"is not as completely absorbed by the interstellar medium as was formerly thought. In an April Fools' Day joke in 2012, NASA announced that the ""MESSENGER"" spacecraft supposedly discovered a moon in orbit around Mercury, which they named jokingly ""Caduceus"", in reference to the caduceus, the staff carried by the Roman god Mercury. ""MESSENGER"" mission used the spacecraft to search for moons of Mercury in 2011 and 2013, thus confirming that Mercury had none. Hypothetical moon of Mercury Mercury's moon would be an undiscovered natural satellite orbiting the planet Mercury. One was briefly thought to exist in the early 1970s,"
"Moons of Uranus Uranus is the seventh planet of the Solar System; it has 27 known moons, all of which are named after characters from the works of William Shakespeare and Alexander Pope. Uranus's moons are divided into three groups: thirteen inner moons, five major moons, and nine irregular moons. The inner moons are small dark bodies that share common properties and origins with Uranus's rings. The five major moons are massive enough to have reached hydrostatic equilibrium, and four of them show signs of internally driven processes such as canyon formation and volcanism on their surfaces. The largest of"
"may appear as a bright star-like object, but is often far more difficult to observe than Venus. The planet telescopically displays the complete range of phases, similar to Venus and the Moon, as it moves in its inner orbit relative to Earth, which reoccurs over the so-called synodic period approximately every 116 days. Mercury is tidally locked with the Sun in a 3:2 spin-orbit resonance, and rotates in a way that is unique in the Solar System. As seen relative to the fixed stars, it rotates on its axis exactly three times for every two revolutions it makes around the"
"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"
"Moon's, indicating that it has been geologically inactive for billions of years. Having almost no atmosphere to retain heat, it has surface temperatures that vary diurnally more than on any other planet in the Solar System, ranging from at night to during the day across the equatorial regions. The polar regions are constantly below . The planet has no known natural satellites. Two spacecraft have visited Mercury: """" flew by in 1974 and 1975; and ""MESSENGER"", launched in 2004, orbited Mercury over 4,000 times in four years before exhausting its fuel and crashing into the planet's surface on April 30,"
"Moons of Saturn The moons of Saturn are numerous and diverse, ranging from tiny moonlets less than 1 kilometer across to the enormous Titan, which is larger than the planet Mercury. Saturn has 62 moons with confirmed orbits, 53 of which have names and only 13 of which have diameters larger than 50 kilometers, as well as dense rings with complex orbital motions of their own. Seven Saturnian moons are large enough to be ellipsoidal in shape, yet only two of those, Titan and Rhea, are currently in hydrostatic equilibrium. Particularly notable among Saturn's moons are Titan, the second-largest moon"
"on Earth. Combined with a 3:2 spin–orbit resonance of the planet's rotation around its axis, it also results in complex variations of the surface temperature. The resonance makes a single solar day on Mercury last exactly two Mercury years, or about 176 Earth days. Mercury's orbit is inclined by 7 degrees to the plane of Earth's orbit (the ecliptic), as shown in the diagram on the right. As a result, transits of Mercury across the face of the Sun can only occur when the planet is crossing the plane of the ecliptic at the time it lies between Earth and"
"into an elliptical orbit, then chemical rockets will fire to deposit the mapper probe into a circular orbit. Both probes will operate for one terrestrial year. The mapper probe carries an array of spectrometers similar to those on ""MESSENGER"", and will study the planet at many different wavelengths including infrared, ultraviolet, X-ray and gamma ray. 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"
"than the other planets. In 1800, Johann Schröter made observations of surface features, claiming to have observed mountains. Friedrich Bessel used Schröter's drawings to erroneously estimate the rotation period as 24 hours and an axial tilt of 70°. In the 1880s, Giovanni Schiaparelli mapped the planet more accurately, and suggested that Mercury's rotational period was 88 days, the same as its orbital period due to tidal locking. This phenomenon is known as synchronous rotation. The effort to map the surface of Mercury was continued by Eugenios Antoniadi, who published a book in 1934 that included both maps and his own"
"planet Mercury, though only around half as massive. The three inner moons—Io, Europa, and Ganymede—are in a 4:2:1 orbital resonance with each other. Because of their much smaller size, and therefore weaker self-gravitation, all of Jupiter's remaining moons have irregular forms rather than a spherical shape. The Galilean moons were observed in either 1609 or 1610 when Galileo made improvements to his telescope, which enabled him to observe celestial bodies more distinctly than ever. Galileo's observations showed the importance of the telescope as a tool for astronomers by proving that there were objects in space that cannot be seen by"
"2015. The ""BepiColombo"" spacecraft will arrive at Mercury in 2025. Mercury appears to have a solid silicate crust and mantle overlying a solid, iron sulfide outer core layer, a deeper liquid core layer, and possibly a solid inner core. Mercury is one of four terrestrial planets in the Solar System, and is a rocky body like Earth. It is the smallest planet in the Solar System, with an equatorial radius of . Mercury is also smaller—albeit more massive—than the largest natural satellites in the Solar System, Ganymede and Titan. Mercury consists of approximately 70% metallic and 30% silicate material. Mercury's"
"Hypothetical moon of Mercury Mercury's moon would be an undiscovered natural satellite orbiting the planet Mercury. One was briefly thought to exist in the early 1970s, but it turned out to be misinterpreted data from a star. Observation of a moon of Mercury from Earth would be difficult because Mercury is relatively close to the Sun. For example, Mercury was not observed in the infrared spectrum until 1995. NASA's ""MESSENGER"" spacecraft, which orbited Mercury from 2011 to 2015, did not detect any moon. A moon of Mercury was for a short time thought to exist. On March 27, 1974, two"
"() is the ruling planet of Gemini and is exalted in Virgo and/or Aquarius. In classical Roman mythology, Mercury is the messenger of the gods, noted for his speed and swiftness. Echoing this, the scorching, airless world Mercury circles the Sun on the fastest orbit of any planet. Mercury takes only 88 days to orbit the Sun, spending about 7.33 days in each sign of the zodiac. Mercury is so close to the Sun that only a brief period exists after the Sun has set where it can be seen with the naked eye, before following the Sun beyond the"
"of heavier elements contained in the solar nebula. The four inner or terrestrial planets have dense, rocky compositions, few or no moons, and no ring systems. They are composed largely of minerals with high melting points, such as the silicates which form their solid crusts and semi-liquid mantles, and metals such as iron and nickel, which form their cores. The Mariner 10 mission (1974) mapped about half the surface of Mercury. On the basis of that data, scientists have a first-order understanding of the geology and history of the planet. Mercury's surface shows intercrater plains, basins, smooth plains, craters, and"
"of the Earth, the ""Commentariolus"" gives 1 for Mars, 5 for Jupiter, and 9 for Saturn. For the ratios of the radii of their deferents to the radii of the larger of their epicycles, it gives 6 for Mars, 12 for Jupiter, and 11 for Saturn. In the last two sections Copernicus talks about Venus and Mercury. The first has a system of circles and takes 9 months to complete a revolution. Mercury's orbit is harder than any of the other planets' to study because it is visible for only a few days a year. Mercury, just like Venus, has"
"has an observed magnetic field, which is believed to be generated within its metallic core. Mercury's core occupies 85% of the planet's radius, making it the largest core relative to the size of the planet in the Solar System; this indicates that much of Mercury's surface may have been lost early in the Solar System's history. Mercury has a solid silicate crust and mantle overlying a solid iron sulfide outer core layer, followed by a deeper liquid core layer, and then a possible solid inner core making a third layer. The composition of Venus' core varies significantly depending on the"
"came from materials in the Oort cloud, associated with comets, and not from the materials that formed Saturn in earlier times. Studies based on Enceladus's tidal-based geologic activity and the lack of evidence of extensive past resonances in Tethys, Dione, and Rhea's orbits suggest that the moons inward of Titan may be only 100 million years old. Moons of Saturn The moons of Saturn are numerous and diverse, ranging from tiny moonlets less than 1 kilometer across to the enormous Titan, which is larger than the planet Mercury. Saturn has 62 moons with confirmed orbits, 53 of which have names"
"Inter-crater plains on Mercury Inter-crater plains on Mercury are a land-form consisting of plains between craters on Mercury. Of the eight planets in the solar system, Mercury is the smallest and closest to the Sun. The surface of this planet is similar to the Moon in that it shows characteristics of heavy cratering and plains formed through volcanic eruptions on the surface. These features indicate that Mercury has been geologically inactive for billions of years. Knowledge of Mercury's geology was initially quite limited because observations have only been through the ""Mariner 10"" flyby in 1975 and observations from Earth. The"
"Mercury. Mercury remains the least explored of the Terrestrial planets. As of May 2013, the Mariner 10 and ""MESSENGER"" missions have been the only missions that have made close observations of Mercury. ""MESSENGER"" entered orbit around Mercury in March 2011, to further investigate the observations made by Mariner 10 in 1975 (Munsell, 2006b). A third mission to Mercury, scheduled to arrive in 2025, BepiColombo is to include two probes. BepiColombo is a joint mission between Japan and the European Space Agency. ""MESSENGER"" and BepiColombo are intended to gather complementary data to help scientists understand many of the mysteries discovered by"
"the second mission to reach Mercury, after Mariner 10. MESSENGER entered orbit around Mercury on March 18, 2011, and it reactivated its science instruments on March 24, returning the first photo from Mercury orbit on March 29. MESSENGER crashed into Mercury on April 30, 2015 after running out of propellant. The New Frontiers program is a series of space exploration missions being conducted by NASA with the purpose of researching several of the Sun's planets including Jupiter, Venus, and the dwarf planet Pluto. NASA is encouraging both domestic and international scientists to submit mission proposals for the project. New Frontiers"
"by its proximity to the Sun, as it is lost in the Sun's glare for much of the time. Mercury can be observed for only a brief period during either morning or evening twilight. Mercury can, like several other planets and the brightest stars, be seen during a total solar eclipse. Like the Moon and Venus, Mercury exhibits phases as seen from Earth. It is ""new"" at inferior conjunction and ""full"" at superior conjunction. The planet is rendered invisible from Earth on both of these occasions because of its being obscured by the Sun, except its new phase during a"
"Moons of Jupiter There are 79 known moons of Jupiter. This gives Jupiter the largest number of moons with reasonably stable orbits of any planet in the Solar System. The most massive of the moons are the four Galilean moons, which were independently discovered in 1610 by Galileo Galilei and Simon Marius and were the first objects found to orbit a body that was neither Earth nor the Sun. From the end of the 19th century, dozens of much smaller Jovian moons have been discovered and have received the names of lovers or daughters of the Roman god Jupiter or"
"known as flux transfer events, form open windows in the planet's magnetic shield through which the solar wind may enter and directly impact Mercury's surface via magnetic reconnection This also occurs in Earth's magnetic field. The ""MESSENGER"" observations showed the reconnection rate is ten times higher at Mercury, but its proximity to the Sun only accounts for about a third of the reconnection rate observed by ""MESSENGER"". Mercury has the most eccentric orbit of all the planets; its eccentricity is 0.21 with its distance from the Sun ranging from . It takes 87.969 Earth days to complete an orbit. The"
"the planet's former atmosphere in frozen form, and a ""twilight belt"" between the two. This concept of Mercury was disproven in 1965, when radio astronomers discovered that Mercury rotates three times for every two revolutions, exposing all of its surface to the Sun. Authors' descriptions of Mercury changed as knowledge of the planet's environment increased. Fictional works about Mercury can thus be divided into two groups; those, mostly written before 1965, featuring the ""Old"" Mercury with its light and dark sides, and those that reflect more recent scientific knowledge of the planet. The planet has also been a setting for"
"land safely or enter a stable orbit the spacecraft must rely entirely on rocket motors because Mercury has negligible atmosphere. A direct trip to Mercury actually requires more rocket fuel than that required to escape the Solar System completely. As a result, only two space probes, ""Mariner 10"" and ""MESSENGER"", both by NASA, have visited Mercury so far. Furthermore, the space environment near Mercury is demanding, posing the double dangers to spacecraft of intense solar radiation and high temperatures. Historically, a second obstacle has been that Mercury's period of rotation is a slow 58 Earth days, so that spacecraft flybys"
"mantle did not occur because potassium and sulfur would have been driven off by the extreme heat of these events. ""BepiColombo"", which will arrive at Mercury in 2025, will make observations to test these hypotheses. The findings so far would seem to favor the third hypothesis; however, further analysis of the data is needed. Mercury's surface is similar in appearance to that of the Moon, showing extensive mare-like plains and heavy cratering, indicating that it has been geologically inactive for billions of years. Because knowledge of Mercury's geology had been based only on the 1975 flyby and terrestrial observations, it"
"was best placed for observation, the same side faced inward. Radar observations in 1965 demonstrated instead that Mercury has a 3:2 spin–orbit resonance, rotating three times for every two revolutions around the Sun, which results in the same positioning at those observation points. Modeling has demonstrated that Mercury was captured into the 3:2 spin–orbit state very early in its history, within 20 (and more likely even 10) million years after its formation. Venus's 583.92-day interval between successive close approaches to Earth is equal to 5.001444 Venusian solar days, making approximately the same face visible from Earth at each close approach."
"at about 19:38 UTC until the end of the transit. The rover Curiosity observed the Mercury transit of June 3, 2014, marking the first time any planetary transit has been observed from a celestial body besides Earth. The Mercury-Mars synodic period is 100.888 days. It can be calculated using the formula 1/(1/P-1/Q), where P is the orbital period of Mercury (87.969 days) and Q is the orbital period of Mars (686.98 days). The inclination of Mercury's orbit with respect to that of Mars is 5.16°, which is less than its value of 7.00° with respect to Earth's ecliptic. The simultaneous"
"Moons of Pluto The dwarf planet Pluto has five moons down to a detection limit of about 1 km in diameter. In order of distance from Pluto, they are Charon, Styx, Nix, Kerberos, and Hydra. Charon, the largest of the five moons, is mutually tidally locked with Pluto, and is massive enough that Pluto–Charon is sometimes considered a double dwarf planet. The innermost and largest moon, Charon, was discovered by James Christy on 22 June 1978, nearly half a century after Pluto was discovered. This led to a substantial revision in estimates of Pluto's size, which had previously assumed that"
"of moon is 27.322 which compares to 27.32166 in modern calculations. For Mercury it states the period to be 87.97 (modern W: 87.969), Venus 224.7 (W: 224.701), Mars as 687 (W: 686.98), Jupiter as 4,332.3 (W: 4,332.587) and Saturn to be 10,765.77 days (W: 10,759.202). The ""Surya Siddhanta"" also estimates the diameters of the planets. The estimate for the diameter of Mercury is 3,008 miles, an error of less than 1% from the currently accepted diameter of 3,032 miles. It also estimates the diameter of Saturn as 73,882 miles, which again has an error of less than 1% from the"
"Sun. As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years. An observer on Mercury would therefore see only one day every two Mercurian years. Mercury's axis has the smallest tilt of any of the Solar System's planets (about degree). Its orbital eccentricity is the largest of all known planets in the Solar System; at perihelion, Mercury's distance from the Sun is only about two-thirds (or 66%) of its distance at aphelion. Mercury's surface appears heavily cratered and is similar in appearance to the"
"observations. Many of the planet's surface features, particularly the albedo features, take their names from Antoniadi's map. In June 1962, Soviet scientists at the Institute of Radio-engineering and Electronics of the USSR Academy of Sciences, led by Vladimir Kotelnikov, became the first to bounce a radar signal off Mercury and receive it, starting radar observations of the planet. Three years later, radar observations by Americans Gordon Pettengill and R. Dyce, using the 300-meter Arecibo Observatory radio telescope in Puerto Rico, showed conclusively that the planet's rotational period was about 59 days. The theory that Mercury's rotation was synchronous had become"
"Mars appears to be the angular diameter as seen from Earth (0.35°), and sends 40% of the light, approximately the brightness of a slightly cloudy afternoon on Earth. On June 3, 2014, the ""Curiosity"" rover on Mars observed the planet Mercury transiting the Sun, marking the first time a planetary transit has been observed from a celestial body besides Earth. Mars has two small moons: Phobos and Deimos. From the Martian surface, Phobos has one-third to one-half the angular diameter of the Sun while Deimos is barely more than a dot (only 2′ angular diameter). The orbital period of Phobos"