[ON THE PRESENCE OF RADIATE (ASTEROID) FORMATIONS IN SPOROTRICHOSIS].
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Water-rich carbonaceous chondrites contain evidence of aqueous alteration in the early solar system. To see this one must look carefully at the meteorites, and see past the later alteration which has generally obscured mineral textures. We suggest that these materials will dominate, be detectable, and be sampled on the surfaces of C-class asteroids, initially by the Hayabusa2 spacecraft. Thus, hydrous samples returned by this mission will help to reveal the source of water on earth.
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Gravitational interactions between planets and small bodies in the solar system can theoretically send asteroids and comets onto a collision course with Earth. This happens persistently in the fall of meteorites to Earth, though with masses that only rarely do any damage. The finding of craters on almost all solid bodies in the solar system when spacecraft image their surfaces brings home the fact that no planet is spared collisions. Asteroids larger than 50 m across collide with Earth, on average, once every 600 years.
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Most asteroids and comets are thought to be remnant collisional fragments of planetesimals, the building blocks from which planets in our solar system formed around 4.5 billion years ago. Asteroids and comets from diverse regions of the planetary disk probably enriched the early Earth and other planets in minerals, water, and organic materials. In later epochs, impacts of asteroids and comets on the Earth may have abruptly altered the course of evolution and paved the way for mankind. However, mankind should now be aware that this natural process has not ceased. In particular, the current population of so-called near-Earth asteroids contains many objects that are considered potentially hazardous. On the positive side, near-Earth asteroids may prove to be valuable sources of raw materials (metals, water, rocket propellant, etc.) for future generations. I will illustrate the significance of asteroids for life on Earth and describe recent results of astronomical research into relevant physical properties of these bodies. This research may help us to better understand how harmless asteroids become hazardous and how we can prevent a catastrophic impact on our planet.
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Most asteroids and comets are thought to be remnant collisional fragments of the building blocks from which planets in our solar system formed around 4.5 billion years ago. Asteroids and comets from diverse regions of the solar system probably enriched the early Earth and other planets in minerals, water, and organic materials essential for the development of life. In later epochs, impacts of asteroids and comets on the Earth may have abruptly altered the course of evolution and paved the way for mankind.
However, mankind should now be aware that this natural process has not ceased. In particular, the current population of so-called near-Earth asteroids contains many objects that are considered potentially hazardous. On the positive side, near-Earth asteroids may prove to be valuable sources of raw materials (metals, water, rocket propellant, etc.) for future generations. I will illustrate the significance of asteroids and comets for life on Earth and describe current research into the relevant characteristics of these bodies.
This research is helping us to better understand the risk of a devastating asteroid impact on our planet: that such an impact will occur one day is beyond question, unless we develop techniques to modify the orbits of hazardous asteroids.
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L'approche de la Terre et de Mars par des asteroides et des cometes au cours des 25 prochaines annees est detaillee
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