what is the former one comprises of?
The former comprising of the planets  Mercury, Venus, Earth and Mars, is primarily composed of rock and metal.
Solar System
The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal
nine planets of the solar system in order Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. which are the two segments of this system? Inner planets and outer planets.
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Solar System [SEP] Introduction
The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest planets, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.