EXPLORING THE SOLAR SYSTEM

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THE SOLAR SYSTEM

The Solar System consists of the Sun with planets in orbit around it. Most planets have at least one satellite in orbit around them. Gravity provides the centripetal force needed to keep objects in orbit.

We can explore space using manned or unmanned spacecraft.

The Solar System

Solar systems consist of:

  • a star (the Sun)
  • planets and dwarf planets in orbit around the Sun
  • satellites (moons) in orbit around most of the planets
  • comets and asteroids in orbit around the Sun.

You need to know the position of the planets in order from the Sun. Starting with the closest to the sun, the order is:

  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
  • Uranus
  • Neptune

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There are many other smaller objects that orbit the Sun. Three of these are Ceres, Pluto ansd Eris, known as 'the dwarf planets'. Ceres orbits between Mars and Jupiter. Pluto orbits further away from the Sun than Neptune, while Eris orbits further out still.

Stars and galaxies

Stars are very hot and give off their own light, which is why we can see the Sun during the day, and the stars in the night sky. A galaxy is large group of many millions of stars.

Our Sun is just one of at least 200 billion stars in our galaxy, the Milky Way. The observable universe contains around 80 billion galaxies. The universe also contains other objects, such as black holes.

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GRAVITY AND ORBITS

The orbits of the planets in the Solar System are almost circular - with the Sun near the centre. 

Circular motion requires a centripetal force. Without it, the object will fly off in a straight line. The Sun's gravity keeps the planets, dwarf planets, comets and asteroids in orbit. The gravity of a planet keeps its satellites in orbit.

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EXPLORING SPACE

What is space like?

The space between planets is called interplanetary space. These are some of the conditions there:

  • there is no atmosphere
  • the temperature varies from very cold (away from the Sun) to very hot (in sunshine)
  • the gravitational field strength is close to zero, so objects are effectively weightless
  • there is a lot of cosmic radiation (radiation from the Sun and distant objects in space)

If astronauts are to explore space, scientists and engineers must design systems to protect them from these conditions.

Spacecraft

Spacecraft provide the conditions needed for astronauts to survive in space. They provide:

  • an atmosphere (and equipment to remove waste gases such as carbon dioxide)
  • insulation and heating to provide a suitable temperature for life
  • exercise equipment to reduce the effects of weightlessness (bones become weaker the longer an astronaut is in space, and exercise helps to slow this process down
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SPACE PROBES

Space probes are spacecraft that can visit other planets without the need for astronauts. They can send back information about things such as the:

  • temperature, magnetic field strength and radiation levels
  • gravitational field strength, and
  • the surroundings, including the composition of any atmosphere.

Some of the missions undertaken by such craft include:

  • Viking 1 and Viking 2 (landed on Mars in the 1970s, took photographs and analysed soil samples)
  • Mars Global Surveyor (went into orbit around Mars in 1997 and mapped the surface in 3D)
  • Spirit and Opportunity (two robot vehicles that landed on Mars in 2004).

Unmanned space probes do not need to carry food, water or oxygen. They can withstand conditions that would be lethal to astronauts.

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THE DISTANCES TO STARS

Stars are very far away from each other. The distances are measured in light years. One light year is the distance that light travels in one year. Since the speed of light in space is about 300,000,000 metres per second, this is a very large distance indeed (about 9.5 million million km).

Stars are too far away for us to be able to measure the distance directly. So we use the parallax method. The star is observed against a background of distant stars, then again six months later. The star appears to move against the background. The bigger the apparent movement, the nearer the star is to Earth. This is just the same as when you hold a finger up to your face and turn your head from side to side - the finger seems to move against objects in the distance.

Stars are very far away from each other. The distances are measured in light years. One light year is the distance that light travels in one year. Since the speed of light in space is about 300,000,000 metres per second, this is a very large distance indeed (about 9.5 million million km).

Stars are too far away for us to be able to measure the distance directly. So we use the parallax method. The star is observed against a background of distant stars, then again six months later. The star appears to move against the background. The bigger the apparent movement, the nearer the star is to Earth. This is just the same as when you hold a finger up to your face and turn your head from side to side - the finger seems to move against objects in the distance.

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