525 asteroids astrobiology astronomy astrophysics climatechange climaticchanges collisionswithearth comets effectsofradiation/radiationprotection environmentalprotection exobiology extraterrestrialphysics hazardmitigation history impactcraters internationalcooperation lifeonotherplanets near-earthasteroids near-earthobjects origin physics planetaryscience planetology research sci055000 science spacesciences