16:45 〜 17:00
[PAE18-24] Extrasolar planets in habitable zones explored with the Thirty Meter Telescope (TMT)
キーワード：太陽系外惑星、ハビタブルゾーン、地上望遠鏡
Thirty Meter Telescope (TMT) is a next-generation extremely large telescope with aperture size of 30m under construction by international collaboration involving Japan, U.S., Canada, and India. It is significantly larger than any existing ground- or space-based optical-infrared telescopes. TMT with Adaptive Optics (AO) will achieve an angular resolution of 0.01 arcseconds and a sensitivity capable of detecting point sources as faint as 30th magnitude.
A key science of this telescope is exploring the nature of extrasolar planets by direct imaging of Earth-like planets in habitable zones of nearby faint stars and spectroscopy to measure compositions of planets’ atmospheres searching for signatures of life. The current large ground-based telescopes such as the Subaru Telescope and the space telescope JWST have achieved remarkable results, including the direct imaging of Jupiter-like planets orbiting Sun-like stars. The next breakthrough will come from detecting evidence of life beyond Earth. To achieve this, it is essential to discover and thoroughly investigate Earth-like planets within the habitable zone, which is the region around a star where liquid water can exist.
Since the habitable zone is close to the host star, planets in this region cannot be directly imaged with the resolution of current telescopes. The TMT’s high resolution will enable direct imaging of Earth-like planets in the habitable zone around cool main-sequence stars (M dwarfs) for which relatively low brightness contrast between planets and the host star is expected in the infrared range. Follow-up spectroscopic observations will characterize the detected planets. Another approach to search for signatures of life on extrasolar planets is to measure the abundances of molecules indicative of life, such as oxygen molecule (O2), a byproduct of photosynthesis, by spectroscopic observations of the light passing through their atmospheres during transits in front of their host stars. While atmospheric observations of gas giant planets like Jupiter have been conducted previously, TMT will be required for observations of Earth-like planets where life is expected.
An advantage of ground-based extremely large telescopes is that high-resolution spectroscopy is available by mounting very large and heavy instruments. TMT’s high-resolution spectrometers will be used to determine the dynamics of atmospheres for extrasolar planets.
TMT will be equipped with three observing instruments during the commissioning of the telescope, namely IRIS (Infrared Imaging Spectrograph), WFOS (Wide-Field Optical Spectrometer) and MODHIS (Multi-Objective Diffraction-limited High-resolution Infrared Spectrograph). Following these first-light instruments, High-Resolution Optical Spectrometer (HROS), a high contrast instrument (Planetary System Instrument: PSI) and a mid-infrared instrument (MIR Camera, High-dispersion spectrometer, and IFU: MICHI) will be developed.
TMT is a unique extremely large telescope to be constructed in the northern hemisphere, necessary for covering targets in the whole sky with ESO Extremely Large Telescope (E-ELT) and Giant Magellan Telescope (GMT). The construction site, Maunakea in Hawaiʻi, has the best condition for astronomical observations by the high elevation (4000m) and stable atmosphere (e.g., isoplanatic angle and coherence time) that are essential for infrared observations with AO. The optical system of TMT will realize a clean point spread function (PSF), which will be a great advantage over E-ELT and GMT in high-contrast observations for extrasolar planets.
Toward the completion in 2030s, Japan is responsible for constructing the telescope structure and the primary mirror segments, as well as developing science instruments. The TMT project is under review of National Science Foundation (NSF) in the U.S. as a part of US-ELT program for the participation of NSF with the U.S. federal funding. The status of the project is briefly reported.
A key science of this telescope is exploring the nature of extrasolar planets by direct imaging of Earth-like planets in habitable zones of nearby faint stars and spectroscopy to measure compositions of planets’ atmospheres searching for signatures of life. The current large ground-based telescopes such as the Subaru Telescope and the space telescope JWST have achieved remarkable results, including the direct imaging of Jupiter-like planets orbiting Sun-like stars. The next breakthrough will come from detecting evidence of life beyond Earth. To achieve this, it is essential to discover and thoroughly investigate Earth-like planets within the habitable zone, which is the region around a star where liquid water can exist.
Since the habitable zone is close to the host star, planets in this region cannot be directly imaged with the resolution of current telescopes. The TMT’s high resolution will enable direct imaging of Earth-like planets in the habitable zone around cool main-sequence stars (M dwarfs) for which relatively low brightness contrast between planets and the host star is expected in the infrared range. Follow-up spectroscopic observations will characterize the detected planets. Another approach to search for signatures of life on extrasolar planets is to measure the abundances of molecules indicative of life, such as oxygen molecule (O2), a byproduct of photosynthesis, by spectroscopic observations of the light passing through their atmospheres during transits in front of their host stars. While atmospheric observations of gas giant planets like Jupiter have been conducted previously, TMT will be required for observations of Earth-like planets where life is expected.
An advantage of ground-based extremely large telescopes is that high-resolution spectroscopy is available by mounting very large and heavy instruments. TMT’s high-resolution spectrometers will be used to determine the dynamics of atmospheres for extrasolar planets.
TMT will be equipped with three observing instruments during the commissioning of the telescope, namely IRIS (Infrared Imaging Spectrograph), WFOS (Wide-Field Optical Spectrometer) and MODHIS (Multi-Objective Diffraction-limited High-resolution Infrared Spectrograph). Following these first-light instruments, High-Resolution Optical Spectrometer (HROS), a high contrast instrument (Planetary System Instrument: PSI) and a mid-infrared instrument (MIR Camera, High-dispersion spectrometer, and IFU: MICHI) will be developed.
TMT is a unique extremely large telescope to be constructed in the northern hemisphere, necessary for covering targets in the whole sky with ESO Extremely Large Telescope (E-ELT) and Giant Magellan Telescope (GMT). The construction site, Maunakea in Hawaiʻi, has the best condition for astronomical observations by the high elevation (4000m) and stable atmosphere (e.g., isoplanatic angle and coherence time) that are essential for infrared observations with AO. The optical system of TMT will realize a clean point spread function (PSF), which will be a great advantage over E-ELT and GMT in high-contrast observations for extrasolar planets.
Toward the completion in 2030s, Japan is responsible for constructing the telescope structure and the primary mirror segments, as well as developing science instruments. The TMT project is under review of National Science Foundation (NSF) in the U.S. as a part of US-ELT program for the participation of NSF with the U.S. federal funding. The status of the project is briefly reported.