Astronomers have for the first time clearly photographed the rings of Uranus, showing them to be made of particles which are darker than any other bodies in the solar system.
Dr. Richard J. Terrile of NASA's Jet Propulsion Laboratory and Dr. Bradford A. Smith of the University of Arizona used special electronic camera system at the Carnegie Institution's Las Campanas Observatory in Chile to record the images last April. The camera utilized charge- couple device (CCD) to record the image.
Photographing the rings is difficult because they are darker than charcoal and very close to the much brighter Uranus. Special computer processing was performed on the images in order to make the rings visible. This processing creates the false three-dimensional look of the images.
The rings can be seen as circle of material concentric around the nearly pole-on view of Uranus. (Uranus travels the solar system with one pole facing the Sun; the rings girdle the planet's equatorial region, giving the Uranian system its bullseye-like appearance.) The five known moons of Uranus can also be seen along with several background stars. Bright vertical lines are caused by minor defects in the detector.
The rings were discovered in 1977 when they blocked out the light of distant star as Uranus passed in front of it. Uranus is known to have nine rings. All are very narrow with the widest of them, called the epsilon ring, having an average width of about 50 kilometers (about 30 miles). This image shows the collective ring system and does not resolve the individual narrow rings.
Analysis of this new photograph shows that the rings reflect back only about two percent of the sunlight falling on them, making them the darkest material found in the solar system. This raises the question as to what the rings are made of: two possibilities have been suggested. Evidence from meteorites and astronomical observations of asteroids suggests that dark organic material is prevalent in the outer solar system and could comprise the rings. Another possiblity is that the rings are made of frozen methane, another common material in the outer solar system. Methane ice, which is normally bright, can be darkened by radiation, either from high-energy particles from the Sun, or from trapped radiation around Uranus (similar to the Van Allen radiation belts around Earth.
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