Thursday, April 26, 2012

April 20 Brazilian fireball was NOT the reentry of an Atlas Centaur r/b

A beautiful, slow, long duration, fragmenting fireball was filmed from Brazil in the evening of April 20 (20 April near 20-21h UT). Movies can be seen here and here.

Soon after the apparition, the question came up: meteoric fireball, or a reentry of "space junk"? Based on the visuals of the two movies available, I noted that it looked like a meteoric fireball, not a reentry.

Subsequently, a piece appeared in Universe Today, claiming it was a reentry: that of an Atlas Centaur rocket, #16102, 85-087B, which launched Intelsat 512 in 1985.

That conclusion is simply wrong however. According to USSTRATCOM the object in question decayed 18.5 hours earlier than the fireball, over the western Pacific at 1:23 UTC (20 April) near 18N, 161 E. It reentered nowhere near Brazil. It did pass over northern Brasil on its final pass an hour before reentry, but that would have been at 00:30 UTC, not 20-21 UTC. Moreover, even that pass would have been too much north to see it from the southern Brasilian location where it was filmed from: it would have passed below the horizon as seen from there.

And even if pieces would have survived longer (highly unlikely in this case), these could not have caused a fireball over Brasil 18.5 hours later: the orbital plane of the r/b was wrongly oriented for that. Around the time of the fireball, any surviving objects in the Centaur orbit would not pass over Brasil but much more north, over Mexico and the Caribean (see below. Note: the object was no longer in orbit at that time!).

So, the object that was filmed was most likely a piece of asteroidal debris, a very nice, very slow and very long duration meteor grazing through the upper atmosphere and breaking to pieces.

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