What would have the very first planets looked like, based on their most likely chemical compositions?
- Were they mostly grey gas giants with atmospheres of hydrogen and helium, coalescing around the first Population II stars?
- Were they blue gas giants, enriched with water vapour?
- Were they brownish-red and grey, like our own Jupiter and Saturn?
- Were they a heterogeneous mix of all sizes, colours, and chemical compositions that included rocky and gas giants?
What papers support research into this area?
Note: By first planets I mean the first planets that most likely existed in the Universe. In The habitable epoch of the early Universe, for example, Loeb suggests that a mere 13.5 ± 3.5 Myr after the Hot Big Bang could have witnessed the first viable supernova followed by planet formation. Another paper (can't find it) suggested that gas giants could have formed from the primordial hydrogen and helium soup before reionization, without needing any stars.