 Main-belt comets may have been a major source of the Earth's oceans because the deuterium-hydrogen ratio is too low for classical comets to have been the principal source.Most asteroids within the asteroid belt have orbital eccentricities of less than 0.4, and an inclination of less than 30°.The orbital distribution of the asteroids reaches a maximum at an eccentricity of around 0.07 and an inclination below 4°.