05 Solar System

1. The inventory

Early Astronomers

They didn't have any idea about the big picture...

Do you have the big picture in this century?

Galileo Galilei (17 cc)

End of 19 cc

20 cc


The Final Inventory

2. Measuring the Planets


Orbital Period



Rotation Period


3. The layout

Titius - Bode Law (1766)

4. Grouping

Terrestrial Planets

Jovian Planets

Notes in Terrestrial Planets

Kuiper Belt

Oort Cloud

5. Interplanetary Matter

Relatively Large Bodies

Small Bodies

6. Main Structure of the Solar System

Terrestrial Planets

Jovian Planets

Asteroids and Comets

7. Asteroids

Top: Orbits of planets (blue lines) around the asteroid belt (white dots) and Jupiter trojans (green and red dots).
Right, upper panel: Apollo orbits (green shade).
Right, lower panel: Amor orbits (green shade) with Mars trojans (brown shades).
M: Mars, V: Venus, E: Earth, H: Mercury.

Asteroid types:

(a) The S-type asteroid Gaspra, as seen from a distance of 1600 km by the space probe Galileo on its way to Jupiter.

(b) The S-type asteroid Ida, photographed by Galileo from a distance of 3400 km. (Ida’s moon, Dactyl, is visible at right.)

Right Panel:

A mosaic of detailed images of the asteroid Eros, as seen by the NEAR spacecraft (which actually landed on this asteroid). Craters of all sizes, ranging from 50 m (the resolution of the image) to 5 km, pit the surface. The inset shows a close-up image of a “young” section of the surface, where loose material from recent impacts has apparently filled in and erased all trace of older craters. 

Kirkwood Gap

Some asteroids, called Trojan asteroids, orbit at the L4 and L5 Lagrangian points of Jupiter’s orbit

(a) The distribution of asteroid semi-major axes shows some prominent gaps caused by resonances with Jupiter’s orbital motion. Note, for example, the prominent gap at 3.3 AU, which corresponds to the 2:1 resonance—the orbital period is 5.9 years, exactly half that of Jupiter.

(b) An asteroid in a 2:1 resonance with Jupiter receives a strong gravitational tug from the planet each time they are closest together (as in panels 1 and 3). Because the asteroid’s period is precisely half that of Jupiter, the tugs come at exactly the same point in every other orbit, and their effects reinforce each other.

8. Comets

Comets move in highly eccentric paths that carry them far beyond the known planets.

Halley’s comet has a smaller orbital path and a shorter period than most comets, but its orbital orientation is not typical of a short-period comet. Sometime in the past, this comet must have encountered a Jovian planet (probably Jupiter itself), which threw it into a tighter orbit that extends not to the Oort cloud, but merely a little beyond Neptune. Edmund Halley applied Newton’s law of gravity to predict this comet’s return 

(a) Diagram of a typical comet, showing the nucleus, coma, hydrogen envelope, and tail. The tail is not a sudden streak in time across the sky, as in the case of meteors or fireworks. Instead, it travels along with the rest of the comet (as long as the comet is sufficiently close to the Sun for the tail to exist). Note how the invisible hydrogen envelope is usually larger than the visible extent of the comet; it is often even much larger than drawn here. 

(b) Halley’s Comet in 1986, about one month before it rounded the Sun at perihelion. 

(a) A comet with a primarily ion tail. Called comet Giacobini–Zinner and seen here in 1959, its coma measured 70,000 km across; its tail was well over 500,000 km long.

(b) Photograph of a comet having both an ion tail (dark blue) and a dust tail (white blue), both marked in the inset, showing the gentle curvature and inherent fuzziness of the dust. This is comet Hale–Bopp in 1997 

(a) Halley’s comet as it appeared in 1910. Top, on May 10, with a 30° tail, bottom, on May 12, with a 40° tail. (b) Halley on its return and photographed with higher resolution on March 14, 1986. 

As it approaches the Sun, a comet develops an ion tail, which is always directed away from the Sun. Closer in, a curved dust tail, also directed generally away from the Sun, may appear. Notice that the ion tail always points directly away from the Sun on both the inbound and the outgoing portions of the orbit. The dust tail has a marked curvature and tends to lag behind the ion tail. 

Origins of Comets:

They come from two distinct regions of space.

Summary of the group

9. Meteors

A bright streak called a meteor is produced when a fragment of interplanetary debris plunges into the atmosphere, heating the air to incandescence.

(a) A small meteor photographed against stars and the Northern Lights provide a stunning background for a bright meteor trail.

(b) These meteors (one with a red smoke trail) streaked across the sky during the height of the Leonid meteor storm of November 2001 

A meteoroid swarm associated with a given comet intersects Earth’s orbit at specific locations, giving rise to meteor showers at certain fixed times of the year.

Larger meteoroids are usually loners from the asteroid belt and have produced most of the visible craters in the Solar System. 

The Earth has about 100 craters more than 0.1 km in diameter; erosion has made most of them hard to discern. This one which is one of the largest, is in Canada.

10. Summary of the Solar System

11. Formation of Solar System

Summary of the system

Nebular Contraction

Nebular Theory

Condensation Theory