The craters on the surface of Mercury have already been named with the help of the Mariner 10 spacecraft's imagery. Picture: Nasa
The Mercury planet has a shell that changes dynamically. This is shown by measurements of the spacecraft Messenger. A sensor aboard the probe found not only charged particles of the elements sodium, silicon and sulfur in the areas around the planet, but also charged simple molecules whose concentration is constantly changing. These charged particles are created by interaction of the outer layers of the Earth-like planet with the solar wind? that flow of particles flowing from the sun into space. A probe aboard the spacecraft Messenger examined the composition of the so-called magnetosphere, the outermost shield of Mercury, which protects the planet at least partially from the radiation of the solar wind. The probe uses a fast-imaging plasma spectrometer, which measures the elemental composition of the magnetosphere by measuring light. It's almost like a forensic analysis, says Thomas Zurbuchen, head of the spectrometer project. In addition to the simple charged particles, the scientists also found smaller molecules such as water and hydrogen sulfide.

The amount of sodium, silicon, and oxygen ions measured in the magnetosphere of Mercury is very high. The ions could either have been blown directly by the solar winds from the planet's surface or at least come from the exosphere, the outermost layer of the atmosphere, the researchers suspect. Another peculiarity are the changing with the day and night concentrations of ions, which are likely to be due to the interaction of the magnetic field with the solar wind, the scientists report.

Because of its close proximity to the Sun, Mercury is difficult to study from both the earth and probes. In January 2008, the spacecraft Messenger reached the sun's closest planet of the solar system. Messenger is only the second probe to visit Mercury after the Mariner 10 spacecraft 33 years ago. Mercury's internal magnetic field was discovered during the first exploration, and scientists have been speculating about the interaction of the solar wind with the magnetosphere and the surface of Mercury ever since.

When analyzing the Messenger data, scientists from various research teams also discovered that volcanic activity has shaped the planet much more than previously thought. Thus, researchers discovered surface formations that point to volcanoes, lava flows and strong volcanic eruptions. display

Thomas Zurbuchen (University of Michigan at Ann Arbor) et al .: Science, Vol. 321, p. 90 ddp / science.de? Uwe Thomanek

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