Group R The Rocky Inner Planets
In our Solar System, astronomers often divide the planets into two groups — the inner planets and the outer planets. The inner planets are closer to the Sun and are smaller and rockier. The outer planets are further away, larger and made up mostly of gas. The inner planets (in order of distance from the sun, closest to furthest) are Mercury, Venus, Earth and Mars. After an asteroid belt comes the outer planets, Jupiter, Saturn, Uranus and Neptune. All the inner planets are made of metals and rocks, hence the name, whereas the outer planets are not solid, and are made of gas.Mercury is the closest inner planet to the sun. It has very little atmosphere and is pockmarked with craters. It's made mostly of iron and nickel and, like Earth, is believed to have a molten iron core. The crust of Mercury is made of silicates.Venus is notorious both for its beauty in the morning and evening skies and also for its atmosphere, which is thick with clouds made of sulfuric acid. Venus also has an iron core, but it spins so slowly that the planet doesn't have a global magnetic field like Earth. Venus is so geologically active, with many volcanoes, that its surface features change constantly.Earth is not only made of rocks and metals, but it is also covered in water, which allows it to support life. Mars might have liquid water, but its atmosphere is so thin that the water probably sublimates, or turns directly from water to gas. Mars seems to have water ice at its poles.
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