A Cosmic Hail Of Bullets

During the lunar Eclipse a few days ago, a meteorite hit, apparently. Researchers have now determined how frequently the bombardment from space, the earth and the moon.

How often big meteorites hit the earth? However, rather rare, at least in the span of a human in terms of life. But if you look at the moon, is clear: in the long term, collisions with smaller celestial bodies that can be by no means uncommon. The visible proof of this is the lunar Eclipse that was visible in the night on Monday in many Parts of the Americas, and Europe. While many eyes and telescopes were focused on the blood-red lit moon, flashed it on the surface for a moment white. Meanwhile, many astronomers are sure that it has traded in the flash of light, the impact of a meteorite - the first observed impact during a lunar Eclipse.

How intense the bombardment is so? American and canadian researchers believe to have found out that the cosmic fire is nearly 300 million years, are suddenly more common. They conclude in the scientific journal Science from the study of impact craters on the moon and the earth. In the professional world, this statement raises, however, is in dispute.

the study is based on a team Sara Mazrouei, of the University of Toronto is craters a new method for the determination of the age of Impact on the moon. There, every couple of days, chunks of rock the size of a washing machine on the surface to bounce on, and much more in addition, so-called micro-meteorites, not larger than roll split. The chunks hit the earth during the Eclipse of the moon, could be about the size of a football. Together with the radiation of the solar wind, this duration of irrigation grinds the lunar soil. This cools in the night phase faster than large blocks of Rock, as the Sand on beaches on earth, the heat capacity of the "moon dust" is lower than that of solid Rock.

300 million years Ago, the impact rate has more than doubled

The impact of an asteroid on the swirls, however, larger chunks of rock from the subsurface, which can be deposited on the crater, and only with time grind. As a result, the coarse-grained edge saves a young crater in the heat better than the outline of the older crater. By Mazroueis Team investigated the heat capacity of the lunar dust in the surroundings of the impact points, were able to connect the researchers to the age of the weft tracks. By using infrared cameras on Board Nasa's space probe "Lunar reconnaissance Orbiter" measured them 111 craters on the moon. The age of nine, this Impact was known, since Apollo had brought astronauts and rock samples to earth. As a result, the researchers Mazrouei were able to calculate the age of the rest of the crater. They conclude that the frequency of strikes about 290 million years ago, has risen to two and a half times the previous Rate. A possible explanation would be that at that time a large Asteroid in the solar system was shattered, its fragments landed in the consequence more on the moon and the earth.

The geophysicist and erosion expert Stefan Hergarten, University of Freiburg holds the hypothesis of a jump increase in the impact rate will be liable, however, for a "house of cards". He has examined the original data from the study, and doubts due to the low number of craters of known age, that such a far-reaching conclusion. May be the age of the rest of the weft is set incorrectly determined. "I have a strong suspicion that the described effect disappears, should be the relationship between the age of the crater and the heat capacity is a little different than accepted," says Hergarten.

Because of the distance between the earth and the moon on astronomical scales is low, have been exposed to both celestial body about the same "bombardment" by asteroids. Therefore, the impacts of history on the moon to draw conclusions on the Situation on the earth. It would have to have been here a jump. To examine this directly, examined Mazrouei and gentlemen, the age of impact holes on the earth. This is already tried and tested methods have been used, especially on the radioactive properties of the rock. The result will be the same as for the craters of the moon, it says in the study: The data were easiest to explain if one assumes that the Rate of strikes has increased about 290 million years.

On earth, there is hardly any crater older than 650 million years

the comparison of The number of impact craters on the earth and the moon, however, is complicated. On earth, most craters have disappeared due to Erosion. This effect, however, believes Stefan Hergarten, was included in the original study too little, since an extremely low erosion rate would be adopted. With colleagues from the University of Freiburg, he comes to the conclusion that the terrestrial crater without a jump increase in the impact rate are explained. That there is less of the old crater, lying, therefore, not due to the fact that less asteroids have reached earth, but the traces of which have disappeared with time. This was in line with the previously established doctrine.

another finding of the new study, is a mystery: On the earth there are almost no craters that are older than 650 million years. This is explained neither by Erosion nor by a Change in the impact rate. The authors Mazrouei speculate that the traces of the time were destroyed in front of almost complete glaciation of the earth. This assumption is known as the snow ball earth hypothesis is known. Also, it is allerdungs among geologists controversial.