# How much sunlight does Mars get than Earth?

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Although with a reduced Atmosphere the effects of Radiation are more severe

If only Mars had 80% of Earth's Mass, it would be a different story

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• The maximum solar irradiance on Mars is about 590 watts/square meter, compared to about 1000 watts/square meter at the Earth's surface.

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• 1/(1.524^2) = 43%

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• The sunlight on Mars is about half the intensity we receive here on Earth.

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• Did you know that if you scaled a cue ball to the size of the Earth, it would be bumpier and less spherical than the Earth?  If you scaled the Earth to the size of a cue ball, its surface would be smoother than the cue ball.  I only mention this because when I tell you to think of the surface of the Earth and Mars to be pretty much flat, when compared to a sphere that has a radius equal to their distances from the Sun, I want you to understand that while it may not be technically true, it's true enough for the purposes of our problem.

The Earth has a radius of about 6378 km and it's about 150,000,000 km away from the Sun

Mars has a radius of about 3390 km and it's about 241,890,000 km away from the Sun.

The Sun is broadcasting radiation in all directions at all times, and the intensity is pretty much the same in all directions at the same distances.  That is, if you are 100,000,000 km away from the Sun, no matter where you are, the Sun will appear the same and you'll get the same amount of illumination from it.  Yes, there are differences when you're directly above the magnetic poles, but that's neither here nor there and it doesn't really matter since the Earth and Mars are in the same orbital plane.

So, if you think of the Sun as exhausting the same amount of energy at every moment, and this energy is moving outward in all directions at the same speed (speed of light), then you have an expanding sphere of energy.  That is, if you were to collect all of the energy that exists at any particular distance from the Sun, then it will be the same.  However, as it spreads out, the energy density (how much energy is in a specific area) decreases.

Because we're comparing areas, then this decrease is related to the square of the distance.

If 1 square meter on Earth receives a certain amount of energy from the sun (we'll call this E), then 1 square meter on Mars will receive (150,000,000/241,890,000)^2 * E of energy.

(150,000,000/241,890,000)^2 =>

(150,000/241,890)^2 =>

(15,000/24,189)^2 =>

(5000/8063)^2 =>

‭0.38454457516892004916817701675825‬

Mars receives, per unit of area on the surface, about 38.45% of the energy from the Sun as the Earth.

Now, if you think of the Earth and Mars as flat disks along these gigantic spheres, we can compare the total amount of energy that is dumped onto the surface in a single moment.

Mars has a radius of 3390 km and the Earth has a radius of 6378 km.  The area of the cross-section of Mars is therefore about (3390/6378)^2 of the area of cross-section of Earth.  In total, at any particular moment, Mars receives on its surface

(3390/6378)^2 * (5000/8063)^2 =>

(3390 * 5000 / (6378 * 8063))^2 =>

‭0.10863682278743797634776822034468‬...

10.86% of the total amount of energy that Earth receives from the Sun.

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• The maximum solar irradiance on Mars is about 590 W/m² compared to about 1000 W/m² at the Earth's surface.

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• Anonymous
1 month ago

Less I'd say. Well, you know. Like photons and gravitation and atmospheres and sh*t. I dunno. Bout to pass out.

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