Sun and the Planets

The dominant body in the solar system is the Sun. Let us consider some of its physical parameters:

• Radius: R = 696,000 km (109 Earth radii)
• Mass: M = 1.989 × 10³⁰ kg (333,000 Earth masses)
• Gravity acceleration at the surface: g = 274 m/s² (28 times Earth’s gravity)

The Sun contains 99.8% of the mass of the entire solar system.

Furthermore, the solar system includes the known eight large planets. Since the decision of the IAU in 2006, Pluto no longer counts as a large planet. The planets have diameters ranging from some 10³ km up to 10⁴ km. They move around the Sun in nearly circular orbits, all of which lie almost exactly in the plane of the ecliptic. The total mass of all the planets together is 448 Earth masses.

The Planets

Enumerating the planets according to their distance from the Sun:

• Mercury
• Venus
• Earth
• Mars
• Jupiter
• Saturn
• Uranus
• Neptune

The newly defined group of the dwarf planets includes Pluto and other objects (Sedna, Ceres, etc.).

Other Solar System Objects

• Asteroids: Mostly smaller than 100 km, located mainly between Mars and Jupiter.
• Kuiper Belt Objects: Beyond Neptune, including Pluto.
• Moons: Satellites of major planets and dwarf planets (e.g., Pluto has five moons).
• Comets: Found in Oort's comet cloud, producing tails when approaching the Sun.
• Interplanetary Matter: Meteoroids, gas, and dust, visible as Zodiacal light.

A Model of the Solar System

The Solar System as Seen from Outside

From the nearest star (Alpha Centauri), the solar system would appear as follows:

• The Sun would have an apparent magnitude of 0.4 and appear as a bright star.
• Earth would have a brightness of 23.4 and be 0.76” from the Sun.
• Jupiter would have a brightness of 22.0 and be 3.94” from the Sun.

Planets do not shine by themselves; they are faint and outshone by their parent star. Detecting extrasolar planets is challenging and often relies on indirect methods such as gravitational microlensing.

Types of Planets

• Terrestrial Planets: Mercury, Venus, Earth, and Mars. They have high density and a solid surface.
• Giant Planets (Jovian Planets): Jupiter, Saturn, Uranus, and Neptune. They are gas planets with no solid surface.
• Ice Planets: Uranus and Neptune, having large cores of ice.