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

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

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

- Universe Today Universe Today How Many Planets are in the Solar System? Article Updated: 16 Oct , 2016 I’m just going to warn you, this is a controversial topic. Some people get pretty grumpy when you ask: how many planets are in the Solar System? Is it eight, ten, or more? I promise you this, though, we’re never going back to nine planets… ever. When many of us grew up, there were nine planets in the Solar System. It was like a fixed point in our brains. As kids, memorizing this list was an early right of passage of nerd pride: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. But then in 2005, Mike Brown discovered Eris, an icy object thought to be about the same size as Pluto, out beyond its orbit. That would bring the total number of planets to ten. Right? There’s no turning back, textbooks would need to be changed. In order to settle the dispute, the International Astronomical Union met in 2006, and argued for, and against Pluto’s planethood.

Some astronomers advocated widening the number of planets to twelve, including Pluto, its moon Charon, the Asteroid Ceres, and the newly discovered Eris. In the end, they changed the definition of what makes a planet, and sadly, Pluto doesn’t make the cut: Here are the new requirements of planethood status: A planet has to orbit the Sun. Okay fine, Pluto does that. A planet needs enough gravity to pull itself into a sphere. Okay, spherical. Pluto’s fine there too. A planet needs to have cleared out its orbit of other objects. Uh oh, Pluto hasn’t done that. For example, planet Earth accounts for a million times the rest of the material in its orbit, while Pluto is just a fraction of the icy objects in its realm. The final decision was to demote Pluto from planet to dwarf planet. But don’t despair, Pluto is in good company. Ceres. Image credit: NASA There’s Ceres, the first asteroid ever discovered, and the smallest of the dwarf planets. The surface of Ceres is made of ice and rock, and it might even have a liquid ocean under its surface. NASA’s Dawn mission is flying there right now to give us close up pictures for the first time.

Haumea, named after the Hawaiian goddess of fertility, is about a third the mass of Pluto, and has just enough gravity to pull itself into an ellipsoid, or egg shape. Even though it’s smaller, it’s got moons of its own. Makemake. Credit: NASA Makemake, a much larger Kuiper belt object, has a diameter about two-thirds the size of Pluto. It was discovered in 2005 by Mike Brown and his team. So far, Makemake doesn’t seem to have any moons. Eris is the most massive known dwarf planet, and the one that helped turn our definition of a planet upside-down. It’s 27% more massive than Pluto and the ninth most massive body that orbits the Sun. It even has a moon: Dysnomia. Pluto. Credit: ESO And of course, Pluto. The founding member of the dwarf family. Want an easy way to remember the eight planets, in order? Just remember this mnemonic: my very excellent mother just served us noodles. For all you currently writing angry tweets to Mike Brown , hold on a sec. Changing Pluto’s categorization is an important step that really needed to happen.

The more we discover about our Universe, the more we realize just how strange and wonderful it is. When Pluto was discovered 80 years ago, we never could have expected the variety of objects in the Solar System. Categorizing Pluto as a dwarf planet helps us better describe our celestial home. So, our Solar System now has eight planets, and five dwarf planets. Podcast (audio): Download (Duration: 3:35 — 3.3MB) July 18, 2008 at 8:57 PM There are 12 planets in the solar system–Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, MakeMake, and Eris. It’s not the International Astronomical Union but four percent of that group that voted on excluding Pluto in a sloppy, nonsensical definition that states a dwarf planet is not a planet at all. The requirement that an object clear its orbit to be considered a planet is vague and if applied literally, could exclude all the planets because none has fully cleared its orbital field of nearby asteroids, and Neptune has not cleared its orbit of Pluto.

Most of the 424 IAU members who voted on this are not planetary scientists. No absentee voting was allowed. Also, many planetary scientists are not members of the IAU and therefore had no say in this matter. Interestingly, almost as many astronomers as those who voted at the IAU General Assembly in 2006 signed a petition saying they will not use the new definition, and a better one is needed. The lead scientist rejecting the IAU decision is Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission and one of the foremost experts in the world on Pluto and the Kuiper Belt. An object orbiting the sun with enough self-gravity to pull itself into a round shape (a condition known as hydrostatic equilibrim) is a planet. With this definition, we keep the term planet as broad as possible while allowing for multiple subcategories such as terrestrial planet, gas giant, ice giant, dwarf planet, hot Jupiters, super Earths, etc. There is no problem with defining a dwarf planet as an object that does not dominate the neighborhood of its orbit. The problem comes in stating that a dwarf planet is not a subtype of planet.

This is where the IAU decision falls short and needs to be revised. This matter will be further discussed in August 2008 at the Great Planet Debate in Laurel, Maryland. More information on this conference, which is open to the public, is available at It is a disservice to readers to portray the planet question as a done deal as opposed to an ongoing debate. I urge you to present both sides of this debate as opposed to choosing one view and presenting it as a foregone conclusion. patience September 4, 2008 at 7:32 AM The explanation based on the nine planet:but i suggest that there was jst nine planet in the solar system.how come the eight now in the solar system.joining the three dwarf planet that is the ceres,eris,and the makemake plus the pluto which is not part of the planet agin making twelve planet in the solar system.can u pls give more explanation based on that.send any information to my email box provided below. M.

Afzal for me its easy if it orbits the sun and it is in are planetary system making it a planet just because its past the Kuiper belt or in it and small does not make it less of a planet so for me Pluto Haumea, Makemake, and Eris. Ceres are planets Dmitri Yatsenko January 12, 2009 at 5:02 PM Laurel Kornfeld I couldn’t agree more. However, what you are calling a planet is actually termed a ‘planemo’, meaning PLANEtary Mass Object. This includes perfect planets AND dwarf planets, as well as moons the size of planets and even interstellar ‘planets’. Pluto, Eris, Haumea, and other dwarf planets, including Ceres, are planemos. You are right; the ‘clearing the neighboorhood’ thing is ABSURD, and I refuse to use the IAU definition of a planet, I will use my own definition (see my second latest comment on ‘why is pluto not a planet/universe today). And I do not agree that a dwarf planet is not a planet even though it is called a dwarf PLANET!

Since both planets and dwarf planets are planemos, then they are. Dwarf planets are not between planets and planetoids, they are closer to planets! However, I do believe that perfect planets and dwarf planets are different things. But, as I said, they are two of several subclasses of planemos. And also, I will just add one thing to your definition of planet/planemo: it needs to be massive enough and typically big enough to get into the planetary span (which, however, needs to be defined roughly). All bodies fullfilling this condition would be in hydrostatic equilibrium. Also, I disagree with you that it is OK to define dwarf planet by whether it has cleared its orbit. Didn’t you mention yourself that it is stupid to determine a planet by that criteria (or, rather, the opposite of it)? caca head January 28, 2009 at 7:37 PM Laurel Kornfeld I couldn’t agree more. However, what you are calling a planet is actually termed a ‘planemo’, meaning PLANEtary Mass Object. This includes perfect planets AND dwarf planets, as well as moons the size of planets and even interstellar ‘planets’.

Pluto, Eris, Haumea, and other dwarf planets, including Ceres, are planemos. You are right; the ‘clearing the neighboorhood’ thing is ABSURD, and I refuse to use the IAU definition of a planet, I will use my own definition (see my second latest comment on ‘why is pluto not a planet/universe today). And I do not agree that a dwarf planet is not a planet even though it is called a dwarf PLANET! Since both planets and dwarf planets are planemos, then they are. Dwarf planets are not between planets and planetoids, they are closer to planets! However, I do believe that perfect planets and dwarf planets are different things. But, as I said, they are two of several subclasses of planemos. And also, I will just add one thing to your definition of planet/planemo: it needs to be massive enough and typically big enough to get into the planetary span (which, however, needs to be defined roughly). All bodies fullfilling this condition would be in hydrostatic equilibrium. Also, I disagree with you that it is OK to define dwarf planet by whether it has cleared its orbit.

Didn’t you mention yourself that it is stupid to determine a planet by that criteria (or, rather, the opposite of it)? caca head January 28, 2009 at 7:38 PM Laurel Kornfeld I couldn’t agree more. However, what you are calling a planet is actually termed a ‘planemo’, meaning PLANEtary Mass Object. This includes perfect planets AND dwarf planets, as well as moons the size of planets and even interstellar ‘planets’. Pluto, Eris, Haumea, and other dwarf planets, including Ceres, are planemos. You are right; the ‘clearing the neighboorhood’ thing is ABSURD, and I refuse to use the IAU definition of a planet, I will use my own definition (see my second latest comment on ‘why is pluto not a planet/universe today). And I do not agree that a dwarf planet is not a planet even though it is called a dwarf PLANET! Since both planets and dwarf planets are planemos, then they are. Dwarf planets are not between planets and planetoids, they are closer to planets! However, I do believe that perfect planets and dwarf planets are different things.

But, as I said, they are two of several subclasses of planemos. And also, I will just add one thing to your definition of planet/planemo: it needs to be massive enough and typically big enough to get into the planetary span (which, however, needs to be defined roughly). All bodies fullfilling this condition would be in hydrostatic equilibrium. Also, I disagree with you that it is OK to define dwarf planet by whether it has cleared its orbit. Didn’t you mention yourself that it is stupid to determine a planet by that criteria (or, rather, the opposite of it)?Laurel Kornfeld I couldn’t agree more. However, what you are calling a planet is actually termed a ‘planemo’, meaning PLANEtary Mass Object. This includes perfect planets AND dwarf planets, as well as moons the size of planets and even interstellar ‘planets’. Pluto, Eris, Haumea, and other dwarf planets, including Ceres, are planemos.

You are right; the ‘clearing the neighboorhood’ thing is ABSURD, and I refuse to use the IAU definition of a planet, I will use my own definition (see my second latest comment on ‘why is pluto not a planet/universe today). And I do not agree that a dwarf planet is not a planet even though it is called a dwarf PLANET! Since both planets and dwarf planets are planemos, then they are. Dwarf planets are not between planets and planetoids, they are closer to planets! However, I do believe that perfect planets and dwarf planets are different things. But, as I said, they are two of several subclasses of planemos. And also, I will just add one thing to your definition of planet/planemo: it needs to be massive enough and typically big enough to get into the planetary span (which, however, needs to be defined roughly). All bodies fullfilling this condition would be in hydrostatic equilibrium. Also, I disagree with you that it is OK to define dwarf planet by whether it has cleared its orbit.

Didn’t you mention yourself that it is stupid to determine a planet by that criteria (or, rather, the opposite of it)?Laurel Kornfeld I couldn’t agree more. However, what you are calling a planet is actually termed a ‘planemo’, meaning PLANEtary Mass Object. This includes perfect planets AND dwarf planets, as well as moons the size of planets and even interstellar ‘planets’. Pluto, Eris, Haumea, and other dwarf planets, including Ceres, are planemos. You are right; the ‘clearing the neighboorhood’ thing is ABSURD, and I refuse to use the IAU definition of a planet, I will use my own definition (see my second latest comment on ‘why is pluto not a planet/universe today). And I do not agree that a dwarf planet is not a planet even though it is called a dwarf PLANET! Since both planets and dwarf planets are planemos, then they are. Dwarf planets are not between planets and planetoids, they are closer to planets! However, I do believe that perfect planets and dwarf planets are different things. But, as I said, they are two of several subclasses of planemos.

And also, I will just add one thing to your definition of planet/planemo: it needs to be massive enough and typically big enough to get into the planetary span (which, however, needs to be defined roughly). All bodies fullfilling this condition would be in hydrostatic equilibrium. Also, I disagree with you that it is OK to define dwarf planet by whether it has cleared its orbit. Didn’t you mention yourself that it is stupid to determine a planet by that criteria (or, rather, the opposite of it)? pluto lover I didnt know that pluto was a dwarf planet I thoght it was normal planet.What else is about pluto? Anonymous May 17, 2011 at 2:44 PM In my opinion, however, I beleieve that there are more that 8 planets and 3 dwarf planets. I think that there are thousands of other planets out there, just that scientists haven’t gotten all the information they need, and we can’t give them all the money that they need to research these planets. I don’t know if I believe aliens or not, but I do believe that there is some sort of life up there.

Astronomer Mike Brown (Jump to full table below) In 2006, when the vote on the definition of "planet" was made, and the eight dominant bodies in the solar system were declared (quite rationally) a class separate from the others, a new class of objects was defined. The "dwarf planets" are all of those objects which are not one of the eight dominant bodies (Mercury through Neptune) yet still, at least in one way, resemble a planet. In other words, a dwarf planet is something that looks like a planet, but is not a planet. Specifically this means that dwarf planets are bodies in the solar system which are large enough to become round due to their own gravitational attraction. Why do astronomers care about round? If you place a boulder in space it will just stay whatever irregular shape it is. If you add more boulders to it you can still have an irregular pile. But if you add enough boulders to the pile they will eventually pull themselves into a round shape.

This transition from irregularly shaped to round objects is important in the solar system, and, in some ways, marks the transition from an object without and with interesting geological and planetary processes occuring (there are many many other transitions that are equally important, however, a fact that tends to be overlooked in these discussions). How many dwarf planets are there? Ceres is the only asteroid that is known to be round. After that it gets complicated. All of the rest of the new dwarf planets are in the distant region of the Kuiper belt, where we can't actually see them well enough to know for sure if they are round or not. While we can't see most of the objects in the Kuiper belt well enough to determine whether they are round or not, we can estimate how big an object has to be before it becomes round and therefore how many objects in the Kuiper belt are likely round. In the asteroid belt Ceres, with a diameter of 900 km, is the only object large enough to be round, so somewhere around 900 km is a good cutoff for rocky bodies like asteroids. Most Kuiper belt objects have a lot of ice in their interiors, though.

Ice is not as hard as rock, so it less easily withstands the force of gravity, and it takes less force to make an ice ball round. The best estimate for how big an icy body needs to be to become round comes from looking at icy satellites of the giant planets. The smallest body that is generally round is Saturn's satellite Mimas, which has a diameter of about 400 km. Several satellites which have diameters around 200 km are not round. So somewhere between 200 and 400 km an icy body becomes round. Objects with more ice will become round at smaller sizes while those with less rock might be bigger. We will take 400 km as a reasonable lower limit and assume that anything larger than 400 km in the Kuiper belt is round, and thus a dwarf planet. How many objects do we know in the Kuiper belt that are 400 km or larger? That question is harder to answer, because we don't actually know how big most of the objects in the Kuiper belt are. While we can see how bright there are, we don't know if they are bright because they are larger or are highly reflective.

In the past, we had to just throw our hands up in the air and say we don't know enough to even make reasonable guesses. But in the past few years, systematic measurements of the sizes of objects from the Spitzer Space Telescope and now the Herschel Space Telescope have taught us enought that we can make some reasonable estimates of how reflective objects are. (It's complicated: read the details here ) These reasonable estimates, combined with all available actually measurements, give us the list of the largest Kuiper belt objects, sorted by diameter, below. Carefully note the lack of any error bars. Every single measurement or estimate below is uncertain to some extent or another. I don't include the individual uncertainties in the table, but instead use the ensemble uncertainties to inform classification below. In other words: take the sizes of specific objects with bigger or smaller grains of salt. I subjectively divide this list into a few categories, taking into account both the uncertainties in the sizes and the uncertainties in the size where an object becomes round. Near certainty: We are confident enough in the size estimate to know that each one of these must be a dwarf planet even if predominantly rocky. Highly likely Anything larger than 600 km is all but certainly round.

Even objects significantly smaller are likely round. The predicted and/or measured size of an object in this category would have to be grossly in error or the composition would have to be primarily rocky in order for it not to be a dwarf planet. Likely: Anything icy larger than 500 km is highly likely to be round. But the size uncertainties are large enough that some of these objects could, in reality, be small enough to be less certain. Probably: All icy satellite larger than 400 km are round, so we expect these objects to be round if the size estimate is correct. Possibly: We don't know where the transition from non-round to round occurs, but in icy satellites it is between 200 and 400 km. Objects this size in the Kuiper belt could thus possible be round, but we don't know. Probably not: Below 200 km no icy satellite are round. We expect the same in the Kuiper belt. A few of these object could be bigger than expected, however, and could turn out to be large enough to round themselves. The table also lists the estimated albedo used to determine the size or the calculated albedo from the measured size.

Also listed is the absolute magnitude, which in this case refers to how bright the object would be if you were looking at it while you were standing on the surface of the sun and the object were at the distance of the earth. As in the rest of astronomy, smaller magnitudes are brighter and every 5 magnitudes represents a factor of 100. In the comments section I list the source of the size or albedo as described here and add subjective comments when required. As of Thu Jan 5 2017 there are: 10 objects which are nearly certainly dwarf planets, 30 objects which are highly likely to be dwarf planets, 75 objects which are likely to be dwarf planets, 148 objects which are probably dwarf planets, and 703 objects which are possibly dwarf planets. rank How Many Planets Are There in the Solar System? How Many Planets Are There in the Solar System?

Home Science Howmanyarethere 03 April 2011 33383 Views There are 8 major planets in our solar system .There were 9 planets which including Pluto too.International Astronomical Union decided that Pluto is no longer a planet , it is a dwarf planet.There are 5 dwarf planets .

Planets from 2006 to present (8) : Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Dwarf planets from 2006 to present (5) : Ceres Pluto Makemake Haumea Eris Planets from 1930 to 2006 (9) : Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Planets from late 19th century to 1930(8) : Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Planets in early 19th century (11) : Mercury Venus Earth Mars Vesta Juno Ceres Pallas Jupiter Saturn Uranus Planets and Dwarf Planets in the Solary System April 5, 2011 at 8:54 pm Our solar system does NOT have only eight planets, and it is far more than a minority of scientists who still view Pluto as a planet and a Kuiper Belt Object. The same is true for Haumea, Makemake, and Eris. Only four percent of the IAU voted on this, and most are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of professional astronomers led by Dr.

Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. Stern and like-minded scientists favor a broader planet definition that includes any non-self-luminous spheroidal body in orbit around a star. The spherical part is important because objects become spherical when they attain a state known as hydrostatic equilibrium, meaning they are large enough for their own gravity to pull them into a round shape. This is a characteristic of planets and not of shapeless asteroids and Kuiper Belt Objects. Pluto meets this criterion and is therefore a planet. Under this definition, our solar system has 13 planets and counting: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, and Eris. April 21, 2013 at 10:35 pm 11? First of all thats not even correct, second the sun is a star, and the moon is…a fucking moon. Arabs also said the earth is flat in 1993, and said man will never go to outer space, right before we went to outer space.

In no calculation of addition, subtraction, or obsoletion can you arrive at the number 11 for the planets in the Milky Way Galaxy. Please do not bring religion into science, fairy tales and facts do not mix. And before you go jihad on me I’m not just attacking your religion, or attacking religion at all. The Christian bible says god made the sun and the stars on the 4th day. Well how do you have 4 days without a sun to orbit around? I side with several other people that there are still 9 planets, since the reasoning discounting Pluto was essentially just on it’s size and orbitational pattern. The fact is it is still a sphere, it does not light itself, and it orbits a star. Not that I am the expert but switching it to a Dwarf planet was so strongly opposed in the science field, and so many scientists still stand by it as a planet, that I do not find enough evidence or reasoning to consider it a dwarf. But again, my opinion doesn’t really matter. Just dont count them based on a book written by cattle sacrificing primitive’s that believe the earth was made in seven days, or that man is to practice religious conversion at the point of a sword.

If you want to believe something that has been shown to be fundamentally false time and again, that is your right, and noone is going to stop you. But please stop trying to get the rest of us to buy in to fiction, when we have plenty of facts to the contrary. January 31, 2012 at 10:19 pm Pluto should be a planet. I’m just amateur astronomer, but there should be no reason why Pluto should not be included along with the other planets. Pluto has an orbit just like any other planet, however eliptical it may be. yes I agree it is very small but it should not be disqualified as a planet just simply because it does not look like on the other planets and it’s not completely round. if were going to get that technical about planets, then I suggest that we consider the gas giants, which we’re not even sure have any definite planeit structure on the inside, should they be disqualified as planets too? Besides it would confuse all of the first-graders when they are trying to memorize the nine planets. Should we change the rhyme to say my very excellent mother just served us nuts?!!

February 4, 2012 at 5:10 pm Hey V Bellator, Ali Harb IS in the right place. I am not sure about the rest of you though. The Quran says there are 10 planets (11 only in Abraham’s dream – Sura 12, the 11th is imaginery). If you guys are really serious about astronomy, planetary systems, inter stellar material,creation of the worlds (yes, plural), the process of the formation of the universe, read Quran. But before you do that, just to get intellectually ready for it, read “The Bible, The Quran and Science” written by Dr. Maurice Bucaille. The book was originally written in French, but translated by Alastair D. Panell. It will take you to a completely different level, scientifically speaking. March 17, 2014 at 3:25 pm I have an idea to rid the solar system of some planets. Add a 4th criteria. A planet must have or at one point in time had an atmosphere. That goes for dwarf planets. Saying an asteroid, Ceres, is any kind of planet is just ridiculous.

Thats like calling Halley’s Comet a dwarf planet. It goes around the sun, has a rotation on its axis, and its self illuminating. Just for fun, the gas giants have a solid core of at least carbon. If Jupiter didn’t have a solid core we would be a two star system. Now to discredit myself. I have been studying the solar system since I was a kid, watch the moons of Saturn go from 16 to 62+ hundreds of moonlets. I have no credentials in schooling or otherwise. Just that when you see a light in the sky, don’t assume its a star. I might be a planet. Peace Dwarf Planets: Classification, Discovery, Definition, Kuiper Belt - Windows to the Universe The Poles of the Dwarf Planets Dwarf Planets In 2006 the International Astronomical Union (IAU) approved a new classification scheme for planets and smaller objects in our Solar System . Their scheme includes three classes of objects: "small solar system bodies" (including most asteroids and comets ), the much larger planets (including Earth , Jupiter , and so on), and the new category of in-between sized "dwarf planets". There are currently five official dwarf planets.

Pluto , formerly the smallest of the nine "traditional" planets, was demoted to dwarf planet status. Ceres , the largest asteroid in the main asteroid belt between Mars and Jupiter, was also declared a dwarf planet. The three other (for now!) dwarf planets are Eris , Makemake , and Haumea . Pluto, Makemake, and Haumea orbit the Sun on the frozen fringes of our Solar System in the Kuiper Belt . Eris, also a Trans-Neptunian Object , is even further from the Sun. What's the difference between regular planets and dwarf planets? As you might guess, it's partly an issue of size, with dwarf planets being smaller. But just how big does a planet need to be to become a full-fledged planet instead of a dwarf? You might think the minimum size requirement is arbitrary, but the size cutoff is actually based on other properties of the object and its history in the Solar System. Both planets and dwarf planets orbit the Sun , not other planets (in which case we call them moons). Both must be large enough that their own gravity pulls them into the shapes of spheres; this rules out numerous smaller bodies like most asteroids, many of which have irregular shapes .

Planets clear smaller objects out of their orbits by sucking the small bodies into themselves or flinging them out of orbit. Dwarf planets, with their weaker gravities, are unable to clear out their orbits. Though there are just five dwarf planets now, their number is expected to grow. Scientists estimate there may be 70 dwarf planets amongst outer solar system objects that have been discovered already. Since we don't know the actual sizes or shapes of many of the objects we've found (because they are so far away), we can't yet determine whether they are actually dwarf planets or not. More observations and better telescopes will help us determine which other objects are dwarf planets. Astronomers speculate that there may be 200 or so dwarf planets out through the distance of the Kuiper Belt , an icy band of frozen planetoids on the edge of our Solar System. Last modified June 9, 2009 by Randy Russell . Shop Windows to the Universe Science Store! The Winter 2010 issue of The Earth Scientist , which includes articles on meteor cratering, classroom glaciers, podcasts in the classroom, and pyro-cumulonimbus clouds, is available in our online store .

Windows to the Universe Community News How many planets are in the solar system? How many planets are in the solar system? May 28, 2013 by Fraser Cain, Universe Today The Solar System. Image Credit: NASA I'm just going to warn you, this is a controversial topic. Some people get pretty grumpy when you ask: how many planets are in the Solar System? Is it eight, ten, or more? I promise you this, though, we're never going back to nine planets … ever. When many of us grew up, there were nine planets in the Solar System. It was like a fixed point in our brains. As kids, memorizing this list was an early right of passage of nerd pride: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto . But then in 2005, Mike Brown discovered Eris, an icy object thought to be about the same size as Pluto, out beyond its orbit. That would bring the total number of planets to ten. Right? There's no turning back, textbooks would need to be changed.

In order to settle the dispute, the International Astronomical Union met in 2006, and argued for, and against Pluto's planethood. Some astronomers advocated widening the number of planets to twelve, including Pluto, its moon Charon, the Asteroid Ceres, and the newly discovered Eris. In the end, they changed the definition of what makes a planet, and sadly, Pluto doesn't make the cut: Makemake. Credit: NASA Here are the new requirements of planethood status: 1. A planet has to orbit the Sun. Okay fine, Pluto does that. 2. A planet needs enough gravity to pull itself into a sphere. Okay, spherical. Pluto's fine there too. 3. A planet needs to have cleared out its orbit of other objects. Uh oh, Pluto hasn't done that. For example, planet Earth accounts for a million times the rest of the material in its orbit, while Pluto is just a fraction of the icy objects in its realm. The final decision was to demote Pluto from planet to dwarf planet. But don't despair, Pluto is in good company. The video will load shortly There's Ceres, the first asteroid ever discovered, and the smallest of the dwarf planets.

The surface of Ceres is made of ice and rock, and it might even have a liquid ocean under its surface. NASA 's Dawn mission is flying there right now to give us close up pictures for the first time. Haumea, named after the Hawaiian goddess of fertility, is about a third the mass of Pluto, and has just enough gravity to pull itself into an ellipsoid, or egg shape. Even though it's smaller, it's got moons of its own. Makemake, a much larger Kuiper belt object, has a diameter about two-thirds the size of Pluto. It was discovered in 2005 by Mike Brown and his team. So far, Makemake doesn't seem to have any moons. Makemake. Credit: NASA Eris is the most massive known dwarf planet, and the one that helped turn our definition of a planet upside-down. It's 27% more massive than Pluto and the ninth most massive body that orbits the Sun. It even has a moon: Dysnomia. And of course, Pluto. The founding member of the dwarf family. Want an easy way to remember the eight planets, in order? Just remember this mnemonic: my very excellent mother just served us noodles.

Pluto. Credit: ESO For all you currently writing angry tweets to Mike Brown, hold on a sec. Changing Pluto's categorization is an important step that really needed to happen. The more we discover about our Universe, the more we realize just how strange and wonderful it is. When Pluto was discovered 80 years ago, we never could have expected the variety of objects in the Solar System. Categorizing Pluto as a dwarf planet helps us better describe our celestial home. So, our Solar System now has eight planets, and five dwarf planets. Astronomers Measured Mass of Largest Dwarf Planet June 18, 2007 Aptly named after the Greek goddess of conflict, the icy dwarf planet, Eris, has rattled the general model of our solar system. The object was discovered by astronomer Mike Brown of Caltech in the outer reaches of the Kuiper ... Recent news on the debate over Pluto's planethood November 29, 2010 Earlier this month, Eris -- the distant world first discovered by Caltech's Mike Brown and colleagues back in 2005, paving the way for the eventual demotion of Pluto from planet to dwarf planet -- passed fortuitously in front ...

The Kuiper Belt at 20 September 3, 2012 Planetary science is celebrating the 20th anniversary of the discovery of the Kuiper Belt. That came in 1992, when the first Kuiper Belt Object (KBO) was discovered. Dwarf planet Makemake reveals its secrets for the first time November 21, 2012 Astronomers have used three telescopes at ESO's observatories in Chile to observe the dwarf planet Makemake as it drifted in front of a distant star and blocked its light. The new observations have allowed them to check for ... Dwarf planet mysteries beckon to New Horizons September 5, 2011 (PhysOrg.com) -- At this very moment one of the fastest spacecraft ever launched -- NASA's New Horizons -- is hurtling through the void at nearly one million miles per day. Launched in 2006, it has been in flight longer ... Picking Planets from Potatoes April 26, 2010 New research indicates that there may be many more dwarf planets similar to Pluto in our solar system than previously thought.

Studying these distant objects can help astrobiologists understand the basic properties of our ... Recommended for you The evolution of massive galaxy clusters January 20, 2017 Galaxy clusters have long been recognized as important laboratories for the study of galaxy formation and evolution. The advent of the new generation of millimeter and submillimeter wave survey telescopes, like the South ... Image: Wavemaker moon Daphnis January 20, 2017 The wavemaker moon, Daphnis, is featured in this view, taken as NASA's Cassini spacecraft made one of its ring-grazing passes over the outer edges of Saturn's rings on Jan. 16, 2017. This is the closest view of the small ... Observations of Ceres indicate that asteroids might be camouflaged January 20, 2017 The appearance of small bodies in the outer solar system could be deceiving. Asteroids and dwarf planets may be camouflaged with an outer layer of material that actually comes from somewhere else.

Freeze-dried food and one bathroom: Six simulate Mars in dome January 20, 2017 Crammed into a dome with one bathroom, six scientists will spend eight months munching on mostly freeze-dried foods—with a rare treat of Spam—and have only their small sleeping quarters to retreat to for solace. Astronomers search for signs of life on Wolf 1061 exoplanet January 19, 2017 Is there anybody out there? The question of whether Earthlings are alone in the universe has puzzled everyone from biologists and physicists to philosophers and filmmakers. It's also the driving force behind San Francisco ... NASA study in Hawaii paving way for human travel to Mars January 19, 2017 A group of NASA-funded researchers is poised to enter an isolated geodesic dome on a remote Hawaii volcano to study human behavior in long-term space exploration, including a planned voyage to Mars.

Meet the Solar System's Dwarf Planets Meet the Solar System's Dwarf Planets By Mike Wall, Space.com Senior Writer | August 22, 2011 06:00am ET MORE Artist's impression of Pluto and Charon as seen from one of Pluto's other moons. Credit: David Aguilar/Center for Astrophysics For three-quarters of a century, schoolkids learned that our solar system has nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. But things changed nearly five years ago today. On Aug. 24, 2006, the International Astronomical Union (IAU) struck Pluto from the list, demoting it to the newly created category of " dwarf planet ." The move was spurred by the discovery of multiple large bodies orbiting even farther from the sun than distant Pluto — particularly an object called Eris, which appeared to be bigger than Pluto.

As a result, the IAU came up with a new definition of "planet": 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. [ Our Solar System: A Photo Tour of the Planets ] Since Pluto shares orbital space with lots of other objects out in the Kuiper Belt — the ring of icy bodies beyond Neptune — it didn't make the cut. So Pluto was newly classified as a dwarf planet, which tend to be smaller than "true" planets and fall short on the "clearing your neighborhood" criterion. Although hundreds, or perhaps thousands, more solar system bodies may eventually join the list, the IAU officially recognizes just five dwarf planets at the moment. Here's a brief tour of all five: Pluto, Eris, Haumea, Makemake and Ceres. Images of the dwarf planet Pluto taken by NASA's Hubble Space Telescope. Credit: NASA, ESA, and M.

Buie (Southwest Research Institute) Pluto: The demoted former planet Pluto was discovered by American Clyde Tombaugh in 1930, as part of a search for the mythical "Planet X" that was thought to be perturbing the orbit of Uranus. The dwarf planet was initially believed to be at least the size of Earth, but astronomers now know that it's about 1,455 miles (2,352 kilometers) across — less than 20 percent as big as our planet. And Pluto is just 0.2 percent as massive as Earth. Pluto has an extremely elliptical orbit that's not in the same plane as the eight official planets' orbits. On average, the dwarf planet cruises around the sun at a distance of 3.65 billion miles (5.87 billion km), taking 248 years to complete one circuit. [ Infographic: Pluto - A Dwarf Planet Oddity ] Because it's so far from the sun, Pluto is one of the coldest places in the solar system, with surface temperatures hovering around minus 375 degrees Fahrenheit (minus 225 degrees Celsius).

Pluto has four known moons: Charon, Nix, Hydra and a newly discovered tiny satellite currently called P4 (its final name may end up being Cerberus). While Nix, Hydra and P4 are relatively small, Charon is about half as big as Pluto. Because of Charon's size, some astronomers regard Pluto and Charon as a double dwarf planet, or binary system. While Pluto is tough to study because it's so far away, scientists think the dwarf planet is about 70 percent rock and 30 percent ice. Its surface is covered predominantly with nitrogen ice. The dwarf planet has a thin atmosphere — composed mainly of nitrogen, methane and carbon monoxide— that extends about 1,860 (3,000 km) into space. Pluto will start coming into clearer focus in a few years' time. NASA's New Horizons probe is due to make a close flyby of the dwarf planet in July 2015, marking the first time a spacecraft has ever visited the frigid, faraway world. Artist's rendering of Eris, announced in July 2005 by Mike Brown of Caltech. It is more massive than Pluto. The sun is in the background.

Credit: NASA/JPL/Caltech Eris: The troublemaker Caltech astronomer Mike Brown led the team that discovered Eris in 2005. The find spurred the IAU to strip Pluto of its planethood and create the "dwarf planet" category a year later. That decision remains controversial to this day, making Eris' name quite fitting : Eris is the Greek goddess of discord and strife, who stirred up jealousy and envy among the goddesses, leading to the Trojan War. Eris' one known moon, Dysnomia, is named after the goddess' daughter, who served as the spirit of lawlessness. Eris is virtually the same size as Pluto, but it's about 25 percent more massive, suggesting that Eris contains considerably more rock (and less ice) than its Kuiper Belt neighbor. However, the surfaces of the two dwarf planets appear to be similar, composed primarily of nitrogen ice. Like Pluto, Eris has a highly elliptical orbit. But Eris is even more far-flung, orbiting the sun at an average distance of about 6.3 billion miles (10.1 billion km).

It takes Eris 557 years to complete one lap around the sun. Artist's concept of the dwarf planet Haumea and its two satellites (Hi’iaka and Namaka). Credit: SINC/José Antonio Peñas Haumea: The oddball Haumea, a Kuiper Belt denizen orbiting slightly beyond Pluto, was discovered by Brown and his team in late 2004. It's one of the weirdest objects in the solar system. Haumea measures about 1,200 miles (1,931 km) across, making it nearly as wide as Pluto. But Haumea is just one-third as massive as Pluto, partly because it's not spherical. Rather, Haumea is shaped like a giant American football. The dwarf planet also completes one full rotation in less than four hours, making it one of the fastest-spinning bodies in the solar system. This super-charged spin is responsible for Haumea's oblong shape , pushing the dwarf planet outward substantially at the equator. Haumea, named after the Hawaiian goddess of childbirth, has two known moons, Hi'iaka and Namaka.

The moons share their names with two of the goddess' daughters, who are deities in their own right. Scientists recently discovered that 75 percent of Haumea's surface is covered with crystalline water ice, similar to the stuff found in your freezer. [ Video: Dwarf Planet Veiled in Water-Ice ] An energy source is generally required to maintain such organized, structured ice. Astronomers theorize that energy may come from radioactive elements inside Haumea, as well as heat generated by the tidal forces the dwarf planet and its moons exert on each other. Haumea makes one complete lap around the sun every 283 years. An artist's illustration of Makemake, a dwarf planet out beyond the orbit of Neptune that also qualifies as a plutoid. Credit: IAU/M. Kornmesser Mysterious Makemake Brown's team also discovered Makemake, spotting the dwarf planet in 2005. Astronomers aren't sure of Makemake's exact size, but the dwarf planet is thought to be about three-quarters as big as Pluto. It's therefore likely the third-largest dwarf planet, after Eris and Pluto.

Makemake orbits the sun from slightly farther away than Pluto, at an average distance of 4.26 billion miles (6.85 billion km), and completes an orbit every 310 years or so. Makemake is the second-brightest Kuiper Belt object (after Pluto) and can be seen with a high-end amateur telescope, according to the IAU. Like Haumea, Makemake is named after a Polynesian deity — in this case, the creator of humanity and god of fertility in the pantheon of the Rapanui, the native people of Easter Island. Like Pluto and Eris, Makemake appears to be a reddish color in the visible-light spectrum. Scientists think its surface is covered by a layer of frozen methane, and the distant world has no known moons. This Hubble Space Telescope image shows Ceres, the most massive object in the asteroid belt, a region between Mars and Jupiter. Hubble images are helping astronomers plan for the Dawn spacecraft's visit to Ceres in 2015. Credit: NASA, ESA, J. Parker (Southwest Research Institute), L.

McFadden (University of Maryland) Ceres: Queen of the asteroid belt Ceres is the only dwarf planet not found in the freezing cold, faraway Kuiper Belt. Rather, it orbits in the main asteroid belt between Mars and Jupiter, completing one lap around the sun every 4.6 years. Ceres is by far the largest object in the asteroid belt, containing about one-third of the belt's mass. However, at 590 miles (950 km) across, it is the smallest known dwarf planet. It is named after the Roman goddess of the harvest and motherly love. Because it's so much closer to Earth than the other dwarf planets, Ceres was discovered far earlier. Italian astronomer Giuseppe Piazzi spotted it first, on Jan. 1, 1801. For the next half-century, many astronomers regarded Ceres as a true planet. That changed when it became apparent that Ceres was just one of many bodies hurtling through space in the asteroid belt.

[ The Seven Strangest Asteroids ] These days, most astronomers regard Ceres as a protoplanet, saying it likely would have continued growing into a full-fledged rocky planet like Earth or Mars if Jupiter hadn't shaken up the asteroid belt long ago. Ceres is thought to be a complex, differentiated body harboring quite a bit of water. Scientists think it has a rocky core surrounded by a water-ice mantle, and its rocky surface may also sport some water ice. Some researchers believe an ocean of liquid water may slosh about beneath Ceres' surface. Scientists and the world will get a much better look at Ceres less than four years from now. In February 2015, NASA's Dawn spacecraft — which is currently orbiting Vesta, the asteroid belt's second-largest resident — will arrive at Ceres to undertake a detailed study of the dwarf planet. You can follow SPACE.com senior writer Mike Wall on Twitter: @michaeldwall . Follow SPACE.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook . Editor's Recommendations

Question: How many dwarf planets are there in our solar system?
Answer: Five