Venus has the hottest planetary surface in the Solar System because its thick carbon-dioxide atmosphere traps heat. Mercury receives more direct sunlight, but it has almost no atmosphere to redistribute or retain that energy. Distance from the Sun alone does not determine a planet’s surface temperature.
An atmosphere changes the heat balance
Sunlight warms a planet’s surface, which then releases energy as infrared radiation. Greenhouse gases in Venus’s dense atmosphere absorb and re-emit some of that outgoing heat, keeping the surface extremely hot. NASA notes that Venus is hotter than Mercury despite being farther from the Sun. [1]
Mercury has dramatic temperature swings
Mercury’s extremely thin exosphere provides little insulation. Its surface can become very hot in daylight and very cold at night. Venus’s thick atmosphere spreads heat and prevents the surface from cooling in the same way.
Distance is only one factor
A planet’s temperature depends on sunlight, reflectivity, atmosphere, clouds, rotation and heat transport. Comparing Venus and Mercury shows why a planet’s atmospheric conditions can matter more than its distance from the Sun.
Is Mercury the hottest planet because it is closest to the Sun?
No. Venus’s dense greenhouse atmosphere makes its surface hotter on average.
Sources and evidence
- NASA Science — Venus facts ↗
States that Venus is hotter than Mercury because its thick atmosphere traps heat.
- NASA Science — Solar System temperatures ↗
Compares planetary temperatures and explains Venus’s greenhouse effect.
Sources consulted: 11 October 2026. Written with AI assistance and checked against the linked references; not independently reviewed by a subject specialist. Sources do not endorse this article. See our editorial policy.
Revision: Initial publication; explanation checked against linked institutional and scientific sources.