Moons
1. How are moons different from planets?
Planets orbit the Sun; moons orbit planets
2. The Earth has one moon. Do all planets?
No. Mercury and Venus have no moon, Mars has 2 and Venus and Saturn both have over 60 each!
3. Do moons have gravitational fields?
Yes, any body that has mass generates a gravitational field. The gravitational field strength on our Moon is
1.62N/kg, which is about 1/6 of the gravitational field strength on Earth.
Gravitational fields
4. Which planet has the largest gravitational field? What is it?
Jupiter = 26N/kg
5. Which planet has the smallest gravitational field? What is it?
Mercury = 4N/kg (Pluto doesn't count! See Q.11)
6. What is the relationship between the mass of the planet and the gravitational field strength of the planet?
The larger the mass of a planet, the stronger the gravitational field strength
Period of orbit
7. Which planet has the shortest period of orbit? What is it?
Mercury = 3 x Earth month = 0.25 x Earth year
(if you lived on Mercury you would be over 60 years old!)
8. Which planet has the longest period of orbit? What is it?
Neptune = 1978 x Earth month = 164 x Earth year
(if you lived on Neptune you would be 0.1 years old!)
9. What is the relationship between the period of orbit of a planet and its distance from the Sun?
The larger the distance from the Sun, the greater the period of orbit
10. What is the relationship between the surface temperature of a planet and its distance from the Sun?
The larger the distance from the Sun, the lower the surface temperature
(the one exception to this rule is Venus which has an exceptionally high surface temperature of +465oC due to an atmosphere of 96% CO2 and clouds of H2SO4!)
Classification of astronomical bodies
11. What 2 classifications are the planets grouped into? What are the key features of each group?
4 Inner "rocky" planets
o Rocky
o Smaller diameters
o Shorter periods
4 Outer "gas giant" planets
o Gaseous
o Larger diameters
o Longer periods
o Have rings (most noticeable for Saturn, but they all have them)
o What are 2 key features of comets and 3 key features of their orbits?
i. Made from ice and dust
ii. Have a tail when they pass close to the Sun
i. Highly elliptical orbit - see blue trace.
o Sometimes pass close to the Sun at very high speeds but spend most of their orbit in the outer reaches of the solar system moving at much lower speeds
iii. Periods can be from a few years to hundreds of thousands of years
13. How do the orbits of asteroids differ from the orbits of comets?
Asteroids are lumps of rock that mostly orbit the Sun in the "Asteroid Belt", between Mars and Jupiter, in approximately circular orbits
14. Which planet in the animation is no longer a planet? (it has been reclassified as a planetoid or dwarf planet)
Pluto was reclassified as a planetoid or dwarf in 2006 for reasons including its highly elliptical and tilted orbit
