Intl efforts led by Chinese scientists discover super-Earth with new technique

<article><section data-type="rtext"><img data-alt="An illustration of the Kepler-725c Photo: Yunnan Observatories of the Chinese Academy of Sciences" src="//img.huanqiucdn.cn/dp/api/files/imageDir/dc1f58195c3b8c5ffe7d1dc339bbddb7.jpeg?imageView2/2/w/750" />Are we alone in the universe, and does another planet exist that could support life like Earth? It is an ancient question that has long captivated humanity. For the first time, an international collaboration led by Chinese researchers with the Yunnan Observatories of the Chinese Academy of Sciences has adopted the transit timing variation (TTV) technique and detected the presence of a "super-Earth" codenamed Kepler-725c within the habitable zone of the sun-like star Kepler-725, which is a promising candidate for potential habitability. The breakthrough was published in the journal Nature Astronomy on Tuesday. And the discovery based on the TTV technique offers researchers a new approach to detecting exo-Earths, making the technique a powerful tool for discovering "invisible planets" in the habitable zones of sun-like stars. It also provides new observational targets and technical support for upcoming Chinese astronomical projects, such as the China Space Station Telescope (CSST) and the Earth 2.0 (ET) project, Global Times learned from the Yunnan observatories on Wednesday. According to the study, the host star has a spectral type similar to that of the sun, but it is younger, only 1.6 billion years old and exhibits much more intense magnetic activity on its surface than the sun. And the super-Earth Kepler-725c has a mass approximately 10 times that of the Earth and orbits its host star every 207.5 days, a period comparable to Earth's own. And more crucially, the planet lies within the habitable zone of its host star, the region around a star where the temperature is suitable for liquid water to exist. Wang Xiaobin, a member of the team and researcher with Yunnan observatories, explained that the TTV technique is akin to "observing whether a clock is running fast or slow to determine if someone has secretly moved its hands." "This method does not require observing the planet-to-be-discovered transiting its host star, nor does it rely on detecting the star's slight wobble along the line of sight. Instead, by simply measuring the transit timing of another planet in orbital resonance with the target planet, we can indirectly sense its presence," Wang said. The TTV technique is particularly well-suited for detecting low-mass, long-period planets in the habitable zone, effectively compensating for the limitations of current transit and radial velocity methods, Wang said, noting that this discovery marks a critical step forward for Chinese research teams in the quest to find a second Earth, or Earth 2.0. "By analyzing the TTV signals of Kepler-725b, a gas giant planet with a 39.64-day period in the same system, the team has successfully inferred the mass and orbital parameters of the hidden planet Kepler-725c," Sun Leilei, the first and co-corresponding author of the study, also from the Yunnan observatories, told the Global Times on Wednesday. Unlike the transit method and radial velocity methods, the TTV technique is not subject to their specific observational challenges. Instead, it can indirectly detect the presence of a planet by analyzing the TTVs of another known planet in orbital resonance with it, Sun said. "It demonstrates the potential of the TTV technique to detect low-mass planets in habitable zones of sun-like stars." Based on the results of this study, once the European PLATO mission and Chinese ET mission are operational, the TTV method is expected to greatly enhance the ability to detect a second Earth, according to the Yunnan observatories. The Global Times learned from the Yunnan observatories that the research was jointly conducted by the Yunnan Observatories of the Chinese Academy of Sciences, Xi'an Jiaotong-Liverpool University, Nanjing Institute of Astronomical Optics and Technology and Hamburg Observatory. At the same time, we will also integrate other observational methods, such as exoplanet transmission spectroscopy, emission spectroscopy and direct imaging, to further investigate whether these habitable zone planets truly possess conditions suitable for Earth-like life, said Wang. "In terms of international collaboration, we will actively participate in the data analysis of Europe's PLATO and ARIEL missions in the future, working together with scientists around the world to advance the search for Earth-like extraterrestrial life."</section></article>

Are we alone in the universe, and does another planet exist that could support life like Earth? It is an ancient question that has long captivated humanity. For the first time, an international collaboration led by Chinese researchers with the Yunnan Observatories of the Chinese Academy of Sciences has adopted the transit timing variation (TTV) technique and detected the presence of a "super-Earth" codenamed Kepler-725c within the habitable zone of the sun-like star Kepler-725, which is a promising candidate for potential habitability.

The breakthrough was published in the journal Nature Astronomy on Tuesday. And the discovery based on the TTV technique offers researchers a new approach to detecting exo-Earths, making the technique a powerful tool for discovering "invisible planets" in the habitable zones of sun-like stars. It also provides new observational targets and technical support for upcoming Chinese astronomical projects, such as the China Space Station Telescope (CSST) and the Earth 2.0 (ET) project, Global Times learned from the Yunnan observatories on Wednesday.

According to the study, the host star has a spectral type similar to that of the sun, but it is younger, only 1.6 billion years old and exhibits much more intense magnetic activity on its surface than the sun. And the super-Earth Kepler-725c has a mass approximately 10 times that of the Earth and orbits its host star every 207.5 days, a period comparable to Earth's own. And more crucially, the planet lies within the habitable zone of its host star, the region around a star where the temperature is suitable for liquid water to exist.

Wang Xiaobin, a member of the team and researcher with Yunnan observatories, explained that the TTV technique is akin to "observing whether a clock is running fast or slow to determine if someone has secretly moved its hands."

"This method does not require observing the planet-to-be-discovered transiting its host star, nor does it rely on detecting the star's slight wobble along the line of sight. Instead, by simply measuring the transit timing of another planet in orbital resonance with the target planet, we can indirectly sense its presence," Wang said.

The TTV technique is particularly well-suited for detecting low-mass, long-period planets in the habitable zone, effectively compensating for the limitations of current transit and radial velocity methods, Wang said, noting that this discovery marks a critical step forward for Chinese research teams in the quest to find a second Earth, or Earth 2.0.

"By analyzing the TTV signals of Kepler-725b, a gas giant planet with a 39.64-day period in the same system, the team has successfully inferred the mass and orbital parameters of the hidden planet Kepler-725c," Sun Leilei, the first and co-corresponding author of the study, also from the Yunnan observatories, told the Global Times on Wednesday.

Unlike the transit method and radial velocity methods, the TTV technique is not subject to their specific observational challenges. Instead, it can indirectly detect the presence of a planet by analyzing the TTVs of another known planet in orbital resonance with it, Sun said. "It demonstrates the potential of the TTV technique to detect low-mass planets in habitable zones of sun-like stars."

Based on the results of this study, once the European PLATO mission and Chinese ET mission are operational, the TTV method is expected to greatly enhance the ability to detect a second Earth, according to the Yunnan observatories.

The Global Times learned from the Yunnan observatories that the research was jointly conducted by the Yunnan Observatories of the Chinese Academy of Sciences, Xi'an Jiaotong-Liverpool University, Nanjing Institute of Astronomical Optics and Technology and Hamburg Observatory.

At the same time, we will also integrate other observational methods, such as exoplanet transmission spectroscopy, emission spectroscopy and direct imaging, to further investigate whether these habitable zone planets truly possess conditions suitable for Earth-like life, said Wang. "In terms of international collaboration, we will actively participate in the data analysis of Europe's PLATO and ARIEL missions in the future, working together with scientists around the world to advance the search for Earth-like extraterrestrial life."