Such objects are considered a separate category of planets, especially if they are gas giants, often counted as sub-brown dwarfs. Rogue planets are those that do not orbit any star. However, the study of planetary habitability also considers a wide range of other factors in determining the suitability of a planet for hosting life. There is special interest in planets that orbit in a star's habitable zone (or sometimes called "goldilocks zone"), where it is possible for liquid water, a prerequisite for life as we know it, to exist on the surface. The discovery of exoplanets has intensified interest in the search for extraterrestrial life. The nearest exoplanets are located 4.2 light-years (1.3 parsecs) from Earth and orbit Proxima Centauri, the closest star to the Sun. However, there is evidence that extragalactic planets, exoplanets farther away in galaxies beyond the local Milky Way galaxy, may exist. Some exoplanets are so far away from the star that it is difficult to tell whether they are gravitationally bound to it.Īlmost all of the planets detected so far are within the Milky Way. Known orbital times for exoplanets vary from less than an hour (for those closest to their star) to thousands of years. ![]() However, according to some definitions of a planet (based on the nuclear fusion of deuterium ), it is too massive to be a planet and might be a brown dwarf instead. The most massive exoplanet listed on the NASA Exoplanet Archive is HR 2562 b, about 30 times the mass of Jupiter. The least massive exoplanet known is Draugr (also known as PSR B1257+12 A or PSR B1257+12 b), which is about twice the mass of the Moon. Assuming there are 200 billion stars in the Milky Way, it can be hypothesized that there are 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if planets orbiting the numerous red dwarfs are included. About 1 in 5 Sun-like stars have an " Earth-sized" planet in the habitable zone. In several cases, multiple planets have been observed around a star. Transit photometry and Doppler spectroscopy have found the most, but these methods suffer from a clear observational bias favoring the detection of planets near the star thus, 85% of the exoplanets detected are inside the tidal locking zone. ![]() There are many methods of detecting exoplanets. The James Webb Space Telescope (JWST) is expected to discover more exoplanets, and also much more about exoplanets, including composition, environmental conditions and potential for life. As of 1 July 2023, there are 5,425 confirmed exoplanets in 4,001 planetary systems, with 868 systems having more than one planet. A different planet, initially detected in 1988, was confirmed in 2003. The first confirmation of detection occurred in 1992. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. Note that this is not a video of real-time observation, but one created using 7-10 still images over a decade, and using a computer to interpolate movement.Īn exoplanet or extrasolar planet is a planet outside the Solar System. Four exoplanets orbiting counterclockwise with their host star ( HR 8799).
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