Asteroids have a way of exploding when they approach a planet. They have an electrical charge at their core which fails to to equalize rapidly enough with the different charge of a planet which creates internal stresses that cause them to become bolides.
See Tunguska Event
http://www.thunderbolts.info/tpod/2006/arch06/060915tunguska1.htm
http://www.thunderbolts.info/tpod/2006/arch06/060918tunguska2.htm
A comet involved in the Chicago and Peshtigo fires:
http://www.thunderbolts.info/tpod/2006/arch06/060920chicagofire.htm
When Comets Break Apart
http://www.thunderbolts.info/tpod/2006/arch06/060825cometsbreak.htm
The Peekskill Meteor (it blew up)
http://www.thunderbolts.info/tpod/2006/arch06/060601meteor.htm
Comet Schwassman-Wachmann 3 Disintegrates 1 & 2
http://www.thunderbolts.info/tpod/2006/arch06/060505cometbreakup.htm
http://www.thunderbolts.info/tpod/2006/arch06/060508cometbreakup2.htm