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
Astronomical symbols Ω (capital omega), which was originally a typographical substitute for the astronomical symbol. The symbols for aspects first appear in Byzantine codices. Of the symbols for the five Ptolemaic aspects, only the three displayed here—for conjunction, opposition, and quadrature—are used in astronomy. Symbols for a comet (☄) and a star () have been used in published astronomical observations of comets. In tables of these observations, ☄ stood for the comet being discussed and for the star of comparison relative to which measurements of the comet's position were made. Astronomical symbols Astronomical symbols are abstract pictorial symbols used to represent astronomical