Easy theory based on observation,and measurements. First not all comets
have tails. All comets that reach speeds of over 70,000 miles per
hour and in the inner planets of the solar system have tails The image
of Hale-Bopp comes to mind as being very bright,and with a tail
92,000,000 miles long. It was not the Sun rays reflecting off
icy molecules of water. It was the fact that its great speed going
through the Sun's solar wind made up of charged particles that was the
material,and energy to create those long beautiful bright tails. This
thinking tells me comets not racing towards the Sun have no tails. If
it was its gases making 100 million mile tails,and reflecting Sun light
the poor comets would melt away very fast. The Solar wind will last
another 5 billion years,and so will comets Bert