What less common cause, noted in asteroid 2005 YU55, can result in a blue appearance separate from trace element excitation?

Answer

Thermal emission during intense heating

A less common cause for a blue appearance can stem directly from thermal emission itself, meaning the intense heat generated during entry causes the blue glow, rather than the specific atomic excitation signature of a trace element like magnesium.

What less common cause, noted in asteroid 2005 YU55, can result in a blue appearance separate from trace element excitation?
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