No such thing as "helicentric" The heliocentric theory states that the Sun (helios) is the center of the solar system (or the universe if you are talking about ancient heliocentric theories - before...
The nebular theory is a theory that ended up being incorrect and was stated correct for a certain amount of time. Here's mine, with a little research: The Nebular Theory, (AKA the Nebular Hypothesis)...
The sun formed from a nebula and the leftover materials became planets, moons, ect. Mercury, Venus, Earth, and Mars were made of rock(which are heavy), so the sun's gravity couldn't push it far away....
well,,i know 2 theories..i hope this can help you...
The Tidal Theory (or Chamberlain-Moulton Theory) suggests that a passing star pulled dust and debris from the forming Sun, leaving a string of...