SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/astro-planet-formation-temperature

Why did rocky planets form mainly near the young Sun?

Only rocky and metallic material could remain solid in the hot inner disk.

Start playing free

  1. Heat vaporized many icy materials ✔
  2. Gravity worked only near the Sun
  3. The outer disk contained no solids

Why: The protoplanetary disk had a strong temperature gradient. Refractory rock and metal condensed near the Sun, while volatile ices survived farther out and helped build giant-planet cores.

Huh, didn't know that: Repeated collisions and sticking among disk clumps built progressively larger planetesimals and protoplanets.

The dad joke
The inner planets are rocky because they could stand the heat.
Like this card?
Play the game

References

Answer: Heat vaporized many icy materials. The protoplanetary disk had a strong temperature gradient. Refractory rock and metal condensed near the Sun, while volatile ices survived farther out and helped build giant-planet cores.

  1. Solar System Facts science.nasa.gov/solar-system/solar-system-facts
    Nearest to the Sun, only rocky material could withstand the heat when the solar system was young.
    Checked 2026-10-10.

Think this answer is wrong? Tap "Challenge this answer" on the card in the game and tell us why.

Test yourself in the game

Astronomy & SpaceWhich kind of light has the shortest wavelength, under 0.01 nanometer?Astronomy & SpaceRoughly what wavelength range is visible light?Astronomy & SpaceWho discovered infrared light in 1800 by putting a thermometer past the red end of a spectrum?

That's stuff everyone should know.