Select the option that can be used as a one-word substitute for the given…

To identify the correct one-word substitute for "a person who studies the science of the universe beyond the Earth's atmosphere," we must define each role:

Definitions
Astronomer: A scientist who studies celestial bodies (stars, planets, comets, galaxies) and phenomena that originate outside the Earth's atmosphere.

Meteorologist: A scientist who studies the Earth's atmosphere, specifically focusing on weather patterns and climate.

Geologist: A scientist who studies the solid Earth, its rocks, and the processes by which they change.

Biologist: A scientist who studies living organisms and their vital processes.

Conclusion
The correct one-word substitute is Astronomer (Option 1).