Happy Aphelion Day, everyone -- today the Earth is at the furthest part of its orbit from the sun. We're about 3 million miles further the sun now than we are at perihelion in January. Earth receives 7% less sunlight now than it does at perihelion. Since Earth's orbit is nearly circular, this doesn't affect the seasons much.
By contrast, Mars has a much more elongated elliptical orbit, and receives 31% more sunlight at perihelion than at aphelion. Perihelion on Mars coincides with southern summer, making the southern summer hotter and the winter colder. Conversely, it moderates the northern seasons, making the summer (at aphelion) cooler and the winter warmer. That's why the southern icecap grows larger in winter than the northern icecap.
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