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The Inner Solar System: Venus

by Dani Johnson

June 30, 2013

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The other day I realized I haven’t written about any of the inner planets. I picked the planet that I’m least familiar with, Venus, the second planet from the sun, Earth’s twin.

Above Image: The planet is enshrouded by a global layer of clouds that obscures its surface to the MESSENGER Dual Imaging System (MDIS) cameras.

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Name & Discovery: Venus [vee-nuhs] was named after the Roman goddess of love and beauty because of its extraordinary brightness. Since Venus is the brightest object in the night sky besides the moon, trying to figure out the first person who spotted the planet is impossible. One thing we can track down, though, is the earliest written record from 1600BC. Also, Galileo Galilei first viewed the brightest planet through a telescope in 1610, taking note that the planet goes through phases like our moon. Like much of Galileo’s work, the observation that Venus has phases provided supporting evidence that the Earth is not the center of the universe, but instead revolves around the Sun with everything else contained in our Solar System.

Quick Facts:

  • Venus is the second planet from the Sun.

  • Venus is thought to be about 4.5 billion years old, roughly the age of the Solar System.

  • The average distance Venus is from the Sun 108,209,475 km (67,238,251 miles).

  • Sidereal Orbital Period (Length of year) in Earth Days 224.70

  • Sidereal Rotation Period (Length of day) in Earth Days -243.018 (retrograde)

  • Venus is not tidally locked to the sun, but it does have a curiously slow and backward rotation.

  • The diameter of Venus is 12,104 kilometers (7, 521 miles).

  • The temperature of the planet reaches at least 462C (864F)!

  • The atmospheric pressure on Venus is 90 times greater than earth.

Exploration: From 1961 to 1983 the Russian space program threw mission after mission to Venus to get a probe to make it all the way to the surface of the planet and last long enough in the extreme pressure and temperature of Venus to record data. Finally, Russia’s Vega 1 and 2 launched in December 1984 and deployed landers and balloons onto the planet. Beginning in 1990, Magellan mapped 98% of the surface of Venus at a resolution of 100-150 meters using synthetic aperture radar to penetrate deep beneath the thick clouds. Having launched in October 1989, Galileo borrowed a little gravity from Venus (and Earth) to give it enough speed to make it all the way to Jupiter, coming briefly into range of the planet and gathering a little data. Following Galileo's example, the Cassini orbiter also used Venus (and Earth, and Jupiter) as a slingshot to shoot it way out to Saturn. Cassini launched in October 1997 and is still in use today. The Japanese tried to send an orbiter to Venus, Akatsuki (meaning "dawn" in English), but it did not achieve orbit insertion in 2010 but mission planners are discussing whether or not they can try again in six years when the spacecraft makes it back to Venus. The Akatsuki was supposed to compliment the European Space Agency's Venus Express that launched in November 2005 and is still in use today.

Physical Characteristics: Venus is often called Earth’s twin because the planet is about 95% as big and 80% as dense. Given the similarities, it is thought that the composition of Venus is also similar to Earth. We know that Venus is a rocky planet and, with all the similarities to Earth, it's also likely to have a rocky mantle and metallic core. The weird part is that Venus does not generate its own magnetic field, and we're really not sure why. One theory suggests that since the planet rotates so slowly that there just isn't enough motion in the core to generate a strong magnetic field. The planet does have a weak magnetic field, though, thought to be caused by the interaction between solar wind and the planet's atmosphere.

Light from the Sun reflects off of the thick, white clouds and is what makes Venus so bright in our night sky. Although we cannot actually see beneath the thick clouds on Venus, radar images taken from spacecraft such as Magellan give us a picture perfect image of what the Venusian landscape really looks like. We are able to see many familiar geological features on our sister planet, including volcanoes, mountains, craters, highlands and plains.

Venus has plenty of large impact structures, but since the planet’s atmosphere is so corrosive, dense, and hot, the smaller meteors are destroyed before they reach the surface. Because of this the planet doesn’t have craters any smaller than about 2 kilometers in diameter.

Venus has more than 1,000 volcanoes on its surface that produce the longest lava flows in the Solar System, extending for hundreds of kilometers. The types of volcanoes on Venus include large and small shield volcanoes, coronas, arachnoids and novas.

There are two highland areas on Venus called Ishtar Terra and Aphrodite Terra. Ishtar Terra is a large highland region that’s about the size of Australia and is located in the north polar region of the planet. Aphrodite Terra is another highland region about the size of South America that is located in the equatorial region of Venus.

Six mountain ranges make up about 35 percent of the surface of Venus. The highest mountain massif on Venus, reaching more than 10 kilometers above the surrounding lowlands, is called Maxwell Montes and it is located within the Ishtar Terra region.

Above Image: This Magellan full-resolution image shows Maxwell Montes, and is centered at 65 degrees north latitude and 6 degrees east longitude. Maxwell is the highest mountain on Venus, rising almost 11 kilometers (6.8 miles) above mean planetary radius.

Image Credit: NASA/JPL

Venus has a very thick and toxic atmosphere made up mostly of carbon dioxide but has trace amounts of nitrogen, water vapor, argon, carbon monoxide, neon and sulfur dioxide. The thick atmosphere traps in heat which causes the temperatures on Venus to rise above 465C (870F). Venus’ atmosphere is about 1,323 pounds per square inch, making it about 90 times heavier than Earth’s atmosphere. To experience that kind of pressure here on Earth, one has to travel 1 kilometer underwater! Despite the slow orbit and slow and backwards rotation of the planet, with winds in the upper atmosphere reaching 360 kilometers per hour (224 miles per hour) the clouds rotate around the planet every four Earth days while the entire planet takes about 243 Earth days to complete a rotation, although we’re not sure why. It’s not surprising that nothing man made has survived on the planet for more than a few hours, but it’s not for the lack of trying.

Above Image: This Magellan image is centered about 3.2 degrees north latitude, 194.9 degrees longitude in the eastern Ovda region of Venus. The image, which is 90 km (56 miles) in width and 80 km (50 miles) in length, shows some small volcanic domes on the flank of the volcano Maat.

Image Credit: NASA/JPL

Above Image: The large circular structure near the center of the image is a corona, approximately 200 kilometers (120 miles) in diameter and provisionally named Aine Corona. Just north of Aine Corona is one of the flat-topped volcanic constructs known as 'pancake' domes for their shape and flap-jack appearance. This pancake dome is about 35 kilometers (21 miles) in diameter and is thought to have formed by the eruption of an extremely viscous lava. Another pancake dome is located inside the western parts of the annulus of the corona fractures. Complex fracture patterns like the one in the upper right of the image are often observed in association with coronae and various volcanic features. They are thought to form because magma beneath the surface follows pre-existing fracture patterns. When eruptions or other movements of the magma occur, the magma drains from the fractures and the overlying surface rock collapses. Other volcanic features associated with Aine Corona include a set of small domes, each less than 10 kilometers (6 miles) across, located along the southern portion of the annulus of fractures, and a smooth, flat region in the center of the corona, probably a relatively young lava flow. The range of volcanic features associated with coronae suggests that volcanism plays a significant role in their formation.

Image Credit: NASA/JPL

Above Image: Magellan radar image of Wheatley crater on Venus.

This 72 km diameter crater shows a radar bright ejecta pattern and a generally flat floor with some rough raised areas and faulting. The crater is located in Asteria Regio at 16.6N,267E.

Image Credit: NASA/JPL


by Dani Johnson

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