Fact File Answers


Planetary Fact Files
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune



  1. Why is the surface temperature of Venus higher than Mercury's?
    Venus has a much thicker atmosphere in which to trap the heat from the Sun.
  2. How many Mercury years are in five Earth years?
    (Earth days in a year x 5) ÷ 88. Note: There are actually 365.25 days in an Earth year (hence the leap year once every four years). So, (365.25 x5) ÷ 88 = 20.75
  3. Why does Mercury have no moons?
    Mercury's closeness to the sun's gravity means nothing can naturally maintain an orbit of the planet.
  4. Based on our current understanding, why can Mercury not support life?
    Thin atmosphere, no water, too hot, and night lasts 88 Earth days at a time.


  1. Why will we not be landing humans on Venus anytime soon?
    It is too hot, rains sulfuric acid, and has a very thick atmosphere that will be difficult to move through
  2. How could we use Venus as an example for why we should avoid increasing the greenhouse effect on Earth?
    The atmosphere of Venus is made up of 96% carbon dioxide (which is a greenhouse gas) which traps so much of the sun's heat its surface temperature is higher even than Mercury.
  3. How long is 5 Earth years in Venus Days?
    (365.25 x 5) ÷ 243 = 7.515. Note: There are actually 365.25 days in an Earth year (hence the leap year once every four years).
  4. What would need to be take into consideration when choosing materials for a Venus rover?
    Needs to be acid and heat resistant. Also, extra power would be needed to drive through the thicker 'air'.


  1. Even with us having a leap year every four years we are still lose 0.006 days per orbit. How long will it take before a double leap year would be required?
    1 ÷ 0.006 = 166.67 years. So with our current calendar system we'd need an extra leap year every 166.67 years.
  2. What do you think is third most common gas in the Earth's atmosphere?
    Most people would guess Carbon Dioxide. However, the correct answer is Argon
  3. Why is the atmosphere on Earth easier to move through than that on Venus?
    Earth's air is thinner than Venus's making it easier to move through.
  4. Give three reasons why having an increasing number of satellites in orbit around Earth is a bad thing.
    Light polution that blocks out the stars for astronomers
    More risk of satellites injuring people when their orbits decay
    Higher risk of collisions between them
    Harder to plot trajectories and arrange launches of other space vehicles to avoid them


  1. Why is Mars one of the most visited planets by Earth spacecraft?
    It is the second closest planet when it passes (only Venus passes closer). Mars is also the more hospitable of our neighbours and therefore better suited for possible colonisation.
  2. How many Earth years are in ten Mars years?
    (10 x 687) ÷ 365.25 = 18.81 Earth Years. Note: There are actually 365.25 days in an Earth year (hence the leap year once every four years).
  3. Why are the moons of Mars the smallest in the solar system?
    Mars has a lower gravity than Earth and therefore cannot hold moons as large as ours in it's orbit.
  4. Why are researchers hopeful of finding some form of life (past or present) on Mars? Life isn't just referring to us, but to any and all living things - including bacteria and viruses.
    There is water present on the planet, one of the main necessities for life, it is also not too extreme in temperatures for hardier life-forms to survive.


  1. If Ganymede is larger than Mercury why is it called a moon rather than a planet?
    It is in orbit around a planet, making it a moon. To be a planet it would have to be in orbit around a star.
  2. How many Jupiter days are in a Jupiter year?
    Step 1: 10 hours ÷ 24 hours = 0.417 Earth days in a Jupiter day
    Step 2: 12 x 365.25 = 4383 Earth days in 12 Earth years
    Step 3: 4383 ÷ 0.417 = 10,510.79 Jupiter Days in a Jupiter Year
  3. Why does NASA not want to risk crashing an orbiter, which could potentially carry Earth microbes, into one of Jupiter's main moons?
    There are indications of water on at least three of these moons and there is a risk that microbes from Earth could survive on these moons and 'infect' them. This would be catastrophic if there is already life present that could be killed by our microbes.
  4. Why does Jupiter have so many moons?
    It is such a large planet it traps natural satellites easily within its orbit.


  1. Why is the discovery of liquid water on Enceladus such big news?
    Water is considered the first indicator that life may exist on a world (whether it's a planet or a moon)
  2. How many Saturn days are in a Saturn year?
    Step 1: (42 ÷ 60) + 10 = 10.7 hours in a Saturn day
    Step 2: 10.7 ÷ 24 = 0.45 Earth Days in a Saturn day
    Step 3: 365.25 x 29 = 10,592.25 Earth Days in a Saturn year
    Step 4: 10,592.25 ÷ 0.45 = 23,538.33 Saturn days in a Saturn year
  3. We had only landed on one moon before Huygen landed on Titan. Which was this?
    Earth's moon.
  4. Why is the flattening effect of high speed spinning more noticeable on Saturn than Jupiter (which travels faster)?
    It is smaller so the flattening is more noticeable, and the rings add emphasis.


  1. What two things do Saturn and Uranus have in common?
    They both rotate on their axis in the opposite directions to all the other planets in the solar system.
    They both have visible permanent rings
  2. Why does Uranus appear blue and white in the above image?
    The atmosphere is made of water and ice crystals
  3. How many Uranus days are in an Uranus year?
    Step 1: (14 ÷ 60) + 17 = 17.23 hours in an Uranus day
    Step 2: 17.23 ÷ 24 = 0.72 Earth days in an Uranus day
    Step 3: 365.25 x 84 = 30,681 Earth days in an Uranus year
    Step 4 30,681 ÷ 0.72 = 42,612.5 Uranus days in an Uranus year
  4. Why have there been so few missions to Uranus?
    It takes years to reach it with our spacecraft due to the long distance between Earth and Uranus (when at our closest it is still 1.6 billion miles away)


  1. Is Neptune's orbital speed faster or slower than Earth's?
    Neptune is 30 times further away from the Sun than Earth. If we say that the distance from the Sun to Earth is x then:
    Step 1: Using circumference = 2πr
    Earth's orbit is 2πx whilst Neptune's orbit is 60πx.
    Step 2: Earth takes one year to travel 2πx
    To match the speed of Earth Neptune would have to complete it's orbit in 60 ÷ 2 = 30 Years
    Step 3: Neptune takes 165 years which is greater than 30 so is therefore slower
  2. What factors would you need to take into account if planning a mission to Neptune?
    The length of time for the journey.
    Surface is hot liquid.
    Highly flammable atmosphere.
  3. How many Neptune days are in a Neptune year?
    Step 1: 16 ÷ 24 = 0.67 Earth days in a Neptune day
    Step 2: 365.25 x 165 = 60,266.25 Earth days in a Neptune year
    Step 3: 60,266.25 ÷ 0.67 = 89,949.63 Neptune days to a Neptune year
  4. Which gas in the atmosphere of Neptune must be responsible for the planet's blue appearance? Hint: look at the main components of Saturn and what colour that appears.
    Methane gives Neptune it's blue colour by absorbing the red light from the sun.

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