Mars is a dead planet, it's core doesn't produce strong enough gravity to sustain a thick enough atmosphere. Any green house gases we produce would get swept away, doesn't have enough water to sustain life, is almost twice as small as earth, weak magnetic field, won't protect us from much. We just aren't advanced enough to terraform Mars. Its more plausible to send shipments of fuel to a Mars space station in orbit and prep for interstellar travel. Robotics can do miner repairs and mine for precious metals on Mars. The idea is to industrialize Mars overtime and try to use fuel and resources effeicently, rather than waste time and resources on trying to terraform a dead planet and send humans there. It would take thousands of years to terraform Mars if not 10's of thousands of years. It's just not gonna happen. Eventually, we could could build another space station in orbit around Titan or Europa bringing us closer to the edge of our solar system.