1) Aristarchus, and later, Copernicus, then Galileo all proposed the Heliocentric model of the Universe. It was essentially correct for the Solar System, but not for the entire Universe. The realization that the Sun is a star and that the stars are millions of times further away than the planets took many years.
2) We are assuming that any form of life needs liquid water to develop and survive. None of the other planets in the Solar System currently has liquid water. It has just been found by the Phoenix Mars Lander that Mars has water ice, but not liquid water.
3) There are more than three previous theories about the organization of the Universe if you consider the differences between each scientist's view:
Previous theories (models) of the Universe
The geocentric model of the universe is the theory that the Earth is at the center of the universe and the Sun and other objects go around it. Belief in this system was common in ancient Greece. It was embraced by both Aristotle and Ptolemy, and most Greek philosophers assumed that the Sun, Moon, stars, and naked eye planets circle the Earth. Similar ideas were held in ancient China.
In the Ptolemaic system, each planet is moved by five or more spheres: one sphere is its deferent. The deferent was a circle centered around a point halfway between the equant and the earth. Another sphere is the epicycle which is embedded in the deferent. The planet is embedded in the epicycle sphere. The deferent rotates around the Earth while the epicycle rotates within the deferent, causing the planet to move closer to and farther from Earth at different points in its orbit, and even to slow down, stop, and move backward (in retrograde motion). The epicycles of Venus and Mercury are always centered on a line between Earth and the Sun (Mercury being closer to Earth), which explains why they are always near it in the sky. The Ptolemaic order of spheres from Earth outward is:
Sphere of Prime Mover
The Greek Thales, who had successfully predicted the sun’s eclipse in 585 B.C., suggested that the sky was a huge bubble, inside of which the cylindrical Earth floating on the surface of water. The stars and planets were embedded in the bubble. His theory didn’t satisfy the scientific community of his time, which wanted to know how the Earth was supported.
In the 6th century BC, Anaximander proposed a cosmology with the Earth shaped like a section of a pillar (a cylinder), held aloft at the center of everything. The Sun, Moon, and planets were holes in invisible wheels surrounding the Earth; through the holes, humans could see concealed fire.
About the same time, the Pythagoreans thought that the Earth was a sphere (in accordance with observations of eclipses), but not at the center; they believed that it was in motion around an unseen fire. Later these views were combined, so most educated Greeks from the 4th century BC on thought that the Earth was a sphere at the center of the universe.
The first person to present an argument for a heliocentric system, however, was Aristarchus of Samos (c. 270 BC). Like Eratosthenes, Aristarchus calculated the size of the earth, and measured the size and distance of the Moon and Sun, in a treatise which has survived. From his estimates, he concluded that the Sun was six to seven times wider than the Earth and thus hundreds of times more voluminous.
The geocentric model held sway into the early modern age; from the late 16th century onward it was gradually replaced by the heliocentric model of Copernicus, Galileo and Kepler.
Tycho Brahe favored a geocentric model because he could not see the parallax of the fixed stars. Tycho proved that the stars would have to be more than hundreds of times further away than the most distant known planet of the time, which was Saturn. But this parallax or retrograde motion of the stars is very small because the stars are actually much further away, so the parallax was not seen for more than 200 years after Tycho. Bradley discovered the abberation of starlight, which is 30 times larger than the largest parallax, roughly one century after Tycho, and this firmly established that the Earth was moving around the Sun. The parallax of stars was finally seen another century later.
In 1543 the geocentric system met its first serious challenge with the publication of Copernicus's De revolutionibus orbium coelestium, which posited that the Earth and the other planets instead revolved around the Sun. The geocentric system was still held for many years afterwards, as at the time the Copernican system did not offer better predictions than the geocentric system, and it posed problems for both natural philosophy and scripture.
With the invention of the telescope in 1609, observations made primarily by Galileo Galilei (such as that Jupiter has moons) called into question some of the tenets of geocentrism but did not seriously threaten it.
In December 1610, Galileo Galilei used his telescope to observe that Venus showed all phases, just like the Moon. This observation was incompatible with the Ptolemaic system, but was a natural consequence of the heliocentric system.
Heliocentrism is the theory that the Sun is at the center of the Solar System. The word came from the Greek (Helios = sun and kentron = center). Historically, heliocentrism was opposed to geocentrism, which placed the earth at the center. (The distinction between the Solar System and the Universe was not clear until modern times, but extremely important relative to the controversy over cosmology and religion.) Although many early cosmologists such as Aristarchus speculated about the motion of the Earth around a stationary Sun, it was not until the 16th century that the Polish mathematician and astronomer Copernicus presented a fully predictive mathematical model of a heliocentric system, which was later elaborated and expanded by Kepler and defended by Galileo, becoming the center of a major dispute.
Over time, however, the Catholic Church began to become more adamant about protecting the geocentric view. Pope Urban VIII, who had approved the idea of Galileo's publishing a work on the two theories of the world, became hostile to Galileo. Over time, the Catholic Church became the primary opposition to the Heliocentric view
The favored system had been that of Ptolemy, in which the Earth was the center of the universe and all celestial bodies orbited it. A geocentric compromise was available in the Tychonic system, in which the Sun orbited the Earth, while the planets orbited the Sun as in the Copernican model. The Jesuit astronomers in Rome were at first unreceptive to Tycho's system; the most prominent, Clavius, commented that Tycho was "confusing all of astronomy, because he wants to have Mars lower than the Sun." (Fantoli, 2003, p. 109) But as the controversy progressed and the Church took a harder line toward Copernican ideas after 1616, the Jesuits moved toward Tycho's teachings; after 1633, the use of this system was almost mandatory. For advancing heliocentric theory Galileo was put under house arrest for the last several years of his life.
The realization that the heliocentric view was also not true in a strict sense was achieved in steps. That the Sun was not the center of the universe, but one of innumerable stars, was strongly advocated by the mystic Giordano Bruno; Galileo made the same point, but said very little on the matter, perhaps not wishing to incur the church's wrath. Over the course of the 18th and 19th centuries, the status of the Sun as merely one star among many became increasingly obvious. By the 20th century, even before the discovery that there are many galaxies, it was no longer an issue.
Newton’s universal law of gravitation was his most important contribution to the study of the solar system. With it he showed why the planets follow the orbits described by Kepler. For the first time astronomers were able to predit the positions of the planets and foretell eclipses, even centuries in the future. With Kepler and Newton, modern astronomy may truly be said to have arrived.