Expert: Jayendra Upadhye - 5/9/2004

Question
I've heard it said that during the first 100 million years of Jupiter's existence, it shone like a second sun. What evidence, if any, do we have for that statement?

Answer
Reg,
Frankly I never imagined that!
Also I suppose that statement was made because in their formative years all planets were very hot, as the process of accretion involoves collisions at speeds ranging from crawling speeds to 20 km/sec!
Even gaseous planets such as jupiter were quite hot then for the same reason. Even now 4.5 billion years after its formation, jupiter radiates double the amount of energy it recieves from the sun! The other gas giants have emission to absorption ratios (except uranus) of greater than one.
But Uranus underwent a terrific collision and was "toppled on its side", and in the process exposed enough of its insides to cool space to become truly cold! it radiates only as much as it recieves.
So one would say the evidence lies in the still "hot" interiors of these giants. Mind you, hot and cold are always relative terms.
Try to find out more about the interiors of these on the web. The answers lie in the source of their magnetic fields which are very strong.
Jayen