Mercury and Venus

MERCURY AND VENUS, THE RED-HOT PLANETS

Mercury and Venus travel along orbits that are internal with respect to the orbit of the Earth. For such reason they always appear near to the Sun, some times before dawn, some times after sunset. They both show the phenomenon of phases when observed with a telescope because, according to the position of the planet on the orbit, different fractions of the illuminated disc face the Earth.
Mercury is the nearest planet to the Sun, its distance being 58 million km. It rotates on its own axis very slowly, in fact, a full rotation takes approximately 58 terrestrial days, that is 2/3 of the orbital period. Such interesting "dynamic resonance" was discovered by Prof. Giuseppe Colombo of the University of Padua. The surface temperature ranges from +350 to -270 degrees. Its size is less than one third of that of the Earth, its radius being 2,400 km, and it has no atmosphere. Its surface appears to be completely covered with craters produced by meteorites.

Venus is the second planet of the Solar System, and the most similar to the Earth as far as size and density. But how different are its superficial conditions! A very dense atmosphere of carbon dioxide wraps the planet, creating a pressure that is 90 times that of our atmosphere. The continuous presence of clouds does not allow us to see the rocky surface but, by reflecting the light of the sun, makes of Venus the most luminous object after the Sun and the Moon. Nevertheless these clouds are not made of little drops of water, but of sulphuric acid that produces corrosive rain, while the green house effect generated by the carbon dioxide raises the superficial temperature up to approximately 500 degrees, thus rendering such world absolutely hostile.

Mariner 10. The probe was launched in 1973 for the study of Mercury and Venus, the inner planets of the Solar System. (JPEG, 261 K)
(NASA-JPL)

Mosaic of pictures taken in 1974 by Mariner 10. The surface of the planet is covered with craters generated by the impact of meteorites, and resembles that of the Moon. (JPEG, 58 K)
(NASA-JPL).

The Magellan Mission, dedicated to the mapping of the surface of Venus by using a radar, gave us a spectacular vision of its rocky structures, when it penetrated the thick clouds of the planet. The artistic image shows the probe which reached Venus in 1990, at the minimum distance of 294 km. (JPEG, 124 K)
(NASA-JPL)

Image taken by the approaching Mariner 10, in 1974. (JPEG, 233 K)
(NASA-JPL)

The night face of Venus photographed in the infrared by the Galileo probe in 1990. (JPEG, 187 K)
(NASA-JPL)

The clouds of sulphuric acid conceal the volcanic surface of Venus in this picture taken by Hubble Space Telescope. (JPEG, 225 K)

These radar pictures, taken by the Magellan probe, show in fake colours how our eye would see the surface of the planet. Here are the regions of the Danu mountains (1,500 m) and of Mount Maat. (JPEG, 520 K)
(NASA-JPL)

Detail of the Sacajawea volcano on Venus (base of 120x215 km) in fake colours. (JPEG, 293 K)
(NASA-JPL)

The Aurelia crater, generated by the impact of a large meteorite, has a diameter 31.9 km long. The picture was taken by the Magellan probe. (JPEG, 356 K)
(NASA-JPL)

The whole disc of the planet Venus seen through the layer of clouds by the Magellan probe. (JPEG, 395 K)
(NASA-JPL)

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