Earth is just right
The planet Venus orbits one step closer to the sun than Earth does. And Mars orbits one step farther out. On Venus, it’s hot enough to melt lead! And Mars is a cold, dry desert. But Earth is juuust right for people and other forms of life.
This is what some scientists call the Goldilocks problem. Why is Venus too hot, Mars too cold, but Earth just right for life? Venus is closer to the sun than Earth – and Mars is farther away – but that’s not the whole story. The answer also involves an invisible gas called carbon dioxide – or CO2.
Carbon dioxide is a greenhouse gas. That means it lets sunlight pass through to a planet’s surface – but traps the resulting heat. Venus has a lot of CO2 – in thick clouds that surround the planet. And Venus is real hot. Earth has less CO2 in its atmosphere. And on Mars, the CO2 stays in the ground – so Mars stays cold.
So Earth is a nice place to live because we’re just the right distance from the sun – and because we have just the right amount of carbon dioxide – or CO2.
