MERCURY         In Roman mythology Mercury is messenger of the gods, and son of the god Jupiter. Mercury is the planet closest to the sun. Its distance from the sun is approximately 58 million km (about 36 million miles); its diameter is 4875 km (3030 miles); its volume and mass are about : that of the earth; and its density is approximately equal to that of the earth. Mercury revolves about the sun in a period of 88 days. Radar observations of …showed first 75 words of 312 total…

…showed last 75 words of 312 total…helium, hydrogen, and oxygen. Mariner 10 also detected a magnetic field 1 percent that of the earth. Unlike that of the earth's moon, the surface of Mercury is criss-crossed by long escarpments, dating perhaps from the period of contraction the planet experienced as it cooled some time early in its history. In 1991 powerful radio telescopes on earth revealed unmistakable signals of vast sheets of ice in Mercury's polar regions, areas that had not been covered by Mariner 10.