Oberon (moon) up to 40 km and its temperature is around 180 K. However, the internal structure of Oberon depends heavily on its thermal history, which is poorly known at present. Oberon is the second-darkest large moon of Uranus after Umbriel. Its surface shows a strong opposition surge: its reflectivity decreases from 31% at a phase angle of 0° (geometrical albedo) to 22% at an angle of about 1°. Oberon has a low Bond albedo of about 14%. Its surface is generally red in color, except for fresh impact deposits, which are neutral or slightly blue. Oberon is, in fact, the reddest
Io (moon) green glows in the same image) have also been observed. Io (moon) Io (Jupiter I) is the innermost of the four Galilean moons of the planet Jupiter. It is the fourth-largest moon, has the highest density of all the moons, and has the least amount of water of any known astronomical object in the Solar System. It was discovered in 1610 and was named after the mythological character Io, a priestess of Hera who became one of Zeus' lovers. With over 400 active volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is