Interplanetary expedition is a long, costly and risky. And so attempts to organize a round-trip airfare and does can be counted on the fingers of one hand. In fact, lunar soil and to this day remains the only example of a large-scale delivery to Earth extraterrestrial matter.

Specifically, it is the only example of a controlled delivery. In unmanaged mode extraterrestrial substance falls to the Ground almost continuously. For the most part this small dust, but sometimes large samples. In fact, the meteorite is a sample of interplanetary matter, which itself is flying in hand, requires no additional cost.

What is cheap is not always good. To bring to the Earth the lunar soil, it took some effort, but we are not only sure that it lunar soil, but even know exactly where the moon of sample collection. In the case of meteorites we only know what we are dealing with extraterrestrial substance. Its source can be judged only on circumstantial evidence. Sometimes it is possible to restore the orbital parameters of the meteorite to hit the Earth. But the way small bodies in the Solar system change over time, so that, even after knowing which path meteorite flew immediately before the collision, we are unlikely to follow her up to the place of birth of this cosmic body.

The size of meteorites (luckily for us) are small, therefore, it would seem logical to assume that they are related to one or another of the interplanetary detail. However, the composition and structural properties of some meteorites show that in the past they were part of the larger phone On this particular founded one of the options classification of meteorites that divide them into undifferentiated and differentiated.

The first is the meteorites that nothing happened since the formation of the Solar system, or at least, since the formation of the major planets, the notorious "debris", unaffected or hardly affected by subsequent events. The latter allegedly visited part of the whole, had time to get into an iron core and rocky shell (the mantle). Among differentiated meteorites have and iron (the remains of the core)and stone (the remnants of the mantle), and iron-stone (intermediate area). Differentiated bodies in the Solar system, not that much, but they are: the planets, their satellites, large asteroids.

Initially as a source of differentiated meteorites were considered only asteroids (except legends about the Phaeton): it is clear that to shatter on samples easier it is a little body. However, in 1970th years the hypothesis about the origin of the asteroid gradually came into conflict with properties "clan" differentiated meteorites, which includes shergottite, nality and chassignet (group of meteorites is often called a typical representative, and his name, in turn, is based on the name of the city, nearest to the place of falling or findings). On the first letters of the names they are called SNC meteorites.

The commonality of chemical and isotopic composition SNC meteorites indicates that they come from the same source. Moreover, the SNC meteorites are different from other basalt meteorites to the relative youth: the first evaluation indicated that their age does not exceed 1.3 billion years now there has been some variation, but the essence has not changed). It is hard to imagine that igneous rocks could be formed on the asteroid ever, except for the first hundred million years of their existence. We have to assume that the source SNC meteorites is not an asteroid, and some of the larger body.

Large bodies from basalt volcanism in the Solar system, not so much. Mercury malmasion, so throw away his substance simple. But for delivery of this substance on Earth will have to overcome not the attraction of mercury, and the attraction of the Sun, what is more difficult. Venus massive and shrouded in dense atmosphere; it is unlikely that it could fly. The same problems are also connected with the potential emission of substances into space from the surface of the Earth. The moon (and mercury) can be discarded chemical composition.

In General, as said Sherlock Holmes, when you drop all impossible ways, faithful have to be considered as the only remaining, no matter how unbelievable it may seem. So if at the end of 1970-ies in articles about SNC meteorites their source was called simply "parent body", then by the beginning of 1980-ies to the parent body were increasingly added "probably Mars".

The key moment was the article Donald Bogarda and Pratt Johnson, published in the journal Science in 1983. They explored gas bubbles in shergottite EETA79001 found in Antarctica, hoping to clarify the age of meteorite, and simultaneously measured relative abundance of isotopes of argon, and xenon. (By the way, encased in the meteorite atmosphere parent body - another argument against asteroids.) It turned out that these relations: 1) within the errors are consistent with the contents of the noble gas isotopes in the atmosphere of Mars; 2) do not agree with their content anywhere else in the Solar system.

It would seem that all the arguments indicate the only possible source. However, the idea of Martian origin SNC meteorites long fought their way. The article itself of Bogarda and Johnson's edition of Science, even after receiving positive feedback from reviewers, was released four months. Reasons were at least two. First, it is unclear was how to dispose of the substance from Mars, and not just thrown away, but disposed in a relatively intact condition. Secondly, if possible release of a substance from Mars, why on Earth there meteorite from the moon? The first lunar meteorite was found in the same 1983, so that the second objection has been shot. But with the first objection, it was not so simple.

The principal explanation offered in 1984 JC melos: according to his "models spallation", the falling of a large meteorite on Mars (or to the moon) a minor part of the agents are able to acquire the speed is higher escape velocity, not suffered significant damage. However, at that time was considered preferable two-stage delivery" substances from Mars to Earth: first from Mars released a fragment of a diameter of a few tens of meters, and then it breaks up into small pieces in a collision with another asteroid. And fall to the Ground already these secondary (or tertiary) fragments.

To get from Mars twenty-meter-high rock, on the planet fall big asteroid, leaving a crater with a diameter of tens of kilometers. The dispersion properties of shergottites shows that they spawned several collisions. So often over the last billion years large asteroids to Mars fell. However, in 2002, James head, JC Melosh and Boris Ivanov has published a model in which future SNC meteorites are ejected from Mars in "finish" form, without further fragmentation. In this case, the emissions are possible and at the formation of a crater with a diameter of only a few kilometers. To achieve agreement with statistics craters allow other options, such as model almost tangent collision proposed in 2004 by Natallya Artemieva and Boris Ivanov.

There is other evidence. For example, some of the fragments that have not reached escape velocity, should fall on the surface of Mars. Such separately lying cobble - Bounce Rock - caught in the path of the Mars Rover Opportunity. A detailed analysis showed that the structure and chemical composition the cobblestone very similar to shergottite.

Summing up, one can say that on the Martian origin SNC meteorites (and joined them meteorite ALH84001) indicate several independent evidence: age, structure, chemical and isotopic composition. And isotopic composition is not only unique, but not chronologically the first sign. The precise answer to the question of how the SNC meteorites came from Mars to Earth for a long time will not be received. However, imagine that in a forest near Pervouralsk you met marsupial animal from protruding ears, elongated muzzle powerful hind legs and a long tail moving jumps. Will you laugh at the suggestion that this is a kangaroo, just because kangaroo could not get to Pervouralsk from Australia?