aphelion

Variations in the timing of perihelion and 'aphelion' are caused by a ‘wobbling’ in the Earth's axis of rotation as it rotates around the Sun.

Mars is at 'aphelion'

Furthermore, any resonance with the Earth is illusory in that Mercury is not well placed for observations except during its brief greatest elongations near its 'aphelion' .

There are small cyclic variations in those apparent sizes because the Earth-Moon distance changes as the latter moves between perigee and apogee, and the Earth-Sun separation alters as the former moves between perihelion and 'aphelion' .

Mars is at 'aphelion'

This affects the climate because the influx of solar energy to our planet would then vary between perihelion and 'aphelion' by a larger proportion than at present.

This is because at 'aphelion' the planet is moving slowest, and consequently it is less likely to pass across the Sun during the critical window.