The idea of somehow terraforming Mars to make it more habitable is a visionary, sci-fi dream. But though global terraforming of Mars is out of reach, the idea persists. But now, a material called silica aerogel might make the whole idea of terraforming Mars slightly less impossible.
Notable people from Carl Sagan to Elon Musk have proposed warming Mars and giving it an atmosphere, and the trick lies in the frozen CO2 and water in the planet's polar caps. Sagan said if those caps could be vaporized somehow, then the CO2 greenhouse effect would do the rest. Musk said, glibly and half-jokingly, that atomic bombs dropped on the poles would do the trick.
There's serious scientific work going on to explore the idea, at least in theory. The central question is, does Mars have enough CO2 and water to create an atmospheric density similar to Earths?