[curiousuburb]

Moon craters mapped in new detail.

Originally Posted by Guardian.co.uk The violent history of our nearest celestial neighbour has been laid bare by the most detailed map of moon craters ever produced. Scientists used instruments aboard Nasa's Lunar Reconnaissance Orbiter to scan the surface of the moon for impact craters measuring at least 20km wide. Pictures sent back by the spacecraft revealed 5,185 large craters caused by lumps of space rock thumping into the lunar surface over the past few billion years. Some regions of the moon are so pocked with craters they have reached what planetary scientists call "saturation equilibrium", where each additional crater wipes out an older one, so the number of craters remains the same. The moon is thought to have formed 4.5 billion years ago, when a heavenly body the size of Mars struck Earth and dislodged an enormous cloud of debris that ultimately condensed into our planet's natural satellite. A team led by James Head at Brown University in Providence, Rhode Island, used an instrument called a laser altimeter on the Lunar Reconnaissance Orbiter to map craters on the moon. The instrument bounces laser pulses off the lunar surface every 25 metres as it hurtles overhead. By measuring how long each laser pulse takes to bounce back to the spacecraft, scientists can map the surface contours of the moon to a vertical accuracy of 10cm. To produce the crater map took 2.4 billion laser pulses. By analysing the craters and their positions, the researchers determined that the oldest regions of the lunar surface were the southern areas that face Earth and the northern region of the far side of the moon. The study is published in the journal Science. Some parts of the moon are younger than others because ancient volcanic eruptions spewed out material that covered vast areas of land and erased the craters that were there before. The map confirms previous lunar surveys that found older parts of the moon's surface have a greater number of craters than younger areas. This suggests the moon was pummelled with larger space rocks in its early life than it was later on. One possible explanation is that fewer huge chunks of rock were flung out of the asteroid belt and onto a collision course with the moon once Jupiter and Saturn – the planets with the most mass and so the greatest gravitational pulls – had settled into their orbits. "We know the asteroid belt has been spinning off projectiles at a relatively constant rate for three and a half billion years, but now we go back earlier in the solar system's history and suddenly things are completely different," said Caleb Fassett, a planetary scientist and co-author on the study. "This map is going to motivate a greater search to understand that."