"surface of its parent star. The team hypothesized that the planet's magnetosphere was transferring energy onto the star's surface, increasing its already high 7,760 °C temperature by an additional 400 °C. Several planets or dwarf planets in the Solar System (such as Neptune and Pluto) have orbital periods that are in resonance with each other or with smaller bodies (this is also common in satellite systems). All except Mercury and Venus have natural satellites, often called ""moons"". Earth has one, Mars has two, and the giant planets have numerous moons in complex planetary-type systems. Many moons of the giant planets"
"proportionately largest moon Charon, is also the site of many eclipses. A series of such mutual eclipses occurred between 1985 and 1990. These daily events led to the first accurate measurements of the physical parameters of both objects. Eclipses are impossible on Mercury and Venus, which have no moons. However, both have been observed to transit across the face of the Sun. There are on average 13 transits of Mercury each century. Transits of Venus occur in pairs separated by an interval of eight years, but each pair of events happen less than once a century. According to NASA, the"
"Earth's own orbit around the Sun—looking down on the ecliptic, the Moon never actually loops back on itself, and in essence it orbits the Sun in its own right. Also many moons, even those that do not orbit the Sun directly, often exhibit features in common with true planets. There are 19 moons in the Solar System that have achieved hydrostatic equilibrium and would be considered planets if only the physical parameters are considered. Both Jupiter's moon Ganymede and Saturn's moon Titan are larger than Mercury, and Titan even has a substantial atmosphere, thicker than the Earth's. Moons such as"
"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,"
"unless they had an alternative source of internal heating, such as tidal heating. Thus, Earth's Moon, which has no alternative source of internal heating is now geologically dead, whereas a moon as small as Enceladus that has sufficient tidal heating (or at least had it recently) and some remaining radioactive heating, is able to maintain an active and directly detectable cryovolcanism. The internal heating within terrestrial planets powers tectonic and volcanic activities. Of the terrestrial planets in the Solar System, Earth has the most internal heating because it is the most massive. Mercury and Mars have no ongoing visible surface"
"from the original solar nebula. The Solar System has four terrestrial planets: Mercury, Venus, Earth, and Mars. Only one terrestrial planet, Earth, is known to have an active hydrosphere. During the formation of the Solar System, there were probably many more terrestrial planetesimals, but most merged with or were ejected by the four terrestrial planets. Dwarf planets, such as Ceres, Pluto and Eris, and small Solar System bodies are similar to terrestrial planets in the fact that they do have a solid surface, but are, on average, composed of more icy materials (Ceres, Pluto and Eris have densities of 2.17,"
"show evidence of Methane and Acetylene but no Ammonia or Carbon Dioxide. There is currently no explanation why this planet shows strong methane absorption, but the other 3 planets in this system do not, despite all 4 planets having similar atmospheric temperatures. HR 8799 e </math></ref> HR 8799 e is a large exoplanet, orbiting the star HR 8799, which lies 129 lightyears from Earth. This gas giant is between 5 and 10 times the mass of Jupiter, the largest planet in the Solar System. Due to their young age and high temperature all four discovered planets in the HR 8799"
"The objects within the Kuiper belt, together with the members of the scattered disc and any potential Hills cloud or Oort cloud objects, are collectively referred to as trans-Neptunian objects (TNOs). Geology of solar terrestrial planets The geology of solar terrestrial planets mainly deals with the geological aspects of the four terrestrial planets of the Solar System – Mercury, Venus, Earth, and Mars – and one terrestrial dwarf planet: Ceres. Earth is the only terrestrial planet known to have an active hydrosphere. Terrestrial planets are substantially different from the giant planets, which might not have solid surfaces and are composed"
"which has an albedo pattern resembling the desert kangaroo mouse, Muad'Dib, on it; the other moon has markings resembling a human hand. A desert planet with no natural precipitation, in ""Dune"" it is established that Arrakis had been ""His Imperial Majesty's Desert Botanical Testing Station"" before the discovery of melange, for which it is the only natural source in the universe. Melange (or, ""the spice"") is the most essential and valuable commodity in the universe, as it extends life and makes safe interstellar travel possible (among other uses). The planet has no surface water bodies, but open canals called qanats"
"A second paper, published in early 2013, covering the properties of seven of the planet candidates, revealed no moons but allowed the astronomers to constrain the moon-to-planet mass ratios for the planets. A third paper, accepted by the ""Astrophysical Journal"", analyzed the transit and radial-velocity signals of Kepler-22b, the first and only habitable-zone planet analyzed by the HEK team as of July 2013. As with previous searches, though, no moons were conclusively discovered, constraining the maximum mass of a Kepler-22b moon below 0.54 Earth masses with 95% confidence. Despite the lack of positive results in one-and-a-half years of operation, several"
"7 light-years away. Compared to many other planetary systems, the Solar System stands out in lacking planets interior to the orbit of Mercury. The known Solar System also lacks super-Earths (Planet Nine could be a super-Earth beyond the known Solar System). Uncommonly, it has only small rocky planets and large gas giants; elsewhere planets of intermediate size are typical—both rocky and gas—so there is no ""gap"" as seen between the size of Earth and of Neptune (with a radius 3.8 times as large). Also, these super-Earths have closer orbits than Mercury. This led to hypothesis that all planetary systems start"
"the asteroids. Terrestrial planets would have no major moons which does not account for Luna. It predicts certain observations such as the similar angular velocity of Mars and Earth with similar rotation periods and axial tilts. In this scheme there are 6 principal planets: 2 terrestrial, Venus and Earth, 2 major, Jupiter and Saturn, and 2 outer, Uranus and Neptune; and 3 lesser planets: Mercury, Mars, and Pluto. This theory has a number of problems, such as explaining the fact that the planets all orbit the Sun in the same direction, which would appear highly unlikely if they were each"
"Geology of solar terrestrial planets The geology of solar terrestrial planets mainly deals with the geological aspects of the four terrestrial planets of the Solar System – Mercury, Venus, Earth, and Mars – and one terrestrial dwarf planet: Ceres. Earth is the only terrestrial planet known to have an active hydrosphere. Terrestrial planets are substantially different from the giant planets, which might not have solid surfaces and are composed mostly of some combination of hydrogen, helium, and water existing in various physical states. Terrestrial planets have a compact, rocky surfaces, and Venus, Earth, and Mars each also have an atmosphere."
"perfectly. Several natural satellites in the Solar System have atmospheres and are subject to atmospheric loss processes. They typically have no magnetic fields of their own, but orbit planets with powerful magnetic fields. Many of these moons lie within the magnetic fields generated by the planets and are less likely to undergo sputtering and pick-up. The shape of the bow shock, however, allows for some moons, such as Titan, to pass through the bow shock when their orbits take them between the Sun and their primary. Titan spends roughly half of its transit time outside of the bow-shock and being"
"the ""New Horizons"" space probe in June 2015. Under this definition, the Earth–Moon system is not currently a double planet; although the Moon is massive enough to cause the Earth to make a noticeable revolution around this center of mass, this point nevertheless lies well within Earth. However, the Moon migrates outward from Earth at a rate of approximately per year; in a few hundred million years, the Earth–Moon system's center of mass will lie outside Earth, which would make it a double-planet system. The center of mass of the Jupiter–Sun system lies outside the surface of the Sun, though"
"source for chemical abundance, despite their rareness (only five have been recovered on Earth). The planets of the Solar System are divided into two groups: the four inner planets are the terrestrial planets (Mercury, Venus, Earth and Mars), with relatively small sizes and rocky surfaces. The four outer planets are the giant planets, which are dominated by hydrogen and helium and have lower mean densities. These can be further subdivided into the gas giants (Jupiter and Saturn) and the ice giants (Uranus and Neptune) that have large icy cores. Most of our direct information on the composition of the giant"
"the naked eye on very clear nights, but, unlike the true naked-eye planets, are always less luminous than several thousands of stars, and as such, do not stand out enough for their existence to be noticed without the aid of a telescope. Classical planet In classical antiquity, the seven classical planets were the seven non-fixed astronomical objects in the sky visible to the naked eye: Mars, Jupiter, Venus, Saturn, Mercury, the Sun, and the Moon. The word ""planet"" comes from two related Greek words, πλάνης ""planēs"" (whence πλάνητες ἀστέρες ""planētes asteres"" ""wandering stars, planets"") and πλανήτης ""planētēs"", both with the"
"and transient, its surface is bathed in radiation. Mercury has an intrinsic magnetic field, so under normal solar wind conditions, the solar wind cannot penetrate its magnetosphere and particles only reach the surface in the cusp regions. During coronal mass ejections, however, the magnetopause may get pressed into the surface of the planet, and under these conditions, the solar wind may interact freely with the planetary surface. The Earth's Moon has no atmosphere or intrinsic magnetic field, and consequently its surface is bombarded with the full solar wind. The Project Apollo missions deployed passive aluminum collectors in an attempt to"
"solar wind around itself called the magnetosphere, which the wind cannot penetrate. The magnetosphere can be much larger than the planet itself. In contrast, non-magnetized planets have only small magnetospheres induced by interaction of the ionosphere with the solar wind, which cannot effectively protect the planet. Of the eight planets in the Solar System, only Venus and Mars lack such a magnetic field. In addition, the moon of Jupiter Ganymede also has one. Of the magnetized planets the magnetic field of Mercury is the weakest, and is barely able to deflect the solar wind. Ganymede's magnetic field is several times"
"god Neptune's trident. Neptune is not visible to the unaided eye and is the only planet in the Solar System found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to gravitational perturbation by an unknown planet. Neptune was subsequently observed with a telescope on 23 September 1846 by Johann Galle within a degree of the position predicted by Urbain Le Verrier. Its largest moon, Triton, was discovered shortly thereafter, though none of the planet's remaining known 13 moons were located telescopically until the"
"the poles and is lower than the surface gravity of Earth. However, the equatorial escape velocity of nearly is much higher than that for Earth. Saturn is the only planet of the Solar System that is less dense than water—about 30% less. Although Saturn's core is considerably denser than water, the average specific density of the planet is due to the atmosphere. Jupiter has 318 times Earth's mass, and Saturn is 95 times Earth's mass. Together, Jupiter and Saturn hold 92% of the total planetary mass in the Solar System. Despite consisting mostly of hydrogen and helium, most of Saturn's"
"Two moons have significant atmospheres: Saturn's moon Titan and Neptune's moon Triton. A tenuous atmosphere exists around Mercury. The effects of the rotation rate of a planet about its axis can be seen in atmospheric streams and currents. Seen from space, these features show as bands and eddies in the cloud system, and are particularly visible on Jupiter and Saturn. Planetary science frequently makes use of the method of comparison to give a greater understanding of the object of study. This can involve comparing the dense atmospheres of Earth and Saturn's moon Titan, the evolution of outer Solar System objects"
"ask ""whether oxygenation, and hence the rise of animals, would ever have occurred on a world where there were no continents to erode"". Extraterrestrial free oxygen has recently been detected around other solid objects, including Mercury, Venus, Mars Jupiter's four Galilean moons, Saturn's moons Enceladus, Dione and Rhea and even the atmosphere of a comet. This has led scientists to speculate whether processes other than photosynthesis could be capable of generating an environment rich in free oxygen. Wordsworth (2014) concludes that oxygen generated other than through photodissociation may be likely on Earth-like exoplanets, and could actually lead to false positive"
"the rate of erosion drops because there are fewer abrasive particles in the water and fewer landslides. Mountains on other planets and natural satellites of the Solar System are often isolated and formed mainly by processes such as impacts, though there are examples of mountain ranges (or ""Montes"") somewhat similar to those on Earth. Saturn's moon Titan and Pluto, in particular exhibit large mountain ranges in chains composed mainly of ices rather than rock. Examples include the Mithrim Montes and Doom Mons on Titan, and Tenzing Montes and Hillary Montes on Pluto. Some terrestrial planets other than Earth also exhibit"
"and south poles, therefore, lie where most other planets have their equators. In 1986, images from ""Voyager 2"" showed Uranus as an almost featureless planet in visible light, without the cloud bands or storms associated with the other giant planets. Observations from Earth have shown seasonal change and increased weather activity as Uranus approached its equinox in 2007. Wind speeds can reach . Uranus is the only planet whose name is derived directly from a figure from Greek mythology, from the Latinised version of the Greek god of the sky Ouranos. Like the classical planets, Uranus is visible to the"
"significant in many cultures, such as being the basis for many calendars. The Moon also does not require any kind of telescope or binoculars to see effectively, making it extremely convenient and common for people to observe. Meteors, often called ""shooting stars"" are also commonly observed. Meteor showers, such as the Perseids and Leonids, make viewing meteors much easier, as a multitude of meteors are visible in a relatively short period of time. Planets are usually observed with the aid of a telescope or binoculars. Venus is likely the easiest planet to observe without the aid of any instruments, as"
"and so would be considered (dwarf) planets if they were in direct orbit about the Sun. The remaining moons were discovered after 1985, either during the ""Voyager 2"" flyby mission or with the aid of advanced Earth-based telescopes. The first two moons to be discovered were Titania and Oberon, which were spotted by Sir William Herschel on January 11, 1787, six years after he had discovered the planet itself. Later, Herschel thought he had discovered up to six moons (see below) and perhaps even a ring. For nearly 50 years, Herschel's instrument was the only one with which the moons"
"it could not exist because there is no sunlight to use for photosynthesis. Microorganisms can produce nutrients using specific chemicals (chemosynthesis) that may provide food and energy for other organisms. Some planets, if conditions are right, may have significant atmospheres and surface liquids like Saturn's moon Titan, which could be habitable for exotic forms of life. Although there are many icy objects in the Solar System, there are no known ice planets (though Pluto was considered an ice planet until its reclassification in 2006). If a 9th planet suggested in 2016 is found, it will be an ice planet of"
"greenhouse effect, aerosol and cloud physics, and atmospheric chemistry and dynamics. Due to its small size (and thus its small gravity), Mercury has no substantial atmosphere. Its extremely thin atmosphere mostly consists of a small amount of helium and traces of sodium, potassium, and oxygen. These gases derive from the solar wind, radioactive decay, meteor impacts, and breakdown of Mercury's crust. Mercury's atmosphere is not stable and is constantly being refreshed because of its atoms escaping into space as a result of the planet's heat. Venus' atmosphere is mostly composed of carbon dioxide. It contains minor amounts of nitrogen and"
"from extreme polar locations. Mars is at its brightest when it is in opposition, which occurs approximately every twenty-five months. Jupiter and Saturn are the largest of the five planets, but are farther from the Sun, and therefore receive less sunlight. Nonetheless, Jupiter is often the next brightest object in the sky after Venus. Saturn's luminosity is often enhanced by its rings, which reflect light to varying degrees, depending on their inclination to the ecliptic; however, the rings themselves are not visible to the naked eye from the Earth. Uranus and sometimes the asteroid Vesta are in principle visible to"
"Solar eclipses on Mars The two moons of Mars, Phobos and Deimos, are much smaller than the Moon, greatly reducing the frequency of solar eclipses on that planet. Neither moon's apparent diameter is large enough to cover the disk of the sun, and therefore they are annular solar eclipses and can also be considered transits. Due to the small size of Phobos (about ) and its rapid orbital motion, an observer on the surface of Mars would never experience a solar eclipse for longer than about thirty seconds. Phobos also takes only 7 hours 39 minutes to orbit Mars, while"
"and observed since it was discovered, it is unlikely that there are any large moons orbiting Pallas. Pallas has not been visited by spacecraft and there are no plans for exploration of Pallas by spacecraft. A flyby after the ""Dawn"" probe's visits to 4 Vesta and 1 Ceres was discussed but was not possible. 2 Pallas Pallas (minor-planet designation: 2 Pallas) is the second asteroid to have been discovered (after Ceres), and is one of the largest asteroids in the Solar System. With an estimated 7% of the mass of the asteroid belt, it is the third-most-massive asteroid, being 10–30%"
"either perpetually in sunlight or perpetually in darkness around the time of its solstices. Among extrasolar planets, axial tilts are not known for certain, though most hot Jupiters are believed to have negligible to no axial tilt as a result of their proximity to their stars. The planets rotate around invisible axes through their centres. A planet's rotation period is known as a stellar day. Most of the planets in the Solar System rotate in the same direction as they orbit the Sun, which is counter-clockwise as seen from above the Sun's north pole, the exceptions being Venus and Uranus,"