Earlier this week, NASA revealed that data gathered by its Curiosity rover suggest that the Gale Crater on Mars used to be a huge lake of water.

Michael Meyer, the lead scientist for the Mars Exploration Program, said that this ancient lake was large enough it may have lasted for millions of years and could have made it possible to start and support life on the planet.

Evidence that the Red Planet had a watery past keeps piling with NASA's Martian instruments finding what may have been flowing river and water-rich minerals, but while the presence of water on Mars can serve as a strong indication that the planet had once sustained life and that water is in fact crucial to the habitability of planet Earth, a prominent researcher pointed out that the presence of liquid water does not mean that Mars indeed supported life.

Astrobiologist Pamela Conrad, from NASA's Planetary Environments Laboratory, said that water is not the only factor crucial for supporting the evolution of life. In a "Perspective" piece published in the journal Science on Dec. 12, Conrad reminded researchers that liquid water is just one of several factors that have to be considered when investigating the past and present habitability of Mars and other cosmic bodies.

Conrad said that there should be the right combination of chemical and physical condition at the perfect place and time for life to emerge and to be sustained. With extreme temperature variation in Mars (70 degrees Fahrenheit during the day and negative 100 degrees at night), for instance, survival may be difficult for early life regardless of the presence of water and the right nutrients.

Mars also have thin atmosphere so radiation can also be a problem because the Martian atmosphere won't sufficiently protect its surface from the damaging rays of the sun. Conrad said that life has less chances of survival with high radiation.

"Chemistry is only part of what is required to make an environment habitable," Conrad wrote. "Physical conditions constrain the chemical reactions that underlie life processes; the chemical and physical characteristics that make planets habitable are thus entangled."

The astrobiologist said that she's not throwing cold water on recent discoveries that indicate the possibility that the Red Planet sustained life in its past. All she wanted is to ensure the researchers keep their eyes open.

"The things that make a place livable are numerous, and sometimes, there's a showstopper you didn't think of," Conrad said. "So it's important to take a poll of the diversity of attributes that could contribute to making an environment livable or not."

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