Kepler-7b stands as a remarkable achievement in the field of exoplanetary science, being one of the first five exoplanets confirmed by NASA's Kepler spacecraft. This discovery, made within the first 33.5 days of Kepler's science operations, unveiled a planet that challenged existing theories and opened new avenues for the study of planets beyond our solar system.
Characteristics and Orbit
Kepler-7b is classified as a hot Jupiter, a type of gas giant that orbits very close to its host star. Despite having only about half the mass of Jupiter, Kepler-7b is nearly 1.5 times its size, making it one of the most diffuse planets known at the time of its discovery. Its density is comparable to expanded polystyrene, a property that puzzled scientists as it did not align with standard theories of planet formation.
The planet orbits a star that is slightly hotter and significantly larger than our Sun, situated in the Lyra constellation. Kepler-7b's host star, Kepler-7, has a radius 184% that of the Sun and a mass 135% greater, indicating that it is nearing the end of its main sequence life. Kepler-7b completes an orbit around this star every 4.8855 days at a distance of approximately 0.06224 AU, making it the furthest orbiting planet among the first five discovered by Kepler.
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| Image Credit: NASA |
One of the most groundbreaking aspects of Kepler-7b's discovery was the creation of the first cloud map beyond our solar system. Using data from both NASA's Kepler and Spitzer space telescopes, astronomers were able to map the planet's cloud coverage. Kepler's visible-light observations revealed a bright spot on Kepler-7b's western hemisphere, which, with the help of Spitzer's data, was determined to be caused by clouds rather than heat. This discovery suggested that these clouds could be composed of rock and iron due to the planet's extremely high temperature, which reaches nearly 1540 K (1267°C or 2313°F). The cloud patterns on Kepler-7b were found to be remarkably stable, differing from the dynamic weather systems we experience on Earth.
Host Star: Kepler-7
Kepler-7, the star around which Kepler-7b orbits, is the largest among the first five stars to host planets discovered by the Kepler mission. It is slightly hotter than the Sun, with an effective temperature of 5933 K, and has 128% of the Sun's iron content. The star's large size and mass suggest it will soon exhaust its nuclear fuel and leave the main sequence, transitioning into the next phase of its stellar evolution.
Discovery and Confirmation
The journey to Kepler-7b's confirmation began in 2009, during the final tests of Kepler's photometer. Kepler observed 50,000 stars, including Kepler-7, and detected light curves indicative of planetary transits. After initial observations and follow-up studies using Doppler spectroscopy, speckle imaging, and radial velocity measurements from various observatories, Kepler-7b was confirmed as a planet. The discovery was officially announced on January 4, 2010, at the 215th meeting of the American Astronomical Society.
In 2011, Kepler-7b was also detected through brightness variations caused by reflected starlight, revealing that the planet has a relatively high geometric albedo of 0.3, indicating it reflects about 30% of the starlight that hits it.
Conclusion
Kepler-7b represents a significant milestone in the exploration of exoplanets. Its discovery not only challenged existing theories of planetary formation but also pioneered new methods of studying the atmospheres and cloud patterns of distant worlds. As the first exoplanet to have a cloud map created, Kepler-7b continues to intrigue scientists and expand our understanding of the universe beyond our solar system.