Look up at the moon and you are looking at the aftermath of a
collision between the Earth and a planet the size of Mars,
scientists have confirmed. Since the 1970s, astronomers have
suspected that such a planet-sized impact roughly 4.5 billion
years ago at the dawn of the solar system led to the moon's
formation. The "giant impact" idea explains why Earth has such a
large moon, one nearly as wide as the planet. In a new Nature
journal study led by Randal Paniello of Washington University,
St. Louis, a look at lunar chemistry finds fresh evidence
confirming a big smash-up as part of the explanation for the
moon. The study examined the zinc seen in the lunar soil and
asked how it differed from the same element as seen on Earth,
Mars and asteroids. In particular, the authors report, the moon
appears conspicuously loaded with a heavier variety of zinc that
doesn't vaporize as easily at high temperatures. The results
suggest that the moon formed not from the left-over crust of the
Mars-sized planet that hit the yo