Home! Earth, the 3d planet from the Sun, formed 4.5 bya and weighs 6.58 billion trillion tons. Earth is not a perfect sphere, but an oblate spheroid, “squashed” a little at the North and South poles. The equatorial diameter is about 7,926 miles, but the polar diameter is 7,899.86 miles. Earth’s spinning molten core produces the magnetosphere, a magnetic shield around the planet which largely protects the atmosphere from being blown away by solar winds.