Venus is hotter than Mercury even though it is farther from the Sun.

Sunlight warms the surface, which emits energy as infrared radiation. Venus’s atmosphere absorbs and re-emits much of that outgoing radiation, making heat escape less readily from the lower atmosphere. This enormous greenhouse effect produces a surface far hotter than a distance-only comparison would suggest.

Mercury receives more sunlight because it orbits closer to the Sun, but it lacks a thick atmosphere. Its exposed ground heats strongly in daylight and cools sharply at night. Venus instead maintains extremely high temperatures on both its day and night sides, despite rotating very slowly.

Venus’s bright clouds reflect a substantial fraction of incoming sunlight. Brightness therefore does not imply a cool surface. Beneath the reflective cloud deck, the atmosphere’s effect on outgoing heat dominates the conditions experienced by a lander. Cloud-top appearance and ground-level weather describe very different environments.

Before spacecraft measurements, Venus’s opaque clouds left room for speculation about the surface. Space exploration replaced that uncertainty with measurements of intense heat and crushing pressure. Soviet Venera landers returned data and photographs from the ground, while orbiters used instruments capable of studying terrain hidden from ordinary visible-light cameras.

NASA’s Magellan mission mapped most of Venus using radar. Radio waves could penetrate the cloud cover and reveal volcanic plains, mountains and other landforms. The maps showed a rocky planet with a complex geological history rather than an interchangeable twin of Earth, despite the two worlds having broadly similar sizes and masses.

The surface atmosphere presses down with roughly 92 times Earth’s sea-level pressure. That pressure is another challenge separate from temperature: a spacecraft must withstand both a hot environment and a heavy atmospheric load. A design suitable for orbit or a brief passage through upper clouds is not automatically suitable for prolonged operation on the ground.

Venus is a useful natural laboratory for comparing planetary climates, but the comparison requires care. Its atmosphere is overwhelmingly carbon dioxide, its available water differs profoundly from Earth’s, and its long-term evolution involved its own history of sunlight, geology and atmospheric escape. The lesson is not that all planets with greenhouse gases inevitably acquire identical climates.

Scientists continue to investigate how Venus reached its present state and how active its surface remains. Atmospheric observations and radar studies answer different pieces of that puzzle. Separating present-day measurements from reconstructions of the distant past prevents a persuasive climate story from being mistaken for a completely settled historical account.

Venus also rotates in the opposite direction from most planets. Its unusual spin is a separate property from the atmospheric greenhouse mechanism responsible for its extreme surface heat.

Mercury's proximity to the Sun makes it an obvious candidate for the hottest planet, but distance does not determine a surface climate by itself. Venus shows why an atmosphere belongs in the comparison. Incoming energy, reflected sunlight and the escape of thermal radiation all help set the temperature of the ground beneath the clouds.

Not through the global opaque cloud cover. Radar mapping is valuable precisely because it can reveal terrain that visible-light images of Venus conceal.

No. Venus still radiates energy to space. Its surface and lower atmosphere reach high temperatures as part of the balance between incoming solar energy and outgoing radiation.

No. The enormous carbon-dioxide inventory and very high pressure make its atmosphere fundamentally different from the nitrogen-and-oxygen mixture at Earth’s surface.