The Planets

File:Planets2013.jpgThe eight planets of our Solar System



  • large globe-shaped objects that orbit a star, such as our Sun.
  • begin life at the same time as their star – from the leftover clouds of gas and dust.

Artist’s conception of a very young star encircled by a disk of gas and dust,
the raw materials from which rocky planets such as Earth are thought to form.


  • planets are never more than 5% of the mass of our Sun – if they were bigger, they would be stars.
  • terrestrial planets – surface of solid rock; others called gas planets – do not have a solid surface, just clouds.

  • our Solar System has eight planets – Pluto was ninth, but it is very small and now it’s called a planetoid (dwarf planet).

Extrasolar planets or Exoplanet

The way that a young exoplanet interacts with its star’s disc
of dust and gas determines the type of exoplanet that will ultimately form.

  • over 200 plants have been detached orbiting other stars – it’s called extrasolar planets or Exoplanets
  • extrasolar planets are too far away to see, but can be detached by its making their stars appear to wobble.
  • many known extrasolar planets are giants, bigger than Jupiter; they orbit rapidly, closer to their stars than Mercury is to the Sun.
  • today improved detection techniques may reveal smaller planets orbiting further out in space.

Exoplanets – planets orbit the stars in the Milky Way.



  Moons of our Solar System


  • moons are the natural satellites of planets – most are small rock globes that continually orbit the planet – held in place by the planet’s gravity.
  • as of October 2008, more than 176+ known natural moons in our Solar System.
  • every planet in our Solar System has a moon or some moons, apart from Mercury and Venus.
  • very few of the moons have atmospheres – including Saturn’s moon Titan, Jupiter’s Io and Neptune’s Triton.

One of the moons have atmosphere – Saturn’s moon Titan

  • Jupiter’s moon – Ganymede, largest moon in the Solar System.
  • second largest is Saturn’s moon – Titan; icy-cold, and is only moon with thick atmosphere of nitrogen gas. (wikipedia – Titan)
  • smallest moons are icy lumps just a few kilometers across, rather like asteroids.

Icy lumps

Saturn’s moon- Iapetus

Saturn’s moon – Iapetus

Colour map of Iapetus

  • Iapetus; white on one side and black on the other side.

Saturn’s moon – Enceladus

Saturn’s moon – Enceladus

  • Enceladus; only 312 miles across, and its icy surface reflects almost all the sunlight.
  • a largely icy world.
  • Cryovolcanic activity in Enceladus is sending geysers of water ice particles out from underneath the surface.

“Tiger stripes”

  • The Cassini spacecraft has imaged these geysers spouting from so-called “tiger stripes” vent areas on this moon.
  • Enceladus is now known to have a subsurface ocean made of liquid water – images from the Cassini spacecraft helped mission scientists deduce and prove the existence of that ocean.


List of natural satellites


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