Pluto – Is it a planet?

Until 2006, the Solar System had nine planets. Now it has eight, plus five 'dwarf planets'. Astronomers at a meeting of the International Astronomical Union in 2006 decided that to be a planet, bodies had to: be big enough for their gravity to have made them become spherical have 'cleared their orbit' of other rocks and debris by colliding with them or disrupting their orbits. Pluto was put into the dwarf planet category, together with Eris, Ceres, and two other bodies orbiting well beyond Pluto. The region just beyond Pluto's orbit is called the Kuiper Belt, and astronomers expect to find more dwarf planets and smaller bodies there. This 'demotion' of Pluto is just one in a series of changes in the way that scientists think about the Solar System. Once most scientists had accepted that the Sun is in the centre of the Solar System, various ideas were put forward to explain how the Sun and the planets formed. These are just some of the theories put forward.

These are just some of the theories put forward. ● Swedish inventor Emanual Swedenborg (1688–1772) first proposed the 'nebular hypothesis' in 1734, which suggested that a cloud of dust and gas collapsed and got pulled together by gravity to form the Sun and the planets. ● In 1749, the French mathematician Georges-Louis Leclerc (1707–1788) suggested that a comet had collided with the Sun and the collision had sent matter shooting off into space. This matter then came together to form the planets. ● In 1917, the British astronomer James Jeans (1877–1946) suggested that a star had passed close to the Sun. The gravity between the two stars had pulled a lot of matter out of the stars and this had condensed to form planets. ● Russian astronomer Otto Schmidt (1891–1956) proposed in 1944 that the Sun passed through a cloud of dust and gas in Space, and that the Sun's gravity had pulled a lot of this matter into orbit. The dust and gas then came together to form planets. None of the theories can explain everything we know about the Solar System, but at the moment the modern version of the nebular hypothesis is the best explanation.

What you need to do Write a newspaper column or magazine article discussing the ‘demotion’ of Pluto and what you think about this. Your column should give your readers some background information about the Solar System and the planets and how scientists find out about them. You should think about including some of these things: a description of how scientists think the Solar System formed (think of a model to help explain this, if you can) and why they think this an explanation of the difference between planets, dwarf planets and asteroids, and how these definitions were arrived at a description of how the status of some of the other bodies in the Solar System has changed with time how scientists explain the formation of the Solar System, and how and why these ideas have changed with time a chart or other way of displaying information about the planets and dwarf planets in the Solar System.

Communicating and collaborating in science Level 3 To reach this level I could: presented data in more than one way, e.g. showing the diameters of some bodies in the Solar System as a table and a bar chart. used scientific words and ideas when explaining simple scientific ideas, e.g. planet, gravity. Level 4 To reach this level I could: chosen a good way to present data, e.g. drawn a bar chart of the diameters of some bodies in the Solar System and clearly marked which are planets and which are dwarf planets. used scientific words and ideas correctly when explaining simple scientific ideas, e.g. planet, dwarf planet, asteroid. used units such as kilometres or kilograms when describing the sizes of planets, and used the correct abbreviations for them.

Level 5 To reach this level I could: used scientific evidence to support or object to the statement that 'Pluto is not a planet'. decided on the best way to present data on the sizes or shapes of planets, dwarf planets and asteroids. used scientific and mathematical words correctly when talking about things that I cannot see directly, e.g. knowing the difference between mass and weight and knowing which units to use for each. explained why better evidence can be collected when people work together, e.g. why most astronomers share their observations with others Level 6 To reach this level I could: said whether evidence is being presented in a balanced way (optional). decided whether it is better to show information in a qualitative (no numbers) or quantitative (with numbers) way. explained that data about the planets gathered by an astronomer is primary information to the astronomer, but it is secondary data to other people using it or explained that ideas about the formation of the Solar System are often based on computer models and simulations, which use primary data.

Level 7 To reach this level I could: explained how information can be altered or presented in such a way that it is biased (optional). used a flowchart to illustrate the process of deciding on the new category of 'dwarf planet'. explained how different scientists with different areas of knowledge have made contributions to our understanding of the Solar System, such as astronomers who study distant stars and planetary scientists who have detailed knowledge about the planets in our Solar System.