Update on the so. Arizona fireball – June 23
June 25, 2009 3 Comments
Reports continue to come in from all over southern and central Arizona of Tuesday evening’s fireball. The most interesting reports involve a series of loud sonic booms heard from Tucson southward. Most of the sonic boom reports are from the Sierra Vista to Green Valley area.
I would like to thanks everyone who has submitted reports. It is greatly appreciated and will help us understand this event better. Also remember to file a report with the American Meteor Society at http://www.amsmeteors.org/fireball/report.html .
I was hoping to find more video of the fireball especially from amateur all-sky fireball cameras. There are 3 such cameras in the area but all were down for maintenance and testing during the time. And yes that is partially my fault. Oh, well, next time… An additional camera near El Paso would have seen it but was clouded out.
Luckily, there is an all-sky camera that runs all day and night on Mount Hopkins, where the 6.5-m MMT telescope resides. This camera is used by the astronomers to check sky conditions during their observing runs. It is usually used to watch for clouds and fog. But it is also great at picking up other things such as meteors and satellites. [Note: all of the movies taken by this camera are archived on line and can be seen by the public at http://skycam.mmto.arizona.edu/ .
The camera takes a series of ~10 second exposures. Tuesday’s fireball was picked up on 2 consecutive images. The 1st image below shows the early stages of the fireball. At this point the fireball is bright but probably not much brighter than Venus. Note the time is 9:21 pm.
The 2nd frame is completely washed out. During the 2nd half of the fireball’s flight, its brightness rivaled the Full Moon. This easily overwhelmed the camera since its len iris was wide open for night-time observing.
The single MMT sky cam image does provide some great information on where the fireball came from and its path. Combing this image with my own naked eye observations, I was able to map out a preliminary path over southern Arizona. The map below (made with Google Earth) combines the MMT sky cam observations of the 1st few seconds of the fireball with my observations of the last few seconds.
Note: This is my first time doing this so the path could be completely wrong. For all of you meteorite hunters out there, don’t completely trust this path. Then again, if it helps you find some pieces, I want one. 🙂
The first detection (by the sky cam) occurs over the border to the east of Nogales at an altitude of 70-80 km. The sky cam is limited to bright objects, so naked eye observers may have been able to see it even earlier. My last observation occurs between Benson and Huachuca City at an altitude of ~20-30 km. The “heartbeat” symbols are reports of sonic booms. These reports cluster nicely near the middle to end of the path when the fireball was breaking up and should have produced sonic booms.
So what was this? It was most likely a small asteroid hitting the atmosphere at ~20 km per seconds (12 miles per second). Originally the asteroid was probably not much bigger than a basketball. Again by combining the data from above, the fireball originated from the direction of the constellation of Corvus (that would be its radiant). There is a very poorly observed meteor shower called the Corvids that may be active right now. It is possible that this fireball is a member of this shower but it is more likely that it was just a Sporadic (meaning it was not associated with any shower).
So the fireball was caused by a small lonely asteroid that just happened to be at the wrong place at the wrong time. Or the right place and time for those lucky enough to have seen it.