Ancient water on asteroid 4 Vesta: evidence from a quartz veinlet in the Serra de Mage eucrite meteorite

摘要

The meteorite Serra de Mage, a eucrite inferred to be from the asteroid 4 Vesta, contains quartz veinlets. They are identical to antitaxial or 'crack-seal' quartz veinlets in terrestrial rocks, and are extraterrestrial and ancient because they pre-date a 4.40 Ga metamorphism. The quartz was likely deposited from liquid water solutions (as are terrestrial veins); other potential solvents or transport mechanisms are inadequate or unlikely. Because there is no indication of internal (magmatic) water in the eucrite meteorites and thus in Vesta, the water from which the veinlet was deposited probably came from outside Vesta. By analogy with water ice deposits on the Moon and Mercury, Vesta and similar asteroids may have had (or now have) polar ice deposits, possibly derived from comet impacts.