What are the Planets of the Solar System? - Universe Today Universe Today What are the Planets of the Solar System? Article Updated: 21 Aug , 2016 by Matt Williams At one time, humans believed that the Earth was the center of the Universe; that the Sun, Moon, planets and stars all revolved around us. It was only after centuries of ongoing observations and improved instrumentation that astronomers came to understand that we are in fact part a larger system of planets that revolve around the Sun. And it has only been within the last century that we’ve come to understand just how big our Solar System is. And even now, we are still learning. In the past few decades, the total number of celestial bodies and moons that are known to orbit the Sun has expanded. We have also come to debate the definition of “planet” (a controversial topic indeed!) and introduced additional classifications – like dwarf planet, minor planet, plutoid, etc. – to account for new finds. So just how many planets are there and what is special about them? Let’s run through them one by one, shall we? Mercury: As you travel outward from the Sun, Mercury is the closest planet.

It orbits the Sun at an average distance of 58 million km (36 million mi). Mercury is airless, and so without any significant atmosphere to hold in the heat, it has dramatic temperature differences. The side that faces the Sun experiences temperatures as high as 420 °C (788 °F), and then the side in shadow goes down to -173 °C (-279.4 °F). MESSENGER image of Mercury from its third flyby. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington Like Venus, Earth and Mars, Mercury is a terrestrial planet, which means it is composed largely of refractory minerals such as the silicates and metals such as iron and nickel. These elements are also differentiated between a metallic core and a silicate mantle and crust, with Mercury possessing a larger-than-average core. Multiple theories have been proposed to explain this, the most widely accepted being that the impact from a planetesimal in the past blew off much of its mantle material. Mercury is the smallest planet in the Solar System, measuring just 4879 km across at its equator.

However, it is second densest planet in the Solar System, with a density of 5.427 g/cm3 – which is the second only to Earth. Because of this, Mercury experiences a gravitational pull that is roughly 38% that of Earth’s (0.38 g). Mercury also has the most eccentric orbit of any planet in the Solar System (0.205), which means its distance from the Sun ranges from 46 to 70 million km (29-43 million mi). The planet also takes 87.969 Earth days to complete an orbit. But with an average orbital speed of 47.362 km/s, Mercury also takes 58.646 days to complete a single rotation. Combined with its eccentric orbit, this means that it takes 176 Earth days for the Sun to return to the same place in the sky (i.e. a solar day) on Mercury, which is twice as long as a single Hermian year. Mercury also has the lowest axial tilt of any planet in the Solar System – approximately 0.027 degrees – compared to Jupiter’s 3.1 degrees, which is the second smallest.

The MESSENGER spacecraft has been in orbit around Mercury since March 2011 – but its days are numbered. Credit: NASA/JHUAPL/Carnegie Institution of Washington Mercury has only been visited two times by spacecraft, the first being the Mariner 10 probe, which conducted a flyby of the planet back in the mid-1970s. It wasn’t until 2008 that another spacecraft from Earth made a close flyby of Mercury (the MESSENGER probe) which took new images of its surface , shed light on its geological history , and confirmed the presence of water ice and organic molecules in its northern polar region. In summary, Mercury is made special by the fact it is small, eccentric, and varies between extremes of hot and cold. It’s also very mineral rich, and quite dense! Venus: Venus is the second planet in the Solar System, and is Earth’s virtual twin in terms of size and mass. With a mass of 4.8676×1024 kg and a mean radius of about 6,052 km, it is approximately 81.5% as massive as Earth and 95% as large.

Like Earth (and Mercury and Mars), it is a terrestrial planet, composed of rocks and minerals that are differentiated. But apart from these similarities, Venus is very different from Earth. Its atmosphere is composed primarily of carbon dioxide (96%), along with nitrogen and a few other gases. This dense cloud cloaks the planet, making surface observation very difficult, and helps heat it up to 460 °C (860 °F). The atmospheric pressure is also 92 times that of Earth’s atmosphere, and poisonous clouds of carbon dioxide and sulfuric acid rain are commonplace. Venus’ similarity in size and mass has led to it being called “Earth’s sister planet’. Credit: NASA/JPL/Magellan Venus orbits the Sun at an average distance of about 0.72 AU (108 million km; 67 million mi) with almost no eccentricity.

In fact, with its farthest orbit (aphelion) of 0.728 AU (108,939,000 km) and closest orbit (perihelion) of 0.718 AU (107,477,000 km), it has the most circular orbit of any planet in the Solar System. The planet completes an orbit around the Sun every 224.65 days, meaning that a year on Venus is 61.5% as long as a year on Earth. When Venus lies between Earth and the Sun, a position known as inferior conjunction, it makes the closest approach to Earth of any planet, at an average distance of 41 million km. This takes place, on average, once every 584 days, and is the reason why Venus is the closest planet to Earth . The planet completes an orbit around the Sun every 224.65 days, meaning that a year on Venus is 61.5% as long as a year on Earth.

Unlike most other planets in the Solar System, which rotate on their axes in an counter-clockwise direction, Venus rotates clockwise (called “retrograde” rotation). It also rotates very slowly, taking 243 Earth days to complete a single rotation. This is not only the slowest rotation period of any planet, it also means that a single day on Venus lasts longer than a Venusian year. Venus’ atmosphere is also known to experience lightning storms . Since Venus does not experience rainfall (except in the form of sulfuric acid), it has been theorized that the lightning is being caused by volcanic eruptions. Several spacecraft have visited Venus, and a few landers have even made it to the surface to send back images of its hellish landscape. Even though there were made of metal, these landers only survived a few hours at best. Venus is made special by the fact that it is very much like Earth, but also radically different. It’s thick atmosphere could crush a living being, its heat could melt lead, and its acid rain could dissolve flesh, bone and metal alike! It also rotates very slowly, and backwards relative to the other plants. Earth: Earth is our home, and the third planet from the Sun.

With a mean radius of 6371 km and a mass of 5.97×1024 kg, it is the fifth largest and fifth most-massive planet in the Solar System. And with a mean density of 5.514 g/cm³, it is the densest planet in the Solar System. Like Mercury, Venus and Mars, Earth is a terrestrial planet. But unlike these other planets, Earth’s core is differentiated between a solid inner core and liquid outer core. The outer core also spins in the opposite direction as the planet, which is believed to create a dynamo effect that gives Earth its protective magnetosphere. Combined with a atmosphere that is neither too thin nor too thick, Earth is the only planet in the Solar System known to support life. The Earth’s layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com In terms of its orbit, Earth has a very minor eccentricity (approx.

0.0167) and ranges in its distance from the Sun between 147,095,000 km (0.983 AU) at perihelion to 151,930,000 km (1.015 AU) at aphelion. This works out to an average distance (aka. semi-major axis) of 149,598,261 km, which is the basis of a single Astronomical Unit (AU) The Earth has an orbital period of 365.25 days, which is the equivalent of 1.000017 Julian years. This means that every four years (in what is known as a Leap Year), the Earth calendar must include an extra day. Though a single solar day on Earth is considered to be 24 hours long, our planet takes precisely 23h 56m and 4 s to complete a single sidereal rotation (0.997 Earth days).

Earth’s axis is also tilted 23.439281° away from the perpendicular of its orbital plane, which is responsible for producing seasonal variations on the planet’s surface with a period of one tropical year (365.24 solar days). In addition to producing variations in terms of temperature, this also results in variations in the amount of sunlight a hemisphere receives during the course of a year. Earth has only a single moon: the Moon . Thanks to examinations of Moon rocks that were brought back to Earth by the Apollo missions , the predominant theory states that the Moon was created roughly 4.5 billion years ago from a collision between Earth and a Mars-sized object (known as Theia ). This collision created a massive cloud of debris that began circling our planet, which eventually coalesced to form the Moon we see today. A picture of Earth taken by Apollo 11 astronauts. Credit: NASA What makes Earth special, you know, aside from the fact that it is our home and where we originated? It is the only planet in the Solar System where liquid, flowing water exists in abundance on its surface, has a viable atmosphere, and a protective magnetosphere.

In other words, it is the only planet (or Solar body) that we know of where life can exist on the surface. In addition, no planet in the Solar System has been studied as well as Earth, whether it be from the surface or from space. Thousands of spacecraft have been launched to study the planet, measuring its atmosphere, land masses, vegetation, water, and human impact. Our understanding of what makes our planet unique in our Solar System has helped in the search for Earth-like planets in other systems. Mars: The fourth planet from the Sun is Mars , which is also the second smallest planet in the Solar System. It has a radius of approximately 3,396 km at its equator, and 3,376 km at its polar regions – which is the equivalent of roughly 0.53 Earths. While it is roughly half the size of Earth, it’s mass – 6.4185 x 10²³ kg – is only 0.151 that of Earth’s. It’s density is also lower than Earths, which leads to it experiencing about 1/3rd Earth’s gravity (0.376 g).

It’s axial tilt is very similar to Earth’s, being inclined 25.19° to its orbital plane (Earth’s axial tilt is just over 23°), which means Mars also experiences seasons. Mars has almost no atmosphere to help trap heat from the Sun, and so temperatures can plunge to a low of -140 °C (-220 °F) in the Martian winter. However, at the height of summer, temperatures can get up to 20 °C (68 °F) during midday at the equator. However, recent data obtained by the Curiosity rover and numerous orbiters have concluded that Mars once had a denser atmosphere. Its loss, according to data obtained by NASA’s Mars Atmosphere and Volatile Evolution (MAVEN), the atmosphere was stripped away by solar wind over the course of a 500 million year period, beginning 4.2 billion years ago. At its greatest distance from the Sun (aphelion), Mars orbits at a distance of 1.666 AUs, or 249.2 million km.

At perihelion, when it is closest to the Sun, it orbits at a distance of 1.3814 AUs, or 206.7 million km. At this distance, Mars takes 686.971 Earth days, the equivalent of 1.88 Earth years, to complete a rotation of the Sun. In Martian days (aka. Sols, which are equal to one day and 40 Earth minutes), a Martian year is 668.5991 Sols. Like Mercury, Venus, and Earth, Mars is a terrestrial planet, composed mainly of silicate rock and metals that are differentiated between a core, mantle and crust. The red-orange appearance of the Martian surface is caused by iron oxide, more commonly known as hematite (or rust). The presence of other minerals in the surface dust allow for other common surface colors, including golden, brown, tan, green, and others. Although liquid water cannot exist on Mars’ surface, owing to its thin atmosphere, large concentrations of ice water exist within the polar ice caps – Planum Boreum and Planum Australe.

In addition, a permafrost mantle stretches from the pole to latitudes of about 60°, meaning that water exists beneath much of the Martian surface in the form of ice water. Radar data and soil samples have confirmed the presence of shallow subsurface water at the middle latitudes as well. MSL Curiosity selfie on the surface of Mars. Image: NASA/JPL/Cal-Tech Mars has two tiny asteroid-sized moons: Phobos and Deimos . Because of their size and shape, the predominant theory is that Mars acquired these two moons after they were kicked out of the Asteroid Belt by Jupiter’s gravity. Mars has been heavily studied by spacecraft. There are multiple rovers and landers currently on the surface and a small fleet of orbiters flying overhead. Recent missions include the Curiosity Rover, which gathered ample evidence on Mars’ water past, and the groundbreaking discovery of finding organic molecules on the surface . Upcoming missions include NASA’s InSight lander and the Exomars rover. Hence, Mars’ special nature lies in the fact that it also is terrestrial and lies within the outer edge of the Sun’s habitable zone.

And whereas it is a cold, dry place today, it once had an thicker atmosphere and plentiful water on its surface. Jupiter: Mighty Jupiter is the fouth planet for our Sun and the biggest planet in our Solar System . Jupiter’s mass, volume, surface area and mean circumference are 1.8981 x 1027 kg, 1.43128 x 1015 km3, 6.1419 x 1010 km2, and 4.39264 x 105 km respectively. To put that in perspective, Jupiter diameter is roughly 11 times that of Earth, and 2.5 times the mass of all the other planets in the Solar System combined. Jupiter has spectacular aurora, such as this view captured by the Hubble Space Telescope. Credit: NASA, ESA, and J. Nichols (University of Leicester) But, being a gas giant, it has a relatively low density – 1.326 g/cm3 – which is less than one quarter of Earth’s.

This means that while Jupiter’s volume is equivalent to about 1,321 Earths, it is only 318 times as massive. The low density is one way scientists are able to determine that it is made mostly of gases, though the debate still rages on what exists at its core (see below). Jupiter orbits the Sun at an average distance (semi-major axis) of 778,299,000 km (5.2 AU), ranging from 740,550,000 km (4.95 AU) at perihelion and 816,040,000 km (5.455 AU) at aphelion. At this distance, Jupiter takes 11.8618 Earth years to complete a single orbit of the Sun. In other words, a single Jovian year lasts the equivalent of 4,332.59 Earth days. However, Jupiter’s rotation is the fastest of all the Solar System’s planets, completing a rotation on its axis in slightly less than ten hours (9 hours, 55 minutes and 30 seconds to be exact).

Therefore, a single Jovian year lasts 10,475.8 Jovian solar days. This orbital period is two-fifths that of Saturn, which means that the two largest planets in our Solar System form a 5:2 orbital resonance. Much like Earth, Jupiter experiences auroras near its northern and southern poles. But on Jupiter, the auroral activity is much more intense and rarely ever stops. The intense radiation, Jupiter’s magnetic field, and the abundance of material from Io’s volcanoes that react with Jupiter’s ionosphere create a light show that is truly spectacular. The Juno spacecraft isn’t the first one to visit Jupiter. Galileo went there in the mid 90’s, and Voyager 1 snapped a nice picture of the clouds on its mission. Credit: NASA Jupiter also experiences violent weather patterns . Wind speeds of 100 m/s (360 km/h) are common in zonal jets, and can reach as high as 620 kph (385 mph). Storms form within hours and can become thousands of km in diameter overnight. One storm, the Great Red Spot , has been raging since at least the late 1600s.

The storm has been shrinking and expanding throughout its history; but in 2012, it was suggested that the Giant Red Spot might eventually disappear . Jupiter is composed primarily of gaseous and liquid matter. It is the largest of the gas giants, and like them, is divided between a gaseous outer atmosphere and an interior that is made up of denser materials. It’s upper atmosphere is composed of about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules, and approx. 75% hydrogen and 24% helium by mass, with the remaining one percent consisting of other elements. The interior contains denser materials, such that the distribution is roughly 71% hydrogen, 24% helium and 5% other elements by mass. It is believed that Jupiter’s core is a dense mix of elements – a surrounding layer of liquid metallic hydrogen with some helium, and an outer layer predominantly of molecular hydrogen. The core has also been described as rocky, but this remains unknown as well.

Jupiter has been visited by several spacecraft, including NASA’s Pioneer 10 and Voyager spacecraft in 1973 and 1980, respectively; and by the Cassini and New Horizons spacecraft more recently. Until the recent arrival of Juno , only the Galileo spacecraft has ever gone into orbit around Jupiter, and it was crashed into the planet in 2003 to prevent it from contaminating one of Jupiter’s icy moons. Illustration of Jupiter and the Galilean satellites. Credit: NASA In short, Jupiter is massive and has massive storms. But compared to the planets of the inner Solar System, is it significantly less dense. Jupiter also has the most moons in the Solar System, with 67 confirmed and named moons orbiting it. But it is estimated that as many as 200 natural satellites may exist around the planet. Little wonder why this planet is named after the king of the gods. Saturn: Saturn is the second largest planet in the Solar System. With a mean radius of 58232±6 km, it is approximately 9.13 times the size of Earth.

And at 5.6846×1026 kg, it is roughly 95.15 as massive. However, since it is a gas giant, it has significantly greater volume – 8.2713×1014 km3, which is equivalent to 763.59 Earths. The sixth most distant planet, Saturn orbits the Sun at an average distance of 9 AU (1.4 billion km; 869.9 million miles). Due to its slight eccentricity, the perihelion and aphelion distances are 9.022 (1,353.6 million km; 841.3 million mi) and 10.053 AU (1,513,325,783 km; 940.13 million mi), on average respectively. With an average orbital speed of 9.69 km/s, it takes Saturn 10,759 Earth days to complete a single revolution of the Sun. In other words, a single Cronian year is the equivalent of about 29.5 Earth years.

However, as with Jupiter, Saturn’s visible features rotate at different rates depending on latitude, and multiple rotation periods have been assigned to various regions. This portrait looking down on Saturn and its rings was created from images obtained by NASA’s Cassini spacecraft on Oct. 10th, 2013. Credit: NASA/JPL-Caltech/Space Science Institute/G. Ugarkovic As a gas giant, Saturn is predominantly composed of hydrogen and helium gas. With a mean density of 0.687 g/cm3, Saturn is the only planet in the Solar System that is less dense than water; which means that it lacks a definite surface, but is believed to have a solid core. This is due to the fact that Saturn’s temperature, pressure, and density all rise steadily toward the core. Standard planetary models suggest that the interior of Saturn is similar to that of Jupiter, having a small rocky core surrounded by hydrogen and helium with trace amounts of various volatiles. This core is similar in composition to the Earth, but more dense due to the presence of metallic hydrogen, which as a result of the extreme pressure.

As a gas giant, the outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium by volume. Trace amounts of ammonia, acetylene, ethane, propane, phosphine and methane have been also detected in Saturn’s atmosphere. Like Jupiter, it also has a banded appearance, but Saturn’s bands are much fainter and wider near the equator. On occasion, Saturn’s atmosphere exhibits long-lived ovals that are thousands of km wide, similar to what is commonly observed on Jupiter. Whereas Jupiter has the Great Red Spot, Saturn periodically has what’s known as the Great White Spot (aka. Great White Oval). This unique but short-lived phenomenon occurs once every Saturnian year, roughly every 30 Earth years, around the time of the northern hemisphere’s summer solstice. The huge storm churning through the atmosphere in Saturn’s northern hemisphere overtakes itself as it encircles the planet in this true-color view from NASA’s Cassini spacecraft. Image credit: NASA/JPL-Caltech/SSI The persisting hexagonal wave pattern around the north pole was first noted in the Voyager images.

The sides of the hexagon are each about 13,800 km (8,600 mi) long (which is longer than the diameter of the Earth) and the structure rotates with a period of 10h 39m 24s, which is assumed to be equal to the period of rotation of Saturn’s interior. The south pole vortex, meanwhile, was first observed using the Hubble Space Telescope . These images indicated the presence of a jet stream, but not a hexagonal standing wave. These storms are estimated to be generating winds of 550 km/h, are comparable in size to Earth, and believed to have been going on for billions of years. In 2006, the Cassini space probe observed a hurricane-like storm that had a clearly defined eye. Such storms had not been observed on any planet other than Earth – even on Jupiter. Of course, the most amazing feature of Saturn is its rings . These are made of particles of ice ranging in size from a grains of sand to the size of a car. Some scientists think the rings are only a few hundred million years old, while others think they could be as old as the Solar System itself.

Saturn has been visited by spacecraft 4 times: Pioneer 11 , Voyager 1 and 2 were just flybys, but Cassini has actually gone into orbit around Saturn and has captured thousands of images of the planet and its moons. And speaking of moons, Saturn has a total of 62 moons discovered (so far), though estimates indicate that it might have as many as 150. A collage of Saturn (bottom left) and some of its moons: Titan, Enceladus, Dione, Rhea and Helene. Credit: NASA/JPL/Space Science Institute So like Jupiter, Saturn is a massive gas giant that experiences some very interesting weather patterns. It also has lots of moons and has a very low density. But what really makes Saturn stand out is its impressive ring system. Whereas every gas and ice giant has one, Saturn’s is visible to the naked eye and very beautiful to behold! Uranus: Next comes Uranus , the seventh planet from the Sun.

With a mean radius of approximately 25,360 km and a mass of 8.68 × 1025 kg, Uranus is approximately 4 times the sizes of Earth and 63 times its volume. However, as a gas giant, its density (1.27 g/cm3) is significantly lower; hence, it is only 14.5 as massive as Earth. The variation of Uranus’ distance from the Sun is also greater than that any other planet (not including dwarf planets or plutoids). Essentially, the gas giant’s distance from the Sun varies from 18.28 AU (2,735,118,100 km) at perihelion to 20.09 AU (3,006,224,700 km) at aphelion. At an average distance of 3 billion km from the Sun, it takes Uranus roughly 84 years (or 30,687 days) to complete a single orbit of the Sun.

The standard model of Uranus’s structure is that it consists of three layers: a rocky (silicate/iron–nickel) core in the center, an icy mantle in the middle and an outer envelope of gaseous hydrogen and helium. Much like Jupiter and Saturn, hydrogen and helium account for the majority of the atmosphere – approximately 83% and 15% – but only a small portion of the planet’s overall mass (0.5 to 1.5 Earth masses). Uranus as seen through the automated eyes of Voyager 2 in 1986. (Credit: NASA/JPL) The third most abundant element is methane ice (CH4), which accounts for 2.3% of its composition and which accounts for the planet’s aquamarine or cyan coloring. Trace amounts of various hydrocarbons are also found in the stratosphere of Uranus, which are thought to be produced from methane and ultraviolent radiation-induced photolysis. They include ethane (C2H6), acetylene (C2H2), methylacetylene (CH3C2H), and diacetylene (C2HC2H).

In addition, spectroscopy has uncovered carbon monoxide and carbon dioxide in Uranus’ upper atmosphere, as well as the presence icy clouds of water vapor and other volatiles , such as ammonia and hydrogen sulfide. Because of this, Uranus and Neptune are considered a distinct class of giant planet – known as “Ice Giants” – since they are composed mainly of heavier volatile substances. The rotational period of the interior of Uranus is 17 hours, 14 minutes. As with all giant planets, its upper atmosphere experiences strong winds in the direction of rotation. Hence its weather systems are also broken up into bands that rotate around the planet, which are driven by internal heat rising to the upper atmosphere. As a result, winds on Uranus can reach up to 900 km/h (560 mph), creating massive storms like the one spotted by the Hubble Space Telescope in 2012. Similar to Jupiter’s Great Red Spot, this “ Dark Spot ” was a giant cloud vortex that measured 1,700 kilometers by 3,000 kilometers (1,100 miles by 1,900 miles). Huge storms on Uranus were spotted by the Keck Observatory on Aug.

5 and Aug. 6, 2014. Credit: Imke de Pater (UC Berkeley), Pat Fry (University of Wisconsin), Keck Observatory One unique feature of Uranus is that it rotates on its side. Whereas all of the Solar System’s planets are tilted on their axes to some degree, Uranus has the most extreme axial tilt of 98°. This leads to the radical seasons that the planet experiences, not to mention an unusual day-night cycle at the poles. At the equator, Uranus experiences normal days and nights; but at the poles, each experience 42 Earth years of day followed by 42 years of night. Uranus was the first planet to be discovered with a telescope; it was first recognized as a planet in 1781 by William Herschel. Beyond Earth-based observations, only one spacecraft (Voyager 2) has ever studied Uranus up close. It passed by the planet in 1986, and captured the first close images. Uranus has 27 known moons . Uranus’ special nature comes through in its natural beauty, its intense weather, its ring system and its impressive array of moons.

And it’s compositions, being an “ice” giant, is what gives its aquamarine color. But perhaps mist interesting is its sideways rotation, which is unique among the Solar planets. Neptune: Neptune is the 8th and final planet in the Solar System, orbiting the Sun at a distance of 29.81 AU (4.459 x 109 km) at perihelion and 30.33 AU (4.537 x 109 km) at aphelion. With a mean radius of 24,622 ± 19 km, Neptune is the fourth largest planet in the Solar System and four times as large as Earth. But with a mass of 1.0243×1026 kg – which is roughly 17 times that of Earth – it is the third most massive, outranking Uranus. Neptune’s system of moons and rings visualized. Credit: SETI Neptune takes 16 h 6 min 36 s (0.6713 days) to complete a single sidereal rotation, and 164.8 Earth years to complete a single orbit around the Sun.

This means that a single day lasts 67% as long on Neptune, whereas a year is the equivalent of approximately 60,190 Earth days (or 89,666 Neptunian days). Due to its smaller size and higher concentrations of volatiles relative to Jupiter and Saturn, Neptune (much like Uranus) is often referred to as an “ice giant” – a subclass of a giant planet. Also like Uranus, Neptune’s internal structure is differentiated between a rocky core consisting of silicates and metals; a mantle consisting of water, ammonia and methane ices; and an atmosphere consisting of hydrogen, helium and methane gas. The core of Neptune is composed of iron, nickel and silicates, with an interior model giving it a mass about 1.2 times that of Earth. The pressure at the center is estimated to be 7 Mbar (700 GPa), about twice as high as that at the center of Earth, and with temperatures as high as 5,400 K. At a depth of 7000 km, the conditions may be such that methane decomposes into diamond crystals that rain downwards like hailstones.

Because Neptune’s axial tilt (28.32°) is similar to that of Earth (~23°) and Mars (~25°), the planet experiences similar seasonal changes. Combined with its long orbital period, this means that the seasons last for forty Earth years. Also owing to its axial tilt being comparable to Earth’s is the fact that the variation in the length of its day over the course of the year is not any more extreme than it on Earth. Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL Just like Jupiter and Saturn, Neptune has bands of storms that circle the planet. Astronomers have clocked winds on Neptune traveling at 2,100 km/hour, which is believed to be due to Neptune’s cold temperatures – which may decrease the friction in the system, During its 1989 flyby, NASA’s Voyager 2 spacecraft discovered the Great Dark Spot on Neptune. Similar to Jupiter’s Great Red Spot, this is an anti-cyclonic storm measuring 13,000 km x 6,600 km across.

A few years later, however, the Hubble Space Telescope failed to see the Great Dark Spot, but it did see different storms. This might mean that storms on Neptune don’t last as long as they do on Jupiter or even Saturn. The more active weather on Neptune might be due, in part, to its higher internal heat. Although Neptune is much more distant than Uranus from the Sun, receiving 40% less sunlight, temperatures on the surface of the two planets are roughly similar. In fact, Neptune radiates 2.61 times as much energy as it receives from the Sun. This is enough heat to help drive the fastest winds in the Solar System. Neptune is the second planet discovered in modern times. It was discovered at the same time by both Urbain Le Verrier and John Couch Adams. Neptune has only ever been visited by one spacecraft, Voyager 2, which made a fly by in August, 1989. Neptune has 13 known moons . Th largest and most famous of these is Triton , which is believed to be a former KBO that was captured by Neptune’s gravity. Global Color Mosaic of Triton, taken by Voyager 2 in 1989.

Credit: NASA/JPL/USGS So much like Uranus, Neptune has a ring system, some intense weather patterns, and an impressive array of moons. Also like Uranus, Neptune’s composition allows for its aquamarine color; except that in Neptune’s case, this color is more intense and vivid. In addition, Neptune experiences some temperature anomalies that are yet to be explained. And let’s not forgt the raining diamonds! And those are the planets in the Solar System thank you for joining the tour! Unfortunately, Pluto isn’t a planet any more, hence why it was not listed. We know, we know, take it up with the IAU! Solar System Planets: Order of the 8 (or 9) Planets Solar System Planets: Order of the 8 (or 9) Planets By Robert Roy Britt | January 22, 2016 12:35pm ET MORE The planets of the solar system as depicted by a NASA computer illustration. Orbits and sizes are not shown to scale. Credit: NASA Ever since the discovery of Pluto in 1930, kids grew up learning about the nine planets of our solar system.

That all changed starting in the late 1990s, when astronomers began to argue about whether Pluto was a planet. In a highly controversial decision , the International Astronomical Union ultimately decided in 2006 to call Pluto a “dwarf planet,” reducing the list of “real planets” in our solar system to eight. However, astronomers are now hunting for another planet in our solar system, a true ninth planet , after evidence of its existence was unveiled on Jan. 20, 2016. The so-called "Planet Nine," as scientists are calling it, is about 10 times the mass of Earth and 5,000 times the mass of Pluto. [ Solar System Pictures: A Photo Tour ] If you insist on including Pluto , then that world would come after Neptune on the list; Pluto is truly way out there, and on a wildly tilted, elliptical orbit (two of the several reasons it got demoted). Interestingly, Pluto used to be the eighth planet, actually. More on that below. Terrestrial planets The inner four worlds are called “ terrestrial planets ,” because, like Earth, their surfaces are all rocky.

Pluto, too, has a solid surface (and a very frozen one) but has never been grouped with the four terrestrials. Jovian planets The four large outer worlds — Jupiter, Saturn, Uranus, and Neptune — are known as the “Jovian planets” (meaning “Jupiter-like”) because they are all huge compared to the terrestrial planets, and because they are gaseous in nature rather than having rocky surfaces (though some or all of them may have solid cores, astronomers say). According to NASA , "two of the outer planets beyond the orbit of Mars — Jupiter and Saturn — are known as gas giants; the more distant Uranus and Neptune are called ice giants." This is because, while the first two are dominated by gas, while the last two have more ice. All four contain mostly hydrogen and helium. Dwarf planets The IAU definition of a full-fledged planet goes like this: A body that circles the sun without being some other object's satellite, is large enough to be rounded by its own gravity (but not so big that it begins to undergo nuclear fusion, like a star) and has "cleared its neighborhood" of most other orbiting bodies. Yeah, that’s a mouthful.

The problem for Pluto, besides its small size and offbeat orbit, is that it shares its space with lots of other objects in the Kuiper Belt , beyond Neptune. Still, the demotion of Pluto remains controversial . The IAU planet definition puts other small, round worlds in the dwarf planet category, including the Kuiper Belt objects Eris , Haumea , and Makemake . Also now a dwarf planet is Ceres , a round object in the Asteroid Belt between Mars and Jupiter. Ceres was actually considered a planet when discovered in 1801 and then later deemed to be an asteroid. Some astronomers like to consider Ceres as a 10th planet (not to be confused with Nibiru or Planet X ), but that line of thinking opens up the possibility of there being 13 planets, with more bound to be discovered. The planets Below is a brief overview of the eight primary planets in our solar system , in order from the inner solar system outward: Mercury The closest planet to the sun, Mercury is only a bit larger than Earth's moon.

Its day side is scorched by the sun and can reach 840 degrees Fahrenheit (450 Celsius), but on the night side, temperatures drop to hundreds of degrees below freezing. Mercury has virtually no atmosphere to absorb meteor impacts, so its surface is pockmarked with craters, just like the moon. Over its four-year mission, NASA's MESSENGER spacecraft has revealed views of the planet that have challenged astronomers' expectations. Discovery: Known to the ancients and visible to the naked eye Named for: Messenger of the Roman gods Diameter: 3,031 miles (4,878 km) Orbit: 88 Earth days Venus' southern hemisphere, as seen in the ultraviolet. Credit: ESA Venus The second planet from the sun, Venus is terribly hot, even hotter than Mercury. The atmosphere is toxic. The pressure at the surface would crush and kill you. Scientists describe Venus’ situation as a runaway greenhouse effect. Its size and structure are similar to Earth, Venus' thick, toxic atmosphere traps heat in a runaway "greenhouse effect." Oddly, Venus spins slowly in the opposite direction of most planets. The Greeks believed Venus was two different objects — one in the morning sky and another in the evening.

Because it is often brighter than any other object in the sky — except for the sun and moon — Venus has generated many UFO reports. Discovery: Known to the ancients and visible to the naked eye Named for: Roman goddess of love and beauty Diameter: 7,521 miles (12,104 km) Orbit: 225 Earth days An image of the Earth taken by the Russian weather satellite Elektro-L No.1. Credit: NTsOMZ Earth The third planet from the sun, Earth is a waterworld, with two-thirds of the planet covered by ocean. It’s the only world known to harbor life. Earth’s atmosphere is rich in life-sustaining nitrogen and oxygen. Earth's surface rotates about its axis at 1,532 feet per second (467 meters per second) — slightly more than 1,000 mph (1,600 kph) — at the equator. The planet zips around the sun at more than 18 miles per second (29 km per second).

Diameter: 7,926 miles (12,760 km) Orbit: 365.24 days Day: 23 hours, 56 minutes Related: Mars researchers are focusing both Earth-based and planet orbiting sensors to better understand sources of methane on the red planet. Image Credit: Space Telescope Science Institute Mars The fourth planet from the sun, is a cold, dusty place. The dust, an iron oxide, gives the planet its reddish cast. Mars shares similarities with Earth: It is rocky, has mountains and valleys, and storm systems ranging from localized tornado-like dust devils to planet-engulfing dust storms. It snows on Mars. And Mars harbors water ice. Scientists think it was once wet and warm, though today it’s cold and desert-like. Mars' atmosphere is too thin for liquid water to exist on the surface for any length of time. Scientists think ancient Mars would have had the conditions to support life, and there is hope that signs of past life — possibly even present biology — may exist on the Red Planet.

Discovery: Known to the ancients and visible to the naked eye Named for: Roman god of war Diameter: 4,217 miles (6,787 km) Orbit: 687 Earth days Day: Just more than one Earth day (24 hours, 37 minutes) Related: Close-up of Jupiter's Great Red Spot as seen by a Voyager spacecraft. Credit: NASA/JPL-Caltech Jupiter The fifth planet from the sun, Jupiter is huge and is the most massive planet in our solar system. It’s a mostly gaseous world, mostly hydrogen and helium. Its swirling clouds are colorful due to different types of trace gases. A big feature is the Great Red Spot, a giant storm which has raged for hundreds of years. Jupiter has a strong magnetic field, and with dozens of moons, it looks a bit like a miniature solar system.

Discovery: Known to the ancients and visible to the naked eye Named for: Ruler of the Roman gods Diameter: 86,881 miles (139,822 km) Orbit: 11.9 Earth years The shadow of Saturn's moon Mimas dips onto the planet's rings and straddles the Cassini Division in this natural color image taken as Saturn approaches its August 2009 equinox. Credit: NASA/JPL/Space Science Institute Saturn The sixth planet from the sun is known most for its rings . When Galileo Galilei first studied Saturn in the early 1600s, he thought it was an object with three parts. Not knowing he was seeing a planet with rings, the stumped astronomer entered a small drawing — a symbol with one large circle and two smaller ones — in his notebook, as a noun in a sentence describing his discovery. More than 40 years later, Christiaan Huygens proposed that they were rings. The rings are made of ice and rock. Scientists are not yet sure how they formed. The gaseous planet is mostly hydrogen and helium. It has numerous moons .

Discovery: Known to the ancients and visible to the naked eye Named for: Roman god of agriculture Diameter: 74,900 miles (120,500 km) Orbit: 29.5 Earth years Day: About 10.5 Earth hours Related: Near-infrared views of Uranus reveal its otherwise faint ring system, highlighting the extent to which the planet is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory Uranus The seventh planet from the sun, Uranus is an oddball. It’s the only giant planet whose equator is nearly at right angles to its orbit — it basically orbits on its side. Astronomers think the planet collided with some other planet-size object long ago, causing the tilt. The tilt causes extreme seasons that last 20-plus years, and the sun beats down on one pole or the other for 84 Earth-years. Uranus is about the same size as Neptune. Methane in the atmosphere gives Uranus its blue-green tint. It has numerous moons and faint rings.

Discovery: 1781 by William Herschel (was thought previously to be a star) Named for: Personification of heaven in ancient myth Diameter: 31,763 miles (51,120 km) Orbit: 84 Earth years Neptune’s winds travel at more than 1,500 mph, and are the fastest planetary winds in the solar system. Credit: NASA/JPL Neptune The eighth planet from the sun, Neptune is known for strong winds — sometimes faster than the speed of sound. Neptune is far out and cold. The planet is more than 30 times as far from the sun as Earth. It has a rocky core. Neptune was the first planet to be predicted to exist by using math, before it was detected. Irregularities in the orbit of Uranus led French astronomer Alexis Bouvard to suggest some other might be exerting a gravitational tug. German astronomer Johann Galle used calculations to help find Neptune in a telescope. Neptune is about 17 times as massive as Earth. Discovery: 1846 Pluto and its moons orbit the sun near the edge of our solar system.

Learn all about Pluto's weirdly eccentric orbit, four moons and more in this Space.com infographic . Credit: SPACE.com/Karl Tate Pluto (Dwarf Planet) Once the ninth planet from the sun, Pluto is unlike other planets in many respects. It is smaller than Earth's moon. Its orbit carries it inside the orbit of Neptune and then way out beyond that orbit. From 1979 until early 1999, Pluto had actually been the eighth planet from the sun. Then, on Feb. 11, 1999, it crossed Neptune's path and once again became the solar system's most distant planet — until it was demoted to dwarf planet status. Pluto will stay beyond Neptune for 228 years. Pluto’s orbit is tilted to the main plane of the solar system — where the other planets orbit — by 17.1 degrees. It’s a cold, rocky world with only a very ephemeral atmosphere. NASA's New Horizons mission performed history's first flyby of the Pluto system on July 14, 2015.

[Related: New Horizons' Pluto Flyby: Latest News, Images and Video ] Discovery: 1930 by Clyde Tombaugh Named for: Roman god of the underworld, Hades Diameter: 1,430 miles (2,301 km) Orbit: 248 Earth years NASA Solar System Exploration: Dwarf Planets Planet Nine Planet Nine orbits the sun at a distance that is 20 times farther out than the orbit of Neptune. (The orbit of Neptune is 2.7 billion miles from the sun at its closest point.) The strange world's orbit is about 600 times farther from the sun than the Earth's orbit is from the star. Scientists have not actually seen Planet Nine directly . Its existence was inferred by its gravitational effects on other objects in the Kuiper Belt, a region at the fringe of the solar system that is home to icy objects left over from the birth of the sun and planets.

Planet Earth - The Solar System on Sea and Sky Galileo photo showing South America & Antarctica (NASA/JPL) The Blue Planet Our first stop in the Terran system is a small planet that could only be described as the most beautiful sight in the entire solar system.Â Sparkling before us is a bright blue gem of dazzling complexity. Delicate white clouds dance above its surface of brilliant blues, greens, and browns.Â This is the planet Earth. It is the third planet from the Sun, and it is our home.Â Only slightly larger than Venus, Earth is the largest of the four terrestrial, or rocky inner planets in the Solar System. It is also the densest of the four. There are two very important factors that distinguish this planet from all others in the Solar System.Â First, it is the only planet known to contain liquid water on its surface.Â It is the availability of this water that gives rise to Earth's second unique feature. It is the only known planet to support life! Apollo 16 closeup photo of Earth showing North America (NASA/JPL) Galileo spacecraft image showing Africa & the Arabian peninsula (NASA/ JPL) Planet of Life The surface of Earth is literally covered with water.

Nearly 3/4 of the planet's surface is liquid water. Water is also found in abundance as ice in the planet's poles and as water vapor in the atmosphere.Â Most of this water was thought to have been deposited by billions of years of volcanic activity.Â Some scientists believe that water may also have been brought to Earth by early comets. It is this water, combined with Earth's perfect distance from the Sun, that has given rise to the Solar System's only known life forms. The atmosphere also played an important factor, providing the right mixture of gases and helping to protect the surface from meteor impacts.Â Because of these perfect conditions, Earth has evolved an unimaginable diversity of millions of different life forms.Â Life on Earth has adapted to all types of environments, including the land, oceans, and air.Â At least one of these has become self-aware and has begun to explore its surroundings.Â We humans have become the first form of life to leave their planetary home and explore the universe. The Sun reflects off the Earth's vast, blue oceans in this stunning image captured by the space shuttle. Earth is the only planet in the Solar System known to have liquid water on its surface.

(NASA/JPL) Features of Earth Earth is a rocky world that is still very much alive and active.Â Volcanic activity continually creates new land while earthquakes reshape the landscape. Earth's surface is constantly changing.Â The crust is divided up into several "plates" (somewhat like a cracked eggshell) that float on a sea of molten rock.Â Where these plates collide, the land is thrust upwards to create enormous mountain ranges.Â The tallest of these mountains, Mt. Everest, rises 29,028 feet (8850 m) above sea level.Â In some places, one plate sinks underneath another forming deep valleys and trenches.Â The deepest of these, the Marianas trench, plunges seven miles (11 km) beneath the sea.

Uneven heating of Earth's atmosphere, combined with its rotation causes complex weather patterns.Â Wind and rain gradually erode the mountains and create vast sandy plains.Â Even though the planet was bombarded by asteroids and meteors throughout its early history, erosion has wiped out most of the craters.Â Some can still be found, however.Â Meteor crater in Arizona is over a mile (1.6 km) wide and almost 600 feet (183 m) deep.Â It is believed that large meteors may have caused mass extinctions throughout Earth's history.Â One of these may have been responsible for wiping out the dinosaurs.Â Although the planet may seem calm and tranquil now, its surface is highly active and ever changing on the wider geologic scale of time. Planet Facts Planet Facts Read some really neat facts about the planets in our solar system! © Contributed by Leanne Guenther Note: The fast facts on this page are appropriate for grades 1 to 3 while the "more about" links are appropriate for grades 4+.

I've listed them in order from closest to furthest from the sun: Mercury Ceres (dwarf planet found in the asteroid belt) Jupiter Pluto (Note: Pluto is considered a dwarf planet now) Eris, Makemake, Haumea, Sedna (also dwarf planets -- found past Pluto) Mercury takes 59 days to make a rotation but only 88 days to circle the Sun. That means that there are fewer than 2 days in a year! Many astronomers believe that Mercury might be the core of what was once a much larger planet -- it appears to be a huge ball of iron covered by a thin layer of rock. Venus is the brightest planet in our sky and can sometimes be seen with the naked eye if you know where to look. It is the solar system's brightest planet -- yellow clouds of sulfuric acid reflect the sun's light. Earth has more exposed water than land. Three quarters of the Earth is covered by water! The earth has one moon . On-Line Jigsaw Puzzles: View of Earth from the Moon Mars is the home of "Olympus Mons", the largest volcano found in the solar system. It stands about 27 kilometers high with a crater 81 kilometers wide.

Between Mars and Jupiter, is a Dwarf Planet known as Ceres. It was discovered in 1801. It is the smallest dwarf planet discovered in our universe (so far) and is the only one found in the asteroid belt. A dwarf planet is NOT a planet -- the solar system is made up of: a star (the sun), dwarf planets (ex: Ceres and Pluto), and small solar system bodies (ex: asteroids and comets). Jupiter is the largest planet in the solar system, but it spins very quickly on its axis. A day on Jupiter lasts only 9 hours and 55 minutes. Ack, I get dizzy just thinking about it! Jupiter is so big that you could fit all the other planets in the solar system inside it. The red spot of Jupiter is the biggest, most violent storm in the known universe -- that spot is at least three times the size of earth! more about Jupiter > (including actual photos) Saturn is the second biggest planet, but it’s also the lightest planet. If there was a bathtub big enough to hold Saturn, it would float in the water! The rings that surrounds Saturn could be the remnants of a moon that was shattered by Saturn's gravity.

Saturn's rings are as wide as 22 planet earths all in a row but are only 30 feet thick! more about Saturn > (including actual photos) Uranus’ axis is at a 97 degree angle, meaning that it orbits lying on its side! Talk about a lazy planet. Uranus has the second most complex set of rings in our solar system (Saturn has the most defined rings). Neptune was discovered in 1846. In 2011 it finally made it's first lap around the sun since we discovered it -- because one Neptune year lasts 165 Earth years! Like Jupiter, Neptune has a dark spot caused by a storm. Neptune's spot is smaller than Jupiter's -- it is only about the size of the planet earth. Pluto’s orbit sometimes brings it closer to the Sun than Neptune. It jumped ahead of Neptune on September 5, 1989 and remained there until February, 1999 when it went back to being the farthest. Note: Pluto is no longer considered a planet -- instead, astronomers call it a dwarf planet or planetoid. Whatever the name, our solar system isn't the neat model we once thought it was.

It takes a bit for grown-ups (like me!) to adapt to the changes in our understanding (I now understand a bit better how folks felt when someone started telling them the earth was round not flat!) NASA photo On July 14, 2015, the NASA space probe "New Horizons" finally made it to Pluto after its 9.5 year journey. It took lots of cool photos of Pluto and its moons and sent them back to us on Earth. Then it continued off into space -- who knows where it will end up! To me, Pluto just keeps getting more awesome despite it losing its place as one of our planets (when I was young, it was my favorite). I love that thanks to projects like New Horizons, we now know that Pluto has a cute little heart shaped area on it. Yep... Pluto has a heart! In January 2005, astronomers in the United States discovered a new body orbiting the sun in our solar system. They named this planetoid, Eris after the Greek goddess of strife. Eris takes approximately 550 earth years to orbit the sun.

The majority of the time, it is further from the sun than Pluto, but for a short time, it is closer. Eris is actually larger than Pluto (it is the ninth largest object orbitting our sun discovered so far!) Makemake and Haumea are dwarf planets just like Pluto, but a little further out in our solar system. Because their orbits are not perfect circles, they trade places in terms of which is closer and which is further from the sun. Both were discovered in late 2004/early 2005. Haumea has a squished egg shape -- thought to be the result of a collision from an asteroid or meteor at some time. In 2004, astronomers in universities in the United States discovered a new body orbiting the sun in our solar system. They named this planetoid, Sedna after the Inuit goddess of the Ocean . This is the furthest orbiting body identified in our solar system to date. Sedna is about three times further from our sun than Pluto.

It takes between 10,500 and 12,000 earth years for Sedna to make one orbit around the sun (we haven't quite figured out exactly how long it takes). the most beautiful craft I've ever seen! Definition of a 'Planet': What makes something 'beautiful'? Is a Picasso painting beautiful? Or do you prefer a photograph? Or perhaps the first frog paper craft ever created by a beloved three year old is where beauty lies for you. Definitions are created by people to describe the universe that surrounds us. But we don't have a 'King of Definitions' to tell us when we've got it right! Sometimes we all agree on what something means and sometimes we don't. There is no 'King of Definitions' in charge of deciding what is a planet and what is not. These decisions are the result of a lot of thinking and conversation by a lot of very smart people. And these decisions change over time as our knowledge grows and changes. Where we stand now, there are 8 'planets' in our solar system and a number of planetoids (dwarf planets).

The biggest deciding factor that makes something a planet is that it orbits on the same plane, that it has significant gravity and that it is a large enough size. It will be interesting to see how our solar system shapes up as astronomers discover more and more through technologies such as the Hubble Telescope! Note: This section last updated in July 2015. Our understanding of our solar system is always being updated due to new technologies and new discoveries! Planets in our solar system | Sun and solar system | Solar System for children | 8 planets elearnin - YouTube Planets in our solar system | Sun and solar system | Solar System for children | 8 planets elearnin 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 Sep 5, 2013 Planets in our solar system | Sun and solar system | Solar System for children | elearnin The Solar System consists of the Sun and its planetary system of eight planets, their moons, and other objects including asteroids and meteors. Our planet Earth is one among the eight planets that revolve around the Sun. It's called solar system because the word solar means relating to the sun. Since Sun is the centre most part of this system, it is called solar system. Objects seem to smaller in size when seen from a great distance but are very huge and large in reality. Similarly, the moon and stars are very big and huge in size, but appear to be smaller in size to our eyes because they are very very far away from the Earth, where we live. The distance between the objects in the solar system is so large that these numbers would run into millions and billions of kms. Hence they are measured with a specific unit called light year. One light year is exactly 9460730472580800 mts. Sun is 149,600,000 km away from earth. Sun is very far from the Earth.

That is the reason why sun looks smaller in size. Solar system is the family of the sun. Sun is very big compared to the moon, probably around 400 times bigger. Sun is also a star but, remember, it's not the biggest star in the Universe. There are lots of stars present in the universe which are very far away from the sun, some of them about thousands of light years away. That is why stars look like dots in the night sky. Sun is like a ball of fire. The sunlight from the sun takes about 8.5 minutes to reach the surface of the earth. Sun is the center of the solar system and all the planets revolve around the sun in orbits. Orbit is a curved path of an object around a point in space. Orbit means moving around in Roman. Earth is one of the planets in the solar system and takes exactly 365.25 days to revolve around the sun. Earth also rotates around its own axis in 24 hours or 1 day. Just like Earth every planet rotates on its own axis and revolves around the Sun.

Mercury: Mercury is the smallest of all planets, it is every hot as it is the closest to the sun, hence no living being can live on this planet. Mercury was named after a roman god Mercury who is the fast flying messenger. Mercury takes only 88 days to revolve around the sun, which makes it the fastest revolving planet around the sun. Venus: Venus is the second closest planet to the Sun. Venus is visible in morning and evening as the brightest star from earth. Venus takes about 244.7 days to orbit around the sun and is named after the roman goddess of love and beauty. Earth: Our planet Earth is the third closest planet to the Sun. It is blue in color as there is lot of water present on the surface of earth. Water constitutes to about 70% of entire surface on the earth. Unlike Earth, moon is not a planet. It is a natural satellite of earth and it revolves around the earth. Satellite is a smaller body which rotates around another rotating body. Earth is the only planet which has animals, trees and human beings. Mars: Mars is called the red planet because it's red in color.

This red color is due to the presence of a chemical called iron oxide. Mars is named after the roman god of war. It two moons that in turn revolve around it. Jupiter: Jupiter is the biggest and largest planet of the solar system and is named after roman god Jupiter. Jupiter is 317 times the mass of Earth. Jupiter may have all the rocky core of the heavier elements making it the biggest and the heaviest planet. Outer atmosphere of Jupiter is divided into several bands at different latitudes, resulting in storms. Jupiter has around 67 moons revolving around it. These are natural satellites of Jupiter. Saturn: Saturn is the only planet has rings around it. Saturn is named after the roman god for agriculture. Saturn has just over 95 times mass as compared to the earth. The rings around the Saturn are mostly composed of the ice particles and some rocky debris and some dust. Saturn has around 62 moons revolving around it. Uranus: Uranus is similar to Neptune and is named after the Greek god of sky Ouranos. It has around 27 natural satellites revolving around it.

The Uranus is a unique as compared to the other planets because of the fact that its axis of rotation is tilted sideways unlike the other planets. Its looks bluish-green in color because the atmosphere of Uranus is very cold and cloudy. Neptune: This is the farthest planet from the sun. It is about 17 times the size of earth. Neptune is light blue in color because it is the coldest of all planets. Neptune is the densest of all planets. It is named after the roman god for sea. There was another planetary object called Pluto which was the 9th planet but is no more considered a planet because Pluto and its moons are now considered to be a region.This region extends from the orbit of Neptune. Category The Planets of the Solar System USOE Our solar system includes many different planets. In the drawing below, click your mouse on each planet to find its name and a short bit of information about that planet. Keep in mind that the following model of the solar system shows the correct order of the planets, but the sizes of the planets or their distances from each other are not drawn to scale. Notice the order of the planets. Make sure you view information for all the planets.

Which planet is closest to the sun? Which planet is the farthest away from the sun? A good way to remember the order of the planets is to memorize the following sentence. My Very Educated Mother Just Served Us Nine Pizzas. Do you get it? Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto! Now it is time for you to take The Planet Quiz. Click on your choice for the correct answer. Need a hint, or want more information? Click on the photo of the planet to the left of the question. Photos courtesy of NASA . 1. What is the fourth planet away from the sun? 2. What planet is closest to the sun? 3. What planet is the third as you move away from the sun? 4. What planet is the farthest away from the sun? 5. What is the seventh planet as you move away from the sun? 6. What planet is the fifth as you move away from the sun? 7. What planet is the eighth as you move away from the sun? 8. What is the second planet as you move away from the sun? 9. What planet is the sixth as you go away from the sun?

Check your answers by highlighting the box at the right! 1. Mars 2. Mercury 3. Earth 4. Pluto 5. Uranus 6. Jupiter 7. Neptune 8. Venus 9. Saturn Mission:Science Science Mission Directorate. "What is a Planet?" Mission:Science. 2009. National Aeronautics and Space Administration. What is the definition of a planet? Before telescopes, scientists relied on their naked eye and careful observations to catalog the night sky. The five planets easily visible with the naked eye have been observed for all of human history: Mercury, Venus, Mars, Jupiter and Saturn. Technically, there was never a scientific definition of the term Planet before 2006. When the Greeks observed the sky thousands of years ago, they discovered objects that acted differently than stars. These points of light seemed to wander around the sky throughout the year. We get the term "planet" from the Greek word "Planetes" - meaning wanderer. Telescopes add to our knowledge In the 1600's scientists began to use telescopes to view our solar system.

As technology got better, scientists discovered more planets orbiting our Sun such as Uranus in 1781, Neptune in 1846 and Pluto in 1930. Then, in 1991, advances in telescope technology enabled scientists to discover many more objects in a disk-shaped cloud beyond Pluto called the Kuiper (KYE per) Belt. These objects were classified as Kuiper Belt Objects (KBO) partly because they are smaller than Pluto. This classification of KBO seemed to work fine as long as objects weren't bigger than Pluto. Clyde Tombaugh discovered Pluto in 1930. Pluto was added to the list of planets and was our 9th planet until August 2006. Eris, the Goddess of Discord It was the recent discovery of an object larger than Pluto within the Kuiper Belt that changed everything. Is this object, now named Eris, our 10th planet since it is larger than Pluto? This discovery and the naming of this new object prompted the IAU to discuss a scientific definition for the term planet. What if Eris is given planet status?

Then our solar system could grow to dozens of planets as more and more Kuiper Belt Objects are discovered. Try remembering all those planet names. But if Eris is not a planet, then is Pluto still a planet? The new definition – Part 1 and 2 Astronomers of the International Astronomical Union (IAU) voted on and passed the first scientific definition of a planet in August 2006. According to this new definition, an object must meet three criteria in order to be classified as a planet. First, it must orbit the Sun. Second, it must be big enough for gravity to squash it into a round ball. Some scientists believe that if Pluto remains classified as a planet, then the dozens of Kuiper Belt Objects (KBO's) orbiting our Sun would also be classified as planets. Our solar system would have the 9 original planets, an additional 43 KBO's, and more as they are cataloged. Part 3 – The Ongoing Debate And third, it must have cleared other objects out of the way in its orbital neighborhood.

To clear an orbit, a planet must be big enough to pull neighboring objects into the planet itself or sling-shot them around the planet and shoot them off into outer space. According to the IAU, Pluto does not meet this third requirement but is now in a new class of objects called "dwarf planets." It is this third part of the definition that has sparked debate. To distinguish a planet from a round asteroid in the asteroid belt, a planet must be massive enough to clear smaller objects – like asteroids – from their own orbit. The gravity of the planet would pull in smaller objects which would become part of the new planet. The problem for Pluto The problem for Pluto is the fact that its orbit is in the Kuiper Belt along with 43 other known Kuiper Belt Objects (KBOs). There are possibly billions of objects in the Kuiper Belt that have not been cataloged yet. Scientists have even found 8 KBOs between Neptune and Pluto. Some scientists view the new definition as unclear. Exactly how much does Pluto have to "clear" from its neighborhood to be considered a planet? And how much has Pluto already influenced its own neighborhood since the planet formed?

These and other questions have been raised in response to the IAU's definition of a planet. Consider this: Pluto crosses into Neptune's orbit, but Neptune is still classified a planet. This is because of the orbits of Pluto and Neptune and that they never get closer to each other than 17AU (AU=distance from Earth to the Sun). Pluto may cross orbits with many other Kuiper Belt Objects, but how close do these objects get to Pluto? How close to objects have to get to Pluto to be considered "in" Pluto's neighborhood? Diagram of the planet orbits in our solar system, including Pluto, distinctly shows the cross over of Neptune's and Pluto's orbits. Journey to the edge NASA's New Horizon spacecraft is speeding toward the edge of the solar system on its mission to Pluto. Launched in January 2006, it will not be until July 2015 that we will reach Pluto. It will swing past Jupiter for a gravity boost and scientific studies in February 2007, and reach Pluto and its moon, Charon, in July 2015.

Then, as part of an extended mission, the spacecraft would head deeper into the Kuiper Belt to study one or more of the icy mini-worlds in that vast region, at least a billion miles beyond Neptune's orbit. Sending a spacecraft on this long journey will help us answer basic questions about the surface properties, geology, interior makeup and atmospheres on these bodies. New Horizon’s Space Craft will reach Pluto in 2015. Mercury In Roman mythology Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the Gods. The planet probably received this name because it moves so quickly across the sky. Mercury has been known since at least the time of the Sumerians (3rd millennium BC). The IAU changed the definition of "planet" so that Pluto no longer qualifies. There are officially only eight planets in our solar system. Of course this change in terminology does not affect what's actually out there. In the end, it's not very important how we classify the various objects in our solar system. What is important is to learn about their physical nature and their histories.

Planet Order from the Sun; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune Our knowledge of our solar system is extensive but it is far from complete. Some of the worlds have never even been photographed up close. The Nine Planets is an overview of what we know today. We are still exploring, much more is still to come: We shall not cease from exploration, and the end of all our exploring will be to arrive where we started and know the place for the first time. -- T. S. Eliot

Question: Which planet in the Solar System is third from the Sun
Answer: Earth