More specifically:
Consider two hypothetical planets with no atmospheres. One orbits the Sun at an average distance of 5.0 AU and the other at an average distance of 10.0 AU, yet both have the same average surface temperature. Explain how this could be possible.
The closer planet has much higher albedo (reflectivity).
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Reflection of sunlight… some materials reflect sun light more then others
More reflection means lower temp blablabla
Also a electro magnetic field might prevent sun radiation from reaching the planet
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internal heat sources also, nuclear, geothermal, etc…
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There are two primary sources of heat for a planet: external (largely resulting from exposure to a star, but possibly also from another nearby planet reflecting solar energy or producing its own energy) and internal (mostly resulting from gravitational compression producing heat, but also from nuclear decay and chemical reaction– to a very small extent, comparatively).
A planet farther away can compensate by having a much larger mass, and/or by being composed of an over-abundance of radioactive material (although this is rather unlikely), thus producing more internal energy.
However, even if the two planets had the same mass (with the same internal energy), the scenario of having the same surface temperature might still be possible. Surface temperature due to external heating is not solely a function of high much energy an object receives, but also how well that object retains the heat. If the nearer planet is highly reflective, the energy is easily lost, and it remains quite cold. If the planetary crust absorbs and retains more of the heat (perhaps by being less reflective, but also by redistributing the energy inward, etc) then the energy would build up, causing the planet to become hotter (compensating for the distance). Essentially, this is exactly what an atmosphere does, but layers of atmosphere can be more efficient/effective at trapping the energy.
I should point out that this effect is not merely a question of reflectivity. A planet that was transparent (allowing the energy to pass through) would lose as much of the heat energy as one that reflected almost all the energy. The retention of energy is more a factor of the refraction of energy to various extents (causing an amount of ENERGY to be refracted back into the planet), and the elemental/molecular absorption and emission properties (absorbing certain wavelengths of light, re-emitting them at other wavelengths… but the re-emission would then be random, so much of it will be back into the planet).
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The farther planet is twice as big or more, therefore having a molten and magnetic inner core which produces inner heat.
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The closer planet has much higher albedo (reflectivity).
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