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The setting I'm interested in would involve a cold planet (cold enough for most bodies of water to be frozen - I'm thinking of an average global temperature of -20C or below). The simplest way would have to have the planet far away from its star. However I'd rather not deal with the low-light aspect, so I was wondering if there's a way to avoid that. The luminosity level I aim for is above 'Sun as seen from Mars'.

Having no atmosphere would be easy, but not exactly what I'm aiming for. I'd prefer an atmosphere that allows human life. (I mean in the breathing sense. Separate shielding for cosmic rays can be provided, if necessary)I'd prefer weather (eg. ground covered in snow, whether water-based or something else, which would also increase the albedo). I realize that Earth had several Snowball eras, but I'm wondering if there could be a planet with the above characteristics whose main state is 'snowball'.

Also - could this be possible with a blue star?

Just remove greenhouse gases from the atmosphere: CO2, H2O, CH4, for example.

This would lower the amount of infrared radiation trapped by atmosphere, lowering as a consequence the temperature.

Keep in mind that since the climate is a complex system with several feed-back and feed-forward, a snowball planet would reinforce its conditions: more water trapped as ice ==> less water in the atmosphere ==> lower temperatures ==> more water trapped as ice.

Our planet is just a few thousand years out of an ice age. To get a habitable planet covered in ice (or mostly covered in ice):

• Make the sun slightly dimmer (less radiated heat)


• Make the planet slightly further from the sun (less intercepted heat)


• Make the planet have slightly less green house gas (less retained heat)


• Be at an extreme cold point in a planets' natural heat/cold cycle

The difference you'd need to have a planet in your required range would be surprisingly slight. Any of these listed tweaks could result in a planet colder than Earth for thousands or maybe millions of years.

As a note: to have native terrestrial life, the planet would have had to have open ocean and warm land at some point to encourage flora and fauna onto the land. Also keep in mind seasonal variation. With seasons due to axial tilt, that would mean open ocean near the equator and further toward one pole for half the year. For seasons caused by elliptical orbits, that would mean open ocean for part of the year and pack ice for the other part.

The answers you've received are great! I'd like to piggy-back off of them - specifically L.Dutch's:

We can add to this answer by incorporating volcanic activity. A decent supervolcano will start a nuclear winter. An overactive, planet-wide 'ring of fire' with many small volcanoes could potentially prevent a forever-cold feedback loop. I could have mentioned something like ozone-creation-supporting environments to prevent the needless build-up of ice + providing a weak greenhouse gas, but volcanoes are cooler haha.