The Hubble Space Telescope image shows the dwarf planet Pluto with its largest moon, Charon.
The red hue of the dwarf planet Pluto is probably a graffiti work of his moons Nix and Hydra. The moons cause a shower of particles to fall on their mother planet, over which a frost layer of solid nitrogen flows on the surface. According to astronomer Alan Stern of the Lunar and Planetary Institute in Houston, this makes the dwarf planet reddish, while its three moons are dipped in dull gray. Since Pluto and his three moons Charon, Nix and Hydra are very far out in the solar system in the so-called Kuiper belt, they are only to be seen as extremely small points of light on pictures such as the Hubble Space Telescope. The Kuiper belt contains many 10, 000 pieces of rock with diameters of more than 100 kilometers? Pluto, with a diameter of 2, 300 kilometers, is one of the largest exponents. From the uniform gray, in which the moons are submerged, astronomers conclude that these satellites originated after a collision.

For the reddish color of the parent planet, Stern has now established an independent theory: The smaller particles of the Kuiper Belt constantly collide with the four heavenly bodies. But while the gravity of Pluto and the Charon, which is only half as big, holds the chunks knocked out, the smaller moons Nix and Hydra lose matter through the bombardment. This matter is reflected in Pluto and Charon.

According to Stern, there must be a layer of dust several centimeters thick on both celestial bodies from this graffiti spray. Covering with nitrogen ice causes Pluto's reddish color, Stern explains. Charon, on the other hand, who has a different composition of atmosphere and surface, remains gray. Ultimately, the color issue can only be clarified by the probe New Horizons of the American Space Agency NASA. This is scheduled to arrive in 2015 at Pluto and later investigate the Kuiper belt.

New Scientist, No. 2659, p. 16 ddp / science.de? Martin Schäfer advertisement

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