Astronomers work for research institutes at university's or private labs. Their pay is based off of grant money they receive from the government or other funding party. Albeit needing a PhD to do most professional work, astronomers and astrophysicists can make anywhere from 65k to like 250k+ depending on where you end up and what you do. So, basically, discovering a planet doesn't really get you paid. The people who use the Kepler telescope are being paid through grant money, and while their discoveries do not get them paid personally, if a project is consistently finding new things, then it can be expected that grant money will keep flowing in. Winning a Nobel will make you a millionaire though.