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.
The outer layer is made of sillicate rock similar to the Earth's mantle.
Venus Venus is named after the Roman goddess of love. It is the second planet
from the Sun and the brightest object in the sky other than the Sun and the
Moon. It was once believed that life could exist in Venus but that has been
proved wrong by various probes.
