Life demands very particular conditions which are quite difficult to meet, even though Nicolaus Copernicus said that the Earth is not located at the center of the solar system, we’re not located at the center of the galaxy, and we’re not located at the center of the universe and we have no special qualities whatsoever, as Earth is only a mediocre planet! The Copernican Principle went further saying that there are no special parts of the universe, everything is the same everywhere (up to statistical variation). This may not sound like a particularly important principle, but it’s actually vital to the history of science, because it represents a fundamental philosophical change in how intellectuals dealt with humanity’s role in the universe, well at least in scientific terms. Copernican Principle advocates have been claiming that just about every other body in the solar system (including the Sun) is able to harbor intelligent life, but today, we know that this is not the case. There is also widespread doubt that even the simplest kinds of life, such as bacteria, could exist anywhere else in the solar system. Just because the Earth is not the physical center of the universe does not mean that it is an ordinary planet, as the necessary conditions to support life are so rare that they may only exist for Earth.
The Goldilocks Zone or circumstellar habitable zone (CHZ), refers to the habitable zone around a star where the temperature is just right, being not too hot and not too cold for liquid water to exist on an planet. Mercury and Venus were thought to be too hot and Mars and the outer planets were thought to be too cold to support life as we know it. Only Earth is just right for life, in fact it is perfect having liquid water, a breathable atmosphere, and a suitable amount of sunshine. Originally we determined that the Goldilocks Zone was a remarkably small region of space not even including the whole Earth. Scientists felt that all life was confined to certain limits, being no colder than Antarctica (where penguins survive), and no hotter than scalding water (where lizards live in the desert), no higher than the clouds (birds), and no lower than a few miles deep (where microbes endure). However, recently our knowledge of life in extreme environments has exploded. Scientists have found microbes in nuclear reactors, microbes that love acid, and microbes that swim in boiling-hot water. Whole ecosystems have been discovered around deep sea vents where sunlight never reaches and this emerging vent-water is hot enough to melt lead, so the Goldilocks Zone is bigger than we thought. This new expanded Goldilocks Zone corresponds roughly with the orbit of Venus and just beyond the orbit of Mars being able to support life. However, because of planetary/atmospheric dynamics, liquid water cannot exist on either Venus (too hot due to a runaway greenhouse effect) or Mars (inadequate atmosphere due to lack of mass to hold onto it). Venus and Mars both at one time did have liquid water and Mars may still have some subsurface water.
Climate models suggests that if our planet were just a little closer to the Sun, a runaway greenhouse effect would render it uninhabitable. If our planet were to receive about one-tenth more solar radiation than it does now, water vapor would trap more heat and more water would evaporate, boosting the greenhouse effect and thus trapping even more heat. The average distance from the Earth to Sun varies by over 3 million miles, during its orbit each year, but Earth is on the inner edge of the Goldilocks Zone and we don’t need our planet getting any hotter.
The more that we learn about our universe, the more non-special our location seems to be. The Earth is orbiting an ordinary star in an ordinary galaxy. The reason the Copernican principle works is that, out of all the places for intelligent life to exist, there are only a slight few special places and many more non-special places. So we are probably more likely to be in one of the many non-special places.