An infrared telescope on Hawaii due to be closed by the National Aeronautics and Space Administration for budget reasons has measured the sizes of the four large moons of the planet Uranus for the first time.
The four-year-old telescope on Mauna Kea has found that the four largest of Uranus' five moons are almost twice as large and three times darker than originally believed.
The telescope was built to catch the infrared light of the sun reflected by the moons of Jupiter and Saturn to support the flights of Voyager 1 and 2 by the two planets and was destined to be closed when the spacecrafts passed the planets.
Voyager 2 is now on its way to a 1986 fly-by of Uranus, a mission that is a surprise benefit of the Voyager program. Even before its scheduled closing was announced, the telescope was pointed at the four large moons of Uranus to see if it could pinpoint their size and brightness so that Voyager's cameras can be better targeted and exposed when the spacecraft arrives.
The telescope found that the moon called Oberon is 1,048 miles in diameter, the moon called Titania, 1,038, a third moon called Ariel, 825, and the fourth moon called Umbriel, 719. All four were thought by previous telescopic measurements to be less than 700 miles in diameter, about the size of the smaller moons of Saturn like Rhea and Iapetus.
"These moons are larger and darker than we ever gussed they would be," said the University of Hawaii's Dr. David Morrison, who made the measurements with Dr. Dale P. Cruickshank and R. Hamilton Brown. "This will definitely help the people directing the flight of Voyager by Uranus to target their cameras and set their exposures."
What Morrison left out was his concern that NASA will still close down the $10 million telescope at the start of the next fiscal year, which begins Oct. 1.
That is long before Voyager 2 reaches Uranus, almost 2 billion miles from Earth, and before the telescope could be used to get still more precise measurements of Uranus' four large moons of Uranus and its fifth moon, Miranda, which is too small to be measured by the telescope at the distance it is today.
All five moons are named for characters in Shakespeare's plays, "The Tempest" and "A Midsummer Night's Dream."