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10 Need-to-Know Things About Venus
- Venus is only a little smaller than Earth.
- Venus is the second closest planet to the sun at a distance of about 108 million km (67 million miles) or 0.72 AU.
- One day on Venus lasts as long as 243 Earth days (the time it takes for Venus to rotate or spin once). Venus makes a complete orbit around the sun (a year in Venusian time) in 225 Earth days.
- Venus is a rocky planet, also known as a terrestrial planet. Venus' solid surface is a cratered and volcanic landscape.
- Venus' thick and toxic atmosphere is made up mostly of carbon dioxide (CO2) and nitrogen (N2), with clouds of sulfuric acid (H2SO4) droplets.
- Venus has no moons.
- There are no rings around Venus.
- More than 40 spacecraft have explored Venus. The Magellan mission in the early 1990s mapped 98 percent of the planet's surface.
- No evidence for life has been found on Venus. The planet's extreme high temperatures of almost 480 degrees Celsius (900 degrees Fahrenheit) make it seem an unlikely place for for life as we know it.
- Venus spins backwards (retrograde rotation) when compared to the other planets. This means that the sun rises in the west and sets in the east on Venus.
Venus and Earth are similar in size, mass, density, composition, and gravity. There, however, the similarities end. Venus is covered by a thick, rapidly spinning atmosphere, creating a scorched world with temperatures hot enough to melt lead and surface pressure 90 times that of Earth (similar to the bottom of a swimming pool 1-1/2 miles deep). Because of its proximity to Earth and the way its clouds reflect sunlight, Venus appears to be the brightest planet in the sky.
We cannot normally see through Venus' thick atmosphere, but NASA's Magellan mission during the early 1990s used radar to image 98 percent of the surface, and the Galileo spacecraft used infrared mapping to view both the surface and mid-level cloud structure as it passed by Venus on the way to Jupiter. In 2010, infrared surface images by the European Space Agency's Venus Express provided evidence for recent volcanism within the past several hundred thousand years. Indeed, Venus may be volcanically active today.
Like Mercury, Venus can be seen periodically passing across the face of the sun. These "transits" of Venus occur in pairs with more than a century separating each pair. Transits occurred in 1631, 1639; 1761, 1769; and 1874, 1882. On 8 June 2004, astronomers worldwide watched the tiny dot of Venus crawl across the sun; and on 6 June 2012, the second in this pair of transits occurred. The next transit is 11 December 2117. Observing these transits helps us understand the capabilities and limitations of techniques used to find and characterize planets around other stars.
Venus' atmosphere consists mainly of carbon dioxide, with clouds of sulfuric acid droplets. Only trace amounts of water have been detected in the atmosphere. The thick atmosphere traps the sun's heat, resulting in surface temperatures higher than 470 degrees Celsius (880 degrees Fahrenheit). The few probes that have landed on Venus have not survived longer than 2 hours in the intense heat. Sulfur compounds are abundant in Venus' clouds; the corrosive chemistry and dense, moving atmosphere cause significant surface weathering and erosion.
The Venusian year (orbital period) is about 225 Earth days long, while the planet's rotation period is 243 Earth days, making a Venus day about 117 Earth days long. Venus rotates retrograde (east to west) compared with Earth's prograde (west to east) rotation. Seen from Venus, the sun would rise in the west and set in the east. As Venus moves forward in its solar orbit while slowly rotating backwards on its axis, the top level of cloud layers zips around the planet every four Earth days, driven by hurricane-force winds traveling at about 360 kilometers (224 miles) per hour. Speeds within the clouds decrease with cloud height, and at the surface are estimated to be just a few kilometers per hour. How this atmospheric "super-rotation" forms and is maintained continues to be a topic of scientific investigation.
Atmospheric lightning bursts, long suspected by scientists, were confirmed in 2007 by the European Venus Express orbiter. On Earth, Jupiter, and Saturn, lightning is associated with water clouds, but on Venus, it is associated with sulfuric acid clouds.
Craters smaller than 1.5 to 2 kilometers (0.9 to 1.2 miles) across do not exist on Venus, because small meteors burn up in the dense atmosphere before they can reach the surface. It is thought that Venus was completely resurfaced by volcanic activity 300 to 500 million years ago. More than 1,000 volcanoes or volcanic centers larger than 20 kilometers (12 miles) in diameter dot the surface. Volcanic flows have produced long, sinuous channels extending for hundreds of kilometers. Venus has two large highland areas - Ishtar Terra, about the size of Australia, in the north polar region; and Aphrodite Terra, about the size of South America, straddling the equator and extending for almost 10,000 kilometers (6,000 miles). Maxwell Montes, the highest mountain on Venus and comparable to Mount Everest on Earth, is at the eastern edge of Ishtar Terra.
Venus has an iron core that is approximately 3,000 kilometers (1,900 miles) in radius. Venus has no global magnetic field - though its core iron content is similar to that of Earth, Venus rotates too slowly to generate the type of magnetic field that Earth has.
How Venus Got its Name
Venus is named for the ancient Roman goddess of love and beauty. (Venus is the Roman counterpart to the Greek goddess Aphrodite.) It is believed Venus was named for the most beautiful of the ancient gods because it shone the brightest of the five planets known to ancient astronomers. Other civilizations have named it for their god or goddess of love/war as well.Image Credit: NASA/JPL
Explanation from: http://solarsystem.nasa.gov/planets/profile.cfmObject=Venus