Scientists discover hidden "super-Earth" with extreme climate shifts that may be habitable
By isabelle // 2025-06-12
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  • Astronomers discovered Kepler-725c, a massive "super-Earth," using indirect transit timing variations (TTVs) without direct observation.
  • The planet orbits a sun-like star 2,472 light-years away with extreme orbital eccentricity, fluctuating in and out of the habitable zone.
  • Kepler-725c’s gravitational influence caused detectable irregularities in the orbit of neighboring gas giant Kepler-725b, revealing its presence.
  • Its elliptical orbit causes wild climate shifts, potentially making it intermittently habitable but with extreme temperature variations.
  • The discovery showcases TTVs as a powerful tool for finding hidden exoplanets, expanding the search for life beyond traditional methods.
In a groundbreaking discovery that pushes the boundaries of exoplanet research, astronomers have identified a massive "super-Earth" orbiting a distant star without ever directly seeing it. The planet, named Kepler-725c, lies 2,472 light-years away and exhibits such extreme orbital eccentricity that it dips in and out of its star’s habitable zone, creating potentially violent climate shifts. This revelation, made possible by an indirect detection method called transit timing variations (TTVs), raises profound questions about the limits of life-supporting conditions in the universe. The findings, published in Nature Astronomy by an international team led by Sun Leilei of China’s Yunnan Observatories, underscore the ingenuity of modern astronomy. While traditional exoplanet hunters rely on direct observations of planets crossing their host stars, Kepler-725c remained hidden—until its gravitational influence betrayed its presence.

The hidden planet revealed

Kepler-725c orbits a sun-like star alongside another known planet, the gas giant Kepler-725b. Researchers detected subtle irregularities in Kepler-725b’s transit schedule, signaling delays and accelerations caused by the gravitational tug of its unseen neighbor. "By analyzing the TTV signals of Kepler-725b, the team has successfully inferred the mass and orbital parameters of the hidden planet Kepler-725c," Sun explained. This method bypasses the limitations of conventional transit detection, which often misses planets with longer orbits or misaligned orbital planes. TTVs, however, expose these hidden worlds by measuring their gravitational fingerprints. Kepler-725c’s mass is staggering—10 times that of Earth—placing it at the upper limit of super-Earth classification. Yet its most striking feature is its elliptical orbit, with an eccentricity of 0.44 (compared to Earth’s near-circular 0.0167).

A world of extremes

The planet’s oval-shaped trajectory means its distance from its star varies dramatically. Over its 207.5-day year, Kepler-725c swings from the inner edge of the habitable zone — where liquid water could exist — to regions far colder. While it receives 1.4 times Earth’s solar radiation on average, this fluctuates wildly. Such extremes could render it habitable only intermittently, with potential consequences for any hypothetical life. "Kepler-725c’s discovery demonstrates the potential of the TTV technique to detect low-mass planets in habitable zones of sun-like stars," Sun noted. The planet’s unusual orbit also provides a real-world test case for climate models of eccentric exoplanets. If it retains an atmosphere, seasonal swings could be catastrophic, with temperatures soaring and plunging as the planet moves closer to or farther from its star.

The search for life beyond Earth

The discovery highlights the challenges of defining habitability. While Kepler-725c spends part of its orbit in the Goldilocks zone, its climate may be too unstable for life as we know it. Unlike transiting planets, its atmosphere cannot be studied with the James Webb Space Telescope, leaving key questions unanswered. Yet hope remains. The European Space Agency’s PLATO mission, launching in 2026, promises to uncover more such worlds using TTVs. Unlike radial velocity or transit methods, which favor short-period planets, TTVs excel at finding longer-orbit exoplanets potentially including more temperate candidates. Kepler-725c joins a growing catalog of super-Earths, a class absent from our solar system. These planets, with masses 2 to 10 times that of Earth, challenge planetary scientists. Could they host plate tectonics? Dense atmospheres? Life? "We don’t really know what such planets are like," admitted researchers, citing the lack of local examples. The study also reinforces a sobering truth: habitability requires more than just orbital position. Stability, atmospheric composition, and geological activity all play critical roles. While Kepler-725c’s extremes make it a poor candidate for life, its detection proves that hidden worlds — some perhaps more Earth-like — await discovery. The unveiling of Kepler-725c marks a triumph of indirect detection methods, expanding our toolkit for exploring the cosmos. As astronomers refine TTV techniques and prepare for next-generation telescopes, the search for life enters a new phase, and it's one in which even invisible planets can no longer hide. For now, Kepler-725c stands as a reminder of the universe’s complexity: a super-Earth with a split personality, alternately welcoming and hostile to the very conditions that sustain life. Sources for this article include: LiveScience.com Earth.com Phys.org Science.NASA.gov
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