- The International Astronomical Union reclassified Pluto from a planet to a dwarf planet due to its small size and eccentric orbit. - Students are tasked with analyzing data about objects in the solar system to determine what characteristics qualify a body as a planet. - The IAU decided that to be a planet, a body must orbit the sun, have a nearly circular orbit, and not cross the orbits of other planets. Students are asked if they agree with reclassifying Pluto as a dwarf planet.

1. Probe Activity 3 Lander Student Sheet 6a
Pluto: a planet no more
The International Astronomical Union (IAU) has downgraded Pluto from
being our ninth planet to the category dwarf planet. Many people are
angry about this decision.
Should Pluto be reinstated as a planet?
Do the tasks to help you decide.
Complete the report form.
Look at the hints to help you write the report to the best grade you can.
Task 1 Task 2
• Study the data cards about • Decide on three
nine big objects in the Solar characteristics that a body
System. must have in order to qualify Task 3
• Use the report form to record as a planet. • The IAU decided that to be a
your findings as you work • Complete this section on the planet, a body must:
through the following: report form. - Orbit the Sun
- Arrange the objects in order - Have an orbit that is circular
of size. • Does Pluto have these (or nearly)
- Put them in order of characteristics? - Not cross the orbits of other
discovery date. • Report your conclusions on the bodies.
- Put them in order of distance report form.
from the Sun. • Do you agree with the decision
- Group them by orbital type. to reclassify Pluto as a dwarf
- Group them by type of planet?
object.
• Report your conclusions on the
report form.
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2. Probe Activity 3 Lander Student Sheet 6c
Pluto Data cards
Object: Mercury Object: Pluto Object: Ceres
Time to orbit Sun: 88 days Time to orbit Sun: 250 years Time to orbit Sun: 4.6 years
When discovered: 2000 BCE When discovered: 1930 When discovered: 1801
Diameter/km: 4800 Diameter/km: 2200 Diameter/km: 1000
Distance from Sun/AU: 0.4 Distance from Sun/AU: 40 Distance from Sun/AU: 2-3 (in the
Orbit and notes: Orbit nearly circular. Orbit and notes: Orbit inclined to the asteroid belt between Mars and
Has cleared its orbit of other objects. orbits of other planets. Elliptical (30-50 Jupiter)
Classification: Planet AU). Crosses orbit of Neptune. Orbit and notes: Does not have a
Classification: Dwarf Planet clear orbit. Was the largest asteroid.
Classification: Dwarf Planet
Object: Charon Object: Eris Object: Sedna
Time to orbit Sun: 250 years (with Time to orbit Sun: 560 years Time to orbit Sun: 10,500 years
Pluto) When discovered: 2003 When discovered: 2004
When discovered: 1978 Diameter/km: 3000 Diameter/km: 1800
Diameter/km: 1200 Distance from Sun/AU: 67 Distance from Sun/AU: 90 at closest
Distance from Sun/AU: 40 Orbit and notes: Elliptical (40-100 Orbit and notes: Very very elliptical.
Orbit and notes: Orbits as a moon of AU). Crosses orbits of Neptune and Crosses orbits of small solar system
Pluto. Very big – almost Pluto’s ‘twin’. Pluto. Was called Xena. bodies.
Classification: Moon of Dwarf Planet Classification: Dwarf Planet Classification: Dwarf Planet
(Pluto)
Object: Europa Object: Mars Object: Io
Time to orbit Sun: 11.8 years (with Time to orbit Sun: 1.9 years Time to orbit Sun: 11.8 years (with
Jupiter) When discovered: when humans first Jupiter)
When discovered: 1610 looked at stars When discovered: 1610
Diameter/km: 3100 Diameter/km: 6800 Diameter/km: 3600
Distance from Sun/AU: 5.0 Distance from Sun/AU: 1.5 Distance from Sun/AU: 5.0
Orbit and notes: Orbits as a moon of Orbit and notes: Orbit nearly circular. Orbit and notes: Orbits as a moon of
Jupiter Has cleared its orbit of other objects. Jupiter
Classification: Moon of Planet Classification: Planet Classification: Moon of Planet
(Jupiter) (Jupiter)
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3. Probe Activity 3 Lander Student Sheet 6b
Pluto report Form
Task 1 The patterns I can see are…
Comparison (using data cards)
Planets Dwarf planets
I think astronomers will not discover more dwarf planets because…
Task 2 To be a planet, a body must have… Does Pluto have this?
1
2
3
Task 3 My personal comments on the action of the IAU to reclassify Pluto…
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4. Probe Activity 3 Lander Student Sheet 6d
Pluto assessment guidelines Pluto assessment guidelines
To be graded level 4, 5 or 6 you need to To be graded level 4, 5 or 6 you need to
4: To get level 4, you need to… 4: To get level 4, you need to…
…describe patterns in Solar System objects. …describe patterns in Solar System objects.
…start to make conclusions based on patterns …start to make conclusions based on patterns
in the data. in the data.
5: Do everything for level 4 plus… 5: Do everything for level 4 plus…
…make conclusions that agree with the …make conclusions that agree with the
evidence. evidence.
6: Do everything for level 5 plus… 6: Do everything for level 5 plus…
…use more than one science idea to …use more than one science idea to
explain the conclusions. explain the conclusions.
…explain why some evidence does not fit …explain why some evidence does not fit
with the conclusions. with the conclusions.
7: Do everything for level 6 plus… 7: Do everything for level 6 plus…
…identify limitations in the data. …identify limitations in the data.
…decide whether there is enough data to …decide whether there is enough data to
properly support your conclusions. properly support your conclusions.
…explain how evidence supports the idea …explain how evidence supports the idea
that Pluto is not a planet. that Pluto is not a planet.
© Association for Science Education and Centre for Science Education 2011 This page may have been changed from the original