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. The Solar System The Solar System Our Solar System is an amazing place. Not only is it home to eight planets, it also hold several dwarf planets, hundreds of moons, and thousands of stars and asteroids.

The eight planets in our Solar System are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. These planets orbit the Sun. Here is a funny song to help you remember the planets The Sun The Sun is the center of our Solar System. It is because of the Sun that our solar system gets its name. Sol is the Roman name for Sun. The Sun is the largest object within the Solar System - it makes up more than 95% of all the matter! It is because of the Sun's large size that the rest of the objects within the Solar System orbit around it. The Sun is very, very hot. It is 10,000 degrees Fahrenheit on its surface. Mercury Mercury is the closest planet to the Sun, making it the first planet in the Solar System. It is named after the Roman messenger god. In mythology, the god was known for being quick - Mercury is the fastest of all the planets to orbit the Sun, because it has the smallest route it has to take!

Mercury can occasionally be seen from Earth Mercury is the second densest planet in the Solar System It is mainly made up of iron There is no atmosphere on Mercury Despite its fast trip around the Sun, Mercury's revolution is very slow - one day on Mercury equals about 59 days on Earth! Venus Venus is the second planet from the Sun. It is named after the Roman goddess of beauty and love. Venus is almost the same size as Earth, but other than size the two planets are very different! Fun Facts about Venus Venus appears to be the brightest planet in the sky due to the reflection of the Sun from its clouds, and its closeness to Earth Venus has an incredibly thick atmosphere. This makes it the hottest of the inner planets Venus rotates East to West Venus is covered in volcanoes Venus does not have any moons Earth Earth is the only known planet that has any life forms in the Solar System. It is the third planet from the Sun. It is the only planet that is not named after a god. Most of the Earth is covered in water - 70%!

Earth has a thin atmosphere, that protects us from dangerous gasses and heat in space Earth is the largest of the inner planets Air, water, and land make up the Earth Earth's axis is tilted at 23.5 degrees This a video showing the many different life forms that Earth has Mars Mars is the fourth planet from the Sun. Named for the Roman god of war, it is also known as the "Red Planet". It is the last of the inner planets. Temperatures on Mars are very similar to temperatures on Earth It is believed that Mars once had water on its surface Mars is called the red planet because its surface is covered in red dust The largest volcano in the Solar System is on Mars. It is called Olympus Mons Mars has two small moons Jupiter Jupiter is the first of the outer planets, and the fifth planet from the Sun. It is named for the king of the Roman gods. It is the largest of all of the planets. Fun Facts about Jupiter Jupiter is best known for its "Great Red Spot" - a mass of hurricanes that have been storming for hundreds of years.

The spot is larger in size than that of Earth Jupiter is made up of gasses - there is no solid surface on it Jupiter is so big; Earth could fit inside of it more than 1,000 times! Jupiter has over 50 moons. Four of these moons are as big as planets Jupiter has the most active volcanic activity in the Solar System Learn more about the Great Red Spot! Saturn Saturn is the sixth planet from the Sun. It is named for the Roman god of agriculture. It is most well known for its highly visible rings. Other Features of the Solar System There are many other exciting elements in the Solar System. Here are a few. Asteroids Asteroids are rocky bodies in the Solar System that are too small to be considered actual planets. In between Mars and Jupiter lies the Asteroid Belt, containing well over 90,000 asteroids. Comets Comets are ice and rock that grow tails the closer they get to the sun. The hotter they get, the longer this "tail" becomes. The sunlight makes comets glow, which causes them to be visible on Earth. Dwarf Planets Dwarf planets are bodies that orbit the sun that are not considered large enough to be actual planets.

The most famous dwarf planet is Pluto, which was considered an actual planet up until 2006. Satellites Satellites are machines put into the Solar System by scientists in order to find out more about the Solar System, and what is in it. These machines take pictures, perform experiments, take data, and much, much more. Without them, we wouldn't have the vast amount of information that we have today. Summary The Solar System is a fascinating place. Each of the eight planets have their own unique features, but are also similar in some ways - much like people! It is amazing to think that the Solar System has been around for more than 4.6 billions years. Each of the eight planets orbits the sun in the same direction, and in their own time. We have so much more we can learn about the Solar System, and so much we have learned already today. sit this page to learn more interesting facts about the Solar System! Want to get an idea of how far apart the planets are? Click here! Resources Our Solar System. Retrieved from Solar System. Retrieved from 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 Planet Mars - The Solar System on Sea and Sky Mars Reconnaissance Orbiter view of Victoria Crater on Mars (NASA/JPL/University of Arizona) God of War With the Terran system well behind us, we next encounter a beautiful, bright red world. This is the planet Mars, and it is the fourth planet from the Sun. It was named after the Roman god of war because its color reminded observers of a bloody Roman battlefield. Early astronomers believed they could see faint, dark lines crossing the surface of the planet. Some believed these to be artificially built canals.

This gave rise to some of the early speculation of intelligent life on Mars. These lines were later found to be an optical illusion. Later unmanned missions to the planet found no evidence of the so-called canals. Still, there is perhaps no other body in the Solar System that has intrigued us more than Mars. To this very day, it is still one of the most likely candidates for extraterrestrial life. In fact, meteorites recently discovered in Antarctica are believed to have originated from the red planet. These ancient Martian rocks may contain fossils of tiny bacteria. If this turns out to be true, it will be the first evidence that life evolved on other planets besides Earth. Viking lander image the Martian surface showing water ice frost (NASA/JPL) Opportunity rover image of Cape St. Vincent in Victoria Crater (NASA/JPL/Cornell) The Red Planet The bright red color of Mars has earned it the name of red planet. This unique color is caused by the chemistry of its surface. Mars does have a thin atmosphere, which helps cause iron compounds to oxidize. It is this iron oxide in the rocks and sand that gives the planet it reddish-brown color. It could very appropriately be called the "rusty" planet.

We have learned a great deal about Mars in the last few decades. Several unmanned space missions have been sent to explore the red planet. Several Mariner spacecraft orbited the planet in the mid and late 1960's. In 1975, two Viking spacecraft landed on the surface, sending back the first color pictures of this alien world. Recently, the Mars Pathfinder mission visited the planet. A small roving vehicle known as the Sojourner Rover explored the surface sending back the sharpest pictures to date. Scientists continue to be fascinated with Mars because of its similarities to Earth. Some have even suggested that we may be able to colonize the planet in the not too distant future. If the planet does turn out to be completely lifeless, it may be a candidate for a process known as terraforming. This process would involve using various chemical and biological means to make the planet warmer and the atmosphere more hospitable for human life. Mars Pathfinder image of the Martian surface. The two mountains in the distance are known as the Twin Peaks and are believed to be about 100 feet (30 meters) tall and are about a kilometer (3300 feet) in the distance.

(NASA/JPL) Features of Mars Mars is a small, rocky world about half the size of Earth. As small as it is, however, it is a planet of extremes. Mars is the home of the largest known volcano in the Solar System. Olympus Mons is an extinct volcanic crater that rises 15 miles above the Martian surface. That is over twice the height of the tallest mountain on Earth, Mt. Everest. It is a scar so large it can be seen from Earth. Another gigantic feature of the red planet is Valles Marinares. This is the Martian equivalent of the Grand Canyon. This one is much bigger, however. Valles Marinares stretches 3000 miles (4829 km) along the surface of Mars and is 435 miles (700 km) wide at its widest point. If this canyon existed on Earth, it would stretch across the continental United States from coast to coast! During the Martian winters, the poles of the planet are covered with large sheets of water ice. Several features that resemble riverbeds suggest that there may have been running water on Mars at one time. The thin atmosphere of Mars is composed mainly of carbon dioxide.

Winds of up to 300 miles per hour whip up enormous dust storms that constantly erode and reshape the surface of the planet. With an average surface temperature of 60 degrees below zero, it may not seem very hospitable. But with its thin atmosphere and abundance of water, Mars remains the most likely candidate for life anywhere in the Solar System. A future manned mission to the planet is in the works. Only then will we be able to tell if the red planet is really a dead planet. Mars Facts: Life, Water and Robots on the Red Planet Mars Facts: Life, Water and Robots on the Red Planet By Charles Q. Choi, Space.com Contributor | November 4, 2014 09:00pm ET MORE NASA's Hubble Space Telescope snapped this shot of Mars on Aug. 26, 2003, when the Red Planet was 34.7 million miles from Earth. The picture was taken just 11 hours before Mars made its closest approach to us in 60,000 years. Credit: NASA/ESA Mars is the fourth planet from the sun.

Befitting the red planet's bloody color, the Romans named it after their god of war. The Romans copied the ancient Greeks, who also named the planet after their god of war, Ares. Other civilizations also typically gave the planet names based on its color — for example, the Egyptians named it "Her Desher," meaning "the red one," while ancient Chinese astronomers dubbed it "the fire star." Physical characteristics Regolith The bright rust color Mars is known for is due to iron-rich minerals in its regolith — the loose dust and rock covering its surface. The soil of Earth is a kind of regolith, albeit one loaded with organic content. According to NASA, the iron minerals oxidize, or rust, causing the soil to look red. Geology The cold, thin atmosphere means liquid water currently cannot exist on the Martian surface for any length of time. This means that although this desert planet is just half the diameter of Earth, it has the same amount of dry land. The red planet is home to both the highest mountain and the deepest, longest valley in the solar system.

Olympus Mons is roughly 17 miles (27 kilometers) high, about three times as tall as Mount Everest, while the Valles Marineris system of valleys — named after the Mariner 9 probe that discovered it in 1971 — can go as deep as 6 miles (10 km) and runs east-west for roughly 2,500 miles (4,000 km), about one-fifth of the distance around Mars and close to the width of Australia or the distance from Philadelphia to San Diego. Space.com Exclusive T-shirt. Available to Populate Mars. Buy Now Credit: Space.com Store Mars has the largest volcanoes in the solar system, including Olympus Mons, which is about 370 miles (600 km) in diameter, wide enough to cover the entire state of New Mexico. It is a shield volcano, with slopes that rise gradually like those of Hawaiian volcanoes, and was created by eruptions of lavas that flowed for long distances before solidifying. Mars also has many other kinds of volcanic landforms, from small, steep-sided cones to enormous plains coated in hardened lava. Some minor eruptions might still occur on the planet.

Scientists think the Valles Marineris formed mostly by rifting of the crust as it got stretched. Individual canyons within the system are as much as 60 miles (100 km) wide. They merge in the central part of the Valles Marineris in a region as much as 370 miles (600 km) wide. Large channels emerging from the ends of some canyons and layered sediments within suggest the canyons might once have been filled with liquid water. Channels, valleys, and gullies are found all over Mars, and suggest that liquid water might have flowed across the planet's surface in recent times. Some channels can be 60 miles (100 km) wide and 1,200 miles (2,000 km) long. Water may still lie in cracks and pores in underground rock . Many regions of Mars are flat, low-lying plains. The lowest of the northern plains are among the flattest, smoothest places in the solar system, potentially created by water that once flowed across the Martian surface. The northern hemisphere mostly lies at a lower elevation than the southern hemisphere, suggesting the crust may be thinner in the north than in the south.

This difference between the north and south might be due to a very large impact shortly after the birth of Mars. The number of craters on Mars varies dramatically from place to place, depending on how old the surface is. Much of the surface of the southern hemisphere is extremely old, and so has many craters — including the planet's largest, 1,400-mile-wide (2,300 km) Hellas Planitia — while that of northern hemisphere is younger and so has fewer craters. Some volcanoes have few craters, which suggests they erupted recently, with the resulting lava covering up any old craters. Some craters have unusual-looking deposits of debris around them resembling solidified mudflows, potentially indicating that impactor hit underground water or ice. Polar caps Vast deposits of what appear to be finely layered stacks of water ice and dust extend from the poles to latitudes of about 80 degrees in both hemispheres. These were probably deposited by the atmosphere over long spans of time. On top of much of these layered deposits in both hemispheres are caps of water ice that remain frozen all year round. Additional seasonal caps of frost appear in the wintertime.

These are made of solid carbon dioxide, also known as "dry ice," which has condensed from carbon dioxide gas in the atmosphere, and in the deepest part of the winter, this frost can extend from the poles to latitudes as low as 45 degrees, or halfway to the equator. The dry ice layer appears to have a fluffy texture, like freshly fallen snow, according to the report in the Journal of Geophysical Research-Planets. Mars 12 inch Globe Buy Here Credit: Space.com Store Climate Mars is much colder than Earth, in large part due to its greater distance from the sun. The average temperature is about minus 80 degrees Fahrenheit (minus 60 degrees Celsius), although they can vary from minus 195 F (minus 125 C) near the poles during the winter to as much as 70 F (20 C) at midday near the equator. The carbon-dioxide-rich atmosphere of Mars is also roughly 100 times less dense than Earth's on average, but it is nevertheless thick enough to support weather, clouds and winds. The density of the atmosphere varies seasonally, as winter forces carbon dioxide to freeze out of the Martian air.

NASA’s Mars Reconnaissance Orbiter found the first definitive detections of carbon-dioxide snow clouds , making Mars the only body in the solar system known to host the unusual winter weather. The red planet also causes water-ice snow to fall from the clouds. The dust storms of the Mars are the largest in the solar system, capable of blanketing the entire red planet and lasting for months. One theory as to why dust storms can grow so big on Mars starts with airborne dust particles absorbing sunlight, warming the Martian atmosphere in their vicinity. Warm pockets of air flow toward colder regions, generating winds. Strong winds lift more dust off the ground, which in turn heats the atmosphere, raising more wind and kicking up more dust. Orbital characteristics The axis of Mars, like Earth's, is tilted with relation to the sun. This means that like Earth, the amount of sunlight falling on certain parts of the planet can vary widely during the year, giving Mars seasons. However, the seasons that Mars experiences are more extreme than Earth's because the red planet's elliptical, oval-shaped orbit around the sun is more elongated than that of any of the other major planets.

When Mars is closest to the sun, its southern hemisphere is tilted toward the sun, giving it a short, very hot summer, while the northern hemisphere experiences a short, cold winter. When Mars is farthest from the sun, the northern hemisphere is tilted toward the sun, giving it a long, mild summer, while the southern hemisphere experiences a long, cold winter. Composition & structure Atmospheric composition (by volume): 95.32 percent carbon dioxide, 2.7 percent nitrogen, 1.6 percent argon, 0.13 percent oxygen, 0.08 percent carbon monoxide, minor amounts of water, nitrogen oxide, neon, hydrogen-deuterium-oxygen, krypton, xenon Magnetic field: Mars currently has no global magnetic field, but there are regions of its crust that can be at least 10 times more strongly magnetized than anything measured on Earth, remnants of an ancient global magnetic field. Chemical composition: Mars likely has a solid core composed of iron, nickel, and sulfur. The mantle of Mars is probably similar to Earth's in that it is composed mostly of peridotite, which is made up primarily of silicon, oxygen, iron and magnesium.

The crust is probably largely made of the volcanic rock basalt, which is also common in the crusts of the Earth and the moon, although some crustal rocks, especially in the northern hemisphere, may be a form of andesite, a volcanic rock that contains more silica than basalt does. Internal structure: Scientists think that on average, the Martian core is about 1,800 and 2,400 miles in diameter (3,000 and 4,000 km), its mantle is about 900 to 1,200 miles (5,400 to 7,200 km) wide and its crust is about 30 miles (50 km) thick. Orbit & rotation Average distance from the sun : 141,633,260 miles (227,936,640 km). By comparison: 1.524 times that of Earth Perihelion (closest): 128,400,000 miles (206,600,000 km).

By comparison: 1.404 times that of Earth Aphelion (farthest): 154,900,000 miles (249,200,000 km). By comparison: 1.638 times that of Earth The moons of Mars The two moons of Mars , Phobos and Deimos, were discovered by American astronomer Asaph Hall over the course of a week in 1877. Hall had almost given up his search for a moon of Mars, but his wife, Angelina, urged him on — he discovered Deimos the next night, and Phobos six days after that. He named the moons after the sons of the Greek war god Ares — Phobos means "fear," while Deimos means "rout." Both Phobos and Deimos are apparently made of carbon-rich rock mixed with ice and are covered in dust and loose rocks. They are tiny next to Earth's moon, and are irregularly shaped, since they lack enough gravity to pull themselves into a more circular form.

The widest Phobos gets is about 17 miles (27 km), and the widest Deimos gets is roughly nine miles (15 km). Both moons are pockmarked with craters from meteor impacts. The surface of Phobos also possesses an intricate pattern of grooves, which may be cracks that formed after the impact created the moon's largest crater — a hole about 6 miles (10 km) wide, or nearly half the width of Phobos. They always show the same face to Mars, just as our moon does to Earth. It remains uncertain how Phobos and Deimos were born. They may have been asteroids captured by Mars' gravitational pull, or they may have been formed in orbit around Mars the same time the planet came into existence. Ultraviolet light reflected from Phobos provides strong evidence for its capture origin, according to astronomers at the University of Padova in Italy. Phobos is gradually spiraling toward Mars, drawing about 6 feet (1.8 meters) closer to the red planet each century. Within 50 million years, Phobos will either smash into Mars or break up and form a ring of debris around the planet. Both moons are potential targets for exploration.

One NASA plan envisions bombarding Phobos with small, spiky spherical rovers called hedgehogs. The planet Mars is the fourth planet from the sun and named after the Roman God of War and is also called the Red Planet. See what makes Mars tick with this Space.com infographic looking inside the Red Planet . Credit: Karl Tate, SPACE.com Research & exploration The first person to watch Mars with a telescope was Galileo Galilei , and in the century after him, astronomers discovered its polar ice caps. In the 19th and 20th centuries, researchers believed they saw a network of long, straight canals on Mars, hinting at civilization, although later these often proved to be mistaken interpretations of dark regions they saw. Robot spacecraft began observing Mars in the 1960s, with the United States launching Mariner 4 there in 1964 and Mariners 6 and 7 in 1969. They revealed Mars to be a barren world, without any signs of the life or civilizations people had imagined there. In 1971, Mariner 9 orbited Mars, mapping about 80 percent of the planet and discovering its volcanoes and canyons.

NASA's Viking 1 lander touched down onto the surface of Mars in 1976, the first successful landing onto the Red Planet. It took the first close-up pictures of the Martian surface but found no strong evidence for life . The next two craft to successfully reach Mars were the Mars Pathfinder, a lander, and Mars Global Surveyor , an orbiter, both launched in 1996. A small robot onboard Pathfinder named Sojourner — the first wheeled rover to explore the surface of another planet — ventured over the planet's surface analyzing rocks. In 2001, the United States launched the Mars Odyssey probe, which discovered vast amount of water ice beneath the Martian surface, mostly in the upper three feet (one meter). It remains uncertain whether more water lies underneath, since the probe cannot see water any deeper. In 2003, the closest Mars had passed to Earth in nearly 60,000 years, NASA launched two rovers, nicknamed Spirit and Opportunity , which explored different regions of the Martian surface, and both found signs that water once flowed on the planet's surface.

In 2008, NASA sent another mission, Phoenix, to land in the northern plains of Mars and search for water, Two orbiters — NASA's Mars Reconnaissance Orbiter and ESA's Mars Express — are keeping Mars Odyssey company over the planet. In 2011, NASA's Mars Science Laboratory mission, with its rover named Mars Curiosity , began to investigate Martian rocks to determine the geologic processes that created them and find out more about the present and past habitability of Mars. Among its findings is the first meteorite on the surface of the red planet. In September 2014, India’s Mars Orbiter Mission reached the red planet, making it the fourth nation to successfully enter orbit around Mars. Robots aren’t the only ones looking to buy a ticket to Mars. A workshop group of government, academic, and industry scientists have found that a NASA-led manned mission to Mars should be possible by the 2030s. But NASA isn’t the only one with Martian astronaut hopefuls.. The Mars One colony project is looking to send private citizens on a one-way trip to the red planet. Possibility of life Mars could have once harbored life. Some conjecture that life might still exist there even today.

A number of researchers have even speculated that life on Earth may have seeded Mars, or that life on Mars seeded Earth. The most public scientific claim for life on Mars came in 1996. Geologist David McKay at NASA's Johnson Space Center in Houston and his colleagues focused on rocks blasted off the surface of Mars by cosmic impacts that landed on Earth. Within they found complex organic molecules, grains of a mineral called magnetite that can form within some kinds of bacteria, and tiny structures that resembled fossilized microbes. However, these claims have proven controversial, and there is no consensus as to whether they are signs of life. Mars may have possessed oceans on its surface in the past, providing an environment for life to develop. Although the red planet is a cold desert today, researchers suggest that liquid water may be present underground, providing a potential refuge for any life that might still exist there. The rover Curiosity has found evidence for a lake that could have once supported life on the red planet, after previously establishing that the planet had the key ingredients present for life to evolve. Enthusiasm and excitement on Earth over the possibility of life on the red planet are revealed by the flurry of excitement that greets interesting objects spotted by orbiters and landers.

While the Face on Mars garnered attention for the past four decades after it was first spotted by Viking 1, rovers today show close-ups of objects — such as a weathered Martian rock claimed to be a ‘thigh bone’ and a likely shiny rock that raised furor on the internet as a UFO light . Additional resources Read about and see pictures of more than 40 missions to Mars . Follow the rover Curiosity as it makes its way across the Martian terrain. Learn more about Mars at NASA's Solar System Exploration website. Related: How Our Solar System Formed (article) | Khan Academy How Our Solar System Formed Email A close look at the planets orbiting our Sun. Planets are born from the clouds of gas and dust that orbit new stars. Billions of years ago, circumstances were just right for Earth and the other planets in our Solar System to form. Illustration of a fledgling solar system. Source: NASA/JPL-Caltech The Solar System that we live in consists of a medium-size star (the Sun) with eight planets orbiting it. The planets are of two different types. The four inner planets, those closest to the Sun, are Mercury, Venus, Earth, and Mars.

They are smaller and composed mainly of metals and rocks. The four outer planets — Jupiter, Saturn, Uranus, and Neptune — are larger and composed mostly of gases. What are planets? Where did they come from? Why would some be rocky and some gaseous? What is our planet like? This essay will try to answer these questions. Each of the planets in our Solar System is unique. They vary in size and composition. Source: NASA and the Big History Project The Birth of the Sun Let’s quickly review how our star came into being. Five billion years ago, a giant cloud floated in one of the spiral arms of the Milky Way galaxy. This cloud, called a nebula by astronomers, was made up of dust and gas, mostly hydrogen and helium, with a small percentage of heavier atoms. These heavier atoms had been formed earlier in the history of the Universe when other stars aged and died. This cloud/nebula began to contract, collapsing in on itself. The atoms, once separated, began to jostle each other, generating heat. In the rising heat, the atoms collided more frequently and more violently.

Eventually, they reached a temperature at which the protons at the centers of the atoms began to fuse, in a process called nuclear fusion. As they did, a tiny bit of matter transformed into a whole lot of energy, and a star was born. In this way, our Sun came into being. The Birth of the Planets The material in the nebula not absorbed into the Sun swirled around it into a flat disk of dust and gas, held in orbit by the Sun’s gravity. This disk is called an accretion disk. Material in the disk accumulated by further accretion — from sticking together. Each planet began as microscopic grains of dust in the accretion disk. The atoms and molecules began to stick together, or accrete, into larger particles. By gentle collisions, some grains built up into balls and then into objects a mile in diameter, called planetesimals. These objects were big enough to attract others by gravity rather than by chance. If the collisions of planetesimals occurred at high speeds, they could shatter the objects. But when impacts were gentle enough, the objects combined and grew.

For some 10 to 100 million years these protoplanets orbited the Sun, some in egg-shaped circuits that resulted in more frequent collisions. This illustration shows the accretion disk of a star that, like our Sun, could go on to form planets from the dust and gas around it. Source: ESO/L. Calçada Worlds collided, combined, and evolved for a dramatic period of time. When it was over, there remained eight stable planets that had swept their orbits clean. A planet is defined as a body that orbits the Sun, is massive enough for its own gravity to make it spherical, and has cleaned its neighborhood of smaller objects. In 2007, researchers at the University of California–Davis determined that our Solar System was fully formed at 4.568 billion years ago. They did this by determining the age of stony materials from the asteroid belt. The Sun sent out energy and particles in a steady stream, called stellar winds. These winds proved so strong that they blew off mostthe gases of the four planets closest to the Sun, leaving them smaller, with only their rocks and metals intact. That’s why they are called rocky, or terrestrial, planets.

The four outer planets were so far from the Sun that its winds could not blow away their ice and gases. They remained gaseous, with only a small rocky core. They were made of more gas (namely hydrogen and helium) than the others to begin with, the Sun’s gravity having pulled closer the heavier materials in the original solar disk. Between the inner and outer planets lies an area filled with millions of asteroids — small rocky, icy, and metallic bodies left over from the formation of the Solar System. No planet formed in this area. Astronomers theorize that Jupiter’s gravity influenced this region so much that no large planet could take shape. Jupiter is 11 times the size (in diameter) of Earth and more than twice as big as all the other planets combined. It is almost large enough to have become a star. Of the four rocky planets, Mercury is the smallest, about two-fifths the size of Earth. Earth and Venus are almost the same size, while Mars is about half their size. Astronomers speculate that a smaller object must have hit Mercury, vaporizing its crust and leaving only the larger-than-usual iron core.

Conditions on Earth When the rocky planets first formed, they were largely melted (molten) rock. Over hundreds of millions of years, they slowly cooled. Eventually Mercury and Mars, because they are small, solidified and became rigid all the way to their centers. Only on Earth, and possibly on Venus, have conditions remained in an in- between state. Earth has stayed partially molten. Its crust is solid rock, and its mantle is rigid in short-term time. But over geologic time the mantle flows slowly. And the center of Earth consists of a solid iron core rotating in hot liquid called magma. Some scientists and Big Historians use the term “Goldilocks Conditions” to describe conditions on Earth. This comes from an Anglo-Saxon children’s story, “Goldilocks and the Three Bears.” In the story, a young girl named Goldilocks wanders into the home of three bears, who are away. She tries out their porridge, their chairs, and their beds, finding some too hot or too cold, too hard or too soft, too large or too small, but one of each just right.

Likewise, Earth is not too hot or too cold, not too big or too little, not too near the Sun or too far away, but just right for life to flourish. Earth’s Moon The rocky object nearest to us is the Moon. Where did it come from? Good question. The Moon orbits Earth, not the Sun, so it is not a planet. The Moon is about one-fourth the size of Earth. The origin of the Moon remains mysterious, but since astronauts walked on the Moon in 1969 and brought back rock and soil samples, we know more about it now than before. The standard argument today holds that a small contending planet, about one-tenth the size of Earth, must have collided with Earth about 4.45 billion years ago. Earth was still red-hot beneath a possible thin new crust. Some of the material from the impact was absorbed into the liquefied Earth but some material ricocheted into space, where it settled into orbit and condensed as the Moon. At first the Moon orbited much closer to Earth. It is still moving away at a rate of almost two inches (four centimeters) per year. The Moon significantly affects conditions on Earth.

The impact that produced the Moon tilted Earth on its axis. This causes Earth’s seasonal variations in temperature, since the side tilted toward the Sun for one-half the year’s journey around the Sun receives more direct sunlight. Also, the Moon’s gravity causes the oceans’ tides, reduces the Earth’s wobble (which helps stabilize climate), and slows the spin of the Earth. The Earth used to complete a rotation on its axis in 12 hours, but now it takes 24. Pluto and Beyond Before 2006, students learned that our Solar System had nine planets, not eight. The one counted as the ninth, Pluto, orbits furthest from our Sun. However, in 2006, the International Astronomical Union declared that Pluto does not count as a planet. It is smaller than Earth’s Moon. It orbits way out in a belt of asteroids beyond Neptune (though Pluto periodically comes closer to the Sun than Neptune), and does not have enough gravity to clear the neighborhood around its path. Therefore, it was downgraded to a “dwarf planet,” or a planetesimal. Dust-and-gas clouds surround nascent stars in the Orion Nebula. Proplyds in the Orion Nebula.

Source: NASA/ESA and L. Ricci (ESO) Astronomers feel confident that our Solar System formed by accretion because now they are able to glimpse a similar process occurring in part of the Orion Nebula. This planet-forming area is on the near side of a giant cloud complex that embraces much of the constellation Orion, 1,500 light- years from Earth. Since 1993, astronomers have discovered several hundred stars there in the process of formation, most of them surrounded by rings of dust in accretion disks, just like the one they believe produced the solar planets. These clouds of dust and gas around new stars in the Orion Nebula may develop into planetary systems similar to our own. In 1995, astronomers in Switzerland found, for the first time, a planet beyond our Solar System orbiting an ordinary star. Such a planet is called an extrasolar planet, or an exoplanet. As of June 2012, more than 700 exoplanets had been discovered and confirmed. Most of them are giants, closer in size to Jupiter, as larger planets have proved easier to detect hundreds of light-years away.

Most are detected not by direct imaging, but indirectly by measuring the effect of their gravity on their parent star or by observing how the light of the parent star dims as the planet passes in front of it. In 2009, the National Aeronautics and Space Administration (NASA) sent a telescope into orbit around the Sun to hunt for habitable exoplanets in the region near the constellations Cygnus and Lyra. This telescope (actually a photometer), the centerpiece of what’s known as the Kepler mission, will monitor 100,000 stars a few hundred to a few thousand light-years away. (One light-year equals 6 trillion miles.) The mission will last three and a half to six years; in the first two years, it has found 17 planets with conditions thought to allow for the development of life. In summary, planets are bodies orbiting a star. Planets form from particles in a disk of gas and dust, colliding and sticking together as they orbit the star. The planets nearest to the star tend to be rockier because the star’s wind blows away their gases and because they are made of heavier materials attracted by the star’s gravity.

In the Sun’s system, Earth is one of four rocky planets, but a unique one, with rigid and molten layers. By Cynthia Stokes Brown Think about the following questions: What were the factors working against life forming on the early Earth? Should we be surprised that life formed here at all? Share your ideas in the Questions Area below. 4.0—Earth & the Formation of Our Solar System Planets For Kids - Solar System Facts and Astronomy Coloring Pages Welcome Welcome to Planets for Kids I really hope you enjoy the information that I have provided on this website. You will find lots of information about our solar system with lots of questions and answers and games for you to play. We also have a color in section where you can download pictures and have fun. Remember everything here is "Kid-friendly" so lets get started.... Introduction We have nine planets in our Solar System. These planets circle around the sun (as I’m sure you know already) this is called orbits. A lot of astronomy people like to think of the Solar System been made up in two parts We have the Inner Solar System which has Mercury , Venus , Earth and not forgetting Mars. These are closest to the sun and are called the terrestrial planets simply because the have very solid rocky surfaces.

The Outer Solar System has Jupiter , Saturn , Uranus , Neptune these are sometimes called the gas giants Out past Neptune you’ll find the small planet of Pluto which has a solid but icier surface. Many don’t class this as a planet anymore but you can read this on the Pluto page . These two systems are separated by the asteroid belt Our Solar System also contains comets, moons, dust, gas and some minor planets.

Question: What is the fourth planet from the sun, in our solar system?
Answer: MARS