approximately 1/6 that mass and several hundred kilometers across. The impact would have stripped away much of the original crust and mantle, leaving the core behind as a relatively major component. A similar process, known as the giant impact hypothesis, has been proposed to explain the formation of the Moon. Alternatively, Mercury may have formed from the nebula before the Sun's energy output had stabilized. The planet would initially have had twice its present mass, but as the protosun contracted, temperatures near Mercury could have been between 2,500 and 3,500 K and possibly even as high as 10,000. Much of Mercury's surface rock could have been vaporized at such temperatures, forming an atmosphere of "rock vapour" that could have been carried away by the solar wind. A third hypothesis proposes that the solar nebula caused drag on the particles from which Mercury was accreting, which meant that lighter particles were lost from the accreting material and not gathered by Mercury. Each hypothesis predicts a different surface composition, and two upcoming space missions, MESSENGER and BepiColombo, both will make observations to test them. MESSENGER has found higher-than-expected potassium and sulphur levels on the surface, suggesting that the giant impact hypothesis and vaporization of the crust and mantle did not occur because potassium and sulphur would have been driven off by the extreme heat of these events. The findings would seem to favour the third hypothesis, however further analysis of the data is needed.
approximately 1/6 that mass and several hundred kilometers across. The impact would have stripped away much of the original crust and mantle, leaving the core behind as a relatively major component. A similar process, known as the giant impact hypothesis, has been proposed to explain the formation of the Moon. Alternatively, Mercury may have formed from the nebula before the Sun's energy output had stabilized. The planet would initially have had twice its present mass, but as the protosun contracted, temperatures near Mercury could have been between 2,500 and 3,500 K and possibly even as high as 10,000. Much of Mercury's surface rock could have been vaporized at such temperatures, forming an atmosphere of "rock vapour" that could have been carried away by the solar wind. A third hypothesis proposes that the solar nebula caused drag on the particles from which Mercury was accreting, which meant that lighter particles were lost from the accreting material and not gathered by Mercury. Each hypothesis predicts a different surface composition, and two upcoming space missions, MESSENGER and BepiColombo, both will make observations to test them. MESSENGER has found higher-than-expected potassium and sulphur levels on the surface, suggesting that the giant impact hypothesis and vaporization of the crust and mantle did not occur because potassium and sulphur would have been driven off by the extreme heat of these events. The findings would seem to favour the third hypothesis, however further analysis of the data is needed.
Terrestrial.docx