Pluto’s relegation to dwarf planet category led Mars on assuming the role of the smallest globe in the solar system. However, recent studies concerning the composition of the planet could bring Mars the impressive title of „Iron Planet”. The cooperation between scientists on the Messenger mission orbiting Mercury and the terrestrial-based ones led to discovering that the planet might have an iron core greater than anticipated. They also believe that part of Mercury’s core is still liquid and covered by frozen iron-rich mineral foam. They managed to learn all this without even touching the planet.
To identify the iron under an impressive number of kilometers of rock layer, scientits have watched its effects: both the satellite’s movement on the orbit and the movement of Mars itself. A team including the geodesist David Smith from Massachusetts Institute of Technology in Cambridge and another sixteen of his colleagues have studied Messenger’s orbital movements. They measured the variation of gravity around Mercury using the relative Doppler frequency changes of its wavelength. Gravity varies due to the unequal mass distribution inside the planet.
The way mass is distributed inside Mercury also influences the way this planet moves. Using a big-dish radar, changes of Mercury’s rotation axis propensity can be precisely measured from Earth. The same technology is able to detect and measure the subtle rotation speed variations caused by the solar tides.
Analyzing gravitational and orbital data makes it possible to obtain a very likely image of Mercury’s inside, which seems to be full of iron. Researchers assume that the core spans 2030 kilometers from the center of the planet, meaning 83% of the planetary radius, which is quite a lot knowing that Earth’s core occupies only 55% of the entire planet.
Information on Mercury’s mass distribution also suggest the existance of iron deposits in an unexpected place, as a layer around its core. Theory based on information gathered by Messenger on Mercury’s surface geochemistry and the chemical reactions specific for iron and its minerals shows that during formation of the planet, a combination of iron and sulfur led to the formation of the frozen layer around the core, with a thickness between a few tens of kilometers and 200 kilometers. This suggests that the planet’s rocky crust would be only about 200 kilometers thick.
David Stevenson of California Institute of Technology in Pasadena states that if all this data is correct, this is a major achievment. Thanks to the new information, scientists might find answers for a number of things they had troubles explaining so far, like why Mercury’s magnetic field is so weak. Now, they foresee a possible cause: planet’s liquid core generates a strong magnetic field, but the iron sulfide layer, which is electrically conductive, is partially covering and depleting it.
The Messenger team continues its study gathering even more data on Mercury’s gravity. They hope the new information would support the alleged existence of a scum layer inside the planet. Also, they use the gravity concerning data accumulated so far in order to verify the radar orbital data.