are, further pointing towards blue skies.
- Mass: 2.0MEarth
- Radius: 1.25REarth
- Average Surface Temp: 25ºC
- Sea Level Pressure: 2.43atm
- Atmosphere Composition: 78.19% N2, 20.45% O2, 1.23% Ar, 0.08% CO2, .05% Trace Gases
- Star Type: K6V (.64MSol, .168LSol, Peak Wavelength ~619.94nm)
- Designing Earth-Like Atmospheres / Artifexian
- 1a. Habitable Pressure Chart / Project Rho
- SKY & PLANT COLOR ft. Worldbuilding Notes / Artifexian
- 2a. Script w/ Sources / Artifexian
- 2b. Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization / Robert A. Frietas Jr
- 2c. Earth: Portrait of a Planet, p697 / Stephen Marshak
- 2d. Atmosphere of Titan / Wikipedia
- 2e. Sky turns orange across UK / Judith Vonberg, Brandon Miller, CNN
- 2f. Why isn't the Martian sky blue like the Earth's? / Dr David Catling
- 2g. The Sky on Alien Worlds / Stephen Inniss, Steve Bowers
- 2h. Activity 1: Exploring Spectra / Sloan Digital Sky Survey
- 2i. Sky Colors for Exo-Earths / Ivan Gonçalves
- Earth-Like Atmospheres 3.0 / Artifexian
- Sky & Plant Color Calculator / Artifexian
- Colors of Alien Skies / Panoptes
- The Worldsmith v3.04 / Artifexian
- Colors of the Sky / C.F. Bohren, A.B. Fraser
EDIT: Accidentally linked the wrong videos, corrected.