muscat 2
The MuSCAT2 Project: A Japanese-Spanish Quest for Exoplanets
The MuSCAT2 (Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets 2) project is a successful international collaboration between the Instituto de Astrofísica de Canarias (IAC) in Spain and the Astrobiology Center (ABC) of the National Institutes of Natural Sciences (NINS) in Japan.
Its primary purpose is to provide critical ground-based follow-up for space-based exoplanet hunting missions, particularly NASA’s Transiting Exoplanet Survey Satellite (TESS). The collaboration is formalized through an official agreement between the two institutions, which was initially signed in 2017 and subsequently renewed until today, demonstrating the ongoing value and success of the partnership.
The instrument at the heart of this project is a powerful and innovative camera installed on the 1.52-meter Telescopio Carlos Sánchez (TCS) at the Teide Observatory in the Canary Islands, Spain. Its most notable feature is its ability to perform simultaneous, high-precision imaging in four different optical bands: g (blue), r (green), i (red), and z_s (near-infrared). This accurate «four-color» capability is a significant technical achievement. The light beam entering the telescope is split into four separate optical paths, each directed to its own dedicated 1024×1024 pixel CCD camera, providing a field of view of 7.4 × 7.4 arcminutes. By observing a star and its potential planet in multiple colors at exactly the same time, MuSCAT2 eliminates a major source of error, the variability in the Earth’s atmosphere, that can plague single-color observations. This allows it to achieve extraordinary photometric precision, with demonstrated root-mean-square residuals as low as 0.050% for a typical star like WASP-12 (V=11.57).
Primary Scientific Goal: Validating TESS Candidates
The primary scientific mission of MuSCAT2 is to validate exoplanet candidates discovered by the TESS mission. TESS scans the entire sky, identifying stars whose brightness periodically dips, a potential sign of a transiting planet. However, these dips, or «transit signals,» can be «false positives» caused by eclipsing binary stars (pairs of stars that eclipse each other along our line of sight). Distinguishing a small planet from a background binary star is a major challenge.
This is where MuSCAT2’s multi-color photometry becomes essential. An exoplanet is an opaque, solid body, so the amount of starlight it blocks (the «transit depth») should be the same in all colors (achromatic). In contrast, the light from a background eclipsing binary star can vary dramatically with color (chromatic). Therefore, if MuSCAT2 observes that a transit signal is achromatic across its four bands, it provides powerful evidence that the signal is indeed caused by a planet. This technique is the cornerstone of MuSCAT2’s validation strategy, enabling astronomers to confirm the existence of new worlds with high confidence.
Main Scientific Results: Validating New Worlds
Since beginning operations in January 2018, MuSCAT2 has been exceptionally productive, leading to the discovery and characterization of numerous exoplanets. Among the most notable MuSCAT2 accomplishments are numerous validation papers of TESS planet candidates orbiting nearby M-dwarf stars. For example, the validation of the ultra-short period substellar object around an M dwarf (TOI-263 b), the confirmation of small earth-size planets around M-dwarfs (TOI-2136 b and TOI-2266 b), and validating planets in the Neptunian Desert.
In addition, MuSCAT2 has been crucial to high-impact discoveries published in Nature and Science, including: the first transiting planet around a White Dwarf (WD 1856b), a rocky exoplanet suitable for atmospheric characterisation (GJ 486b), a multi-planet transiting system with orbital resonances (HD 110067), and an Earth-sized planet that may experience vulcanism (LP 791-18d).
Broader Impact
In summary, the MuSCAT2 project is a model of efficient, international collaboration.
By combining a uniquely capable instrument with a clear scientific strategy, it has successfully validated dozens of new exoplanets, significantly enhancing the scientific return of the TESS mission and bringing us closer to discovering habitable worlds beyond our solar system. The MuSCAT2’s success has also led to the development of its successors, MuSCAT3 and MuSCAT4, installed on telescopes in Hawaii and Australia, respectively, creating a global network for exoplanet follow-up.
Main Projects
SPEAR
Exoplanet Atmospheres
Astrobiology
MuSCAT2
Space Missions
Collaborations
Deciphering the atmospheres of distant worlds
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