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I'm trying to create a habitable planet but with a low atmospheric pressure, similar to Mars. But instead with 15 percent of Earth's atmospheric pressure, what traits can I give my animals so they have the best chances to survive? If the atmospheric composition is about the same as Earth and orbiting a star like the sun at the same distance, it also has only 51% of Earth's gravity. Also 60 percent of its surface is covered by water.

Some other details about the planet,

Distance from primary star - 1 AU

Star - Sunlike

Mass - 0.14949 (M⊕)

Diameter - 6881 km

Gravity - 0.51 g

Oceans - 60% surface coverage

Atmosphere - Earthlike

Density - 5.25 g/cm3, slightly higher than Venus.. Hopefully this unusually high density for a small terrestrial planet is enough to generate, at least, a weak magnetic field, similar to Mercury maybe!

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  • $\begingroup$ I see a down vote but not a comment explaining the reason for it, or an obvious reason within the question. $\endgroup$ – rek Aug 29 '16 at 2:43
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Lower atmospheric pressure equals a lower boiling point for water. Possible lower night temperatures, though will still have to consider the thermal stability due to 60% water coverage, also cloud coverage too will have an influence.

Lower gravity will favour hopping animals like hopping mice, kangaroos & wallabies. Flying animals may be hampered by the lower air density, while the lower gravity will make it easier to get off the ground. Arboreal creatures will do well due to the low gravity. Gliders might have a tough time due to low air density. Swinging & springing critters should do well in the trees.

Expect more amphibians. The lower gravity will make the transition from water to land easier.

These are a few suggestions. You may find it worthwhile to do research into biomechanics when designing your creatures. There is a good starting text by R. McNeill Alexander who is an expert in animal biomechanics.

REFERENCES

Alexander, R.McN. (1983). Animal Mechanics 2nd Edition (Oxford: Blackwell).

Alexander, R.McN. (2003). Locomotion of Animals (Princeton: Princeton University Press).

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  • No birds or other large flying animals. At 15% of Earth's atmospheric density, there is no way Earthly or similar birds would have a chance. On our Earth, birds at least have a 1:2 ratio of body length : wingspan. On your planet, the ratio would perhaps be at least 1:10 or so, which is rather impractical to manage. However, you may have some small (sparrow-sized) birds with 1:4 body shape which can manage flight by extremely rapid wing flapping.

  • Land living animals would probably have weaker/lighter skeletons as compared to Earthly animals, since they would not have to support themselves against such high gravity.

  • Ears would be far less important for animals' survival as compared to Earthly animals. Sound travels in a medium and when the medium is 85% thinner than Earth's medium (atmosphere), sound would travel much slower and have much lesser amplitude, making ears less useful.

  • The sense of smell would have greater emphasis. Odors also travel in the air and a very much thinner air would imply that odors would not fade out as quickly as they do on Earth, since the diffusing medium would be very much thinner.

  • Similarly, vision would be very much enhanced. Forgoing the fact that the visual range would be very much reduced due to the smaller size of the planet, all things would be seen very clearly with virtually no haze effect at all, even for very long distances.

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Lot's of great possibilities. Locomotion: Smaller animals could have small wings, or winglike structures (think flying squirrel). Floating animals (filled with gas) could use that gas for propulsion, like attitude jets on a space craft (and they would not have to be located only at front and rear, you could have a gill-vent for turning, etc.) Considering your planet's 60% water you could reasonably have amphibians who could fly in the air and use the same wing/fin / propulsion combination to move about underwater. Predators: would have to be fast and accurate - think moray eel, both in and out of water. So their prey would have to be faster and smarter and trained from birth (or have genetic memory) for evasion.

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  • $\begingroup$ Do you think a space faring species would be able to evolve on the planet? $\endgroup$ – Stephanie Aug 29 '16 at 0:57
  • $\begingroup$ I think this answer would apply to higher air pressure, not lower. $\endgroup$ – John Feltz Aug 29 '16 at 3:22

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