Smallest exoplanets discovered
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Smallest Exoplanets Discovered: Key Findings
Ultra-Short-Period and Sub-Earth-Sized Exoplanets
Recent discoveries have identified some of the smallest exoplanets, many of which are ultra-short-period (USP) planets with orbits less than one day. Notably, Kepler-879c, with a radius of just 0.4 times that of Earth, is among the smallest known exoplanets, orbiting its host star in less than 16 hours. Other small USPs include Kepler-158d (0.43 Earth radii), Kepler-1489c (0.51 Earth radii), Kepler-963c (0.6 Earth radii), and KOI-4978.02 (0.7 Earth radii). These planets are not only small but also extremely close to their host stars, with orbits within five stellar radii, making them some of the most compact planetary systems discovered to date .
Mars-Sized and Earth-Sized Exoplanets
The smallest validated ultra-short-period planet is KOI-4777.01, a Mars-sized exoplanet with a radius of 0.51 Earth radii, orbiting its M dwarf host every 9.9 hours. This planet is currently the smallest confirmed USP planet . In addition, the Kepler-20 system includes two of the smallest exoplanets: one Earth-sized (1.03 Earth radii) and another even smaller at 0.87 Earth radii. These planets are likely rocky and represent some of the earliest detections of true Earth analogues .
Young, Nearby Earth-Sized Exoplanets
HD 63433d is a recently discovered Earth-sized planet (1.1 Earth radii) orbiting a young, Sun-like star just 22 parsecs away. It is the smallest confirmed exoplanet with an age under 500 million years and is the nearest young Earth-sized planet known. Its host star's brightness makes it an excellent target for further atmospheric studies 23.
Kepler-78b and the Population of Small USPs
Kepler-78b, with a radius of 1.2 Earth radii and an orbital period of just 8.5 hours, is notable for being the smallest planet for which mass, radius, and dayside brightness have all been measured. Studies show that USP planets like Kepler-78b are almost always smaller than twice Earth's radius and are relatively common, often found in compact multi-planet systems .
Broader Context: Kepler’s Contribution
The Kepler mission has been instrumental in discovering the smallest exoplanets orbiting normal stars, including those similar in size to Earth. Kepler’s data have provided the first comprehensive look at the distribution and characteristics of small exoplanets, revealing that planets as small as Earth are common in the galaxy .
Conclusion
The smallest exoplanets discovered to date include Mars-sized and sub-Earth-sized worlds, many of which are ultra-short-period planets orbiting very close to their host stars. Notable examples are Kepler-879c, KOI-4777.01, and the Earth-sized HD 63433d. These discoveries, enabled by advanced detection methods and missions like Kepler and TESS, are crucial for understanding planet formation and the diversity of planetary systems in our galaxy 1236+3 MORE.
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