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Saturn's A Ring From the Inside Out
Saturn's A Ring From the Inside Out

A set of telescopes on Cassini is taking scientists to invisible territory.

The Ultraviolet Imaging Spectrograph (UVIS) is a box of four telescopes that can see ultraviolet light. Ultraviolet (UV) light, known as the cause of sunburn on Earth, is invisible to the human eye.

The instrument measures the views in ultraviolet light, and scientists use these measurements to produce pictures we can see. Since there is no table that maps ultraviolet "colors" to the colors humans see, the team exercises creative freedom when it makes representative images from the collected data.

"It is cool that we can pick our own colors in the pictures we produce," says Dr. Larry W. Esposito, a professor of Astrophysical and Planetary Sciences at the University of Colorado and UVIS Principal Investigator. "No person has ever seen ultraviolet light, although some butterflies can. Our pictures may thus represent a 'butterfly's-eye view' of the Saturn system."

The instrument's unique capabilities expand on the quality of the data collected by Cassini as it orbits the ringed planet.

Clumps in the A Ring
Clumps in the A Ring

"The cool thing about UVIS is that we can 'see' things that are invisible to other instruments!" says Dr. Amanda Hendrix, a planetary scientist at JPL and a UVIS team member who analyzes icy satellite data. "For example, UVIS can 'see' gases in the Saturn system that aren't seen by the camera. The instrument can also see the dark night side of the moons of Saturn, which stand out against the sky because they are bright at ultraviolet wavelengths."

Ultraviolet is particularly interesting because it includes the light characteristics of some key chemical elements and compounds. These light patterns are like fingerprints in UVIS observations. They allow scientists to identify conclusively what distant objects are made of.

"Already, UVIS has detected hydrogen, oxygen, methane, water, acetylene and ethane," Esposito says. "Our measurements tell us about the environment of Saturn that surrounds its moons and rings. We have also learned about the composition of Titan's upper atmosphere."

A special technique is used to investigate planets, moons and rings -- looking past them at a distant star or the Sun. How the object blocks out the starlight gives details about its structure. In this way, UVIS is able to map features in Saturn's rings 10 times smaller than those visible to the Cassini cameras.

Dr. Larry W. Esposito
Dr. Larry W. Esposito

"We detect battleship-sized clumps of particles in Saturn's rings that come together and then disperse on a faster-than-daily basis," Esposito says. "These phenomena can tell us about the history of Saturn's rings."

In January 2006, UVIS will watch the Sun setting behind Titan, allowing scientists to measure the composition, temperature and structure of Titan's atmosphere.

"We will look for clouds and smoggy haze layers. The Cassini project managers have used our results in the past to estimate the safety of landing on Titan; our new results will indicate how closely the Cassini spacecraft can safely approach Titan."

True to the international flavor of the Cassini mission, the UVIS team includes scientists and engineers from the United States, France, Belgium, Germany and Japan.

This translates to a linguistically engaging environment, Esposito says.

"We get to practice foreign languages at UVIS team meetings!"

At a Glance

Ultraviolet Imaging Spectrograph (UVIS) on the spacecraft
UVIS on the Cassini spacecraft

Built by the Laboratory for Atmospheric and Space Physics (LASP) located in the Research Park of the University of Colorado in Boulder, UVIS is a Remote Sensing Instrument (think sight) that captures images of the ultraviolet light reflected off an object. Designed to measure ultraviolet light over wavelengths from 55.8 to 190 nanometers, this instrument is also a valuable tool to help determine the composition, distribution, aerosol particle content and temperatures of their atmospheres. UVIS includes a two-channel, far- and extreme-ultraviolet imaging spectrograph that studies light over wavelengths from 55.8 to 190 nanometers.

  • Mass (current best estimate) = 14.46 kg
  • Peak Operating Power (current best estimate) = 11.83 W
  • Peak Data Rate (current best estimate) = 32.096 kilobits/sec
  • Dimensions (approximate) = 48 cm x 30 cm x 23 cm