The Sun is a typical star that maintains a balanced equilibrium by the fusion of hydrogen into helium at its core, releasing this energy from its outer photosphere. Astronomers classify it as a G-type main-sequence star.

The largest objects that orbit the Sun are the eight planets. In order from the Sun, they are four terrestrial planets (Mercury, Venus, Earth and Mars); two gas giants (Jupiter and Saturn); and two ice giants (Uranus and Neptune).

All terrestrial planets have solid surfaces. Inversely, all giant planets do not have a definite surface, as they are mainly composed of gases and liquids. Over 99.86% of the Solar System's mass is in the Sun and nearly 90% of the remaining mass is in Jupiter and Saturn.

Mercury (0.31–0.59 AU from the Sun) is the smallest planet in the Solar System. Its surface is grayish, with an expansive rupes (cliff) system generated from thrust faults and bright ray systems formed by impact event remnants. The surface has widely varying temperature, with the equatorial regions ranging from −170 °C (−270 °F) at night to 420 °C (790 °F) during sunlight.

In the past, Mercury was volcanically active, producing smooth basaltic plains similar to the Moon. It is likely that Mercury has a silicate crust and a large iron core. Mercury has a very tenuous atmosphere, consisting of solar-wind particles and ejected atoms. Mercury has no natural satellites.

Venus (0.72–0.73 AU) has a reflective, whitish atmosphere that is mainly composed of carbon dioxide. At the surface, the atmospheric pressure is ninety times as dense as on Earth's sea level. Venus has a surface temperatures over 400 °C (752 °F), mainly due to the amount of greenhouse gases in the atmosphere.

The planet lacks a protective magnetic field to protect against stripping by the solar wind, which suggests that its atmosphere is sustained by volcanic activity. Its surface displays extensive evidence of volcanic activity with stagnant lid tectonics. Venus has no natural satellites.

Earth (0.98–1.02 AU) is the only place in the universe where life and surface liquid water are known to exist. Earth's atmosphere contains 78% nitrogen and 21% oxygen, which is the result of the presence of life. The planet has a complex climate and weather system, with conditions differing drastically between climate regions. The solid surface of Earth is dominated by green vegetation, deserts and white ice sheets. Earth's surface is shaped by plate tectonics that formed the continental masses. Earth's planetary magnetosphere shields the surface from radiation, limiting atmospheric stripping and maintaining life habitability.

The Moon is Earth's only natural satellite. Its diameter is one-quarter the size of Earth's. Its surface is covered in very fine regolith and dominated by impact craters. Large dark patches on the Moon, maria, are formed from past volcanic activity. The Moon's atmosphere is extremely thin, consisting of a partial vacuum with particle densities of under 107 per cm−3.

Mars (1.38–1.67 AU) has a radius about half of that of Earth. Most of the planet is red due to iron oxide in Martian soil, and the polar regions are covered in white ice caps made of water and carbon dioxide. Mars has an atmosphere composed mostly of carbon dioxide, with surface pressure 0.6% of that of Earth, which is sufficient to support some weather phenomena. During the Mars year (687 Earth days), there are large surface temperature swings on the surface between −78.5 °C (−109.3 °F) to 5.7 °C (42.3 °F). The surface is peppered with volcanoes and rift valleys, and has a rich collection of minerals. Mars has a highly differentiated internal structure, and lost its magnetosphere 4 billion years ago. Mars has two tiny moons:

Phobos is Mars's inner moon. It is a small, irregularly shaped object with a mean radius of 11 km (7 mi). Its surface is very unreflective and dominated by impact craters. In particular, Phobos's surface has a very large Stickney impact crater that is roughly 4.5 km (2.8 mi) in radius.

Deimos is Mars's outer moon. Like Phobos, it is irregularly shaped, with a mean radius of 6 km (4 mi) and its surface reflects little light. However, the surface of Deimos is noticeably smoother than Phobos because the regolith partially covers the impact craters.