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Location: Chemistry/Physics Building, MUN
Time: 8:00 pm
Present: 20
Chris gave a brief introduction for those who are not familiar with Phil McCausland (pjam). Chris noted International Astronomy Day will be on May 6 this year. We will be holding an event at the Fluvarium.
Doug Grouchy spoke briefly on three motions that are before the National Council, mostly related to membership fees. There was some discussion on these motions and how to fill out your proxy. Doug collected proxies from those interested.
Our next meeting will NOT be on a Wednesday, but instead on Monday, May 15. This is to accommodate Dave Lane's schedule, so he can provide us with a talk on Supernova.
Robert Babb entertained us with some information on upcoming sky events.
"On January 15 of this year the NASA spacecraft Stardust successfully returned samples of Comet Wild II to the Earth, making it the first sample-return mission from a body other than the Moon. As it returned, the Stardust re-entry capsule became an excellent "meteor" with well-known characteristics (mass, size, entry velocity and orbit), and so represented an unusual opportunity to calibrate meteor observations. A team from the University of Western Ontario and Los Alamos National Laboratory travelled to the re-entry zone in western Utah to measure the sound of the meteor's sonic boom, the resultant ground shaking, and the visual phenomena associated with the Stardust capsule reentry. I will present a synopsis of what we found, along with an overview of some of the interesting first findings from the Stardust mission itself."
Member Phil McCausland has returned for a holiday. He, Wayne Edwards, and Doug ReVelle were present in western Utah for the Stardust Reentry on January 15, 2006. Phil is currently with the University of Western Ontario Departments of Meteor Physics and Earth Sciences. The Stardust reentry provided a perfect opportunity to calibrate future instruments for a meteoroid reentry. Stardust had a known mass, size, and velocity. Its track was well defined.
The instruments consisted of an all-sky camera, 2 seismic arrays, and a buried infrasound detector (infrasound is very long wavelength sound waves).
Phil gave us some background about the Stardust encounter and the return from comet Wild 2. He noted the design and construction of the probe, in particular the aerogel panes and the sample return container. Stardust had a return velocity of 12.5 km/s, which is on the order of many meteoroid reentry speeds. Acoustics were already collected when Genesis made a similar reentry (and then crashed!) in the same area. The infrasound measurements give the cleanest information about the energy involved in a reentry event. The actual sound signature is complicated, however, because infrasound is more susceptible to variations in temperature, moisture, and wind speed, providing many complex paths for the sound to follow before it arrives at the sensor.
Wendover AFB was chosen as the best site. The team decided the location of an old runway would provide the best site for burial to isolate the sensor. They spent a day burying the sensor a few feet deep, and attached soaker hoses. The purpose of the hoses is to filter out high frequencies. At this time they also set up the seismic gear, and the all-sky camera.
A typical infrasound setup can be found at http://aquarid.physics.uwo.ca/~pbrown/infrasound.htm .
All of this effort could be for nought if NASA had decided to abort the landing (the wait would be another 3 years). Happily, the probe landed successfully, and Phil and group got good data. The shock recorded was similar to Genesis'. By using the Genesis data, they could more readily understand what happened. Also, their data could be compared with other data collected in the area and surrounding states by different seismic stations. Phil showed some graphs and discussed the meaning of their results so far.
Gary Case brought a copy of the Valles Marineris fly-over video that NASA has put together. After viewing this, we watched a video of a computer simulation of colliding black holes: http://www.nasa.gov/centers/goddard/universe/gwave.html .
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