Smallest planet solar system
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The Smallest Planet in the Solar System
Mercury: The Smallest Planet
Mercury holds the title of the smallest planet in our solar system. With a diameter of approximately 4,880 kilometers, it is only about 2/5 the size of Earth8. Despite its small size, Mercury is a significant planet due to its proximity to the Sun and its unique characteristics.
Characteristics of Mercury
Size and Composition
Mercury's small size makes it even smaller than some of the moons in our solar system, such as Ganymede and Titan, which orbit Jupiter and Saturn, respectively8. Mercury is primarily composed of a large metallic core surrounded by a silicate mantle and crust. This composition is similar to that of Earth, but Mercury's core is proportionally larger.
Surface and Atmosphere
Mercury's surface is heavily cratered, resembling the Moon, and it lacks a significant atmosphere to protect it from meteoroid impacts9. This cratered surface provides valuable insights into the conditions of the early solar system and the processes that shaped planetary bodies9.
Comparison with Other Small Planets and Exoplanets
Exoplanets Smaller than Mercury
Recent discoveries have identified exoplanets that are even smaller than Mercury. For instance, Kepler-37b, an exoplanet orbiting the star Kepler-37, is significantly smaller than Mercury, with a size comparable to that of the Moon6. This tiny planet is likely rocky and lacks an atmosphere, similar to Mercury6.
Earth-Sized and Smaller Exoplanets
The discovery of Earth-sized and smaller exoplanets has expanded our understanding of planetary formation and characteristics. For example, the Kepler-20 system hosts two planets, one Earth-sized and another smaller than Earth, with radii of 1.03 and 0.87 times that of Earth, respectively10. These planets are believed to be rocky, composed of iron and silicate, and provide a comparison to Mercury's composition and size10.
Conclusion
Mercury remains the smallest planet in our solar system, with unique characteristics that offer insights into planetary formation and the early solar system. Comparisons with smaller exoplanets, such as Kepler-37b, highlight the diversity of planetary sizes and compositions beyond our solar system. Understanding these small planets, both within and outside our solar system, continues to be a crucial aspect of planetary science.
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Most relevant research papers on this topic
Occurrence and core-envelope structure of 1–4× Earth-size planets around Sun-like stars
Small, 1–4 Earth-size planets are extremely common around Sun-like stars, with 26% having them with orbital periods under 100 days, and 11% receiving 1–4 the incident stellar light that warms our Earth.
Highly CitedHyades Member K2-136c: The Smallest Planet in an Open Cluster with a Precisely Measured Mass
K2-136c is the smallest planet in an open cluster with a precisely measured mass, and it is one of the youngest planets with a mass measurement.
Zodiacal Exoplanets in Time (ZEIT). VI. A Three-planet System in the Hyades Cluster Including an Earth-sized Planet
Three planets, including an Earth-sized one, have been discovered in the Hyades cluster, enabling a test of earlier claims that young planets are less dense than older ones.
Highly CitedDiscovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager
The Gemini Planet Imager has discovered a Jupiter-like planet orbiting a young star, offering a new insight into solar system origins and a new era in next-generation planetary imaging.
Highly CitedA sub-Mercury-sized exoplanet
Kepler-37b, a sub-Mercury-sized exoplanet, is likely rocky and without atmosphere or water, similar to Mercury, orbiting a Sun-like star.
Highly CitedThe HARPS survey for southern extra-solar planets. II. A 14 Earth-masses exoplanet around μ Arae
A 14 Earth-mass exoplanet has been discovered orbiting the star mu Ara, with a mass slightly smaller than Uranus, and may be considered an ice giant or super-earth planet depending on core-accretion and migration models.
Highly CitedTwo Earth-sized planets orbiting Kepler-20
Two Earth-sized and smaller planets have been discovered orbiting Kepler-20, with the likelihood of their being rocky and possibly with thick water vapour atmospheres.
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