Venus is considered the sister planet to Earth in size, mass and density, but is not compatible with the probability of life. However, the similarities are more accurate with Mars Respert the possibility of life.
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On Mars lasts 24 hours, 39 minutes, 35,244 seconds, while the day lasts 24 Earth hours. Mars has an axial tilt of 25.19 °, compared with 23.44 ° of the Earth, resulting in seasons possessing similar to our planet, but they last twice as long.
In recent expeditions to Mars NASA, robots like Spitit and Opportunity have confimed the presence of water on the surface and studies indicate that Mars has the characteristics needed to establish that life existed many years ago.
On the other hand, the amount of carbon dioxide (CO2) on Mars is 52 times greater than on Earth revealing that plants exist on that planet.
Being frthest from the Sun, Mars is colder than the Earth and record temperatures from -140 ° C and 10 ° C. It also receives half of solar radiation that Earth receives.
Like Earth, Mars has an atmosphere that provides protection to solar radiation and cosmic filing. Although very thin, only 0.7 thickness of the atmosphere can be considered a void: a human being without a space suit would lose the sense in 20 seconds and would not survive on the surface.
Despite the conditions on Mars, the chances of life are more likely than in other planets, which include very high temperatures such as Venus or the extreme cold as Pluto. If proven theories, Mars and Earth are the only planets in our solar system have colonization.