Terraforming is a term often associated with space exploration. It is hypothetical process of modifying the atmosphere and land of a planet to make it habitable to life as we know it. Overly optimistic scientists across the globe had plans to modify the Mars for sustain humans.
It is widely accepted that Mars once has proper atmosphere and even surface water. However, a few billion years ago, it all went away. Bases on this theory, scientists were thinking of building up the atmosphere by releasing the carbon dioxide possibly trapped in the Martian crust. However, a recent discovery made by the MAVEN (Mars Atmosphere and Volatile Evolution) craft mostly washed away such hopes.
NASA announced that Mars’ carbon dioxide did not get trapped in the crust. Around 4.2 billion years ago, the planet lost its magnetic field. With no protection from the solar wind, Mars was stripped off its atmosphere. This means that the CO2 was washed away in the deep black space. Leaving a cold and dry planet behind.