Direct Imaging of Earth-like Planets from Space (TPF-C)

摘要

The "big question" that the average person will ask an astronomer today is, "Are there Earth-like planets?" followed immediately by "Is there life on those planets?" We live in an age when we are privileged to be able to ask such a question, and have a reasonable expectation of receiving an answer, at least within the coming decade. As astronomers and physicists we are even more privileged to be the people who can provide those answers. This paper discusses the roles of four space missions that are planned by NASA to search for and characterize extrasolar planets: Kepler, Space Interferometer Mission (SIM-PlanetQuest), Terrestrial Planet Finder Coronagraph (TPF-C), and Terrestrial Planet finder Interferometer (TPF-I). The Kepler and SIM-PlanetQuest missions will search for and discover planets down to the few-Earth size and mass, around distant and nearby stars respectively. In favorable cases they will even be able to find Earth-size or mass planets. But to answer the questions "is a given planet habitable?" and "does it show signs of life?" we will need the TPF-C and TPF-I missions. Only these missions can isolate the light of the planet from the confusion of otherwise blinding starlight, and only these missions can perform spectroscopy on the planets. Visible and thermal infrared spectroscopy together will tell us if a planet is habitable and shows signs of life. TPF-C and TPF-I will build on the legacy of Kepler and SIM-PlanetQuest, and together these four missions will provide complete and unambiguous answers to our "big questions." This paper concentrates on the TPF-C mission.