Re: Kerala Fireball, English news

From: Frank Reed via Seesat-l <>
Date: 1 Mar 2015 11:50:38 -0800
You wrote:
"Does this group have any assessment about what this could have been - if
it's a reentry? 
The incident occurred over central parts of Kerala (roughly, 10 degrees
North, 76.5 degrees East) at about 10 p.m. India time (4:30 p.m. UTC) on
Friday, 27th February, 2015."

There's no evidence that I can see that this was a re-entry (of an artificial satellite, a rocket body, or other manmade debris). I have seen two videos that appear to be actual footage of the object in question. They show an event of very brief duration and high speed. Reports filed at also indicate a relatively brief event. This matches a natural fireball. By contrast, re-entering space debris (from a satellite or rocket) would be travelling at a lower speed (low Earth orbital speed is more than 40% lower than the slowest possible meteor/fireball speed) and due to a relatively shallow entry angle would be seen travelling across the sky for a great distance. The high speed and short duration argue strongly against the space debris possibility. 

So what was it? The event can be described as "a relatively spectacular fireball caused by the hyper-sonic entry of a small meteoroid in the upper atmosphere dozens of miles above ground". There are thousands of fireballs like this globally every year. Until recently, in the past five years especially, fireballs were not widely reported, and those that were observed remained "local news". The object that created this fireball would have been a natural object, probably a "stone", on the order of one to several meters in diameter entering the atmosphere at high speed and then disintegrating due to the high temperatures and high dynamic pressure as it slammed into the thin air many miles above ground. A small amount of material would have reached ground though it's usually impossible to track. Reports of shadows cast by the fireball as well as some reports of sonic booms (reported as "tremors") and indications that it was brighter than the full Moon suggest a larger object.

A fireball is not rare in the global sense, but it is quite rare for any indIvidual to see such a spectacular fireball (since each of us spend so little time looking at the night sky). For a comparison, if we hold a lottery every week and sell 100,000 tickets (with only one possible winner), then the odds that any one individual would win are very low even if you buy a ticket every week for a year, but the odds that someone will win are 100% every week. Seeing a fireball is like a lottery: they are up there, and if the event occurs over a populated region, the odds that the event will be seen by someone are high, and yet for any one person it may be a once in a lifetime observation.

Be forewarned that many of the photographs that have been published by various Internet "news" sites claiming to show this fireball over Kerala are in fact stock photos. If you go to Google Images here and search on "meteor fireball", you will immediately find two of the images that were used in stories about the Kerala fireball. These images have been on the Internet for many years. They were used simply to fill space in the recent articles. There are also a number of videos that have been posted, e.g. on youtube, that are fake or that display old footage or intentionally display footage of unrelated re-entry events. This is common on Internet video sites since advertising can be attached to videos which will generate a little income for the poster regardless of whether the video is real or not.

Reports of a "crater" seen in some media reports are also likely spurious. Meteors enter the upper atmosphere at hyper-sonic speeds, but the brilliant event that we see occurs dozens of miles above ground. By the time they appear to "burn out" the speed is greatly reduced, typically to low supersonic speeds, and by the time any remnants reach ground level they are travelling at air-limited, subsonic "terminal velocity", a speed which varies based on mass and size but is typically a couple of hundred kilometers per hour for small stony objects. At such speeds, falling rocks do not create craters, though they can create small "pits" in soft soil. One might find a fragment resting in a small pit or hole, but not a large bowl-shaped impact crater. Impact craters on Earth are never found except with cataclysmic events precisely because the atmosphere nulls out the speed of any small objects. As a result there are no actual impact craters on Earth smaller than about one kilometer !
 in diameter. Reports of "charring" on the ground are almost certainly unrelated. Since meteor fragments reach the ground at relatively low speed, they are normally cold when they hit. In fact, because they were in deep space minutes before, and since the heating of re-entry only affects a thin surface layer, meteorites found immediately after impact have been found to be icy cold.

Frank Reed
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Received on Sun Mar 01 2015 - 13:51:59 UTC

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