"Mercury (planet) Mercury is the smallest and innermost planet in the Solar System. Its orbital period around the Sun of 87.97 days is the shortest of all the planets in the Solar System. It is named after the Roman deity Mercury, the messenger of the gods. Like Venus, Mercury orbits the Sun within Earth's orbit as an ""inferior planet"", and never exceeds 28° away from the Sun. When viewed from Earth, this proximity to the Sun means the planet can only be seen near the western or eastern horizon during the early evening or early morning. At this time it"
"Proxima Centauri b Proxima Centauri b (also called Proxima b or Alpha Centauri Cb) is an exoplanet orbiting in the habitable zone of the red dwarf star Proxima Centauri, which is the closest star to the Sun and part of a triple star system. It is located about 4.2 light-years (1.3 parsecs, 40 trillion km, or 25 trillion miles) from Earth in the constellation of Centaurus, making it the closest known exoplanet to the Solar System. Proxima Centauri b orbits the star at a distance of roughly with an orbital period of approximately 11.2 Earth days, and has an estimated"
"the Sun, which it orbits every 87.97 days. Kepler-9d Kepler-9d, formerly known as KOI-377.03, is a planet in orbit around the sunlike star Kepler-9. Initially discovered by Kepler spacecraft, a terrestrial planet-searching satellite built and operated by NASA, Kepler-9d is most likely a Super-Earth, with an estimated radius approximately 60% larger than that of Earth's, although its exact mass cannot be determined. Kepler-9d orbits Kepler-9 every 1.56 days at a distance of .0273 AU from its star, an extremely close distance. Although Kepler-9d is the closest planet to its star in its system, it is named Kepler-9d instead of Kepler-9b"
"may be orbiting Sun-like stars. The nearest such planet may be 12 light-years away. Scientific findings since the 1990s have greatly influenced the scope of the fields of astrobiology, models of planetary habitability and the search for extraterrestrial intelligence (SETI). NASA and the SETI Institute have proposed categorising the increasing number of planets found using a measure called the Earth Similarity Index (ESI) based on mass, radius and temperature. According to this measure, as of 23 July 2015, the confirmed planet currently thought to be most similar to Earth on mass, radius and temperature is Kepler-438b. Scientists estimate that there"
"Venus's orbit is the closest to circular, with an eccentricity of less than 0.01. When Venus lies between Earth and the Sun in inferior conjunction, it makes the closest approach to Earth of any planet at an average distance of . The planet reaches inferior conjunction every 584 days, on average. Because of the decreasing eccentricity of Earth's orbit, the minimum distances will become greater over tens of thousands of years. From the year 1 to 5383, there are 526 approaches less than 40 million km; then there are none for about 60,158 years. All the planets in the Solar"
"Venus for the seventh and last time, decreasing its period to 88 or 89 days and allowing it to approach closer to the Sun. The perihelion distances above are from the center of the Sun. For altitude above the surface, subtract one solar radius ≈ 0.7 Gm.<br> By way of comparison, the planet Mercury orbits the Sun at a distance varying from about 46.0 Gm (46,001,200 km) at its closest to about 69.8 Gm (69,816,900 km) at its farthest. Parker Solar Probe Parker Solar Probe (previously Solar Probe, Solar Probe Plus, or Solar Probe+, abbreviated PSP) is a NASA robotic"
"Neptune Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times the mass of Earth and slightly larger than Neptune. Neptune orbits the Sun once every 164.8 years at an average distance of . It is named after the Roman god of the sea and has the astronomical symbol ♆, a stylised version of the"
"to as ""volatiles"". The distance from Earth to the Sun is . For comparison, the radius of the Sun is . Thus, the Sun occupies 0.00001% (10 %) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly one millionth (10) that of the Sun. Jupiter, the largest planet, is from the Sun and has a radius of , whereas the most distant planet, Neptune, is from the Sun. With a few exceptions, the farther a planet or belt is from the Sun, the larger the distance between its orbit and"
"approach to the Sun) is estimated to have occurred around September 2010. Aphelion (furthest distance from the Sun) is estimated to have occurred around February 2016. , the asteroid is estimated to be from Earth. Perihelion (closest approach to the Sun) may not occur again until August 2021. Orbits computed with only a handful of observations can be unreliable. Short observation arcs can result in computer generated orbits rejecting some data unnecessarily. The 2018 JPL orbit determination shows a semi-major axis of 4.9 AU (albeit with a large 20 AU uncertainty) which would be near Jupiter's orbit. Such an orbit"
"in the WGSN's second bulletin issued in October 2016. The next additions were done on 1 February, 30 June, 5 September and 19 November 2017, and on 6 June 2018. All are included on the current List of IAU-approved Star Names, last updated on 1 June 2018. The star nearest to Earth is typically referred to simply as ""the Sun"" or its equivalent in the language being used (for instance, if two astronomers were speaking French, they would call it ""le Soleil""). However, it is sometimes called by its Latin name, Sol, in science fiction. With the advent of the"
"Sun's mass and that is orbited by a white dwarf, Sirius B. The nearest brown dwarfs are the binary Luhman 16 system at 6.6 light-years. Other systems within ten light-years are the binary red-dwarf system Luyten 726-8 (8.7 ly) and the solitary red dwarf Ross 154 (9.7 ly). The closest solitary Sun-like star to the Solar System is Tau Ceti at 11.9 light-years. It has roughly 80% of the Sun's mass but only 60% of its luminosity. The closest known free-floating planetary-mass object to the Sun is WISE 0855−0714, an object with a mass less than 10 Jupiter masses roughly"
"that between Saturn and the Sun (11.2 AU). Alpha Centauri C, or Proxima Centauri, is a small and faint red dwarf (Class M). Though not visible to the naked eye, Proxima Centauri is the closest star to the Sun at a distance of , being slightly closer than Alpha Centauri AB at a distance of . Currently, the distance between Proxima Centauri and Alpha Centauri AB is about , equivalent to about 430 times the radius of Neptune's orbit. Proxima Centauri b is an Earth-sized exoplanet in the habitable zone of Proxima Centauri; it was discovered in 2016. ""α Centauri"""
"the Drake equation, which estimates the number of intelligent, communicating civilizations that exist in the Milky Way. There are exoplanets that are much closer to their parent star than any planet in the Solar System is to the Sun, and there are also exoplanets that are much farther from their star. Mercury, the closest planet to the Sun at 0.4 AU, takes 88 days for an orbit, but the shortest known orbits for exoplanets take only a few hours, e.g. Kepler-70b. The Kepler-11 system has five of its planets in shorter orbits than Mercury's, all of them much more massive"
"of the distance from the Earth to the Sun. Comparatively, Mercury, the closest planet to the Sun, has a semi-major axis distance of 0.39 AU. Proxima Centauri b receives about 65% of the amount of radiative flux from its host star that the Earth receives from the Sun - for comparison Mars receives about 43%. Most of the radiative flux from Proxima Centauri is in the infrared spectrum. In the visible spectrum the exoplanet receives only ~3% of the PAR (400-700 nm) of Earth irradiance - for comparison Jupiter receives 3.7% and Saturn 1.1%. So it would usually not get"
"course of its year. A body's closest approach to the Sun is called its ""perihelion"", whereas its most distant point from the Sun is called its ""aphelion"". The orbits of the planets are nearly circular, but many comets, asteroids, and Kuiper belt objects follow highly elliptical orbits. The positions of the bodies in the Solar System can be predicted using numerical models. Although the Sun dominates the system by mass, it accounts for only about 2% of the angular momentum. The planets, dominated by Jupiter, account for most of the rest of the angular momentum due to the combination of"
"Kepler-20f Kepler-20f (also known by its Kepler Object of Interest designation ""KOI-70.05"") is an exoplanet orbiting the Sun-like star Kepler-20, the second outermost of five such planets discovered by NASA's ""Kepler"" spacecraft. It is located approximately 929 light-years (285 parsecs, or about km) from Earth in the constellation Lyra. The exoplanet was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured. The planet is notable as it has the closest radius to Earth known so far. Kepler-20f is very likely (>95% chance) a rocky"
"Earth's orbit All celestial bodies in the Solar System, including planets such as our own, orbit around the Solar System's centre of mass. The sun makes up 99.76% of this mass which is why the centre of mass is extremely close to the sun. Earth's orbit is the trajectory along which Earth travels around the Sun. The average distance between the Earth and the Sun is 149.60 million km (92.96 million mi), and one complete orbit takes days (1 sidereal year), during which time Earth has traveled 940 million km (584 million mi). Earth's orbit has an eccentricity of 0.0167."
"is one third of the Sun. Kepler-42 has an appreciable proper motion of up to 431±8 mas/yr. Due to its small size and low temperature, the star's habitable zone is much closer to the star than Earth is to the Sun. On 10 January 2012, using the Kepler Space Telescope three transiting planets were discovered in orbit around Kepler-42. These planets' radii range from approximately those of Mars to Venus. The Kepler-42 system is only the second known system containing planets of Earth's radius or smaller (the first was the Kepler-20 system pictured at left). These planets' orbits are also"
"was found that it will pass through its perihelion (the point of its orbit where it is closest to the Sun) on 9 April 1990 at a distance of about 53 million kilometres, inside the orbit of Mercury, the planet closest to the Sun. Thereafter it will move outwards again and, by good luck, it will come within 38 million kilometres of the Earth on May 25. It will be well situated in the sky for observation from the northern hemisphere after 20 April 1990 when it can be seen low above the NW horizon, just after sunset, and even"
"are easier to detect. On November 4, 2013, astronomers reported, based on ""Kepler"" data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs in the Milky Way. 11 billion of these may be orbiting Sun-like stars. Proxima Centauri b, located about 4.2 light-years (1.3 parsecs) from Earth in the constellation of Centaurus, is the nearest known exoplanet, and is orbiting in the habitable zone of its star. The CHZ is also of particular interest to the emerging field of habitability of natural satellites, because planetary-mass moons in"
"are gravitationally bound to the star. Almost all of the planets detected so far are within the Milky Way. Nonetheless, evidence suggests that extragalactic planets, exoplanets further away in galaxies beyond the local Milky Way galaxy, may exist. The nearest exoplanet is Proxima Centauri b, located 4.2 light-years (1.3 parsecs) from Earth and orbiting Proxima Centauri, the closest star to the Sun. The discovery of exoplanets has intensified interest in the search for extraterrestrial life. There is special interest in planets that orbit in a star's habitable zone, where it is possible for liquid water, a prerequisite for life on"
"by the Apollo program. </math>, where ""m"" is the mass of Earth, ""a"" is an astronomical unit, and ""M"" is the mass of the Sun. So the radius in AU is about formula_1.</ref> Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year."
"orbit. The orbital ellipse goes through each of the six Earth images, which are sequentially the perihelion (periapsis — nearest point to the Sun) on anywhere from January 2 to January 5, the point of March equinox on March 19, 20, or 21, the point of June solstice on June 20, 21, or 22, the aphelion (apoapsis — farthest point from the Sun) on anywhere from July 3 to July 5, the September equinox on September 22, 23, or 24, and the December solstice on December 21, 22, or 23. The diagram shows an exaggerated shape of Earth's orbit; the"
"Kepler-9d Kepler-9d, formerly known as KOI-377.03, is a planet in orbit around the sunlike star Kepler-9. Initially discovered by Kepler spacecraft, a terrestrial planet-searching satellite built and operated by NASA, Kepler-9d is most likely a Super-Earth, with an estimated radius approximately 60% larger than that of Earth's, although its exact mass cannot be determined. Kepler-9d orbits Kepler-9 every 1.56 days at a distance of .0273 AU from its star, an extremely close distance. Although Kepler-9d is the closest planet to its star in its system, it is named Kepler-9d instead of Kepler-9b because two gas giants, Kepler-9b and Kepler-9c, were"
"Kepler-20e Kepler-20e is an exoplanet orbiting Kepler-20. The planet is notable as it is the first planet with a smaller radius than Earth found orbiting a Sun-like star. The planet is second-closest to the star after Kepler-20b, and at , it is far too hot to have liquid water on its surface. Along with the other four planets in the system, Kepler-20e was announced on 20 December 2011. With a semimajor axis of 0.0507 AUs, Kepler-20e's orbit has a period of 6.098 days (with an extremely small margin of error). The orbit has an inclination of 87.50°, making its transits"
"billion Earth-sized planets orbiting in the habitable zones of sun-like stars and red dwarf stars within the Milky Way Galaxy. 11 billion of these estimated planets may be orbiting sun-like stars. Since there are about 100 billion stars in the galaxy, this implies is roughly 0.4. The nearest planet in the habitable zone is Proxima Centauri b, which is as close as about 4.2 light-years away. The consensus at the Green Bank meeting was that had a minimum value between 3 and 5. Dutch science journalist Govert Schilling has opined that this is optimistic. Even if planets are in the"
"than the distance from the Sun to Mercury. Its mass makes it more likely to be a Class II or Class III planet in the Sudarsky model. The presence of surface liquid water is possible on sufficiently massive satellites should they exist. Gliese 876 e, discovered in 2010, has a mass similar to that of the planet Uranus and its orbit takes 124 days to complete. Gliese 876 Gliese 876 is a red dwarf approximately 15 light-years away from Earth in the constellation of Aquarius. It is the one of the closest known stars to the Sun confirmed to possess"
"its mission, Rosetta was crashed into the comet′s surface in 2016. Near-Earth object A near-Earth object (NEO) is any small Solar System body whose orbit brings it to proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). If a NEO's orbit crosses the Earth's and the object is larger than across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids, but a small fraction are comets. There are over 19,000 known near-Earth asteroids (NEAs), over a"
"Earth days and its orbital radius is only about 7% that of the Earth, about 11 million km, while the Earth is 150 million kilometres from the Sun. Since the host star is smaller and colder than the Sun—and thus less luminous—this distance places the planet on the ""warm"" edge of the habitable zone around the star according to Udry's team. Note that in astrophysics, the ""habitable zone"" is defined as the range of distances from the star at which a planet could support liquid water on its surface: it should not be taken to mean that the planet's environment"
"observable from the Solar System. Like the other planets of the system, the planet has a high maximum eccentricity of 0.28, but the lowest in that system. Kepler-20e Kepler-20e is an exoplanet orbiting Kepler-20. The planet is notable as it is the first planet with a smaller radius than Earth found orbiting a Sun-like star. The planet is second-closest to the star after Kepler-20b, and at , it is far too hot to have liquid water on its surface. Along with the other four planets in the system, Kepler-20e was announced on 20 December 2011. With a semimajor axis of"
"about 4.4 light-years away. Alpha Centauri A and B are a closely tied pair of Sun-like stars, whereas the small red dwarf, Proxima Centauri, orbits the pair at a distance of 0.2 light-year. In 2016, a potentially habitable exoplanet was confirmed to be orbiting Proxima Centauri, called Proxima Centauri b, the closest confirmed exoplanet to the Sun. The stars next closest to the Sun are the red dwarfs Barnard's Star (at 5.9 ly), Wolf 359 (7.8 ly), and Lalande 21185 (8.3 ly). The largest nearby star is Sirius, a bright main-sequence star roughly 8.6 light-years away and roughly twice the"
"Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane, producing seasons on Earth. The gravitational interaction between Earth and"
"Earth is approximately which is close to the correct value (0.016710219) (see Earth's orbit). The calculation is correct when perihelion, the date the Earth is closest to the Sun, falls on a solstice. The current perihelion, near January 3, is fairly close to the solstice of December 21 or 22. It took nearly two centuries for the current formulation of Kepler's work to take on its settled form. Voltaire's ""Eléments de la philosophie de Newton"" (Elements of Newton's Philosophy) of 1738 was the first publication to use the terminology of ""laws"". The ""Biographical Encyclopedia of Astronomers"" in its article on"