QUESTION: Why hasn't NASA come up with a plan to save Hubble?
– Ken Rollins
ANSWER: The Hubble Space Telescope was launched in 1990 with a 15-year mission. That was extended to 20 years, but the Columbia tragedy led to the cancellation of the last scheduled Hubble servicing flight. Hubble was built to dock with the space shuttle; therefore, it would be difficult to service it using another spacecraft.
Servicing is necessary to repair worn out parts, particularly gyroscopes. New software that will permit Hubble to function on two gyroscopes rather than three, should extend Hubble's life span until about 2007, but this is well before the next generation space telescope, the James Webb, is scheduled to be launched in 2011.
NASA examined the possibility of a robotic servicing mission, but recently NASA Administrator Mike Griffin said he wanted to "take the robotic mission off the plate." A robotic mission is seen as unfeasible because of cost (estimates are in the $2-billion-dollar range) and limited amount of time for planning and design.
A 1-liter glass bottle of sparkling water looked normal when it arrived at our table, but within eight to 10 seconds of being opened, most of the water turned to ice. It solidified from the top and worked its way down the bottle. What is the explanation for this occurrence?
– Cathy Taylor
It may have occurred because opening the bottle relieved some of the pressure on the water. Water at normal atmospheric pressure freezes more easily than water under pressure because water expands when it freezes. In ice, the H2O molecules are held apart (and together) in an ordered, latticelike structure. On melting, this structure partially collapses, so liquid water takes up less space.
Pressure is not the only possible explanation. The rapid freezing phenomenon can also occur with nonsparkling water, sometimes simply upon tilting the bottle. It occurs because water can be supercooled (the temperature reduced to less than 0 degrees centigrade) without freezing if the water molecules lack a surface, also called a nucleation site, on which to form crystals.
A small particle in the water, or a rough surface on the bottle, can serve as a nucleation site. Tap water usually has plenty of impurities, but distilled water in a very smooth bottle can become supercooled for lack of nucleation sites. Tilting the bottle may allow the water to contact a scratch or a tiny piece of ice in the lid. Once an ice crystal forms, more water molecules can pack themselves in place around it, and the ice will grow from there.
Sherry Seethaler has a doctorate in science education and is a UCSD science writer and educator. Send your scientific questions to her at Quest, San Diego Union-Tribune, P.O. Box 120191, San Diego, CA 92112-0191. Or e-mail sseethaler@ucsd.edu . Please include your name, city of residence and phone number.
