The moon, Venus, Mars, and the star Spica appear in a quadruple conjunction as seen from Azul, Argentina.
The first spacecraft to set mechanical feet on another planet landed on Venus. In the 1960s and '70s, the former Soviet Union's Venera probes plunged through the planet's punishing atmosphere, with a handful even sending back data from its rocky surface. In December 1970, for instance, the Venera 8 lander transmitted atmospheric data for more than 50 minutes after its turbulent touchdown. These early missions provided an important lesson: Venus is like a massive pressure cooker.
Although the planet is the second closest planet to the sun, it's by far the hottest of the eight worlds in our solar system. Its thick atmosphere is mostly made of carbon dioxide with clouds of sulfuric acid, which traps the sun's heat and creates a runaway greenhouse effect.
Thanks to this atmospheric blanket, temperatures on Venus' surface can soar over 880 degrees Fahrenheit—hot enough to melt lead. The surface pressure is around 90 times that on Earth, which would feel like standing under about a half a mile of water. Wintertime doesn't even provide a reprieve from the heat. With an axial tilt of three degrees, Venus has just one season: hot.
The only planet named after a female figure, Venus is a celestial oddball. Though its rocks are shades of grey, its atmosphere imparts an eerie orange glow to the landscape. Together with Mercury, it's one of the few planets in our solar system without a moon. And like Uranus, it turns on its axis in the opposite direction to the rest of our celestial family. Due to this retrograde rotation, if you were to stand on Venus' surface, the sun would rise in the West and set in the East.
But don't count on catching many Venusian sunsets; the planet turns stunningly slow. A single day there takes 243 Earth days—longer than a Venusian year, which lasts 225 Earth days. And because the planet rotates in the opposite direction as its orbit, 117 Earth days pass between each sunrise and sunset.
Hellish Earth twin
Despite the strange and scorching conditions, Venus shares a surprising number of features with Earth. Measuring 7,520 miles across, Venus is roughly the same diameter as our home planet. It also has a similar structure, sporting a rocky surface and an iron core, although the planet doesn't rotate fast enough to generate an Earth-like magnetic field.
Thousands of volcanoes dot Venus' surface, some of which may still be active. Volcanic rock from cooled lava covers most of its surface—the oldest of which dates back some 500 million years. Many mountains also rise into Venusian skies. Its largest, dubbed Maxwell Montes, stands 36,000 feet tall.
The processes driving the formation of this network of formations is unusual, however. Venus doesn't appear to harbor a churning seismic engine like that on Earth, which drives our bumper-car network of tectonic plates. Yet the planet does appear to have a spidery network of breaks in its surface, hinting at an entirely new type of plate tectonics.
Scientists suspect that for up to two billion years after it formed, the planet may have even been habitable—harboring liquid oceans on its surface. Fascination with what drove that transition from happy to hellish has led many scientists to campaign for more robotic visits to Venus.
Venus' dense cloud cover has benefits for us Earthlings. It reflects the sun's rays, making the planet the brightest in the night sky. It's often called the morning star or evening star because its bright, steady glow persists either around sunrise or sunset. Ancient peoples spotted these dazzling points in the sky and believed them to be two different objects, one that glows in the morning and another that glows in the evening.
Similar to Mercury, Venus can occasionally be seen making a lazy trip across the sun's face, known as a transit. But while Mercury zips across the sun every 13 to 14 years, Venus transits are much more rare. The planet's orbit is almost a perfect circle but is slightly tipped relative to Earth's path around our star. This means it's incredibly hard for the sun, Venus, and Earth to align in the right way.
The last time a transit of Venus happened was in 2012, and it won't happen again until 2117.