<P> Philosophers have pointed out that the size of the universe is such that a near - identical planet must exist somewhere . In the far future, technology may be used by humans to artificially produce an Earth analog by terraforming . The multiverse theory suggests that an Earth analog could exist in another universe or even be another version of the Earth itself in a parallel universe . </P> <P> On November 4, 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth - sized planets orbiting in the habitable zones of Sun - like stars and red dwarf stars within the Milky Way galaxy. 11 billion of these estimated planets may be orbiting Sun - like stars . The nearest such planet may be 12 light - years away . </P> <P> Scientific findings since the 1990s have greatly influenced the scope of the fields of astrobiology, models of planetary habitability and the search for extraterrestrial intelligence (SETI). NASA and the SETI Institute have proposed categorising the increasing number of planets found using a measure called the Earth Similarity Index (ESI) based on mass, radius and temperature . According to this measure, as of 23 July 2015, the confirmed planet currently thought to be most similar to Earth on mass, radius and temperature is Kepler - 438b . Scientists estimate that there may be billions of Earth - size planets within the Milky Way galaxy alone . </P> <P> Between 1858 and 1920, Mars was thought by many, including some scientists, to be very similar to Earth, only drier with a thick atmosphere, similar axial tilt, orbit and seasons as well as a Martian civilization that had built great Martian canals . These theories were advanced by Giovanni Schiaparelli, Percival Lowell and others . As such Mars in fiction portrayed the red planet as similar to Earth but with a desert like landscape . Images and data from the Mariner (1965) and Viking space probes (1975--1980), however, revealed the planet as a barren cratered world . However, with continuing discoveries, other Earth comparisons remained . For example, the Mars Ocean Hypothesis had its origins in the Viking missions and was popularised during the 1980s . With the possibility of past water, there was the possibility that life could have begun on Mars and it was once again perceived to be more Earth - like . </P>

Which planet is most similar in temperature to earth