Earth's Hellish Twin
Venus, the second planet from the Sun, is often called Earth's twin because the two planets share similar sizes, masses, and compositions. Venus has a diameter of 12,104 kilometers compared to Earth's 12,742 kilometers, and its mass is approximately 82 percent of Earth's. However, the similarities end with these basic physical parameters. Venus is the hottest planet in the Solar System despite being farther from the Sun than Mercury, with a surface temperature of approximately 465 degrees Celsius that remains nearly constant across the entire planet, day and night, equator to poles. This extreme and uniform heat is the result of a runaway greenhouse effect driven by a thick atmosphere composed of 96.5 percent carbon dioxide, which traps solar energy so effectively that the surface is hotter than the inside of a conventional oven.
The atmosphere of Venus is one of the most hostile environments in the Solar System. Surface atmospheric pressure on Venus is approximately 92 times that of Earth, equivalent to the pressure experienced at a depth of nearly one kilometer in Earth's oceans. The atmosphere contains clouds of sulfuric acid that completely obscure the surface from view in visible light, creating the brilliant white appearance that has made Venus one of the brightest objects in the night sky throughout human history. Winds at the cloud tops reach speeds of 360 kilometers per hour, circling the entire planet in approximately four Earth days despite Venus itself rotating extremely slowly, taking 243 Earth days to complete a single rotation on its axis, longer than its orbital period of 225 days.
The surface of Venus, mapped in detail by the Magellan spacecraft using synthetic aperture radar in the early 1990s, reveals a geologically complex world dominated by volcanic features. Approximately 80 percent of the surface consists of smooth volcanic plains formed by extensive lava flows, dotted with over 1,600 major volcanoes and thousands of smaller volcanic features. Unlike Earth, Venus shows no evidence of plate tectonics, and scientists believe the planet may release its internal heat through episodic global resurfacing events in which massive volcanic activity covers much of the surface with fresh lava over geologically short time periods. Recent observations by the Venus Express orbiter and ground-based telescopes have detected potential signs of ongoing volcanic activity, including transient infrared hotspots and variations in atmospheric sulfur dioxide that suggest Venus may still be volcanically active today. Future missions including NASA's VERITAS and DAVINCI and ESA's EnVision aim to investigate Venus's geology, atmosphere, and the tantalizing question of whether life could exist in the temperate cloud layers high above the planet's hellish surface.