Based on the Hubble measurements made with the Space Telescope Imaging Spectrograph, an international team found that Sirius B has a mass that is 98 percent that of our own Sun. Despite this large mass Sirius B is only 12,000 kilometers in diameter, making it smaller than even the Earth and much denser. Sirius B’s powerful gravitational field is 350,000 times greater than Earth’s, meaning that a 68 kilogram person would weigh 25 million kilograms standing on its surface.