The vast majority of detected still space objects are rocky asteroids. Comets and asteroids that pose a threat to Earth, are under scrutiny, thanks to the International Observation Program Spaceguard.
However, astronomers from the UK claim that many comets may remain undetected. Under certain circumstances, it may be that these dark, dormant comets may become invisible and deadly threat to Earth.
Scientists have suggested that periodic crossing of the galactic plane of the solar system pushes a comet in our direction. And it seems that these periodic comet rains correspond with the dates of occurrence of the ancient craters found on Earth. This implies that most of the space object crashed into our planet in the past, were comets, not asteroids.
British astronomers have warned that some of these comets may still be worn around the solar system. At the current rate the appearance of bright comets in the solar system, there should be about 3000. To date, only 25 of them are known. Perhaps we just do not see them simply because they are too dark.
Such dark comets - not a new phenomenon. Comet darkens when reflecting light water ice evaporates, leaving behind an organic crust that reflects very little light.
For example, in 1983 the comet IRAS-Araki-Alcock (IRAS-Araki-Alcock) flew past Earth at a distance of five million kilometers, which is the closest distance that the approaching any known comet for 200 years. It was noticed only two weeks before the approach to Earth at the smallest distance. Only 1 percent of the surface has been active with the rest of it covered with very dark spots that do not reflect light.
However, some scientists are skeptical about the discovery by British scientists. They believe that these dark comets have good absorb sunlight and, therefore, they can be found on the radiated heat. Hot news, science and technology, the only first-hand.