While Mars is no Earth, many scientists believe that there could still could be life on the surface of the Red Planet just waiting for us to discover, despite the differences between the two planets.  So why do scientists believe there could still be life on Mars?  Here's why:

Mars Used to Look More Like Earth

While Mars may look like a dry and deserted wasteland today, in the past Mars looked very different.  According to Jennifer Eigenbrode, an astrobiologist at NASA, said that while it may look empty today, there is evidence that in the past Mars used to look a lot like Earth.  Of course you would have to go back billions of years to see it. 

At one time an ocean was thought to have existed and there is evidence that Mars used to be much warmer in the past, meaning that life could have once existed and then died off as Mars changed.

Life Exists in Extreme Places Here on Earth

Life is more resilient than often thought, existing in some of the most extreme places here on Earth.  It thrives in locations such as the Atacama Desert where it rains once every 10 to 15 years and fungi even grows in the radiation-poisoned Chernobyl.

"Life exists in all extremes on Earth," Eigenbrode says. "Every time we think 'No there's no way life could live here,' we're proven wrong."

Ingredients for Life Exist on Mars

The rovers covering terrain on Mars are already searching for the ingredients of life, and many have already been found.  For example, nitrogen, a critical part of amino acids, has been discovered as well as carbon monoxide that is needed for microbes.  There is even evidence of salty, liquid water flowing beneath the surface.

We Have Barely Explored the Surface

While we have had rovers roaming the surface of Mars for years now, we have still only explored a small fraction of the surface.  When you consider the area that has been searched and analyzed, we still could have missed something.  Faulty techniques could have been used when searching for life.  The Martian soil contains perchlorate, which destroys organic material.  It is possible that any organic material was destroyed before it could be discovered.

Mars once was a very different place than it is today, and even in the harsh environment of the Martian surface, the possibility of discovering life still exists.  Pamela Conrad, Deputy Principal Investigator for Sample Analysis at Mars, says she one day hopes to see a human lab on the Red Planet, giving humans flexibility in experiments to provide much better soil analysis to increase the chances of discovering life.