Work of NASA (National Aeronautics And Space Administration)

Parameter to maintain life:

There is a huge problem that by which parameter we can guess life can exist on any planet. Following parameters play an important role in the maintenance of life:

• Presence of water
• Presence of oxygen and carbon dioxide
• Suitable temperature
• Presence of organic compound
• Rocky soil
• presence of gravitational force

Work of NASA (National Aeronautics And Space Administration):

NASA plays an important role to explore the secret of universe. It was started in 1985 as a part of the United States government. NASA is in charge of U.S. science and technology that has to do with airplanes or space. When NASA started, it began a program of human spaceflight. The Mercury, Gemini and Apollo programs helped NASA to learn about flying in space and resulted in the 1st human landing on Moon in 1969. Currently, NASA has astronauts living and working on the International Space Station. NASA's robotic space probes have visited every planet in the solar system. Telescopes have allowed scientists to look at the far reaches of space. 

From all above discussion it is clear that  there  are few planets and moons which has suitable circumstances for life in which Mars is at the top of the list.