A team of Chinese researchers has proposed launching a space telescope to look for a nearby “cousin” of the Earth – a planet of similar size and mass as our own, and orbiting in the habitable zone around a sun-like star. No such planet has been found yet, but it may hold the key to the question of “whether life is unique to Earth or ubiquitous in the universe”, according to project lead Ji Jianghui of the Purple Mountain Observatory at the Chinese Academy of Sciences (CAS) in Nanjing. Among the 5,000-plus exoplanets, or planets outside our solar system, detected so far, many are much larger than the Earth or dwell in the habitable zone of smaller and cooler stars such as a red dwarf, which are conditions less likely to host liquid water or life as we understand it. The Closeby Habitable Exoplanet Survey (CHES) mission, which Ji’s team has been working on for almost a decade, aims to monitor about 100 sun-like stars within a distance of 32 light years from the solar system, and measure tiny changes in their relative position in the sky to search for Earth-like planets around them. A planet and its host star influence each other’s motions due to mutual gravitational pull, and if scientists can detect a slight but periodic wobble in the host star’s position, there is a good chance it is being orbited by a planet. Ji said such a detection method was highly efficient, because “it can spot any Earth-like planet that exists in or near the habitable zone of a star”. In comparison, popular exoplanet-hunting missions such as Nasa’s Kepler telescope and TESS (Transiting Exoplanet Survey Satellite) can only observe planets whose orbits happen to align with our line of sight, which lowers their detection rate to only around 0.5 per cent. The CHES project expected to detect roughly 50 Earth-like planets or so-called super-Earths, he said. The astrometry method used by CHES was a classic technique in astronomy, but only became applicable to exoplanet research in recent years thanks to technological advances, noted Wang Wei, a scientist at the National Astronomical Observatories of China in Beijing. CHES needed to measure the wobble of a star to the accuracy of 1 micro arcsecond, which is as small as a one-millimetre move on the moon seen from the Earth, said Wang, who is not part of the CHES team. To achieve this accuracy, which is 10 times higher than what is now being used for the world’s flagship astrometry missions, Ji’s team has been working on and made breakthroughs with a key technology called laser focal plane metrology, funded by the CAS. China’s rover finds evidence of water on Mars more recently than thought The project will soon be reviewed by a panel of experts to decide if it will receive final approval to move from design to the implementation phase. If they get the green light, the team hopes to finish building the telescope in about five years’ time, and put it into orbit 1.5 million km (932,000 miles) away from the Earth at a location known as the Sun-Earth L2 Lagrange point, a stable and fuel-saving observation spot favoured by many existing spacecraft, including Nasa’s James Webb Space Telescope. Besides CHES, there are at least three other proposals related to exoplanet detection now being studied by the scientific community in China. Earth 2.0 will use seven telescopes to survey exoplanets in the Milky Way galaxy, with a transit approach similar to the Kepler telescope but a field of view 10 times more powerful. Like CHES, Earth 2.0 is also set to go through panel review in June and aims for 2026-2027 launch, if approved. Still in the conceptual design phase are the Miyin project, which plans to use multiple small-sized telescopes to search for habitable planets, and a very ambitious space telescope called HABITATS (HABItable Terrestrial planetary ATmospheric Surveyor). This 6-metre-aperture space telescope aims to detect water, oxygen and ozone molecules in the atmosphere of exoplanets, and aims to start operations within 15 to 20 years.