Approach and departure of 2004 YD5 on 19 Dec.
 2004, animation by Pasquale Tricarico.

The Sun-side approach and night-sky departure of 2004 YD5, as seen from that tiny perch (perhaps 5 meters/yards
wide) looking at the Earth, in an animation by Pasquale Tricarico made with his orbital dynamics software, ORSA.
The object flew under Earth and over Antarctica at an altitude of 5.31 Earth radii.

2004 YD5 as meteor event   by Marco Langbroek

This text is adapted from a message the author sent to the FMO Project members mailing list in answer to a query about how hazardous 2004 YD5 would have been if it had entered Earth's atmosphere.

With the orbit given in MPEC 2004-Y35, 2004 YD5 would have a geocentric velocity of 24.9 km/s (15.5 mile/s), approximatelly corresponding to an atmospheric entry velocity of 27.3 km/s (17.0 mile/s). Then, looking in Hills & Goda's "The fragmentation of small asteroids in the atmosphere" (Astronomical Journal 105 (1993), 1114-1144) and taking the nominal 5-meter size value:

Even at the upper range of the size estimate (13 meters wide) the results would be quite similar.

Would this object have been slower (about half the actually calculated speed), then the results might have been much more significant as the airburst would be lower in the atmosphere with a possibility of (seizable) fragments remaining.

So spectacular, yes; lethal, no. We narrowly missed a darn good fireball...

For those interested, the theoretical radiant of the fireball is at RA 263.0, dec. -27.4, which is in the southern part of Ophiuchus close to Scorpio, and close to the Sun. Hence it would have been daylight fireball, but bright enough to be seen in daylight. The object does not have a known meteor stream assocation.

See A/CC's news thread on 2004 YD5, and also the author's analysis on another close flyby, "2004 FH as meteor event."

2004 YD5's passage, seen at bottom traveling from left to right, in relation to Earth satellites. Illustration and explanation by Pasquale Tricarico: Low Earth, GPS, and geosynchronous sats are shown. 2004 YD5 was not too far from the GPS constellation, with minimum orbit intersection distance (MOID) between a GPS sat (GPS BIIA-19) and the asteroid of 1.88 Earth radii (ER). The MOID with geosynchronous sats was about 2.4 ER.

2004 YD5's passage in relation to Earth satellites, illustration by Pasquale Tricarico.
http://www.HohmannTransfer.com/mn/0412/04yd5.htm - first posted 22 Dec. 2004, revised
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