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The ancient question of whether life exists beyond Earth continues to fascinate us. A significant discovery now brings us closer to an answer. An international team, led by Chinese scientists from the Yunnan Observatories, has used a clever method called transit timing variation (TTV) to find a promising planet. They detected a “super-Earth”, named Kepler-725c, orbiting within the habitable zone of a sun-like star, Kepler-725.

The planet’s host star resembles our Sun but is younger, only 1.6 billion years old, with stronger surface magnetic (磁的) activity. Kepler-725c itself is large, about ten times Earth’s mass. It completes an orbit every 207.5 days, placing it within the habitable zone — where temperatures might allow liquid water– a key need for life. This system lies about 2,472 light years away from the solar system.

How did scientists find a planet they couldn’t directly observe? Researcher Wang Xiaobin explained the TTV method: it’s like noticing a clock running fast or slow, indicating someone secretly moved its hands. Instead of needing to see the planet transit its star or measuring the star’s wobble (摆动), TTV works differently. By carefully measuring tiny timing changes in the transits of another known planet in the system, the gas giant Kepler-725b (orbiting every 39.64 days), scientists inferred Kepler-725c’s presence, mass, and orbit.

The TTV technique is especially powerful for finding smaller, potentially Earth-like planets with longer orbits in habitable zones. It overcomes limitations of the transit and radial velocity methods. As researcher Sun Leilei noted, this discovery proves TTV’s potential to find low-mass planets around sun-like stars. It provides valuable targets and technical support for upcoming Chinese projects like the China Space Station Telescope (CSST) and the Earth 2.0 (ET) project.

The research team, a collaboration between the Yunnan Observatories, Xi’an Jiaotong-Liverpool University, the Nanjing Institute of Astronomical Optics and Technology, and Hamburg Observatory, emphasizes that more study is needed. They will combine TTV with other methods like transmission spectroscopy to see if Kepler-725c truly has Earth-like conditions.

1.1. What makes Kepler-725c possible for supporting life?

A Strong magnetic field.

B Host star’s youth.

C Close distance to Earth.

D Habitable zone position.

解析：选D。 D 细节理解题。第一、二段原文明确该行星位于宜居带（“within the habitable zone—where temperatures might allow liquid water”），这是支持液态水（生命的关键要素）存在的关键条件。故选D。

2.2. The method of transit timing variation(TTV) fundamentally measures ______.

A star brightness changes

B planet orbital shifts

C magnetic activity levels

D light-year distances

解析：选B。B 推理判断题。原文中通过时钟比喻说明TTV的原理，并且进一步解释“By carefully measuring tiny timing changes in the transits of another known planet in the system, the gas giant Kepler-725b (orbiting every 39.64 days), scientists inferred Kepler-725c’s presence, mass, and orbit.”通过仔细测量该系统中另一颗已知行星——气体巨星开普勒-725b（每39.64天绕轨道运行一次）的微小时间变化，科学家推断出开普勒-725c的存在、质量和轨道。由此可知，这个方法的本质是测量另一已知行星的轨道周期变化。故选B。

3.3. What advantage does TTV have over traditional methods?

A Detecting older stars.

B Finding distant solar systems.

C Locating small habitable planets.

D Measuring precise planet mass.

解析：选C。C 细节推理题。根据第四段中的“The TTV technique is especially powerful for finding smaller, potentially Earth-like planets with longer orbits in habitable zones.”可知，TTV技术在寻找更小的、可能与地球类似的、轨道更长、位于宜居带的行星方面尤其强大。故选C。

4.4. The research team plans to ______.

A develop new telescopes

B confirm planet conditions

C study only Kepler-725b

D abandon current methods

解析：选B。B 推理判断题。根据最后一段中的“They will combine TTV with other methods like transmission spectroscopy to see if Kepler-725c truly has Earth-like conditions.”可知，他们将把TTV与透射光谱等其他方法结合起来，看看开普勒-725c是否真的具有类似地球的条件。对应B项的“确认该行星的条件”。故选B。