Cosmic rays are fast-moving elementary particles, such as protons, electrons and atomic nuclei, that strike the Earth from outer space. They travel almost at the speed of light. Scientists believe they originate from supernovas, black holes and quasars.Know More
The Earth's atmosphere provides protection from cosmic rays. With no atmosphere, these particles would pass through humans and damage their DNA.
Prolonged exposure leads to radiation poisoning and development of medical conditions such as cancer, brain damage and cataracts. During long space missions, like a manned mission to Mars, it is still necessary to find a way to shield travelers from the adverse effects of cosmic rays.Learn more about Comets & Asteroids
As of 2014, the last four "great comets" that were visible from Earth are Comet Hyakutake (1996), Comet Hale-Bopp (1997), Comet McNaught (2007) and Comet LoveJoy (2011). These and other great comets have been seen only once, except for the periodic Halley's Comet, which was last seen in 1986.Full Answer >
Halley's comet takes 76 years to pass by Earth. This comet is an example of a short-period comet, one whose orbit is influenced by the gravities of the outer planets of the solar system and so usually stays within the area of the planets.Full Answer >
Meteors from Mars arrive on Earth as the result of impacts on the planet by other bodies, which launch material out into space. Some of this debris is pulled in by the gravity of the Earth, falling as Martian meteorites.Full Answer >
The term "doomsday asteroid" is usually applied to an asteroid that, if it impacted Earth, would cause sufficient destruction to significantly disrupt the balance of life and possibly cause major extinctions. Such an asteroid would have to have an orbit that intersects the path of the Earth.Full Answer >