Analyse and interpret planetary data about orbital distance, orbital duration, density, surface temperature and uniform gravitational field strength at the planet's surface

6.1.2 The Solar System 🚀

Objective

Analyse and interpret planetary data about orbital distance, orbital duration, density, surface temperature and uniform gravitational field strength at the planet's surface.

1️⃣ Orbital Distance (AU)

The orbital distance is how far a planet is from the Sun, measured in Astronomical Units (AU). 1 AU ≈ 149.6 million km, the average Earth‑Sun distance.

• Think of the Sun as the centre of a giant playground swing. The farther you stand, the longer the swing arm.
• Mercury is 0.39 AU away, Venus 0.72 AU, Earth 1 AU, Mars 1.52 AU, and the gas giants start at 5.2 AU (Jupiter) and beyond.

2️⃣ Orbital Duration (Days)

This is the time a planet takes to complete one orbit around the Sun.

1. Earth’s year is 365.25 days.
2. Mercury’s year is only 88 days – it’s like a fast‑moving skateboarder on the swing.
3. Jupiter’s year is 12 years – a slow, majestic dancer.

Kepler’s Third Law (simplified): \$T^2 \propto a^3\$ – the farther out (larger a), the longer the period T.

3️⃣ Density (g cm⁻³)

Density tells us how compact a planet is.

• Earth’s density is 5.52 g cm⁻³ – like a solid rock.
• Jupiter’s density is only 1.33 g cm⁻³ – it’s mostly gas, so it’s “light” compared to its size.
• Neptune’s density is 1.64 g cm⁻³ – a mix of ice and gas.

4️⃣ Surface Temperature (°C)

Surface temperature depends on distance from the Sun and atmospheric composition.

1. Mercury averages ~167 °C (hot) but can drop to –173 °C at night.
2. Venus is scorching at ~464 °C due to a runaway greenhouse effect.
3. Earth averages ~15 °C – just right for life.
4. Mars is cold, ~–80 °C on average.

5️⃣ Gravitational Field Strength (g) at the Surface

The surface gravity tells you how heavy you feel on each planet.

Formula: \$g = \frac{GM}{r^2}\$ where G is the gravitational constant, M the planet’s mass, and r its radius.

• Earth’s gravity is 9.81 m s⁻² – that’s our “1 g”.
• Mercury’s gravity is 3.7 m s⁻² – you’d feel lighter.
• Jupiter’s gravity is 24.79 m s⁻² – you’d feel over twice as heavy.

📊 Planetary Data Summary

🔍 How to Use This Data

1. Compare two planets: Density vs. Surface Gravity – a denser planet usually has stronger gravity, but size matters too.

2. Relate Orbital Distance to Surface Temperature – the farther from the Sun, the colder.

3. Use the Kepler’s Third Law to predict the orbital period of a new planet if you know its distance.

Remember: the Sun’s gravity keeps all these planets dancing in their orbits, just like a giant invisible hand pulling them around.