THE SOLAR SYSYEM

The Solar System is our home in the universe. It consists of the Sun, the nine planets, asteroids, comets, and meteoroids.

The volume of planetary system is about 10 raise to negative 30 of that of the observable universe.

If the visible universe were as small as your classroom, then the Solar System would be about ten millionth of a trillionth of a particle of chalk dust.

Almost all of the Solar System is empty space. If the earth were as small as a grain of table sugar, about 0.3 millimeter in diameter, then the moon would be about 1 centimeter away. The Sun would be the size of the ping-pong ball, 4 meters from Earth. Jupiter would be a guava seed 20 meters from the Sun. Pluto, the farthest planet, would be 150 meters from the ping-pong ball.

REVOLUTION AND ROTATION OF THE PLANETS

The planets of the Solar System in the order of their distance from the sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

The planets revolve around the sun in orbits that lie nearly on the same plane.

Mercury, the closest planet, has an orbit that is tipped 7 degree to the orbit of the Earth; while Pluto, the farthest planet, has an orbit that is tipped 17.2 degree.

The rest of the planets have orbits that are inclined by no more than 3.4 degree.

Therefore, the Solar System is practically disk-shaped.

TWO TYPES OF PLANETS

The planets, except Pluto, can be classified into two, namely, the terrestrial or Earth-like and Jovian or Jupiter-like.

The terrestrial planets are small, dense, and rocky with less atmosphere than the Jovian planets. These terrestrial planets are Mercury, Venus, Earth and Mars.

The Jovian planets are large, gaseous, have low densities, and lie beyond the asteroids. The Jovian planets are the ff. Jupiter, Saturn, Uranus and Neptune.

Pluto does not fall in either category. This is because it is small like the terrestrial planets, but has a low density and lies far from the Sun like the Jovian planets.

Studies the Jovian planets show that their interiors are mostly hydrogen in to two states, as shown in figure 6.3. The pressure at the deeper layers of Jupiter and Saturn is so high that the electrons are free to move. High pressure forces hydrogen to condense to the liquid state. The material is then called metallic hydrogen.

The centers of the Jovian planets are hot. Their cores are almost the size of the Earth and are composed of heavy elements.

Jovian planets have a large number of satellites or moons. Jupiter and Saturn have at least 16 moons each. Uranus has ten satellites and Neptune have two. Jupiter and Uranus have rings consisting of orbiting chunks of rocks. Saturn has bright rings composed of ice particles.

SPACE OF DEBRIS

Aside from the planets, the solar system is littered with three type space debris. These are the asteroids, comets, and meteoroids.

The asteroids are small, irregular-shaped rocks, most of which circle the sun between the orbits of mars and Jupiter.

CORE

METALLICHYDROGEN

LIQUIDHYDROGEN

A few asteroids have orbits that bring them into the inner solar system. Some are located at Jupiter’s orbit and some had been found near the orbit of Saturn. Observations show that asteroids rotate as they orbit the sun.

In contrast to asteroids, the comets are beautiful objects. It appears to have a glowing head and a gas tail. The core of a comet is made up of ice materials. When a comet enters the inner solar system, the sun’s radiation vaporizes the ice producing gas and dust. The solar wind pushes the gas and dust away from the sun, forming a long tail.

Unlike the comets, meteors flash across the sky for a few seconds only. They are known as “shooting stars”. They are not really stars, but bits of rock and metal falling through the earth’s atmosphere. The heat due to friction with the air produces an incandescent vapor about 80km above the ground.

In space, before falling through the earth’s atmosphere, meteors are called meteoroids. Any part of meteoroid that survives the burning passage through the earth’s surface is called a meteorite. Most meteorites are dust, grains of sand, or tiny pebbles.

THE ATOM AND THE AGE OF THE SOLAR SYSTEM

The most accurate to determine the age of an astronomical body is through a technique called radioactive dating.

Just like the Solar system with the sun and its center and surrounded by planets, an atom consists of a small center nucleus surrounded by a cloud of whirling electrons, as shown in the figure.

An atom is very small but the nucleus is even 1,000,000 times smaller. Like the Solar System, the atom is almost an empty space.

The nucleus of a typical atom is more complicated than that of a hydrogen atom. It contains two types of particles, namely, protons and neutrons.

NUCLEUS

ELECTRON

The protons have a positive charge, while the neutrons are neutral.

Changing the number of neutrons in the nucleus does not significantly change the atom. Atoms that have the same number of protons but have different numbers of neutrons are called isotopes.

While the protons and neutrons are tightly bound in the nucleus, the electrons are held loosely in the electron cloud. Rubbing your comb through your hair removes a few electrons from its atoms. This process is known as ionization.

A material with an unstable nuclei is said to be radioactive and the decay is known as radioactive decay.

EARLY HELIOCENTRIC THEORIES ON THE FORMATION OF THE SOLAR SYSTEM

Evolutionary theories. These theories hold that the solar system was formed as a natural by-product of the formation of t he Sun.

Nebula hypothesis. This theory holds that the sun and the planets formed from a spinning interstellar cloud which flattened into a disk.

Catastrophic theories. These theories envision a solitary sun in the beginning.

Accretion theory. This theory states that once the sun had formed, its gravity trapped materials from the surrounding interstellar medium which formed the planets.

THE CHARACTERISTICS OF THE SOLAR SYSTEM

The solar system is disk-shaped and the orbits of the planets lie on the same plane.

There are two planetary types, namely, terrestrial and Jovian.

Jupiter, Saturn, and Uranus have rings and several satellites.

There are space debris –asteroids, comets and meteoroids.

The Earth, the Moon, the Sun, and the meteorites all have a common age of about 4.6 billion years.

The sun and the planets revolve and rotate in the same direction.

The Titus-Bode rule. This is a simple series of arithmetic steps that produces numbers which approximately match the radii of the orbits of the planets.