Why did the then PhD student Didier Queloz get the Nobel prize? When Didier Queloz did the work that earned him a Nobel prize (along with Michel Mayor), he was still a PhD student. 

Jocelyn Bell Burnell stated 


  I believe it would demean Nobel Prizes if they were awarded to research students, except in very exceptional cases


What made this case so exceptional that he got the Nobel in spite of having been a PhD student at the time? Why wasn't the Nobel just awarded to his supervisor, Michel Mayor?
He shared the 2019 Nobel Prize "for the discovery of an exoplanet orbiting a solar-type star".  It was shared with Michel Mayor. Maybe Queloz did much of the work and Mayor thought he rightfully deserved some of the credit. Queloz only got a fourth of the money because the prize was split between Mayor-Queloz and James Peebles. Peebles got his half for "for theoretical discoveries in physical cosmology."

This was a very unique case because it involved no new physics really just the discovery of what most astronomers knew existed.