Its the axial obliquity I tell you!

[smjjames]

Its in the same vein of the axial tilt article here: http://www.space.com/14295-alien-life-exoplanets-tilt-red-dwarf-stars.html , even the same guy who did that study is involved in this one.

http://www.space.com/14509-alien-planets-planetary-tilt-search-life.html

I know Fiah already talked about axial tilt, but this is how much the planet is tilted. The effects of obliquity is much better understood. Also, the article should say complex alien life, it doesn't rule out primitive life forms from emerging. After all, we have extremophiles in some of the harshest environments possible on Earth.

It also makes life around red dwarfs that much harder, but if life can arise in such a hostile environment, that shows just how tough life forms can be.

Seems like having a moon to stabilize the planets axial tilt is going to be a major factor in how Earthlike a planet can get.

Also, IMO, a planet with a low axial tilt (less than 5 degrees), probably won't keep life from evolving complex forms, but it might have consequences for evolution, climate, and habitat types, After all, climate change and change of habitats helps drive evolution and diversity on Earth.

[Omnigeek6]

Hmm...

http://en.wikipedia.org/wiki/Habitability_of_red_dwarf_systems#Light_emission_and_tidal_lock

The tidally locked planet would likely need an atmosphere thick enough to transfer some of the star's heat from the day side to the night side; this would prevent the colder night side's atmospheric temperature from dropping below condensation point, causing a drop in atmospheric pressure that would draw more of the atmosphere towards the night side until all of the atmosphere gets frozen on the night side. It was long assumed that an atmosphere would need to be so thick as to impede photosynthesis from any plants on the day side surface. However, more recent research has suggested otherwise. A 2010 study concluded that Earth-like aquaplanets tidally locked to their stars would still have temperatures above -33 Celsius on the night side.[7] Studies by Robert Haberle and Manoj Joshi of NASA's Ames Research Center in California have shown that a planet's atmosphere (assuming it included greenhouse gases CO2 and H2O) need only be 100 mb, or 10% of Earth's atmosphere, for the star's heat to be effectively carried to the night side.[8] This is well within the levels required for photosynthesis on the day side, though some of their models still had water frozen on the dark side. Martin Heath of Greenwich Community College, has shown that seawater, too, could effectively circulate without freezing solid if the ocean basins were deep enough to allow free flow beneath the night side's ice cap. Geothermal heat might also help keep the lower parts of any ocean liquid.[citation needed] Further research—including a consideration of the amount of photosynthetically active radiation—has suggested that tidally locked planets in red dwarf systems might at least be habitable for higher plants.[9]

I'm imagining that the temperature variation for a high-obliquity or low-obliquity planet would still be a little bit less than the variation for a tidally locked planet if all other conditions were constant.

Some things to think about for how life would adapt to a high axis tilt:
most life would probably either go dormant during the coldest parts of the year (the winter solstice at higher latitudes... but BOTH solstices at the equator) or migrate between hemispheres. Dormancy isn't necessarily incompatible with high complexity... one could imagine the most complex life on a high-obliquity planet evolving from a creature somewhat like a tardigrade which could dehydrate itself in response to cold temperatures.

[smjjames]

Yea, plant seeds can lay dormant for years, if not decades or longer. Sessile plant-like organisms or otherwise photosynthesizing organisms could follow the strategies of desert plants or even those in the arctic circle.

Of course though, the article implies that a decreasing axial tilt may have influenced the rise of complex organisms. However, that's just Earth and the axial tilt may have just been a coincidence of the Snowball Earth event (which had more to do with decreased CO2 than the axial tilt) which is believed to have been a trigger for the rise of complex organisms.

The geological and climatic histories of alien planets with life are likely to be vastly different, so we won't really know whether the axial tilt has an effect on the rise of complex organisms until we can actually get there.