Venus Due to similarities in size, mass, and composition, Venus is often referred to as Earth's sister planet Modern measurements and probes that have visited the planet have revealed one of the most uninhabitable places in the Solar System Venus Properties Semimajor Axis Orbital Eccentricity Orbital Period Rotation Period Mass Radius Average Density Surface Gravity Surface Temperature Atmosphere 0.72 A.U. 0.007 224.7 days -243.0 days 4.87 x 10 24 kg 6052 km 5.24 g/cm 3 8.87 m/s 2 730 K 96.5% CO 2 0.82 x Earth 0.95 x Earth 0.95 x Earth 0.91 x Earth ~300 K for Earth Interior of Venus It is assumed that the interior is much like that of Earth, with a molten iron core surrounded by a mantle and crust Evidence of past (and possibly recent) volcanic activity on the surface suggests much of the interior is still molten 1
The surface of Venus was a mystery due to the thick cloud layers surrounding the planet Surface of Venus Remember that these images are not true color, but they do show many surface features Surface of Venus The maps below show a topographical representation of Venus and Earth on essentially the same scale Note that there are two main elevated bodies on Venus (Ishtar Terra and Aphrodite Terra) Surface of Venus 2
Almost all the features on the surface point toward very intense volcanic activity in the past Surface Features Most volcanoes are shield volcanoes, formed by a hot spot in the crust (like Hawaii) Lava Domes In areas of high volcanic activity, large circular formations called coronae are formed Surface Features These are formed when a large bubble of lava rises to the surface, forms a thin shell, then collapses once the lava recedes Surface Features Cracks in the surface provide locations for lava to emerge and form the smooth surroundings plains 3
Surface Features There are relatively few impact craters on the surface of Venus, compared to the Moon or Mercury Two reasons Volcanic activity leads to a rejuvenation of the surface over time The thick atmosphere caused much of the smaller meteors to disintegrate or break up before impact 'Flying' Over Venus Movie Views from the Surface Multiple Soviet missions landed on the surface (Venera) Probes could only transmit for ~1 hour before electronics melted 4
The Atmosphere of Venus The atmosphere of Venus contains about 90 times more mass than that of Earth The pressure at the surface is equivalent to the pressure at ~1 km below the ocean surface on Earth The cloud layers that surround Venus are comprised mainly of sulfuric acid The Atmosphere of Venus The majority of Venus' atmosphere is made up of carbon dioxide Due to their similarities, the Earth and Venus should have begun their lives with very similar atmospheres What happened to make Venus so different today? _ Venus in UV light Runaway Greenhouse Effect The thick clouds of Venus reflect some visible light, and let some through Of the visible light that reaches the surface, some is reflected, some is absorbed As the surface heats up, it reradiates the light, this time in the infrared Visible light from Sun Visible light reflected into space Infrared light trapped This energy is now trapped in the atmosphere of Venus 5
Why Not Earth? Venus and Earth began their lives with the same basic conditions The cooler conditions on Earth led to many of the initial greenhouse gases to become trapped in rock Venus' greenhouse gases remained in the atmosphere and created the conditions we see today Venus is by far the brightest planet in the sky, and is about 10 times brighter than the brightest star Observing Venus Like Mercury, it will always be close to the Sun, giving it the improper name Morning or Evening Star The Odd Rotation of Venus Remember that Venus undergoes retrograde rotation, opposite the direction of its revolution around the Sun Since Venus is rotating in the opposite direction, its solar day is actually quite shorter than the sidereal day 6
Visiting Venus Some of these missions were fly-bys, some entered orbit, and some landed on the surface The majority of the missions were performed by the Soviet Union's Venera craft The latest mission launched by the ESA, the Venus Express, entered orbit in April, 2006 UV Light Approach of Venus Express 7