Explain our ideas about why the terrestrial planets are rocky and have less gas than the giant planets.

Answer: The terrestrial planets are mainly comprised of silicate minerals and also there is presence of some metals, which were subsequently formed in the geological time scale, after the accumulation of smaller dust particles, due to the gravitational pull, during the time of formation of the planets.

Due to the location of these terrestrial planets near to the sun, their surface temperature is high enough to hold the gases like hydrogen and helium. Thus, they have a high density but less gases compared to the outer planets.