For years, scientists have had evidence pointing towards the existence of liquid water on Mars at some point in the past. They assumed that greenhouse gases had once been abundant in the red planet, making liquid water possible. However, data collected in orbit and more recent data collected from the Curiosity rover suggest otherwise. It turns out that greenhouse gas levels were hundreds of times too low to warm Mars sufficiently for the existence of liquid water. Scientists now need to revise their theories to understand how Mars might have maintained liquid water.