Asteroids are often battered and bruised, mere piles of rubble held together by gravity. Asteroid 21 Lutetia, however, seems to have sailed serenely above the fraya pristine block of rock that has remained nearly untouched since the solar system's birth.The European Space Agency's Rosetta probe zipped past Lutetia in July 2010 on its way to a comet. Rosetta's measurements suggest the 121-kilometre-long asteroid is denser than granite. Lutetia's exterior, which occasionally gets bruised in minor impacts, is probably rocky, while its interior is made of heavy metals.
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