Infographics

Just a place to keep track of some infographics I make to summarize some of the key points in the main posts.

Sizes and surface gravities for planets with earthlike compositions

The m, r, and g values are the mass, radius, and surface gravity relative to Earth. Every planet has the same bulk composition as Earth (32% iron-nickel core, 68% rocky mantle) but more massive planets are denser due to compression in the interior; I used the formulas in this paper to estimate radius.

0.05-10 Earth masses is a very optimistic estimate for the range of planets that could have Earthlike habitability (liquid water on the surface with sufficient sunlight for photosynthesis for billions of years). More realistically, most planets below 0.25 Earth masses are likely to lose their atmospheres too quickly and most planets above 2 Earth masses are likely to retain too much of their primordial hydrogen/helium atmospheres.

More detail on planet size and its relationship to habitability.

 Appearance of Stars from the Perspective of Orbiting Planets

Full resolution version.

 

This chart is designed to be standalone, so it pretty much explains itself. Most of the values for the properties of the various stars are pulled off wikipedia, and the RGB colors for blackbody temperatures are from here. Since making this, I've come to understand that some red dwarfs may emit redder light than an ideal blackbody of the same effective temperature, but it shouldn't be a huge difference.

Another factor that can't properly be shown is intensity; each star contains the same total light distributed across its "disk". The brown dwarfs would probably appear as mellow disks that you could comfortably look at, while the bluest stars will appear as intense points of light that could pose a blinding hazard.

More detail on stars and the appearance of "alien skies".