a person who studies planets is a planetologist.
Astronomer
An astronomer.
astronomist
You call someone that studies metal a metallurgist.
A physicist.
Someone who studies the planet would be called a Geologist. Someone who studies Space would be called an astronaimist. Both work together to gather information about earth.
florist
Microbiologists
An Anthropologist.
malacologist
A Zoologist
Brocollogist