The Solar System


Assignment 1: The Solar System
The solar system consists of the Sun; the nine planets, 67 satellites of the planets and a large number of small bodies (comets and asteroids).
The inner solar system contains the Sun, Mercury, Venus, Earth and Mars:
The planets of the outer solar system are Jupiter, Saturn, Uranus, Neptune and Pluto: The orbits of the planets are ellipses with the Sun at one focus, though all except Mercury and Pluto are very nearly circular. The orbits of the planets are all more or less in the same plane (called the ecliptic and defined by the plane of the Earth's orbit). The ecliptic is inclined only 7 degrees from the plane of the Sun's equator. Pluto's orbit deviates the most from the plane of the ecliptic with an inclination of 17 degrees. Below you see a diagram that show some relative information about most of the objects in our Solar System:
Diameter (km) Moons Surface temp. Surface gravity Axial inclination Axial rotation
The Sun 1 390 000 - 5800c - - 25 - 36 days
Mercury 4 878 None 350c / -170c 0.38 0 58 days
Venus 12 104 None 480c 0.9 178 243 days
The Earth 12 756 1 20c 1 23.4 23h 56m
Mars 6 787 None -23c 0.38 24 24h 37m
Jupiter N/A 16 -150c 2.64 3.1 9h 50m
Saturn 199 300 18 -180c 1.2 26.7 10h 39m
Uranus 51 800 15 -210c 1.2 98 17h 10m
Neptune 49 500 8 -220c 1.2 29.5 18h 24m
Pluto 2 320 1 N/A 0.04 50 178 years
The Moon 3 474 - 107c / -153c 0.17 1.5 27 days
The Sun
The sun is the most important part of our solar system. It is the biggest object and does have about 98% of the whole mass of the solar system. About 1,3 billion earths would fit inside the sun.
The sun travels around the galaxy together with planets and other objects bound to it by gravitational forces. The largest of the bodies we call planets, most of which are in turn are orbited by smaller moons or satellites. These objects, together with many lesser masses, are known as the Solar system.
The Sun is just a star, one of a hundred billion inhabiting our galaxy alone. Being a star the Sun is an example of the fundamental building blocks of our universe. It formed, 4.5 billion years ago, as the nucleus of a cloud of gas which was collapsing under its own gravitational attraction.
At formation, hydrogen was the most abundant gas, as elsewhere in the universe, and accounted for three quarters of the Sun's original material. This will changes as the hydrogen is burned, and within the very central regions virtually all the hydrogen has been converted to helium. The outer regions have not yet taken part in hydrogen burning. Astronomers have measured the chemical composition of the Sun, and can thus estimate that of the initial solar nebula from which the sun and planets formed. In addition to 78 percent by weight of hydrogen, they find 20 percent to be helium, while only 2 percent remains for other elements such as oxygen, carbon, nitrogen, and iron.
Later, as its hydrogen becomes depleted, it will evolve into a giant red star, swelling to engulf the earth and the inner planets. The remnant Sun will fade gradually to oblivion, passing through the white dwarf stage on its way.
Mercury
Mercury is named after the messenger of the Roman gods. It is the smallest of the inner planets and the second smallest in the whole Solar System. It has a very weak magnetic field and - being the closest planet to the Sun - has only a very thin atmosphere of helium captured from the solar wind.
The surface of Mercury is very much like the Moon's - with craters, mountains and valleys. Since there is no form of atmosphere, life on Mercury is impossible. Nor will there be any manned flights in the forseeable future. However, there will be new unmanned probes sent out, if only to complete the map of the surface.
Although Mercury has only a third the diameter of Earth, its density is about the same. This suggests that 65 to 70 percent of Mercury's weight is made up of a heavy material, probably iron. This is concentrated in Mercury's large core.