Venus

Venus is the second planet from the Sun and the hottest in the solar system, with a surface around 464 °C — hot enough to melt lead. A thick atmosphere of carbon dioxide traps heat in a runaway greenhouse effect, and dense clouds of sulphuric acid hide the surface from view.

Similar in size and composition to Earth, Venus is often called our sister planet, yet it rotates slowly and backwards: its day is longer than its year, and the Sun would rise in the west.

The table above shows just how close a twin Venus is in size. Its radius of 6,051.8 km is about 95% of Earth’s and its mass 0.815 of ours, giving a surface gravity of 8.87 m/s² — close enough that you would weigh only about a tenth less standing there than you do here. Everything beyond the size is alien. At 0.723 AU Venus receives roughly twice the sunlight Earth does, but sunlight alone cannot account for a mean surface temperature of 464 °C; the carbon-dioxide atmosphere trapping that heat is what does.

The 117-day figure in the table is the solar day — sunrise to sunrise. Venus turns on its axis more slowly still, taking longer than its own 225-day year, and it turns backwards, which is why the Sun would cross the sky from west to east and why fewer than two sunrises fit into a Venusian year. There are no moons at all, so nothing lights that long night. Compare its orbit with Earth’s in the 3D solar system simulator.