Portal:Solar System/Selected article
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Portal:Solar System/Selected article/1
Eris was first spotted in 2003 by a Mount Palomar-based team led by Mike Brown but not identified until 2005. It is a trans-Neptunian object (TNO) native to a region of space beyond the Kuiper belt known as the scattered disc. Eris has one moon, Dysnomia; recent observations have found no evidence of further satellites. The current distance from the Sun is 96.7 AU, roughly three times that of Pluto. With the exception of some comets, the pair are the most distant known bodies in the Solar System. Because Eris is larger than Pluto, its discoverers and NASA called it the Solar system's tenth planet. This, along with the prospect of other similarly sized objects being discovered in the future, motivated the International Astronomical Union (IAU) to define the term "planet" for the first time. Under a new definition approved on August 24, 2006, Eris was designated a "dwarf planet" along with Pluto and Ceres.
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The Sun is the star at the center of the Solar System. The Earth and other matter (including other planets, asteroids, meteoroids, comets and dust) orbit the Sun, which by itself accounts for about 99.8% of the Solar System's mass. Energy from the Sun—in the form of sunlight—supports almost all life on Earth via photosynthesis, and drives the Earth's climate and weather.
The Sun is composed of hydrogen (about 74% of its mass, or 92% of its volume), helium (about 25% of mass, 7% of volume), and trace quantities of other elements. The Sun has a spectral class of G2V. G2 implies that it has a surface temperature of approximately 5,500 K, giving it a white color which, because of atmospheric scattering, appears yellow as seen from the surface of the Earth. This is a subtractive effect, as the preferential scattering of blue photons (causing the sky color) removes enough blue light to leave a residual reddishness that is perceived as yellow.
Portal:Solar System/Selected article/3
Mercury is the innermost and smallest planet in the solar system, orbiting the Sun once every 88 days. It ranges in brightness from about −2.0 to 5.5 in apparent magnitude, but is not easily seen as its greatest angular separation from the Sun (greatest elongation) is only 28.3°. It can only be seen in morning or evening twilight. Comparatively little is known about the planet: the only spacecraft to approach Mercury was Mariner 10 from 1974 to 1975, which mapped only 40%–45% of the planet’s surface.
Physically, Mercury is similar in appearance to the Moon as it is heavily cratered. It has no natural satellites and no substantial atmosphere. The planet has a large iron core which generates a magnetic field about 0.1% as strong as that of the Earth. Surface temperatures on Mercury range from about 90 to 700 K (−180 to 430°C, −292 to 806°F), with the subsolar point being the hottest and the bottoms of craters near the poles being the coldest.
Portal:Solar System/Selected article/4
Venus (IPA: /ˈvi.nəs/) is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. It is the brightest natural object in the night sky, except for the Moon, reaching an apparent magnitude of −4.6. Because Venus is an inferior planet, from Earth it never appears to venture far from the Sun: its elongation reaches a maximum of 47.8°. Venus reaches its maximum brightness shortly before sunrise or shortly after sunset, for which reason it is often called the Morning Star or the Evening Star.
Classified as a terrestrial planet, it is sometimes called Earth's "sister planet", for the two are similar in size, gravity, and bulk composition. Venus is covered with an opaque layer of highly reflective clouds of carbon dioxide, preventing its surface from being seen from space in visible light; this was a subject of great speculation until some of its secrets were revealed by planetary science in the twentieth century. Venus has the densest atmosphere of all the terrestrial planets, consisting mostly of carbon dioxide. The atmospheric pressure at the planet's surface is 90 times that of the Earth.
Portal:Solar System/Selected article/5
Earth (IPA: /ɝθ/) is the third planet from the Sun and is the largest of the terrestrial planets in the Solar System, in both diameter and mass. Home to the human species, it is also referred to as "the Earth", "Planet Earth", "Gaia", "Terra", "the World", and "the Blue Planet".
The Earth is the first planet known to have liquid water on the surface and is the only place in the universe known to harbor life. Earth has a magnetic field that, together with a primarily nitrogen-oxygen atmosphere, protects the surface from radiation that is harmful to life. The atmosphere also serves as a shield that causes smaller meteors to burn up before they strike the surface.
The Earth formed around 4.57 billion years ago and its only known natural satellite, the Moon, began orbiting it around 4.53 billion years ago. At present, the Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis (which is equal to 365.26 solar days). The Earth's axis of rotation is tilted 23.5° (away from the perpendicular to its orbital plane), producing seasonal variations on the planet's surface.
Portal:Solar System/Selected article/6
The Moon is Earth's only natural satellite. The average center-to-center distance from the Earth to the Moon is 384,403 kilometres (238,857 miles), which is about 30 times the diameter of the Earth. The Moon has a diameter of 3,474 kilometers (2,159 m) — slightly more than a quarter that of the Earth. This means that the volume of the Moon is only 1/6th that of Earth. Its gravitational pull is about a 1/6th of Earth's. The Moon makes a complete orbit around the Earth every 27.3 days, and the periodic variations in the geometry of the Earth–Moon–Sun system are responsible for the lunar phases that repeat every 29.5 days. The gravitational attraction, and the centrifugal forces generated by the rotation of the Moon and Earth around a common axis, the barycentre, is largely responsible for the tides on Earth. The energy dissipated in generating tides is directly responsible for the reduction in potential energy in the Moon-Earth orbit around the barycentre, resulting in a 3.8 cm yearly decrease in the distance between the two bodies. The Moon will continue to move quicly away from the Earth until the tidal effects between the two are no longer of significance, whereupon the Moon's orbit will not stabilize.
Portal:Solar System/Selected article/7
Mars (IPA: /ˈmɑrz/), the fourth planet from the Sun, is sometimes known as the Red Planet because of its reddish appearance as seen from Earth. The planet is named after Mars, the Roman god of war. A terrestrial planet, Mars has a thin atmosphere and surface features reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts and polar ice caps of Earth. It is the site of Olympus Mons, the highest known mountain in the solar system, and of Valles Marineris, the largest canyon. In addition to its geographical features, Mars's rotational period and seasonal cycles are likewise similar to those of the Earth.
Until the first flyby of Mars by Mariner 4 in 1965, it was speculated that there might be liquid water on the planet. This was based on observations of periodic variations in light and dark patches, particularly in the polar latitudes, which looked like seas and continents, while long, dark striations were interpreted by some observers as irrigation channels for liquid water. These straight line features were later proven not to exist and were instead explained as optical illusions. Still, of all the planets in our solar system, Mars is the most likely, other than Earth, to harbor liquid water, and perhaps life.
Portal:Solar System/Selected article/8
Ceres (IPA: /ˈsɪr.iz/, Latin: Cerēs), also designated 1 Ceres (see minor planet names), is the smallest dwarf planet in the Solar System and the only one located in the main asteroid belt. Its name is derived from the Roman goddess Ceres — the goddess of growing plants, the harvest, and of motherly love. It was discovered on January 1, 1801, by Giuseppe Piazzi. With a diameter of about 950 km, Ceres is by far the largest and most massive body in the asteroid belt, and contains approximately a third of the belt's total mass. Recent observations have revealed that it is spherical, unlike the irregular shapes of smaller bodies with less gravity.
Portal:Solar System/Selected article/9
The Oort cloud is a spherical cloud of comets believed to lie roughly 50,000 AU, or nearly a light-year, from the Sun; this distance places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The Kuiper belt and scattered disc, the other two known reservoirs of trans-Neptunian objects, are less than one thousandth the Oort cloud's distance. The outer extent of the Oort cloud defines the boundary of our Solar System.
The Oort cloud is thought to comprise two separate regions: a spherical outer Oort cloud and a disc-shaped inner Oort cloud, or Hills cloud. Objects in the Oort cloud are largely composed of ices such as water, ammonia and methane. Astronomers believe that the matter comprising the Oort cloud formed closer to the Sun, and was scattered far out into space by the gravitational effects of the giant planets early in the Solar System's evolution. While no confirmed direct observations have been made, the Oort cloud is likely the source of comets. The only known trans-Neptunian objects, 90377 Sedna and 2000 CR105, are considered possible members of the inner Oort cloud.
Portal:Solar System/Selected article/10
Jupiter is the fifth planet from the Sun and the largest planet within the solar system. It is two and a half times as massive as all of the other planets in our solar system combined. Jupiter, along with Saturn, Uranus, and Neptune, is classified as a gas giant. When viewed from Earth, Jupiter can reach an apparent magnitude of -2.8, making it the fourth brightest object in the night sky. The planet was known by astronomers of ancient times and was associated with the mythology and religious beliefs of many cultures. Jupiter is primarily composed of hydrogen with only a small proportion of helium; it may also have a rocky core of heavier elements. The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence and storms along their interacting boundaries. A prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the seventeenth century. Surrounding the planet is a faint planetary ring system and a powerful magnetosphere. There are also at least 63 moons, including the four large moons called the Galilean moons that were first discovered by Galileo Galilei in 1610. Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager fly-by missions and later by the Galileo orbiter.
[edit] 11 through 20
Portal:Solar System/Selected article/11
Uranus is the seventh planet from the Sun; it is the third largest and fourth most massive planet in the solar system. Uranus was the first planet discovered in modern times. Though it is visible to the naked eye like the five classical planets, it was never recognised as a planet by ancient observers due to its dimness. Sir William Herschel announced its discovery on March 13, 1781, expanding the known boundaries of the solar system. Uranus' atmosphere, although similar to Jupiter and Saturn in being composed primarily of hydrogen and helium, contains a higher proportion of "ices" such as water, ammonia and methane, along with the usual traces of hydrocarbons. It has the coldest planetary atmosphere in the solar system, with a minimum temperature of 49 K, and has a complex layered cloud structure in which water is thought to make up the lowest clouds, while methane makes up the uppermost layer of clouds. In 1986, images from the Voyager 2 space probe showed Uranus as a virtually featureless planet in visible light without the cloud bands or storms associated with the other giants. The wind speeds on Uranus can reach 250 m/s (560 mph).
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[edit] Nominations
Feel free to add featured, top or high importance articles about the Solar System to the above list. Other Solar System-related articles may be nominated here.
