Terraforming Mars

In an interview with Astrobiology Magazine, Mars researcher Jean-Loup Bertaux outlines a plan for creating a local habitat on the red planet, suitable for humans and plants. Suggestions for converting the hostile environments of other planets into more Earth-like substrates, are always impressively bold. But this guy has a really ambitious plan. A 45 kilometer deep hole...

"The idea is you dig a big hole, maybe at a 45-degree inclination, in the Hellas crater, which is already at low altitude. Maybe you need a hole of 45 kilometers [28 miles], which is not so easy. But the whole atmosphere of Mars is going to go down into the hole. Two things would happen. First of all, the pressure at the bottom of the hole would be about 1 bar - much higher than at the surface. It would also be a much warmer temperature, because when you go down, the pressure increases and the temperature also goes up." (from Space.com)

Just for comparison, the deepest point on the Earth's surface is 11km down, at the bottom of the Mariana Trench.