The European Space Agency (ESA) has published a new image from the Hubble Space Telescope. It shows Uranus and its four largest moons.
Uranus’ orbit lies 3.2 billion km from Earth, making it the seventh planet in the Solar System. Only Neptune lies further away. Uranus has narrow rings, consisting mainly of objects ranging in size from 20 cm to 20 meters, as well as a fairly numerous family of moons. At present, astronomers have identified 28 companions of the planet.
Moons were Hubble’s main target. Its image shows Uranus’ largest moons: Ariel, Umbriel, Titania, and Oberon. The Hubble photo also shows the planet’s rings and the shadow cast by Ariel on its surface.
At such a great distance, Uranus’ moons appear as tiny points of light. But thanks to the ultraviolet capabilities of the Hubble Telescope, astronomers were able to determine the characteristics of their surfaces.
Previously, scientists predicted that the planet’s magnetic field would give the moons a characteristic two-tone color, with their trailing hemisphere darker than their leading hemisphere (the hemisphere facing the direction of motion around Uranus). But, to their surprise, they found the exact opposite on Titan and Oberon, Uranus’ two largest outer moons. They look darker on the leading side. The most likely explanation is that they collect dust as they move in orbit, similar to how insects accumulate on a car windshield while driving.
Titan and Oberon also appear to protect two inner moons, Ariel and Umbriel, from dark dust. The inner moons do not show the expected difference in brightness between the hemispheres.
Earlier, we reported on how Hubble helped determine the length of a day on Uranus.
According to ESA
