An astronomer
When the scientist studies the stars that's an astronomer, and in space it's an astronaut. The person might also be a father or mother, or a footballer, because people tend to be multi-skilled.
An astronomer.
A person who studies Mars is typically referred to as a Martian scientist or a Mars researcher.
Astronoms
A person who studies snowflakes is called a cryologist or a snowflake scientist.
Astronomers
A biotechnology scientist.
An Oceanographer. Marine Biologist, that sort of thing.
A scientist that studies viruses is called a virologist.
A scientist who studies mollusks is called a teuthologist.
A scientist that studies bears would be called an ursinologist.
virologist
An aviologist.
biologist
A meteorologist.
A vulcanologist
Mineralogists