An extreme method of greenhousing Mars has recently been proposed by scientists Christopher McKay and Robert Zubrin, authors of The Case For Mars. This extreme method involves hurling large, icy asteroids containing ammonia towards Mars.When the asteriods bombard the surface of Mars, it will produce tons of greenhouse gases and water. For this to be done, nuclear thermal rockets would have to be attached to asteriods within our solar system. According to McKay and Zubrin, the rockets would move the asteriod at a speed of 4km/s for a period of 10 years. After the 10 years the rockets would shut off and allow the huge asteroids to glide, unpowered towards Mars. Energy released upon impact would be about 130 million megawatts of power. Thatís enough energy to supply the entire Earth power for an entire decade!If it is probable to crash an asteroid of such size into Mars, the energy of a single impact could increase the surface temperature of Mars about 3 degrees Celsius. A sudden increase in temperature on the planet would be capable of melting approximately 1 trillion tons of water. Over the years multiple missions would create a temperate climate and enough liquid water to cover 25% of the planetís surface.
Unfortunately, human exploration and colonization of the planet would be delayed for centuries because of the immense amounts of energy and radiation released from the asteroid impacts on the small planet.