Gradient PLUS surface temperature

What part of simple school-grade maths don't you understand?

Y=mX +C

If the year-round average surface temperature at the equator is - 40 C, and at the poles it is - 140C the why wouldn't you need to go MUCH deeper at the poles to get the same temperature?

Do you think there is a magic electric blanket on Mars that says that the "temperature at 1 km is -35C. whatever the surface temperature is?"

Temperatures underground depend on surface temperature.

Please, please don't tell me that "heat from under the ground will make the surface warm"

Do some Maths on this. If you wish to debate the point, gird your loins, check your maths, and get your science right. I WILL be merciless, and cruel...