Okay, so the planets are basically formed the is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Then there is the other stuff; there was at this time a lot proto-planets, asteroids and comets, all in the spaces between the planets, most noticeably between Mars and Jupiter. Each of the planets, as they swept through their orbits, gathered some of them and knocked others out of the area. Planets with larger masses had larger effects than those with less mass. Jupiter, being the closest gas giant to the Sun, corralled numerous proto-planets and planetary scraps between its orbit and Mars. Neptune, being the last large mass planet from the Sun, corralled numerous proto-planets and comets on the outside of it's orbit. All the other planets also swept clean their orbits knocking some in or out of the solar system, or sent the debris into its own mass. This time was known as The Period of Intense Bombardment. Planets without atmospheres still bear the scars from this time. There was one other effect of the scattering, many of the planets captured proto-planets and debris as moons. Mars has two moons which are clearly asteroids and all of the gas giants have similar objects. The gas giants have numerous larger bodies about the size of our moon that are clearly proto-planets. And then there is our moon.
Our moon is a special case. We did not as much capture it as much as survive it. In 1969, people landed on the moon and gathered up some of the rocks and brought them back to Earth for analysis and what they discovered was very interesting. The composition of the materials was very similar to rock from this planet, identical in fact. Calculations of the mass of the Moon we knew that it had a almost no iron core. The question was, how did it form and where did it come from. The consensus of scientist's belief is that when much of the Earth was molten and only a skim of crust had formed, a secondary large planetoid hit the Earth. The collision hit with a lot of energy, but both bodies were mostly molten. The core of the planetoid joined our own, being mostly iron nickel, and its crust and our crust mixed together too, but the energy of the impact caused about a seventh of the combined mass to be knocked off the other side. By luck, and only luck the knocked off matter did not have sufficient energy to escape the gravity of the Earth but did have enough energy to make a stable orbit.
There were other large impacts, the face on the Moon is the result of major impacts after the Moon's crust had formed and Mercury had a giant impact that was so powerful that the shock waves from the impact through up mountains where the shockwaves converged. There must have been a massive impact on Venus, as the rotation is so slow and retrograde at that, something must have slowed it down. Most certainly the gas giants had massive impacts, but their size and composition prevents us from seeing any impact, but something must have pushed Uranus over on its side.
Comets impacted every planet as well. The water that came from these comets did different things on different planets. On Mercury, the water evaporated and was stripped from the planet. On Mars, the water existed for a time and then seems to have disappeared, probably froze below the surface after the planet ceased to be tectonically active, hundreds of millions of years ago. The effect of the addition of water to Venus and Earth had different effects at different times, because the Sun has changed over time.
About five billion years ago, the Sun was smaller and less intense, it was seventy percent of today's own size. Venus is seventy percent of the distance of Earth's orbit from the Sun. So, the water that fell on Venus, after the planet formed a surface, was probably liquid. As the Sun grew more intense and larger the water vaporized and then things got interesting. The hydrogen was stripped off the water and the oxygen combined with carbon making carbon dioxide and a very thick heavy atmosphere.
When the water came to the Earth, at first it remained as ice and later as the Sun grew hotter, it remained ice. It was only as tectonic processes began and some carbon dioxide was released and the ice melted. But it has always been tenuous for our planet, many times ice has threatened to overwhelm the planet, and not just in the past million years, but throughout its history.
Life in the solar system. We have discovered life on the earth in the hottest geysers, the deepest mines, buried deep in the rocks in fossil water, deep in the oceans beside volcanic vents, in short everywhere and in places we thought it should not exist. So we think the rule for life is, if it is possible to exist it will. It might exist on Mars, and it might exist on some other moons of Jupiter and Saturn.
No comments:
Post a Comment