Celestial Body - Universe Today Universe Today by Jerry Coffey [/caption]The term celestial body is as expansive as the entire universe, both known and unknown. By definition a celestial body is any natural body outside of the Earth’s atmosphere. Easy examples are the Moon, Sun, and the other planets of our solar system. But those are very limited examples. The Kuiper belt contains many celestial bodies. Any asteroid in space is a celestial body. So, what do you write about with such a broad topic? How about a sampling of five of my favorites and leave it at that for now? Which five, though. Well, let’s cover Ceres, the Kuiper belt, the asteroid Cruithne , Achernar, and Apophis. Ceres is a celestial body that is by far the largest and most massive asteroid in the belt between Mars and Jupiter. It is approximately the size of Texas or 975km x 909 km with a mass of 9.5×1020. It actually represents 1/3 of all of the mass of the asteroid belt. It has enough mass for self gravity which is a major requirement to be considered a dwarf planet.

It revolves around the sun every 1679.819 days with a very small axial tilt. The surface is relatively warm. The high temperature is thought to be in the neighborhood of -38°C(235 K). Ceres has a visual brightness magnitude of +6.9 to +9. When it is at the brightest point possible, Ceres is nearly bright enough to be seen with the naked eye. It can be seen with binoculars whenever it is above the horizon on a completely dark night. The Kuiper belt contains many a celestial body. It is actually a disk-shaped region in the outer solar system lying beyond the orbit of Neptune and extending to a distance of about 50 astronomical units, containing thousands of small icy bodies, some of which are on highly elliptical orbits, periodically visiting the inner solar system as comets. It is thought to be a collection of the remnants of the formation of the solar system. Who knows what may be found when we are able to send spacecraft to its edges? As a celestial body, the asteroid Cruithne is sort of small and indistinct until you consider that it is locked in a 1:1 orbit with the Earth.

The asteroid is sometimes referred to as the Earth’s second moon. It is not a true moon because the Earth’s gravity does not effect it nor does its effect the Earth. Cruithne’s nearest pass to Earth is .1 AU (40 moon lengths), although right now it never comes closer than .3 AU. The asteroid sort of runs like a corkscrew around the Earth while both are revolving around the Sun. The asteroid Cruithne is in a normal elliptic orbit around the Sun. Its revolution around the Sun, approximately 364 days at present, is almost equal to that of the Earth. Because of this, Cruithne and Earth appear to follow each other in their paths around the Sun. The celestial body Achernar is a bright, blue, B3-type star of six to eight solar masses lying approximately 144 light years away. It is classified as a dwarf, but it is 3,000 times more luminous than our Sun. It is in the deep southern sky and never rises above 33°N. Achernar is best seen from the southern hemisphere in November; it is circumpolar below 33°S.

Achernar spins so quickly that is spherical in shape. The distance along its equator is 50% greater than its polar diameter. It is the brightest star in the Eridanus constellation. It is also the 9th brightest star in the night sky. Of the 10 brightest stars, other than our Sun, it is the hottest and bluest. The celestial body Apophis is one of the most intriguing, to me. It is the stuff that many sci-fi legends have been based on. Apophis is most famous for the stir it caused in 2004. The asteroid was discovered on its way towards the Earth and was predicted to have a 2.7% chance of impacting the Earth. That in and of itself is not significant. Objects impact the Earth on a yearly basis. The size of Apophis was the major concern. Even a small chance that an asteroid the size of a small town hitting the Earth rightly caused a large commotion. It achieved the highest score ever on the Torino scale and it stayed on an elevated level for longer than any other asteroid ever has. It was eventually studied enough to know that it would not hit the Earth in 2004.

The asteroid will pass again in 2029. Scientists predict that it will not hit the Earth, but it may pass through a gravitational keyhole that could alter its orbit enough that it could impact in 2036. The chances are slight, but real. Even if it doesn’t hit a keyhole in 2029 it will return every seven years and may pose a serious threat in the future. Scientists have proposed that Apophis be nudged out of its present orbit into an orbit that takes it further from the keyhole. NASA scientist David Morrison says, “After 2029, the deflection would have to be vigorous enough to miss not just a tiny keyhole but the much larger target of the Earth itself. And such a deflection is far beyond present technology for an asteroid this large.”. Many things can make a celestial body interesting. Everyone has their favorites. Mine happen to be the five I have listed. Each can be further researched here on Universe Today. Follow these links to find what you need: Ceres , the Kuiper belt , the asteroid Cruithne , Achernar, and Apophis.

Astronomy Cast offers a good episode about the mind-boggling possibility of multiple universes. Here’s a list of the 10 brightest stars . Sources: Ceres (Dwarf Planet) Part of Our Inner Solar System - YouTube Ceres (Dwarf Planet) Part of Our Inner Solar System Want to watch this again later? Sign in to add this video to a playlist. Need to report the video? Sign in to report inappropriate content. The interactive transcript could not be loaded. Loading... Rating is available when the video has been rented. This feature is not available right now. Please try again later. Published on Dec 12, 2013 Ceres, minor-planet designation 1 Ceres, is the largest asteroid and the only dwarf planet in the inner Solar System. It is a rock--ice body 950 km (590 mi) in diameter and the smallest identified dwarf planet. It contains about one-third of the mass of the asteroid belt. Discovered on 1 January 1801 by Giuseppe Piazzi, it was the first asteroid to be identified, though it was classified as a planet at the time.

It is named after Ceres, the Roman goddess of growing plants, the harvest, and motherly love. The Cererian surface is probably a mixture of water ice and various hydrated minerals such as carbonates and clays. It appears to be differentiated into a rocky core and icy mantle, and may harbor an ocean of liquid water under its surface. From Earth, the apparent magnitude of Ceres ranges from 6.7 to 9.3, and hence even at its brightest it is still too dim to be seen with the naked eye except under extremely dark skies. The unmanned Dawn spacecraft, launched on 27 September 2007 by NASA, is expected to be the first to explore Ceres after its scheduled arrival there in 2015. After having orbited asteroid 4 Vesta since July 2011, the spacecraft departed about 5 September 2012. Read more about Dwarf Planet Ceres below: Dwarf Planets Dwarf Planets SUMMARY: Major discoveries in the past decade have forced astronomers to review the definition of a planet. Our solar system now has three classified dwarf planets: our beloved Pluto, Eris, and Ceres. Sections: What Defines a Planet?

The definition of a planet was revised again in 2006. According to NASA, the International Astronomical Union (IAU) most recently defines a planet as a celestial body that: Is in orbit around a star, but is not itself a satellite* Has sufficient mass so it is nearly spherical in shape* Has cleared the neighborhood around its orbit* On the other hand, a dwarf planet is defined as a celetial body that: Is in orbit around a star, but is not itself a satellite* Has sufficient mass so it is nearly spherical in shape* Has not cleared the neighborhood around its orbit* The only difference between a planet and a dwarf planet is the area surrounding each celestial body. A dwarf planet has not cleared the area around its orbit, while a planet has. Since the new definition, three objects in our solar system have been classified as dwarf planets: Pluto, Ceres and Eris. *Text courtesy of NASA Pluto For 76 years (until 2006), Pluto was known as the ninth planet in our solar system. Since then, Pluto has been relegated to dwarf planet status.

Discovered in 1930, Pluto is a member of the outer region of our solar system known as the Kuiper belt. It has a highly inclined and eccentric 248-year orbit around the Sun. As the second-largest known dwarf planet, Pluto is approximately 2,390 km in diameter and is composed primarily of ice and rock. It is very difficult to precisely determine the diameter of Pluto since it is so far away. Pluto is, on average, 40 times farther from the Sun than Earth. Pluto and its largest moon, Charon (click to enlarge) The New Horizons spacecraft, scheduled to arrive at Pluto in 2015, will be able to provide us with more accurate measurements of Pluto. Pluto's surface is made almost entirely of nitrogen ice, with traces of methane and carbon monoxide. Data from Hubble Space Telescope leads scientists to believe Pluto's interior is about 60% rock and 40% ice, which is consistent with the composition of a comet. Pluto has a thin atmosphere made of the same components of its surface: nitrogen, methane and carbon monoxide.

Like a comet, Pluto's atmosphere freezes as it moves away from the Sun and the ices sublimate as it approaches the Sun. Pluto's Moons In 1978, the discovery of Pluto's largest moon, Charon, gave scientists an opportunity to learn more about Pluto. The two icy objects eclipsed each other from Earth's point of view from 1985-1990 allowing scientists to more precisely determine their diameters and masses. At approximately 1,186 km, Charon's diameter is just less than half of Pluto's. Pluto is also eight times more massive than Charon. Pluto and its three known satellites Charon, Nix and Hydra. (click to enlarge) It is not uncommon for a moon to be locked synchronously with its planet, just as Earth's moon is locked to Earth. It is far less common, however, for a planet to be locked synchronously with its moon. The Pluto-Charon system is the only planet-moon system in our solar system locked synchronously together, with each always showing the same face to the other. Two more moons were discovered orbiting Pluto in 2005.

Nix and Hydra are considerably smaller than Pluto and Charon, at only 40 km and 160 km in diameter, respectively. Nix orbits Pluto at 48,700 km from the center of mass of the system, more than twice the orbital distance of Charon. Hydra is the outermost of Pluto's satellites, orbiting at 64,800 km from the center of mass of the Plutonian system. Dwarf Planets: Science and Facts About Solar System’s Smaller Worlds Dwarf planet Eris Credit: ESO/L. Calçada Dwarf planets are worlds that are too small to be considered full-fledged planets, but too large to fall into smaller categories. In recent years, there's been a lot of hubbub about Pluto losing its status as one of the planets in our solar system. Pluto is no longer considered the ninth planet in the series of major planetary objects, but instead is now just one of the many so-called "dwarf planets." Astronomers estimate that there could be as many as 200 dwarf planets in the solar system and Kuiper Belt . But the differences between planets and dwarf planets may not be obvious at first.

Dwarf planets of the solar system The International Astronomical Union defines a planet as being in orbit around the sun, has enough gravity to pull its mass into a rounded shape (hydrostatic equilibrium), and has cleared its orbit of other, smaller objects. This last criterion is the point at which planets and dwarf planets differ. A planet's gravity either attracts or pushes away the smaller bodies that would otherwise intersect its orbit; the gravity of a dwarf planet is not sufficient to make this happen. [ Meet the Dwarf Planets of the Solar System ] Meet the dwarf planets of our solar system, Pluto Eris, Haumea, Makemake and Ceres . Credit: Karl Tate, SPACE.com contributor As of 2014, the IAU recognizes five named dwarf planets: Ceres, Pluto, Eris, Haumea, and Makemake. Other solar system bodies that are possibly dwarf planets include Sedna and Quaoar , small worlds far beyond Pluto's orbit, and 2012 VP113 , an object that is thought to have one of the most distant orbits found beyond the known edge of our solar system. According to NASA , scientists think that there may be more than a hundred dwarf planets awaiting discovery.

However, the debate over the status of dwarf planets, particularly Pluto, remains a hot topic, and one that NASA’s New Horizons probe may inadvertently feed this summer. The primary concern stems from the requirement for a planet to clear out its local neighborhood. "In no other branch of science am I familiar with something that absurd," New Horizons principle investigator Alan Stern told Space.com in 2011 . "A river is a river, independent of whether there are other rivers nearby. In science, we call things what they are based on their attributes, not what they're next to." Stern challenged popular astrophysicist Neil de Grasse Tyson to participate in a debate on Pluto’s planetary status last year, but Tyson turned down the invitation , having participated in the scientific conference termed the Great Planet Debate in 2008. In late 2014, a Harvard-Smithsonian Center for Astrophysics webcast titled “What is a Planet?” brought in three experts to debate Pluto’s classification. At the conclusion, the audience in the room voted that the tiny favorite retain its planet title. Is a dwarf planet a separate entity from a planet, or simply another classification? The question may not be settled in the near future.

The dwarf planet Ceres, also the largest asteroid in the solar system, is seen here in an amazing view from the Hubble Space Telescope. In March 2015, NASA's Dawn spacecraft is expected to enter orbit around Ceres to study the object like never before. Credit: NASA, ESA, J. Parker (Southwest Research Institute), L. McFadden (University of Maryland) Ceres Ceres is the earliest-known and smallest of the current category of dwarf planets. Ceres was discovered in 1801 by the Sicilian astronomer Giuseppe Piazzi, based on the prediction that the gap between Mars and Jupiter contained a missing planet. It is only 590 miles (950 km) in diameter and has a mass of just 0.015 percent that of Earth. In fact, Ceres is so small that it is classified as both a dwarf planet and an asteroid, and is often named in scientific literature as one of the largest asteroids in the solar system . Although it makes up approximately a fourth of the mass of the asteroid belt, it is still 14 less massive than Pluto. Unlike its asteroid neighbors, Ceres has a nearly round body.

The rocky dwarf planet may have water ice beneath its crust. In 2014, The European Space Agency’s Herschel Space Observatory detected water vapor spewing from two regions on Ceres. NASA's unmanned Dawn mission will perform an exploration of Ceres after it arrives at the asteroid/dwarf planet in March 2015. Pluto Pluto is the most well-known of the dwarf planets. Since its discovery in 1930 and until 2006, it had been classified as the ninth planet from the sun. Pluto's orbit was so erratic, however, that at times it was closer to the sun than the eighth planet, Neptune. In 2006, with the discovery of several other rocky bodies similar in size or larger than Pluto, the IAU decided to re-classify Pluto as a dwarf planet . This is the most detailed view to date of the entire surface of the dwarf planet Pluto, as constructed from multiple NASA Hubble Space Telescope photographs taken from 2002 to 2003. Credit: NASA, ESA, and M.

Buie (Southwest Research Institute) Despite its small size — 0.2 percent the mass of Earth and only 10 percent the mass of Earth's moon — Pluto's gravity is enough to capture five moons of its own . The pairing between Pluto and its largest moon, Charon, is known as a binary system, because both objects are orbiting around a central point which is not within the mass of Pluto. NASA’s New Horizons mission, set to arrive at the Pluto-Charon system in the summer of 2015, will be the first spacecraft to study the most famous dwarf planet. The spacecraft woke up from its nine-year hibernation in the winter of 2014 and began studying the system from a distance. Eris When it was first discovered, Eris was thought to be the largest of the dwarf planets, with a mass 27 percent larger than that of Pluto and a diameter of approximately 1,400 to 1,500 miles (2,300 to 2,400 km). It was the discovery of Eris that prompted the IAU to reconsider the definition of a planet.

Further observation went on to suggest that the dwarf planet is slightly smaller than its neighbor. The orbit of Eris is very erratic, crossing that of Pluto and nearly intersecting the orbit of Neptune , but is still more than three times larger than Pluto’s orbit. It takes 557 years for Eris to orbit the sun. At its furthest point from the sun, a point that is also called its aphelion, Eris and its satellite travel far beyond the Kuiper belt. An early artist's interpretation of the dwarf planet Makemake beyond Pluto. Credit: NASA Haumea and Makemake Haumea and Makemake are the most recently named dwarf planets in the solar system. Haumea is unique because of its ellipsoid shape, only just meeting the hydrostatic equilibrium criteria for dwarf planet status. The elongated shape of the dwarf planet is due to its rapid rotational spin, not a lack of mass, which is about one-third that of Pluto. The cigar-shaped dwarf planet rotates on its axis every four hours, likely a result of a collision. The odd object also hosts a red spot and a layer of crystalline ice .

Finally, Haumea is the only object in the Kuiper belt other than Pluto known to host more than one moon. Makemake is also unique among the known dwarf planets, being the only one of those discovered so far to lack a satellite. This lack makes it more difficult to measure the mass of the dwarf planet, though its diameter is known to be about two-thirds that of Pluto. Makemake is also of value to the astronomical community, as it is another reason for the reconsideration of the definition of a planet. Its comparable mass and diameter to Pluto would grant it planet status if Pluto wasn't also stripped of that title. Dwarf planets as 'plutoids' Pluto, Eris, Haumea and Makemake are all known as " plutoids ," unlike the asteroidal dwarf planetoid Ceres. A plutoid is a dwarf planet with an orbit outside that of Neptune. Plutoids are sometimes also referred to as " ice dwarfs " due to their diminutive size and cold surface temperatures. The outer planets show evidence of interaction with plutoids.

Triton, the largest moon of Neptune , is likely a captured plutoid, and it is even possible that the odd tilt of Uranus on its axis is due to a collision with a plutoid. Similarly to dwarf planets, there are potentially hundreds of plutoid objects in the solar system that have yet to be given official status. RELATED: See our overview of Solar System Facts . Also, learn more about the Solar System Planets . Additional reporting by Nola Taylor Redd, Space.com Contributor Solar System Solar System 2008/9 Schools Wikipedia Selection . Related subjects: Space (Astronomy) The Solar System consists of the Sun and those celestial objects bound to it by gravity . These objects are the eight planets and their 166 known moons, four dwarf planets and billions of small bodies, including asteroids , icy Kuiper belt objects, comets , meteoroids , and interplanetary dust. These objects are grouped in a number of distinct regions. Moving outwards from the Sun, the major components are four terrestrial inner planets, an asteroid belt, four gas giant outer planets, the Kuiper belt, the scattered disc , and ultimately the hypothetical Oort cloud.

A stream of charged particles from the Sun, called the solar wind, defines the heliosphere which permeates the Solar System out to around the scattered disc. In order of their distances from the Sun, the eight planets are: Six of the planets and two of the dwarf planets are in turn orbited by natural satellites, usually termed "moons" after Earth's Moon , and each of the outer planets is encircled by planetary rings of dust and other particles. Terminology The zones of the Solar system: the inner solar system, the asteroid belt, the giant planets (Jovians) and the Kuiper belt. Sizes and orbits not to scale. Objects orbiting the Sun are divided into three classes: planets, dwarf planets, and small Solar System bodies. On August 24, 2006, the International Astronomical Union defined the term "planet" for the first time, prompted by the discovery of Eris and subsequent discussions over its classification. A planet is any body in orbit around the Sun that has enough mass to form itself into a spherical shape and has cleared its immediate neighbourhood of all smaller objects.

By this definition, the Solar System has eight known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto was demoted from planetary status, as it has not cleared its orbit of surrounding Kuiper belt objects . A dwarf planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting the Sun that is massive enough to be rounded by its own gravity but which has not cleared its neighbouring region of planetesimals and is not a satellite. By this definition, the Solar System has four known dwarf planets: Ceres , Pluto , Makemake, and Eris . Other objects that may become classified as dwarf planets are Sedna , Orcus, and Quaoar. Dwarf planets that orbit in the trans-Neptunian region are called " plutoids." The remainder of the objects in orbit around the Sun are small Solar System bodies (SSSBs). Natural satellites, or moons, are those objects in orbit around planets, dwarf planets and SSSBs, rather than the Sun itself. Astronomers usually measure distances within the Solar System in astronomical units (AU).

One AU is the approximate distance between the Earth and the Sun, or roughly 149,598,000 km (93,000,000 mi). Pluto is roughly 38 AU from the Sun while Jupiter lies at roughly 5.2 AU. One light-year, the best known unit of interstellar distance, is roughly 63,240 AU. A body's distance from the Sun varies in the course of its year. Its closest approach to the Sun is called its perihelion, while its farthest distance from the Sun is called its aphelion. Informally, the Solar System is sometimes divided into separate zones. The inner Solar System includes the four terrestrial planets and the main asteroid belt. Some define the outer Solar System as comprising everything beyond the asteroids. Since the discovery of the Kuiper belt, others define it as the region beyond Neptune, with the four gas giants considered a separate "middle zone". Layout and structure The ecliptic viewed in sunlight from behind the Moon in this Clementine image. From left to right: Mercury, Mars, Saturn.

The principal component of the Solar System is the Sun, a main sequence G2 star that contains 99.86 percent of the system's known mass and dominates it gravitationally . Jupiter and Saturn, the Sun's two largest orbiting bodies, account for more than 90 percent of the system's remaining mass. Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic while comets and Kuiper belt objects are usually at significantly greater angles to it. The orbits of the bodies in the Solar System to scale (clockwise from top left) All of the planets and most other objects also orbit with the Sun's rotation (counter-clockwise, as viewed from above the Sun's north pole). There are exceptions, such as Halley's Comet . Objects travel around the Sun following Kepler's laws of planetary motion . Each object orbits along an approximate ellipse with the Sun at one focus of the ellipse. The closer an object is to the Sun, the faster it moves. The orbits of the planets are nearly circular, but many comets, asteroids and objects of the Kuiper belt follow highly elliptical orbits.

To cope with the vast distances involved, many representations of the Solar System show orbits the same distance apart. In reality, with a few exceptions, the farther a planet or belt is from the Sun, the larger the distance between it and the previous orbit. For example, Venus is approximately 0.33 AU farther out than Mercury, while Saturn is 4.3 AU out from Jupiter, and Neptune lies 10.5 AU out from Uranus. Attempts have been made to determine a correlation between these orbital distances (see Titius-Bode law), but no such theory has been accepted. Sun The Sun as seen in the x-ray region of the electromagnetic spectrum The Sun is the Solar System's parent star, and far and away its chief component. Its large mass gives it an interior density high enough to sustain nuclear fusion, which releases enormous amounts of energy , mostly radiated into space as electromagnetic radiation such as visible light. The Sun is classified as a moderately large yellow dwarf, but this name is misleading as, compared to stars in our galaxy , the Sun is rather large and bright. Stars are classified by the Hertzsprung-Russell diagram, a graph which plots the brightness of stars against their surface temperatures . Generally, hotter stars are brighter.

Stars following this pattern are said to be on the main sequence; the Sun lies right in the middle of it. However, stars brighter and hotter than the Sun are rare, while stars dimmer and cooler are common. The Hertzsprung-Russell diagram; the main sequence is from bottom right to top left. It is believed that the Sun's position on the main sequence puts it in the "prime of life" for a star, in that it has not yet exhausted its store of hydrogen for nuclear fusion. The Sun is growing brighter; early in its history it was 75 percent as bright as it is today. Calculations of the ratios of hydrogen and helium within the Sun suggest it is halfway through its life cycle. It will eventually move off the main sequence and become larger, brighter, cooler and redder, becoming a red giant in about five billion years. At that point its luminosity will be several thousand times its present value. The Sun is a population I star; it was born in the later stages of the universe's evolution. It contains more elements heavier than hydrogen and helium (" metals" in astronomical parlance) than older population II stars.

Elements heavier than hydrogen and helium were formed in the cores of ancient and exploding stars, so the first generation of stars had to die before the universe could be enriched with these atoms. The oldest stars contain few metals, while stars born later have more. This high metallicity is thought to have been crucial to the Sun's developing a planetary system, because planets form from accretion of metals. Interplanetary medium The heliospheric current sheet. Along with light , the Sun radiates a continuous stream of charged particles (a plasma ) known as the solar wind. This stream of particles spreads outwards at roughly 1.5 million kilometres per hour, creating a tenuous atmosphere (the heliosphere) that permeates the Solar System out to at least 100 AU (see heliopause ). This is known as the interplanetary medium. Geomagnetic storms on the Sun's surface, such as solar flares and coronal mass ejections, disturb the heliosphere, creating space weather. The Sun's rotating magnetic field acts on the interplanetary medium to create the heliospheric current sheet, the largest structure in the solar system. Aurora australis seen from orbit.

Earth's magnetic field protects its atmosphere from interacting with the solar wind. Venus and Mars do not have magnetic fields, and the solar wind causes their atmospheres to gradually bleed away into space. The interaction of the solar wind with Earth's magnetic field creates the aurorae seen near the magnetic poles. Cosmic rays originate outside the Solar System. The heliosphere partially shields the Solar System, and planetary magnetic fields (for those planets that have them) also provide some protection. The density of cosmic rays in the interstellar medium and the strength of the Sun's magnetic field change on very long timescales, so the level of cosmic radiation in the Solar System varies, though by how much is unknown. The interplanetary medium is home to at least two disc-like regions of cosmic dust. The first, the zodiacal dust cloud, lies in the inner Solar System and causes zodiacal light. It was likely formed by collisions within the asteroid belt brought on by interactions with the planets. The second extends from about 10 AU to about 40 AU, and was probably created by similar collisions within the Kuiper belt. Inner Solar System The inner Solar System is the traditional name for the region comprising the terrestrial planets and asteroids.

Composed mainly of silicates and metals, the objects of the inner Solar System huddle very closely to the Sun; the radius of this entire region is shorter than the distance between Jupiter and Saturn. Inner planets The inner planets. From left to right: Mercury , Venus , Earth , and Mars (sizes to scale) 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 crusts and mantles, and metals such as iron and nickel , which form their cores. Three of the four inner planets (Venus, Earth and Mars) have substantial atmospheres; all have impact craters and tectonic surface features such as rift valleys and volcanoes . The term inner planet should not be confused with inferior planet, which designates those planets which are closer to the Sun than Earth is (i.e. Mercury and Venus). Mercury Mercury (0.4 AU) is the closest planet to the Sun and the smallest planet (0.055 Earth masses).

Mercury has no natural satellites, and its only known geological features besides impact craters are lobed ridges or rupes, probably produced by a period of contraction early in its history. Mercury's almost negligible atmosphere consists of atoms blasted off its surface by the solar wind. Its relatively large iron core and thin mantle have not yet been adequately explained. Hypotheses include that its outer layers were stripped off by a giant impact, and that it was prevented from fully accreting by the young Sun's energy. Venus Venus (0.7 AU) is close in size to Earth, (0.815 Earth masses) and like Earth, has a thick silicate mantle around an iron core, a substantial atmosphere and evidence of internal geological activity. However, it is much drier than Earth and its atmosphere is ninety times as dense. Venus has no natural satellites. It is the hottest planet, with surface temperatures over 400 °C, most likely due to the amount of greenhouse gases in the atmosphere. No definitive evidence of current geological activity has been detected on Venus, but it has no magnetic field that would prevent depletion of its substantial atmosphere, which suggests that its atmosphere is regularly replenished by volcanic eruptions.

Earth Earth (1 AU) is the largest and densest of the inner planets, the only one known to have current geological activity, and the only planet known to have life . Its liquid hydrosphere is unique among the terrestrial planets, and it is also the only planet where plate tectonics has been observed. Earth's atmosphere is radically different from those of the other planets, having been altered by the presence of life to contain 21% free oxygen . It has one natural satellite, the Moon , the only large satellite of a terrestrial planet in the Solar System. Mars Mars (1.5 AU) is smaller than Earth and Venus (0.107 Earth masses). It possesses a tenuous atmosphere of mostly Carbon dioxide">carbon dioxide. Its surface, peppered with vast volcanoes such as Olympus Mons and rift valleys such as Valles Marineris, shows geological activity that may have persisted until very recently. Its red colour comes from rust in its iron-rich soil. Mars has two tiny natural satellites ( Deimos and Phobos) thought to be captured asteroids .

Asteroid belt Image of the main asteroid belt and the Trojan asteroids Asteroids are mostly small Solar System bodies composed mainly of rocky and metallic non-volatile minerals. The main asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3 AU from the Sun. It is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter. Asteroids range in size from hundreds of kilometres across to microscopic. All asteroids save the largest, Ceres , are classified as small Solar System bodies, but some asteroids such as Vesta and Hygieia may be reclassed as dwarf planets if they are shown to have achieved hydrostatic equilibrium. The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter . Despite this, the total mass of the main belt is unlikely to be more than a thousandth of that of the Earth. The main belt is very sparsely populated; spacecraft routinely pass through without incident. Asteroids with diameters between 10 and 10-4 m are called meteoroids .

Ceres Ceres Ceres (2.77 AU) is the largest body in the asteroid belt and is classified as a dwarf planet. It has a diameter of slightly under 1000 km, large enough for its own gravity to pull it into a spherical shape. Ceres was considered a planet when it was discovered in the 19th century, but was reclassified as an asteroid in the 1850s as further observation revealed additional asteroids. It was again reclassified in 2006 as a dwarf planet. Asteroid groups Asteroids in the main belt are divided into asteroid groups and families based on their orbital characteristics. Asteroid moons are asteroids that orbit larger asteroids. They are not as clearly distinguished as planetary moons, sometimes being almost as large as their partners. The asteroid belt also contains main-belt comets which may have been the source of Earth's water. Trojan asteroids are located in either of Jupiter's L4 or L5 points (gravitationally stable regions leading and trailing a planet in its orbit); the term "Trojan" is also used for small bodies in any other planetary or satellite Lagrange point.

Hilda asteroids are in a 2:3 resonance with Jupiter; that is, they go around the Sun three times for every two Jupiter orbits. The inner Solar System is also dusted with rogue asteroids, many of which cross the orbits of the inner planets. Mid Solar System The middle region of the Solar System is home to the gas giants and their planet-sized satellites. Many short period comets, including the centaurs, also lie in this region. It is occasionally referred to as the "outer Solar System", although recently that term has been more often applied to the region beyond Neptune. The solid objects in this region are composed of a higher proportion of "ices" (water, ammonia, methane) than the rocky denizens of the inner Solar System. Outer planets From top to bottom: Neptune, Uranus, Saturn, and Jupiter (not to scale) The four outer planets, or gas giants (sometimes called Jovian planets), collectively make up 99 percent of the mass known to orbit the Sun. Jupiter and Saturn consist largely of hydrogen and helium. The bulk of Uranus and Neptune consist of “ices”, such as water , ammonia and methane .

Some astronomers suggest they belong in their own category, “ice giants.” All four gas giants have rings, although only Saturn's ring system is easily observed from Earth. The term outer planet should not be confused with superior planet, which designates planets outside Earth's orbit (the outer planets and Mars). Jupiter Jupiter (5.2 AU), at 318 Earth masses, masses 2.5 times all the other planets put together. It is composed largely of hydrogen and helium . Jupiter's strong internal heat creates a number of semi-permanent features in its atmosphere, such as cloud bands and the Great Red Spot . Jupiter has sixty-three known satellites. The four largest, Ganymede, Callisto, Io, and Europa, show similarities to the terrestrial planets, such as volcanism and internal heating. Ganymede, the largest satellite in the Solar System, is larger than Mercury. Saturn Saturn (9.5 AU), famous for its extensive ring system, has similarities to Jupiter, such as its atmospheric composition. Saturn is far less massive, being only 95 Earth masses.

Saturn has sixty known satellites (and three unconfirmed); two of which, Titan and Enceladus, show signs of geological activity, though they are largely made of ice. Titan is larger than Mercury and the only satellite in the Solar System with a substantial atmosphere. Uranus Uranus (19.6 AU), at 14 Earth masses, is the lightest of the outer planets. Uniquely among the planets, it orbits the Sun on its side; its axial tilt is over ninety degrees to the ecliptic. It has a much colder core than the other gas giants, and radiates very little heat into space. Uranus has twenty-seven known satellites, the largest ones being Titania, Oberon, Umbriel, Ariel and Miranda. Neptune Neptune (30 AU), though slightly smaller than Uranus, is more massive (equivalent to 17 Earths) and therefore more dense. It radiates more internal heat, but not as much as Jupiter or Saturn. Neptune has thirteen known satellites. The largest, Triton, is geologically active, with geysers of liquid nitrogen . Triton is the only large satellite with a retrograde orbit.

Neptune is accompanied in its orbit by a number of minor planets, termed Neptune Trojans, that are in 1:1 resonance with it. Comets Comet Hale-Bopp Comets are small Solar System bodies, usually only a few kilometres across, composed largely of volatile ices. They have highly eccentric orbits, generally a perihelion within the orbits of the inner planets and an aphelion far beyond Pluto. When a comet enters the inner Solar System, its proximity to the Sun causes its icy surface to sublimate and ionise , creating a coma: a long tail of gas and dust often visible to the naked eye. Short-period comets have orbits lasting less than two hundred years. Long-period comets have orbits lasting thousands of years. Short-period comets are believed to originate in the Kuiper belt , while long-period comets, such as Hale-Bopp , are believed to originate in the Oort cloud. Many comet groups, such as the Kreutz Sungrazers, formed from the breakup of a single parent. Some comets with hyperbolic orbits may originate outside the Solar System, but determining their precise orbits is difficult.

Old comets that have had most of their volatiles driven out by solar warming are often categorised as asteroids. Centaurs The centaurs, which extend from 9 to 30 AU, are icy comet-like bodies that orbit in the region between Jupiter and Neptune. The largest known centaur, 10199 Chariklo, has a diameter of between 200 and 250 km. The first centaur discovered, 2060 Chiron, has been called a comet since it develops a coma just as comets do when they approach the Sun. Some astronomers classify centaurs as inward-scattered Kuiper belt objects along with the outward-scattered residents of the scattered disc . Trans-Neptunian region The area beyond Neptune, or the " trans-Neptunian region", is still largely unexplored. It appears to consist overwhelmingly of small worlds (the largest having a diameter only a fifth that of the Earth and a mass far smaller than that of the Moon) composed mainly of rock and ice. This region is sometimes known as the "outer Solar System", though others use that term to mean the region beyond the asteroid belt.

Kuiper belt Plot of all known Kuiper belt objects, set against the four outer planets The Kuiper belt, the region's first formation, is a great ring of debris similar to the asteroid belt, but composed mainly of ice. It extends between 30 and 50 AU from the Sun. It is composed mainly of small Solar System bodies, but many of the largest Kuiper belt objects, such as Quaoar, Varuna, (136108) 2003 EL61 and Orcus, may be reclassified as dwarf planets. There are estimated to be over 100,000 Kuiper belt objects with a diameter greater than 50 km, but the total mass of the Kuiper belt is thought to be only a tenth or even a hundredth the mass of the Earth. Many Kuiper belt objects have multiple satellites, and most have orbits that take them outside the plane of the ecliptic. Diagram showing the resonant and classical Kuiper belt divisions The Kuiper belt can be roughly divided into the " classical" belt and the resonances. Resonances are orbits linked to that of Neptune (e.g.

twice for every three Neptune orbits, or once for every two). The first resonance actually begins within the orbit of Neptune itself. The classical belt consists of objects having no resonance with Neptune, and extends from roughly 39.4 AU to 47.7 AU. Members of the classical Kuiper belt are classified as cubewanos, after the first of their kind to be discovered, (15760) 1992 QB1. Pluto and Charon Pluto (39 AU average), a dwarf planet, is the largest known object in the Kuiper belt. When discovered in 1930, it was considered to be the ninth planet; this changed in 2006 with the adoption of a formal definition of planet . Pluto has a relatively eccentric orbit inclined 17 degrees to the ecliptic plane and ranging from 29.7 AU from the Sun at perihelion (within the orbit of Neptune) to 49.5 AU at aphelion. Pluto and its three known moons It is unclear whether Charon, Pluto's largest moon, will continue to be classified as such or as a dwarf planet itself.

Both Pluto and Charon orbit a barycenter of gravity above their surfaces, making Pluto-Charon a binary system. Two much smaller moons, Nix and Hydra, orbit Pluto and Charon. Pluto lies in the resonant belt and has a 3:2 resonance with Neptune, meaning that Pluto orbits twice round the Sun for every three Neptunian orbits. Kuiper belt objects whose orbits share this resonance are called plutinos. Makemake Makemake is the largest classical KBO, is the brightest object in the Kuiper belt after Pluto. Originally designated 2005 FY9, it was granted a name (and the status of dwarf planet) on July 11, 2008. Makemake's orbit is far more inclined than Pluto's (29°) and, unlike Pluto, as a classical KBO, its orbit is not affected by Neptune. Scattered disc Black: scattered; blue: classical; green: resonant The scattered disc overlaps the Kuiper belt but extends much further outwards. This region is thought to be the source of short-period comets.

Scattered disc objects are believed to have been ejected into erratic orbits by the gravitational influence of Neptune's early outward migration. Most scattered disc objects (SDOs) have perihelia within the Kuiper belt but aphelia as far as 150 AU from the Sun. SDOs' orbits are also highly inclined to the ecliptic plane, and are often almost perpendicular to it. Some astronomers consider the scattered disc to be merely another region of the Kuiper belt, and describe scattered disc objects as "scattered Kuiper belt objects." Eris and its moon Dysnomia Eris Eris (68 AU average) is the largest known scattered disc object, and caused a debate about what constitutes a planet , since it is at least 5% larger than Pluto with an estimated diameter of 2400 km (1500 mi). It is the largest of the known dwarf planets. It has one moon, Dysnomia. Like Pluto, its orbit is highly eccentric, with a perihelion of 38.2 AU (roughly Pluto's distance from the Sun) and an aphelion of 97.6 AU, and steeply inclined to the ecliptic plane.

Farthest regions The point at which the Solar System ends and interstellar space begins is not precisely defined, since its outer boundaries are shaped by two separate forces: the solar wind and the Sun's gravity. The solar wind is believed to surrender to the interstellar medium at roughly four times Pluto's distance. However, the Sun's Roche sphere, the effective range of its gravitational influence, is believed to extend up to a thousand times farther. Heliopause The Voyagers entering the heliosheath. The heliosphere is divided into two separate regions. The solar wind travels at its maximum velocity out to about 95 AU, or three times the orbit of Pluto. The edge of this region is the termination shock, the point at which the solar wind collides with the opposing winds of the interstellar medium. Here the wind slows, condenses and becomes more turbulent, forming a great oval structure known as the heliosheath that looks and behaves very much like a comet's tail, extending outward for a further 40 AU at its stellar-windward side, but tailing many times that distance in the opposite direction.

The outer boundary of the heliosphere, the heliopause, is the point at which the solar wind finally terminates, and is the beginning of interstellar space. The shape and form of the outer edge of the heliosphere is likely affected by the fluid dynamics of interactions with the interstellar medium, as well as solar magnetic fields prevailing to the south, e.g. it is bluntly shaped with the northern hemisphere extending 9 AU (roughly 900 million miles) farther than the southern hemisphere. Beyond the heliopause, at around 230 AU, lies the bow shock, a plasma "wake" left by the Sun as it travels through the Milky Way . No spacecraft have yet passed beyond the heliopause, so it is impossible to know for certain the conditions in local interstellar space. It is expected that NASA's Voyager spacecraft will pass the heliopause some time in the next decade, and transmit valuable data on radiation levels and solar wind back to the Earth. How well the heliosphere shields the Solar System from cosmic rays is poorly understood. A NASA-funded team has developed a concept of a "Vision Mission" dedicated to sending a probe to the the heliosphere.

Oort cloud Artist's rendering of the Kuiper Belt and hypothetical Oort cloud. The hypothetical Oort cloud is a great mass of up to a trillion icy objects that is believed to be the source for all long-period comets and to surround the Solar System at roughly 50,000 AU (around 1 light-year (LY)), and possibly to as far as 100,000 AU (1.87 LY). It is believed to be composed of comets which were ejected from the inner Solar System by gravitational interactions with the outer planets. Oort cloud objects move very slowly, and can be perturbed by infrequent events such as collisions, the gravitational effects of a passing star, or the galactic tide, the tidal force exerted by the Milky Way . Telescopic image of Sedna Sedna and the inner Oort cloud 90377 Sedna is a large, reddish Pluto-like object with a gigantic, highly elliptical orbit that takes it from about 76 AU at perihelion to 928 AU at aphelion and takes 12,050 years to complete.

Mike Brown, who discovered the object in 2003, asserts that it cannot be part of the scattered disc or the Kuiper belt as its perihelion is too distant to have been affected by Neptune's migration. He and other astronomers consider it to be the first in an entirely new population, which also may include the object 2000 CR105, which has a perihelion of 45 AU, an aphelion of 415 AU, and an orbital period of 3420 years. Brown terms this population the "Inner Oort cloud," as it may have formed through a similar process, although it is far closer to the Sun. Sedna is very likely a dwarf planet, though its shape has yet to be determined with certainty. Boundaries Much of our Solar System is still unknown. The Sun's gravitational field is estimated to dominate the gravitational forces of surrounding stars out to about two light years (125,000 AU). The outer extent of the Oort cloud, by contrast, may not extend farther than 50,000 AU.

Despite discoveries such as Sedna, the region between the Kuiper belt and the Oort cloud, an area tens of thousands of AU in radius, is still virtually unmapped. There are also ongoing studies of the region between Mercury and the Sun. Objects may yet be discovered in the Solar System's uncharted regions. Galactic context Location of the Solar System within our galaxy The Solar System is located in the Milky Way galaxy , a barred spiral galaxy with a diameter of about 100,000 light-years containing about 200 billion stars. Our Sun resides in one of the Milky Way's outer spiral arms, known as the Orion Arm or Local Spur. The Sun lies between 25,000 and 28,000 light years from the Galactic Centre, and its speed within the galaxy is about 220 kilometres per second, so that it completes one revolution every 225–250 million years. This revolution is known as the Solar System's galactic year. The Solar System's location in the galaxy is very likely a factor in the evolution of life on Earth.

Its orbit is close to being circular and is at roughly the same speed as that of the spiral arms, which means it passes through them only rarely. Since spiral arms are home to a far larger concentration of potentially dangerous supernovae , this has given Earth long periods of interstellar stability for life to evolve. The Solar System also lies well outside the star-crowded environs of the galactic centre. Near the centre, gravitational tugs from nearby stars could perturb bodies in the Oort Cloud and send many comets into the inner Solar System, producing collisions with potentially catastrophic implications for life on Earth. The intense radiation of the galactic centre could also interfere with the development of complex life. Even at the Solar System's current location, some scientists have hypothesised that recent supernovae may have adversely affected life in the last 35,000 years by flinging pieces of expelled stellar core towards the Sun in the form of radioactive dust grains and larger, comet-like bodies.

Neighbourhood Artist's conception of the Local Bubble The immediate galactic neighbourhood of the Solar System is known as the Local Interstellar Cloud or Local Fluff, an area of dense cloud in an otherwise sparse region known as the Local Bubble, an hourglass-shaped cavity in the interstellar medium roughly 300 light years across. The bubble is suffused with high-temperature plasma that suggests it is the product of several recent supernovae. The solar apex, the direction of the Sun's path through interstellar space, is near the constellation of Hercules in the direction of the current location of the bright star Vega. There are relatively few stars within ten light years (95 trillion km) of the Sun. The closest is the triple star system Alpha Centauri, which is about 4.4 light years away. Alpha Centauri A and B are a closely tied pair of Sun-like stars, while the small red dwarf Alpha Centauri C (also known as Proxima Centauri ) orbits the pair at a distance of 0.2 light years.

The stars next closest to the Sun are the red dwarfs Barnard's Star (at 5.9 light years), Wolf 359 (7.8 light years) and Lalande 21185 (8.3 light years). The largest star within ten light years is Sirius , a bright main sequence star roughly twice the Sun's mass and orbited by a white dwarf called Sirius B. It lies 8.6 light years away. The remaining systems within ten light years are the binary red dwarf system Luyten 726-8 (8.7 light years) and the solitary red dwarf Ross 154 (9.7 light years). Our closest solitary sunlike star is Tau Ceti, which lies 11.9 light years away. It has roughly 80 percent the Sun's mass, but only 60 percent its luminosity. The closest known extrasolar planet to the Sun lies around the star Epsilon Eridani, a star slightly dimmer and redder than the Sun, which lies 10.5 light years away.

Its one confirmed planet, Epsilon Eridani b, is roughly 1.5 times Jupiter's mass and orbits its star every 6.9 years. Formation and evolution Hubble image of protoplanetary disks in the Orion Nebula , a light-years-wide "stellar nursery" likely very similar to the primordial nebula from which our Sun formed. The Solar System is believed to have formed according to the nebular hypothesis, which holds that it emerged from the gravitational collapse of a giant molecular cloud 4.6 billion years ago. This initial cloud was likely several light-years across and probably birthed several stars. Studies of ancient meteorites reveal traces of elements only formed in the hearts of very large exploding stars, indicating that the Sun formed within a star cluster, and in range of a number of nearby supernovae explosions. The shock wave from these supernovae may have triggered the formation of the Sun by creating regions of overdensity in the surrounding nebula, allowing gravitational forces to overcome internal gas pressures and cause collapse.

Solar System's Most Dwarf Planets of Our Solar System (Infographic) Dwarf Planets of Our Solar System (Infographic) By Karl Tate, SPACE.com Infographics Artist | November 21, 2012 01:00pm ET MORE Pluto was demoted to dwarf planet status in 2006, joining Eris, Haumea, Makemake and Ceres. Credit: Karl Tate, SPACE.com contributor In 2006 the organization responsible for classifying celestial bodies, the International Astronomical Union, decided that a new class of objects was needed. The solar system's erratic ninth planet, Pluto, was assigned to the new “ dwarf planet ” category along with four other bodies, all tinier than Earth’s moon. Some astronomers expect there may be as many as 50 dwarf planets in the solar system. Eris , the largest dwarf planet, is only slightly bigger than Pluto, at 1,445 miles in diameter (2,326 km).

Discovered in 2003, Eris orbits at an average distance of 68 AU (that is, 68 times the Earth’s distance from the sun) and takes 561.4 Earth years to circle the sun. Eris has the orbit that is most highly inclined of all the dwarf planets, tilted nearly 47 degrees from the plane of the planets’ orbits. A day on Eris takes 25.9 hours. Eris has one moon, Dysnomia. Pluto , discovered in 1930, orbits the sun at an average of 39.5 times the Earth’s distance. Its diameter is 1,430 miles (2,302 km). Pluto takes 247.9 Earth years to orbit the sun, and its day is 6.39 times as long as Earth’s. Pluto has five known moons: Charon, Nix, Hydra and two that were recently discovered and have not yet been named. Haumea was discovered in 2003. This dwarf planet has an extremely elongated shape, with its longest dimension being about 1,218 miles long (1,960 km).

Haumea rotates very rapidly and has the shortest day of all the dwarf planets, only 3.9 hours. Orbiting 43.1 times farther from the sun than Earth does, Haumea takes nearly 282 Earth years to complete one orbit. Haumea has two moons, Hi’iaka and Namaka. Makemake , discovered in 2005, has no known moons. Makemake orbits at 45.3 times Earth’s distance and takes more than 305 years to complete a circuit of the sun. Its day is 22.5 hours. Makemake’s average diameter is 882 miles (1,420 km). Ceres , first spotted by astronomers in 1801, was first called a planet and later an asteroid. In 2006 it was reclassified as a dwarf planet. Ceres is the closest dwarf planet to Earth, orbiting at only 2.8 times Earth’s distance from the sun. Its year takes 4.6 Earth years and its day is 9.1 hours. Ceres has no known moons.

Dwarf Planet Facts - Interesting Facts about the Dwarf Planets Eris Dwarf Planet Facts There are 5 officially recognised dwarf planets in our solar system , they are Ceres , Pluto , Haumea , Makemake and Eris . With the exception of Ceres, which is located in the asteroid belt , the other dwarf planets are found in the outer solar system. There are another 6 objects in our solar system that are almost certainly dwarf planets and there may as many as 10,000. Of the dwarf planets only 2 have been visited by space probes, in 2015 NASA’s Dawn and New Horizons missions reached Ceres and Pluto respectively. What is Dwarf Planet? Dwarf planets share many of the same characteristics as planets though there is one significant difference. The International Astronomical Union’s definition of a dwarf planet is: A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

The key difference is that a planet has cleared other objects in the area of its orbit while a dwarf planet has not. Sizes of the Dwarf Planets The Dwarf Planets Ceres, Pluto, Haumea, Makemake and Eris The largest dwarf planet in the solar system is Pluto followed by Eris, Makemake, Haumea, with the smallest being Ceres. The order of the dwarf planets from closest to Sun outwards is Ceres, Pluto, Haumea, Makemake, with Eris being the furthest from the Sun. Name

Question: Which celestial body is the only dwarf planet and largest asteroid found in the inner solar system?
Answer: Ceres