NASA scientists announced Tuesday that an analysis of the rover's first drill sample on the Red Planet revealed clay minerals that could have only formed in water.
The discovery of other substances alongside the clays, such as calcium phosphate, suggest the soil was neutral or mildly alkaline, making the environment suitable for microbes.
Researchers said while there is no evidence of past life, the sample revealed the most hospitable environment ever detected beyond Earth.
"We have found a habitable environment that is so benign and supportive of life, that if you lived there, the water would have been pure enough to drink," said Curiosity project scientist John Grotzinger.
Curiosity has been very busy since its arrival on Mars last August. The rover has been exploring an area in the basin of the Gale crater called Yellowknife Bay.
Scientists believe the bay region was the end of an ancient network of rivers or an old lake bed that was wet at various times in the planet's history.
Curiosity is ultimately headed to the 18,000-foot Mount Sharp in the crater’s center. Scientists believe the mountain’s rock layers are an ideal place to look for organics
The latest clues to the Martian environment came from data sent back to NASA scientists by the rover's sample analysis on Mars, with its chemistry and mineralogy instruments.
The rover, also known as the Mars Science Laboratory (MSL), was sent to the planet to answer a simple question: was Mars ever hospitable to life?
"A fundamental question for this mission is whether Mars could have supported a habitable environment," Michael Meyer, a lead scientist on NASA's Mars Exploration Program, said. "From what we know now, the answer is yes."
Among the results the rover beamed back to Earth, scientists were surprised to find chemical compounds in different states of oxidation. Similar variations in chemical makeup are used as an energy source by some microbes on Earth.
The partial oxidation of some minerals first revealed itself when drilled samples appeared grey instead of red in the rover's camera.
The $2.5 billion mission will last one Martian year, or 687 Earth days.
Curiosity is expected to pave the way for future Mars missions, including the first human exploration. President Obama has set a goal of sending an astronaut to Mars by the 2030s.