The four planets closest to the Sun are called

The four planets closest to the Sun—Mercury, Venus, Earth, and Mars—are classified as terrestrial planets [5]. These inner planets are characterized by their solid, rocky surfaces and high densities, being composed largely of refractory minerals like silicates and metals such as iron and nickel [4]. Unlike the outer gas giants, terrestrial planets have relatively small bodies, few or no moons, and lack planetary ring systems [5]. They are located between the Sun and the asteroid belt. Geologically, they feature a central metallic core surrounded by a silicate mantle, with surface landforms such as volcanoes, craters, and valleys [1]. In contrast, the outer planets (Jupiter, Saturn, Uranus, and Neptune) are known as giant planets or gas giants due to their massive size and gaseous composition [6].

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 2: The Solar System > Inner Planets > p. 27
2. [4] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 2: The Solar System > 2.4. Planets > p. 25
3. [5] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 13: Our Home: Earth, a Unique Life Sustaining Planet > 13.2 What Do the Planets of Our Solar System Look Like? > p. 213
4. [6] https://gml.noaa.gov/infodata/info_activities/pdfs/TBI_terrestrial_planets.pdf