Comet Shoemaker–Levy 9 this time a more compact and strong object, probably a small undiscovered asteroid, was the cause. The impact of SL9 highlighted Jupiter's role as a "cosmic vacuum cleaner" (or in deference to the ancients' planetary correspondences to the major organs in the human body, a "cosmic liver") for the inner Solar System (Jupiter Barrier). The planet's strong gravitational influence leads to many small comets and asteroids colliding with the planet, and the rate of cometary impacts on Jupiter is thought to be between 2,000–8,000 times higher than the rate on Earth. The extinction of the dinosaurs at the end of
Shoemaker (lunar crater) named Mawson (after the Antarctic explorer Douglas Mawson). It was officially named Shoemaker in honor of Eugene Shoemaker, the geologist whose remains were on board the Lunar Prospector spacecraft that impacted this crater floor. This crater became of interest to scientists when the Lunar Prospector detected unusually high concentrations of hydrogen on the floor of this and other nearby craters using a neutron spectrometer. The floor of this crater is kept in permanent shadow from the Sun, and thus maintains a temperature below . Thus the floor forms a cold trap, and any molecules of water that wander into the