Venus was once a mystery until cloud-penetrating radar in 1961 revealed its hot surface of 425C, crushing speculation about life. The surface is very flat, with the highest point being the Maxwell Montes, and about 10% of the planet’s surface consists of two main “continents” called plateaus. Venus has about 900 impact craters, and other features include volcanoes that may be active and mysterious structures called arachnoids.
The planet Venus, covered in a thick carbon dioxide-nitrogen atmosphere containing reflective clouds of high-altitude sulfuric acid, was extremely mysterious to astronomers until very recently in history. Before the survey of Venus with cloud-penetrating radar in 1961, astronomers knew absolutely nothing about its surface. Some writers have speculated that beneath its clouds is a warm tropical world.
They were right about the hot part. Microwave and infrared radiometers mounted on Mariner 2, a space probe that made a flyby of Venus in 1962, revealed that the surface was incredibly hot — 425C (797F), hot enough to melt lead. This crushed all speculation about life to the surface. On the plus side, the cloud tops of Venus were found to be relatively cold, comparable to temperatures on Earth. The pressure at the surface was found to be about 92 times greater than at sea level on Earth, similar to the pressure 1 km (0.62 mi) below the ocean.
Throughout the 1970s and 1980s, intensive surveys of Venus were conducted, using both ground-based radars and space probes. Ground-based radar only reveals surface features larger than about 5 km (3 mi), so further investigation requires probes.
The surface of Venus was found to be very flat, due to the enormous weight of its atmosphere and the lack of tectonic activity. The highest mountain range is the Maxwell Montes, which have their highest point 12 km (7.4 mi) above the surface. Because of this altitude, Maxwell Montes is the coolest and least pressurized place on the surface of Venus, but it would still kill any human in seconds. The distance between the highest and lowest point on Venus is only 13 kilometers (8.1 mi), while on Earth the difference is about 20 kilometers (12.4 mi). 51% of the Venusian surface is within 500 meters (1640 feet) of the planet’s median radius (Venus’ equivalent of “sea level”).
About 10% of the planet’s surface consists of two main “continents” called plateaus. These include Aphrodite Terra, the size of Africa, and Ishtar Terra, which contains the Maxwell Montes. Along with these plateaus, there are several major insurgencies created by volcanic action, including Beta Regio, Phoebe Regio, Themis Regio, Alpha Regio, Eistla Regio, Bell Regio, and Tholus Regio. The largest of these volcanoes was discovered in the first radar surveys of the early 1960s.
Venus has about 900 impact craters, almost all larger than 30 kilometers (18 miles) in diameter. The reason is because smaller asteroids burn up in the thick atmosphere before they can hit the surface. If an asteroid has the momentum to pass through the atmosphere, it is certain to leave a large crater. Some well known craters include Danilova, Aglaonice and Saskja. All were given names, generally after female figures from history and mythology.
Other features on Venus include volcanoes that may be active, as well as mysterious structures called arachnoids found nowhere else. Arachnoids consist of concentric ovals surrounded by a complex network of fractures and can be up to 200 km (124 mi) in diameter. They may have a volcanic origin or be formed through some other process.
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