Does the size of a planet affect its average temperature?

Question

For a school test I said Mars has a lower average temp. than Earth because it's smaller so its surface area is less, which means it is hit by less of the sun's rays. Is my answer right?

Answer 1

No....
Jupiter is the largest planet but its the coldest.
Venus is smaller than Earth and its the hottest.

Size doesn't have much to do with anything. It has to do with the atmosphere make up of the planet. For example Venus is heavily condensed with CO2 which makes a greenhouse effect making it the hottest planet.

The distance from the Sun effects the temperature. However, it all starts when everything was in a nebulae. At the beginning when all the planets were planetismals the distance had caused their atmosphere makeup. That is why certain temperatures on planets are the way they are.

Answer 2

No.
The temperature of a planet is such that the energy the planet receives is the same as the energy that the planet radiates.

It receives energy at a rate determined by its cross section (pi*R^2) and generates heat through its entire surface area (4*pi*R^2).

So the number of W/m^2 that is gives off is always 1/4 of the number of W/m^2 that it absorbs. Two planets of different size, but same distance from the sun, will have the same temperature.

A planet that is further from the Sun receives a lot less energy per square metre.

So the planet further from the sun will be colder.

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The other thing that can affect the temperature is the albedo (the amount of light that is reflected back in space without being absorbed).
Earth reflects 37% but Mars only reflect 15%.

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a detailed calculation:

At Earth's orbit, the solar flux is 1370 Watts per square metre. Earth's albedo is 37% (meaning that we only absorb 63% of the heat) so we capture 863 W/m^2.

We must emit the same quantity (but we have four times as much surface area as cross section): 216 W/m^2. This is the number that determines our nominal temperature (our real temperature could be higher because of greenhouse effects).

Mars is further from the Sun (1.524 times further). The solar flux diminishes as the square of the distance from the Sun: 1370 / (1.524)^2 = 590 W/m^2

Mars has an albedo of 15%, so it keeps 85% of the flux: 500 W/m^2.

It must emit the same quantity, through its surface area: 500/4 = 125 W/m^2

Earth temperature will be that needed to emit 216 W/m^2.
Mars temperature will be that needed to emit 125 W/m^2.

Mars is colder.

Answer 3

The temperature at the surface of any planet is directly related to the distance from its sun and the size and temperature of the sun.

Its true that the overall amount of sunlight Mars receives is less than earth due to its smaller size.
But if you take a square meter of surface on Mars and a square meter of surface on the earth, the area on the earth is warmer because its closer to the sun than the same amount of area on Mars.

Answer 4

No.

The things that control temperature are proximity to the heat source and ability of object to trap heat.

Venus is the prime example - with an dense atmosphere of 96% CO2 and a distance of 67,000,000 miles from the Sun, it's temperature is over 400 degrees F.

Mars, with it's thin atmosphere and 130,000,000 miles from the sun, the temperature rarely gets above the freezing point of water at noon in summer.

Earth is in the middle. Little CO2, and 93,000,000 miles from the sun, it's temperature is ideal.

Jupiter, next planet out from Mars, VERY dense atmosphere, but VERY far from the Sun means it's temperature is about -200.

Answer 5

No, unfortunately, you were wrong.

All the energy that is absorbed by a planet has to be radiated back into space in the form of infrared energy so the temperature is stable. The surface that absorbs energy is the same surface that radiates back.

Answer 6

Depends on distance from the sun and orbit of the planet (ie how evenly is heat distributed) also the composition of the planets mass/atmosphere certain elements conduct/hold heat better than others.

Answer 7

Yes, you aced it for planets. Also, for animals, if a body is small, it cannot store as much heat (less volume, as well as less surface area). That's why small creatures feel colder than a big dog.

Answer 8

I think it mainly depends on the distance from the sun.