The mass of Neptune is 17 times that of Earth. This indicator corresponds to 15 times in Uranus, which is considered the twin of Neptune.Due to its distance from the Sun, the surface temperature of the planet is -218 °C, making Neptune the coldest known planet in the Solar System after Uranus. The temperature at the center of Neptune is thought to be about 5100 °C. Neptune has a weak ring system. Although the planet's rings were known in the 1960s, their existence was confirmed by the Voyager 2 spacecraft.