What will happen to the other planets when the Sun becomes a white dwarf?

In one line

The rule

A white dwarf is the small, dense core left after a star like our Sun uses up its fuel and sheds its outer layers.

The Sun will lose much of its mass and become a faint, hot ball about the size of Earth, called a white dwarf.

Let's understand it simply

Imagine the Sun is like a big bonfire in the center of your village. It gives light and warmth to everyone sitting around. If the fire slowly burns out, only a small glowing coal is left. Now, everyone feels cold and can barely see. The planets are like people sitting around the fire. When the Sun becomes a white dwarf, it is like that last coal—very hot but not bright or warm enough for the whole village.

How it works

1. The Sun will run out of hydrogen fuel in about 5 billion years.
2. It will expand into a red giant and swallow Mercury and Venus (maybe even Earth).
3. The Sun will lose its outer layers, blowing them into space as a cloud called a planetary nebula.
4. The core left behind will shrink into a white dwarf—very dense, about the size of Earth, but with half the Sun’s mass.
5. The Sun’s gravity will become weaker because it lost mass, so the planets will move to wider orbits.
6. The white dwarf will not give enough light or heat, so the planets will freeze and be in darkness.

The story behind it

Scientists first noticed white dwarfs in the 1800s when they saw stars that were small but very heavy. The most famous is Sirius B, discovered in 1862. The idea that our Sun would one day become a white dwarf came from studying how stars change as they age. This helped us understand the life cycle of stars and what happens to solar systems over billions of years.

Where you see it in real life

• Sirius B: A real white dwarf star, the companion to the bright star Sirius, shows what our Sun will become.
• Planetary nebulae: Beautiful clouds like the Ring Nebula are made when stars shed their outer layers—what will happen to our Sun.
• Frozen planets: In science fiction, planets around dead stars are shown as cold, dark worlds—this is close to what will happen.
• Solar system models: Some planetarium shows use lights to show how the Sun’s brightness changes as it ages.
• Astrophysics research: Scientists study white dwarfs to learn about the fate of planets and life in the universe.
• Meteorites: Some meteorites have elements made in dying stars, showing this process really happens.

Why it matters

• Future of Earth: Knowing what happens to the Sun helps us understand the long-term fate of our planet.
• Space science: It explains why some planets in other solar systems are cold and dead.
• Astrobiology: Shows why life needs a stable star; when the star dies, life struggles to survive.
• Physics of stars: Helps us learn about gravity, heat, and how elements are made in space.

Worked example

Let’s see what happens to Earth’s orbit:

Given: Sun loses about half its mass when it becomes a white dwarf.
Step 1: Gravity depends on the Sun’s mass. Less mass = weaker pull.
Step 2: Planets move to wider orbits. (Kepler’s law: a ∝ 1/M)
Step 3: Earth’s orbit could become almost twice as wide.
Step 4: With less sunlight, temperature drops far below freezing.

Common mistakes

• Thinking the Sun will explode: The Sun is not big enough to go supernova (explode). It will gently shed its outer layers.
• Believing planets will disappear: Most planets will stay, but in colder, wider orbits. Mercury and Venus may be swallowed by the Sun earlier.
• Assuming the white dwarf is still bright: It will be very faint, not enough for life.
• Forgetting about gravity changes: When the Sun loses mass, its pull weakens, so orbits change.

Remember it

When the Sun becomes a white dwarf, the planets will freeze and drift farther away, lost in the dark.