  The Closeby Habitable Exoplanet Survey (CHES) mission is proposed to discover
habitable-zone Earth-like planets of the nearby solar-type stars ($\sim
10~\mathrm{pc}$ away from our solar system) via micro-arcsecond relative
astrometry. The major scientific objectives of CHES are: to search for Earth
Twins or terrestrial planets in habitable zones orbiting 100 FGK nearby stars;
further to conduct a comprehensive survey and extensively characterize the
nearby planetary systems. The primary payload is a high-quality,
low-distortion, high-stability telescope. The optical subsystem is a coaxial
three-mirror anastigmat (TMA) with a $1.2 \mathrm{~m}$-aperture, $0.44^{\circ}
\times 0.44^{\circ}$ field of view and $500 \mathrm{~nm}-900 \mathrm{~nm}$
working waveband. The camera focal plane is composed of 81 MOSAIC scientific
CMOS detectors each with $4 \mathrm{~K} \times 4 \mathrm{~K}$ pixels. The
heterodyne laser interferometric calibration technology is employed to ensure
micro-arcsecond level (1 $\mu$as) relative astrometry precision to meet the
requirements for detection of Earth-like planets. CHES satellite operates at
the Sun-Earth L2 point and observes the entire target stars for 5 years. CHES
will offer the first direct measurements of true masses and inclinations of
Earth Twins and super-Earths orbiting our neighbor stars based on
micro-arcsecond astrometry from space. This will definitely enhance our
understanding of the formation of diverse nearby planetary systems and the
emergence of other worlds for solar-type stars, and finally to reflect the
evolution of our own solar system.
