Subaru Telescope 2.0
Science Goal > To identify Earth-like exoplanet candidates
Science Goal #4: To identify Earth-like exoplanet candidates
Are there other planets like our Earth in the Universe? Does life exist there? Since the first discovery of an exoplanet in 1995, thousands of exoplanet candidates have been found. The Subaru Telescope has contributed to the search, including its direct imaging of a “second Jupiter” by the SEEDS Project.
Some of them orbit in the habitable zone, a favorable region from a star where they can maintain liquid water to support life. Some discovered exoplanets are rocky planets like Earth. Discovering habitable planets adjacent to Earth and studying them in detail is the key to advancing research on life in the Universe.
Subaru Telescope 2.0 endeavors to discover Earth-size planets by indirectly detecting planets from wobbling stars through the InfraRed Doppler (IRD) while continuing the research through direct imaging of exoplanets. IRD looks for planets around lower masses and temperatures than the Sun (M-type stars, or M stars). Given the abundance of M stars near the Solar System, the proximity of the habitable zone to the host star due to the M star’s low temperature, and the relatively large wobble of the host star to the planet due to the M star’s low mass, it would be relatively easy to spot habitable Earth-size planets.
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(Left) Diagram showing the region of the habitable zone from the host star. The habitable zone of a low-temperature star is close to the host star, while the habitable zone of a high-temperature star is far from the host star. (Credit: Astrobiology Center)
(Right) Artist’s impression of the planetary system where seven Earth-like planets orbit around a low-temperature, low-mass M-type star TRAPPIST-1. The Subaru Telescope’s IRD found that the planetary orbits are almost aligned with the host star’s rotation. (Credit: NAOJ)
Observation Targets
M-type stars near the Solar System
Subaru Telescope’s objectives
(1) Detect Earth-like planets in the habitable zone through IRD’s intensive observation of more than 100 M-type stars near the Solar System.
(2) Determine the characteristics of Earth-like planets and other objects through collaboration with NASA’s Transiting Exoplanet Survey Satellite (TESS). IRD looks into details of exoplanet candidates detected by TESS.
(3) Coordinate with the future extremely large ground telescope Thirty Meter Telescope (TMT) for observation of likely candidates for a “second Earth” that could harbor life.
(4) Verify the technology of extreme adaptive optics, which will allow TMT and other telescopes to directly observe Earth-like planets and develop it for practical use for successful observation.
Searching for life in the Universe is essential for finding an answer to the origin of life and understanding our own origin. Subaru Telescope 2.0 will identify candidate objects for Earth-like exoplanets through the ultra-precise measurement of the radial velocity to provide stepping stones to this grand theme. Detailed investigation of atmospheric composition, the existence of signature of life, etc., will be conducted for these candidate objects, including observation with ultra-high sensitivity and resolution by the next generation of extremely large telescopes.
Are there other planets like our Earth in the Universe? Does life exist there? These simple but fundamental questions were long asked from a philosophical viewpoint rather than scientific goals. The discovery of the first exoplanet in 1995 changed them into concrete research topics that astronomy should deal with. The Subaru Telescope, ALMA, and other cutting-edge telescopes challenge these questions by employing a variety of approaches.
The Subaru Telescope has focused on direct imaging of exoplanets in the combination of adaptive optics and high-contrast instruments, which has resulted in a series of successes. Subaru Telescope 2.0 continues and advances this observation to detect Earth-size planets indirectly by spectroscopic observation with ultra-high precision. Using the Doppler technique, the movement of a host star caused by a planet’s orbiting is measured by a change in the star’s spectrum (Doppler shift). This technique is better at detecting small planets like Earth-size planets when host stars have lower masses because even a weak gravity of a small planet can cause a relatively large wobble of the host star. Search for Earth-size exoplanets targeting low-mass stars that weigh less than half of the Sun’s mass (M-type stars) attracts researchers’ attention.
Given that M-type stars mainly emit near-infrared light due to their low temperatures, instruments for near-infrared observation can bring favorable results. No other telescopes of the 8-10 m class are equipped with an ultra-high precision spectroscopic capability in the near-infrared region that the Subaru Telescope’s InfraRed Doppler (IRD) can offer, which places IRD in a unique position in this field of research. Installed in 2019, IRD was used for a large-scale observation program for 170 nights called the IRD-Subaru Strategic Program (IRD-SSP), which runs for five years. This program and relevant observations focus on high-precision near-infrared spectroscopic observation of more than 100 M-type stars. For monitoring observation by collaborating with other telescopes, we focus on discovering Earth-like planets in the habitable zone where life can exist. These planets detected in this program will become essential targets for the next generation of extremely large telescopes (TMT, GMT, and E-ELT) for detailed investigation. The development of extreme adaptive optics is the key to extremely-large telescopes’ observation. The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system plays a role in technology verification for this development.
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Relevant Research
- "Bare" Super-Earths Offer Clues to Evolution of Hot Atmospheres (Science Result on September 26, 2021)
- Astronomers Detect New Chemical Signature in an Exoplanet's Atmosphere using Subaru Telescope (Science Result on April 26, 2021)
- TRAPPIST-1 Planetary Orbits not Misaligned: First Scientific Result by the New Spectrograph on the Subaru Telescope (Science Result on May 13, 2020)
- The Orbital Planes of "Young Planets" Are Not Inclined? : New Knowledge About the Evolution of Planetary Systems (Science Result on September 3, 2020)
- Subaru Telescope Sheds New Light on an Obscured Infant Solar System (Science Result on May 13, 2019)
