Formation and evolution of the Solar System owe its substantially lower mass simply to having formed a few million years after Jupiter, when there was less gas available to consume. T Tauri stars like the young Sun have far stronger stellar winds than more stable, older stars. Uranus and Neptune are thought to have formed after Jupiter and Saturn did, when the strong solar wind had blown away much of the disc material. As a result, those planets accumulated little hydrogen and helium—not more than each. Uranus and Neptune are sometimes referred to as failed cores. The main problem with formation theories for these planets is the
Solar eclipses on Jupiter to 357" at aphelion. Unlike the near coincidence of the apparent sizes of the Moon and Sun as viewed from Earth, this perspective exaggerates the apparent diameters of all the Galilean moons in comparison to the Sun. Even distant Callisto is over 50% larger, and Io is nearly six times as large. This disparity in angular size makes the moons' shadows on Jupiter more defined than the lunar shadow on Earth during a total solar eclipse, as it narrows the penumbra for a given distance. Solar eclipses on Jupiter Solar eclipses on Jupiter occur when any of the natural satellites