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Just curious, how much solar energy can power an (herbivore) animal? Specifically, is it enough sunlight on Mercury (4 to 10 times brighter than on Earth) to "feed" a zebra? Will it be sufficient at 10x more effective photosynthesis? Notwithstanding lack of atmosphere, water being buried deep and other minor problems, of course :)

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1 Answer 1

BMR is the amount of energy an animal uses just by being alive. BMR is proportional to the mammal's mass. More precisely, BMR is proportional to the mammal's mass to the power of 3/4. A 0.1 kg mammal has a BRM of 10 kcal. Using the aforementioned proportionality, a 600 kg mammal (average mass of a cow) will have a BMR of 6800 kcal.

This means that a cow would need about 6800 kcal of energy per 24 hours (1440 minutes) to survive.

The amount of solar energy reaching the earth’s atmosphere is 0.00194 kcal per square centimeter per minute. Since, according to you, there is 10 times the amount of sun in Mercury, there should be 0.0194 kcal per square centimeter per minute hitting Mercury.

0.0194 kcal per minute for 720 minutes (counting only day - since there is no sun during the night) equals 13.968 kcal per square centimeter per day. At this rate, the sun has to hit an area of 486 cm squared to harness enough energy for the cow.

In summary:

  • The average cow needs about 6800 kcal per day to survive (BMR)
  • On Mercury, the sun generates 13.968 kcal per square cm
  • Which means, the sun has to hit an area of 486 square cm

In one sentence:

  • In order to power a cow on Mercury, the sun has to hit an area of 486 cm for 720 minutes.

To learn more:

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According to wikipedia's [phoyosynthetic efficiency] (en.wikipedia.org/wiki/Photosynthetic_efficiency) a typical plant will convert about 1% of solar energy into chemical energy. But if our chlorofylled cow utilize sugar cane's 8%-efficient photosynthesis, then deal with overradiation, we get 6075 sq. cm area needed. Since day on Mercury is very long, we can require cow migration toward zenith, doubling energy production and eliminating 40% loss on photo-respiration. Finally, we got 1735 sq cm to light up. 40x43 cm, fine. –  mechmind Mar 14 at 13:42

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