Pluto – planet no more
Amidst emotional scenes, the meeting of the International Astronomical Union (IAU) in Prague this summer downgraded Pluto to the new category of Dwarf Planet. In this activity, students study data on planets, dwarf planets and moons. They use the data to devise their own criteria for classifying a solar system body as a planet. Finally, they examine the reasons for the IAU’s conclusion and decide whether they
think the relegation of Pluto was the most logical conclusion the IAU could have come to.
; How science works – interpreting data and using creative thought to test and
develop theories; uncertainties is scientific knowledge and ideas; the role of
the scientific community
; Solar system
; The solar system
11 – 14 The solar system (KS3 QCA module 7L)
; Our solar system includes the Sun, its planets and asteroids and
the natural satellites of the planets
; The planets orbit the Sun in similar ways to the Earth
; How evidence about the solar system has been collected and
Ideas and evidence in science
; About the ways in which scientists work today and how they
worked in the past, including the roles of evidence and creative
thought in the development of scientific ideas
14 – 16 How science works
; 1b: how interpretation of data, using creative thought, provides
evidence to test ideas and develop theories
; 3a: recall, analyse, interpret, apply and question scientific information
; 4c: how uncertainties in scientific knowledge and scientific ideas
change over time and about the role of the scientific community in
validating these changes
14 – 16 Environment, Earth and Universe
; 8c: The solar system is part of the universe, which has changed since
its origin and continues to show long-term changes
AQA Core: Radiation and the Universe - What do we know about the origins of the universe and how it continues to change?
; P1b 13.7 Observations of the solar system can be carried out on the Earth or
Edexcel core: Topic 12 – space and its mysteries
; P1b 12.15 Use data sources to compare the relative sizes of and distances
between Earth, our Moon, the planets, the Sun, galaxies and the Universe
OCR Twenty first century core Module P1 The Earth in the Universe
; P1.1.7 Distinguish between planets, moons, the Sun, comets, asteroids and
be aware of their relative sizes and motions
Students will learn that:
; astronomers collected data on solar system bodies and looked for patterns in
it to devise definitions for ‘planet’ and ‘dwarf planet’
; ideas about what planets are have changed over time as the result of new
observations, more accurate data and uncertainty about data interpretation
; the scientific community – in this case the IAU – played a vital role in
validating these changing ideas
Running the activity
Display page 1, and ask students what they feel about the downgrading of Pluto to a Dwarf Planet. Tell them that they will interpret data to decide whether or not they agree that the decision to downgrade Pluto was the most logical decision the IAU could have made.
Divide the class into small groups. Display page 2 and give each group a set of nine
cards made from page 3. Tell them to discuss the questions posed in tasks 1 and 2 of page 2. Emphasise that, at this stage, there is no one right answer to the questions of task 3 – the point of this activity is to get students to interpret data themselves and use creative thought to develop their own definition of a planet. For information, ‘distance from the Sun’ is given in Astronomical Units. One AU = the distance from the Earth to the Sun.
Display page 4. Go through the information here. Emphasise the dramatic scenes at the conference, and point out that some of the astronomers at the conference got very emotional. The final decision was taken by a majority vote, so whilst the consensus was that Pluto should be downgraded to Dwarf Planet status, some astronomers were unhappy with the decision and have started a petition to get it reinstated! Also point out that improved measuring and observation equipment – for
example the Hubble space telescope – has been an important factor in the decision-
making process. Without this equipment, astronomers would not have been able to observe solar system objects such as Sedna and Eris, so there would have been less need to question Pluto’s status as a planet. For information, Eris was formerly known as 2003 UB313 and as Xena.
Finally, get students to do task 3 on page 2 – using the information on page 4 under
the heading ‘how can a body qualify as a planet’ and the data on the cards – how
confident are they that the reclassification of Pluto was the most logical action the IAU astronomers could have taken?
For the news story with lots of useful links, see:
For a report from the IAU meeting in Prague, see:
For an orbit simulation of Solar System bodies, look at:
For information about Pluto and other bodies in Wikipedia, see:
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