Mariner 2 was launched August 27, 1962, and passed within 21,598 miles (34,758 km) of Venus on December 14 of that year. Back to Earth it transmitted about 65 million bits of data about the planet, which indicated not only that the surface temperature of Venus is about 800 degree Fahrenheit (400 deg C) but also that the atmospheric temperatures show little difference between the sun-lit and dark sides of the planet. Mariner 2's data also indicated that the planet's magnetic field is either nonexistent or extremely weak.