The factors that set these planets on almost opposite paths began, most likely, in the swirling disk of gas and dust from which they were born. Somehow, 4. Several might well have moved in closer, or farther out, as the solar system formed.
If we could slice Venus and Earth in half, pole to pole, and place them side by side, they would look remarkably similar. Each planet has an iron core enveloped by a hot-rock mantle; the thinnest of skins forms a rocky, exterior crust. On both planets, this thin skin changes form and sometimes erupts into volcanoes in response to the ebb and flow of heat and pressure deep beneath.
Other possible similarities will require further investigation — and perhaps another visit to a planet that has hosted many Earth probes, both in orbit and briefly on the surface. Subduction is believed to be the first step in creating plate tectonics.
Magellan saw a land of extreme volcanism. The orbiter saw a relatively young surface, one recently reshaped in geologic terms , and chains of towering mountains.
The broiling surface of Venus has been a topic of heated discussion among planetary scientists. The traditional picture includes a catastrophic, planetwide resurfacing between and million years ago. In other words, Venus appears to have completely erased most traces of its early surface. The causes: volcanic and tectonic forces, which could include surface buckling and massive eruptions.
But newer estimates made with help from computer models paint a different portrait. While the same forces would be at work, resurfacing would be piecemeal over an extended time. The average age of surface features could be as young as million years, with some older surfaces mixed in.
Venus is a landscape of valleys and high mountains dotted with thousands of volcanoes. Its surface features — most named for both real and mythical women — include Ishtar Terra, a rocky, highland area around the size of Australia near the north pole, and an even larger, South-America-sized region called Aphrodite Terra that stretches across the equator.
One mountain reaches 36, feet 11 kilometers , higher than Mt. Notably, except for Earth, Venus has by far the fewest impact craters of any rocky planet, revealing a young surface. Or stroll through a deep canyon, Diana, named for the Roman goddess of the hunt. Tesserae, terrain with intricate patterns of ridges and grooves that suggest the scorching temperatures make rock behave in some ways more like peanut butter beneath a thin and strong chocolate layer on Venus.
The Soviet Union landed 10 probes on the surface of Venus, but even among the few that functioned after landing, the successes were short-lived — the longest survivor lasted two hours; the shortest, 23 minutes.
Photos snapped before the landers fried show a barren, dim, and rocky landscape, and a sky that is likely some shade of sulfur yellow. With the hottest surface in the solar system, apart from the Sun itself, Venus is hotter even than the innermost planet, charbroiled Mercury. Venus is similar in size to Earth. Earth is just a little bit bigger. Venus is unusual because it spins the opposite direction of Earth and most other planets.
And its rotation is very slow. It takes about Earth days to spin around just once. Because it's so close to the Sun, a year goes by fast. It takes Earth days for Venus to go all the way around the Sun. All other planets spin anti-clockwise on their axis and orbit the Sun in an anti-clockwise direction. Venus also orbits the Sun anti-clockwise, but its unusual axis rotation is due to being upside down - it was knocked off its upright position earlier in its history! Astronomers believe that at some point, a colliding celestial body tilted Venus so far off its original position that it is now upside down.
The only other planet to spin in a weird direction is Uranus which spins on its side, probably the result of another collision early on in its life. It is thought that Venus was named after the beautiful Roman goddess counterpart to the Greek Aphrodite due to its bright, shining appearance in the sky. Of the five planets known to ancient astronomers, it would have been the brightest. Because Venus is easy to spot with the naked eye, it is impossible to say who discovered the planet.
The cause of this retrograde rotation is still poorly understood. The most likely explanation if a giant collision with another large body during the planet formation phase. The venusian atmosphere could also have played a role: heated by solar radiation, it would thicken; the tidal forces acting on Venus could then have slowed its rotation to the point of stopping the planet and even make it turn in the other direction.
This slow retrograde rotation is the origin of the solar day being shorter than the sidereal day. The latter are longer for planets characterized by anterograde rotation. The Earth, for example, has a solar day average of 24 hours and a sidereal day of 23h 56min 4. On Venus the solar day is a little less than half of the sidereal day i. This means a little more than 2 complete solar days in one sidereal day!
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