At the last meeting of the American astronomical society in anchorage (USA) astronomer Sean Solomon of the Carnegie institution of Washington revealed a number of observations of interplanetary automatic station Mercury MESSENGER, 2011 revolving around the nearest planet to the Sun.
MESSENGER quickly discovered in the polar craters of mercury are many places likely location of water ice. ( illustration NASA.)

It seems that several traditional theories about mercury will have to be rejected, and others to review.

Station Mercury MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging, "Mercurial surface, space environment, Geochemistry and measurement of distances, as we all remember, last year after a seven-year journey started rotating in a circular orbit around mercury, began its intensive study. In a relatively short time machine could strongly to puzzle astronomers. Its data seriously conflict with existing models of education are close to the Sun barren planet, so rich in iron and such a poor light elements.

Let's remind, now there are two. First: once mercury had normal composition with a smaller number of metals and abundance of light elements. The mass of the planet was approximately 2.25 times more than at present. Then mercury experienced a collision with planetesimal, approximately six times easier him and moving with the speed of 20 km/S. Most of the crust and upper layer of the mantle was carried into space, the core of the planet, consisting of heavier elements have been preserved.

Option two: mercury formed in already extremely depleted by light elements, inner part of the protoplanetary disk, because the light elements were driven by solar radiation in the outer region of the Solar system.

Alas, both hypotheses are now under suspicion.

First, geochemically mercury have been very diverse. The theory of dense planet with a large iron core and a lower content of light elements needs some revision. Yes, despite its small size, gravity on the surface is equal to Mars. And yet light elements are there. The polar regions MESSENGER found extremely bright (in the sense of reflection of the radar signals) region. Apparently, this water ice is not melting because of eternal shadows of poles (the inclination of the orbit of the mercury is several times smaller than the earth).

Second, mercury was the rich history of volcanism, because its surface is strewn with thick layers relatively smooth lava. Compared to the moon and even Mars surface is very smooth: as a rule, these vast plains with a height difference in a few kilometers. The hypothesis of the planet-engine just does not fit in with this: for volcanic activity need a full mantle and the crust. MESSENGER also found subsurface concentration of material bodies - presumably, asteroids, buried under layers of lava.

Mercury freaked "pockmarks" - bright small lows (depression) unclear nature. On the same moon is nothing like that. It looks like the surface of the planet - and recently - had large, locally concentrated masses very volatile substances, which later disappeared. Under the influence of what? If the Sun, why don't they vanished before? According to modern theories, mercury always here was," that is formed near the Sun. However, in the XIX century there was a theory that mercury in the past was a satellite of Venus, which it subsequently "lost". A century were carried out calculations have demonstrated that this hypothesis explains well the big lengthening (eccentricity) the orbit of mercury and its resonant character of revolution around the Sun, and the loss of torque as mercury and Venus, and the recent acquisition of an abnormal rotation, opposite to the principal in the Solar system.

In addition, on the basis of the available data was made this conclusion: the rocky crust of the planet has three layers. First, in the mantle, are iron sulfides, then fayalite, surrounding itself iron core. These layers are not mixed together. Furthermore, on the surface by the method of x-ray fluorescence spectrometry was found abundance of radioactive potassium-40 in comparison with radioactive isotopes of thorium-232 and uranium-238. However, uranium and thorium much more refractory, and if their concentration is low on the background of relatively volatile potassium, no heating of the surface in a collision with a large planetesimal say no: potassium would be very little, and uranium and thorium many more.

Such structure of the subsurface layers and composition of the surface have nothing common with the theory of formation of mercury near the Sun immediately without light elements, or loss of crust and mantle as a result of collision with a large celestial body. Because then no clear, unmixed layers just could not be. The only thing that can explain such a structure, and "pockmarks", - the formation of the planet in cooler conditions.

Some (not quite as big as it was considered) the deficit of light elements on the surface caused rather, their evaporation as heat the sun. Nevertheless, astronomers far from returning to the idea of migration of mercury to the Sun, according to new estimates, up to the full "resorption" protoplanetary disk even close to a star on the planet may be a large number of light elements, which does not evaporate "protection" of gas, the scattering of the radiation of a nearby star. Well, after this security has disappeared, light elements evaporated.

More complex is the hypothetical "polar cap" (more precisely, the ice in the polar regions), reflected on the radar as a bright spot. These data come from 1990-ies, when astronomers first recorded reflected radiation radars from local Subpolar region. It was believed that this material comets, preserved almost miraculously, when part of such material fell into deep craters at the poles.

According to the observations MESSENGER, this reflects radio waves material is present not just in craters, and strictly in their day, which never rays of Sun. While such "aquifer" craters were many of them - more than expected.

Finally, new data on mercury cause another, more General question: if we can so wrong with the origin and chemical diversity of the surface of terrestrial planets in our own Solar system, how much our incomplete understanding of exoplanets orbiting other suns?

Other fresh views on the internal structure of mercury can be read here.

Based on the materials Discovery News.