Science 9: Space Exploration Topic 7 - The Solar System

Basic Details ► The solar system is centered on the sun. The sun provides the gravity that keeps the planets in their orbits. Just like anything else the solar system will not last forever. The sun will go nova in about 5 billion years and when it does some of the planets will fly off into space. ► The solar system is broken up into four main parts: The sun, the inner rocky planets and their moons, the outer gas-giant planets with their moons, and Pluto and its moon Charon.

The Sun ► The sun is an average sized star with an average amount of brightness. It’s middle aged. The sun is 1.4 million km wide (compared to km for the Earth).

The Sun’s a Nuclear Fusion Reactor ► The Sun is made up of mostly hydrogen. The sun is so large that its gravity causes a nuclear fusion reaction producing huge amounts of energy. Hydrogen atoms fuse together to form Helium atoms. This reaction produces all the heat and light energy that keeps the Earth alive. Eventually the hydrogen atoms in the sun will run out and the sun will start fusing helium atoms together. This process keeps going until the elements become heavy enough to resist fusion, the sun starved of its fuel explodes off its outer layers, leaving a cold white dwarf star behind.

The Inner Rocky Planets ► The inner planets are smaller than the outer planets and are rocky in composition. ► The inner planets consist of Mercury, Venus, the Earth, and Mars. Only the Earth and Mars have natural satellites. ► Because these planets are much closer to the Earth they have been studied more closely by spacecraft than the outer planets. Mars especially has been very well studied. It currently has three spacecraft doing remote sensing on it from orbit and two working rovers on its surface.

The Moon ► The first celestial body that was studied by and visited by humans is the Moon. Humans first landed on the Moon in The Moon has helped life on Earth by acting as a kind of shield protecting the Earth from many meteor impacts.

The Outer Gas-Giant Planets ► These planets are much larger, and much farther away from the Earth. In fact NASA still doesn’t have rockets powerful enough to reach them in a reasonable amount of time, so gravitational assists are used to reach them. ► Outer planets are made up of mostly gaseous atmosphere. They do have a rocky or liquid core. The gas giants are Jupiter, Saturn, Uranus, and Neptune.

Pluto the Planetoid (or Dwarf Planet) ► Pluto doesn’t fit into either of the first two groups. It’s the smallest planet in the Solar System, and it’s the furthest out. No spacecraft has ever visited the planet, but one is on its way and is speeding towards Jupiter to get a gravitational assist or ‘slingshot.’ ► Scientists aren’t sure, but suspect that it’s made up of a mixture of rock and methane ice. Many scientists feel that Pluto shouldn’t even count as a planet at all.

Pioneer and Voyager Space Probes and the ‘Golden Disks’ ► There are four spacecraft that NASA scientists sent out in the 1970s. All four have either reached or passed the edge of the solar system. They are now traveling in inter- stellar space. These probes travel around km/h.

Pioneer and Voyager Space Probes and the ‘Golden Disks’ ► Because the speed of light is finite, the time-lag to get radio signals from the satellite to radio antenna on Earth is increasing everyday. As of now it takes 24 hours for radio signals from the spacecraft to arrive on Earth. ► On the Voyager probes NASA scientists put two golden disks on them with a summary of information on the Earth and the human race. It was designed as a friendly greeting to any aliens who happen upon the Voyager spacecraft. It contains: ► A diagram of a human man and woman. ► Some mathematical formulas and proofs: showing that we’re an advanced species. ► Some classical and modern (1950s Chuck Berry) music tracks in CD format. ► Triangulation instructions for these aliens to visit us.