Why does Mercury have almost no atmosphere?
Quick Answer
Mercury is small, hot and close to the Sun, so its weak gravity can't hold onto gases, which are blasted away by heat and the solar wind.
The Full Story
Mercury is the smallest planet, with surface gravity only about 38% of Earth's. Being the closest planet to the Sun, its daytime surface reaches about 430°C, giving gas molecules enough energy to escape. The intense solar wind also strips particles away. What remains is an extremely thin exosphere made of atoms such as oxygen, sodium, hydrogen, helium and potassium, constantly replenished from the surface and the solar wind. Without a proper atmosphere to trap heat, night-time temperatures plunge to about −180°C.
Key Facts
YouTube Angle
Suggested video title for this topic:
"The planet with 600 degrees of temperature swing — and no air to blame."