The Sciences

Texas fireball: what's known so far

Bad AstronomyBy Phil PlaitFeb 15, 2009 10:10 PM


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So my blog post from earlier about the Texas fireball is now a bit of a mess from all the updates, so I thought I'd post a cleaner version of what's going on now. 1) A tremendous fireball -- also called a bolide, or a very bright meteor -- was seen in southern Texas on Sunday, February 15th, just before 11:00 a.m. local time. Many people have described it as very bright, small, and moving rapidly. 2) A video of the fireball has been released, taken by a person videotaping a footrace. The video matches the description of many eyewitnesses. 3) Some people have attributed this event to debris from the two satellites that collided over the Earth last week. I was initially very skeptical of this, then relented a bit. Now I am sure it was not debris from the satellites. Why? OK, that deserves it's own number. 4) The video shows the fireball to be moving very rapidly. Typically, meteors come into Earth's atmosphere at 20-50 km/sec (though they can be moving much faster), and burn up 50-100 km high. Man-made space debris re-entering is moving at slower than orbital speed so the max speed is about 8 km/sec. It also burns up lower, and generally you can see flames and whatnot coming off. I've seen man-made debris re-enter, and it's very different than natural meteors. The difference in speed is very obvious. Right there, that's enough to make me think this was a single natural object. It's possible to get collisional debris moving more rapidly, but it's difficult. The two satellites closed in on each other at about 10 km/sec, and any shrapnel from that event would most likely be moving at roughly that same speed. If one satellite slammed into, say, an antenna first, then the lower mass antenna might get a pretty hefty acceleration from it, but the amount of energy dumped into it would most likely turn it into a bunch of teeny pieces (remember, the energy of impact was like several tons of TNT). A small object would not have been as bright as the fireball seen. Also, you'd have to have a pretty special set of circumstances to get any debris from the satellites to re-enter our atmosphere so soon after the collision. It's far more likely that it will be months before we see any of that shrapnel burning up. So all in all, I am pretty sure what was seen was natural: a rock or a piece of metal from an asteroid. 5) A fireball was reported in Kentucky Friday night. It's unlikely these two events were related; if the Texas bolide were from a natural object, then it was a totally different object that entered over Kentucky. At a speed of, say, 20 km/sec, the two objects would have been separated by more than 100,000 km, making a connection pretty far-fetched. And if they were from the satellite collision, again being separated by a day makes it unlikely they were connected. 6) This was certainly unrelated to a NORAD warning of a Russian booster re-entering, which later was determined to have fallen near Africa. 7) There were reports that an FAA official had confirmed this object was from the satellite collision. But those reports never gave a name! When a report came in naming Roland Herwig, he was quoted as saying it was possibly from the collision. Still the false confirmation spread like wildfire via Twitter, when a popular breaking news account stated it as fact (no provenance was ever given for that quotation). Rumors spread rapidly, truth far more slowly. Also, why the FAA? They are not the go-to agency for this. NORAD would make far more sense, since they specifically track such things. And there was no warning at all from them, indicating once again this was not from the satellite collision. Any piece big enough to be bright enough to be seen in broad daylight is big enough for them to have been tracking for some time. Conclusions: This was a fascinating event, both astronomically and socially. I received an email less than an hour after the event from a reader (who, wonderfully, gave both his exact location and the direction to the fireball) as well as a tweet about it. Within a few minutes I had a post up and tweeted about it myself. I started to receive dozens of tweets over the next hour (I'm not sure how many total, but probably well over 100) with information. After an hour or so the misinformation (FAA officials, satellite debris, etc.) started coming in. Someone posted on iReport their own description, and added a photo of a totally different event as an example, and at least ten tweets referred to it as the actual Texas fireball. Using various websites that track keywords on Twitter helped enormously. I could look for "Texas" and "fireball" and "satellite". That was tremendously helpful. As info came in I updated the blog post, but that was awkward. Tweeting info is fine, but a more permanent and easily-accessible repository was needed. Now, after the fact, I can collate that info and make a more linear post. If someone has a better way to collect, disseminate, and store breaking astronomical news, I'm all ears. Between the blog and Twitter I think this went pretty well, with a minimum of bad information being spread. As time goes on I'm sure more video and pictures will surface. I'll post links to those as I find them. My personal thanks to everyone who saw this event and tweeted, or left comments. This was very exciting!

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