Facts About Venus, the Hottest Planet

What kind of planet is Venus?

Venus is the second planet from the Sun and Earth's closest planetary neighbor. It's a rocky planet, about 95 percent as wide as Earth and made of similar rock and metal, which is why people call it Earth's twin. But under its clouds, Venus is the most hostile planet in the solar system.

It's also the easiest planet to see. After the Sun and the Moon, Venus is the brightest natural object in our sky, glowing near sunrise or sunset. It's the only planet named after a female figure, the Roman goddess of love, and most of its features have women's names.

Venus's size, distance, day and year

Source: NASA Planetary Fact Sheet and NASA Science.

Venus breaks two rules at once. It spins backward compared with most planets, so the Sun rises in the west and sets in the east. And it spins incredibly slowly: one turn takes 243 Earth days, longer than its whole year of 225 days. One sunrise to the next takes about 117 Earth days.

Why is Venus the hottest planet?

Venus is almost twice as far from the Sun as Mercury, yet it's hotter. The reason is its air.

Venus's atmosphere is mostly carbon dioxide, and it is incredibly thick. Sunlight gets through the clouds and warms the ground, but the heat can't escape back to space. This is called the greenhouse effect, and on Venus it has run away: the surface is about 465 °C (870 °F), hot enough to melt lead, day and night, at the poles and at the equator.

The air is also heavy. NASA says the pressure at the surface is about 93 times Earth's, the same as being about 900 meters (3,000 feet) under the ocean. A person there would be crushed and cooked at once.

High above, things are gentler. About 50 kilometers up, the temperature and pressure are close to Earth's, which is why some scientists have suggested floating research stations someday.

Clouds of acid

Venus is wrapped in a thick, yellowish layer of clouds made of sulfuric acid. They reflect so much sunlight that Venus shines brilliantly in our sky, and they hide the surface completely from ordinary telescopes. At the cloud tops, winds race around the planet at up to 360 kilometers per hour, far faster than the planet itself turns.

Some dark streaks in the clouds absorb ultraviolet light, and scientists still aren't sure what makes them.

What's inside Venus?

Scientists think Venus is built much like Earth. Tap the cutaway in the diagram to explore:

1. Clouds and atmosphere: the thick carbon dioxide blanket with sulfuric acid clouds.
2. Crust: rock shaped by volcanoes. The surface is young for a planet, perhaps only about 150 million years old on average.
3. Mantle: hot rock that feeds Venus's volcanoes.
4. Iron core: no spacecraft has measured it yet, so its size is an estimate.

One big difference from Earth: Venus has no magnetic field made inside the planet. It has only a weak one created where the solar wind meets its upper atmosphere.

Volcanoes, mountains and highlands

Radar can see through the clouds, and NASA's Magellan spacecraft used it to map almost all of Venus between 1990 and 1994. Here's what it found:

• Volcanoes everywhere: thousands of them, plus odd flat "pancake domes" up to 62 kilometers wide, made of thick, sticky lava.
• Maxwell Montes: the tallest mountain on Venus, about 11 kilometers (36,000 feet) high, taller than Mount Everest. It rises from a highland near the north pole called Ishtar Terra, about the size of Australia.
• Aphrodite Terra: an even bigger highland along the equator, about the size of South America.
• Few craters: apart from Earth, Venus has the fewest impact craters of the rocky planets, a sign that lava has repaved much of the surface.

Missions to Venus

• The Soviet Venera program sent ten probes to the surface between the 1960s and 1980s. The heat and pressure destroyed them fast; NASA notes the longest-lasting survived about two hours and the shortest 23 minutes.
• NASA's Mariner 10 photographed Venus's clouds in 1974 on its way to Mercury.
• NASA's Magellan finished its radar map in 1994.

New missions to Venus have been planned by NASA and the European Space Agency, but none has launched yet.

Venus has phases, too

Through a telescope, Venus goes through phases like the Moon, from a thin crescent to a nearly full disk, about every 584 days. In 1610, Galileo saw these phases and realized they only made sense if Venus orbits the Sun, not Earth. It was one of the first pieces of evidence that the Sun is at the center of the solar system.

Fun facts about Venus

• A day on Venus is longer than its year.
• Venus has no moons and no rings.
• Its axis is tipped only about 3 degrees from upright (counting it as spinning backward), so it has almost no seasons.
• If you weigh 80 pounds on Earth, you'd weigh about 73 pounds on Venus.
• Although Venus comes closest to Earth, Mercury is, on average, our nearest planet, because it never wanders far from the Sun.

Learning about Venus at home

Try a simple greenhouse experiment: put two thermometers in the sun, one inside a clear jar, and compare after 20 minutes. The trapped heat in the jar is a tiny model of what Venus's air does. Then take the facts quiz above and print the labeled Venus diagram.

Next, compare Venus with its neighbors, Mercury and Earth, or see where it sits among the planets in order.