You don't see this everyday

I was on a flight into Sydney last month and I found myself staring out the window, looking at this photo. Look very closely:

It looked like a plane from Virgin Blue. It was belching out a thick smoke! I wonder if that was normal, coz we were miles above the ground. Perhaps the atmosphere was playing tricks on colour and really that was a colourless smoke. What do you think? I don't think so. It was a scary sight. I have never sighted a plane from above, while in the skies!! Who knows how far that was. Looks like not that far away!