Marc Kuchner is an American astrophysicist, a staff member at NASA's Goddard Space Flight Center (GSFC) known for work on images and imaging of disks and exoplanets. Together with Wesley Traub, he invented the band-limited coronagraph, a design for the proposed Terrestrial Planet Finder (TPF) telescope, also to be used on the James Webb Space Telescope (JWST). He is also known for his novel supercomputer models of planet-disk interactions and for developing the ideas of ocean planets, carbon planets, and helium planets. Kuchner appears as an expert commentator in the National Geographic television show "Alien Earths" and frequently answers the "Ask Astro" questions in Astronomy Magazine. He currently serves as the principal investigator of the citizen science websites Disk Detective and Backyard Worlds.

An ocean world, ocean planet or water world is a type of planet that contains a substantial amount of water in the form of oceans, as part of its hydrosphere, either beneath the surface, as subsurface oceans, or on the surface, potentially submerging all dry land. The term ocean world is also used sometimes for astronomical bodies with an ocean composed of a different fluid or thalassogen, such as lava, ammonia or hydrocarbons. The study of extraterrestrial oceans is referred to as planetary oceanography.