Exemplar for Internal Assessment Resource Earth and Space Science Level 3. Resource title: Space Exploration. Investigate an aspect of astronomy

Transcription

1 Exemplar for internal assessment resource Earth and Space Science 3.6B for Achievement Standard Exemplar for Internal Assessment Resource Earth and Space Science Level 3 Resource title: Space Exploration This exemplar supports assessment against: Achievement Standard Investigate an aspect of astronomy Student and grade boundary specific exemplar The material has been gathered from student material specific to an A or B assessment resource. Date version published by Ministry of Education December 2012 To support internal assessment from 2013 Introductory comments: An aspect of astronomy may include: an event a discovery phenomena principles knowledge gained from space probes or telescopes. Images have removed because of copyright and paragraphs not directly related to the task have also been removed. Crown 2012

2 Exemplar for internal assessment resource Earth and Space Science 3.6B for Achievement Standard Grade Boundary: Low Excellence For Excellence the student needs to investigate comprehensively an aspect of astronomy. This involves explaining the key links between the astronomy aspect and the key science. The student has produced a report showing integrated links between explanation of the astronomical aspects and explanations of the key science. Good understanding is lacking in places which is why it is a Low Excellence. A wide range of reliable information was selected and processed related to the astronomical aspect and the relevant science and sighted by the teacher. Example: Thirdly, whether they can actually be seen or not depends on how bright, or reflective, their surface is Eris s orbit is highly erratic, and in its 560 year long orbit around the Sun comes as close as 38 AU and as far away as 98 AU. The highlighted paragraph shows good integration of explanations of astronomical aspects and key science. There are no other good integrated passages in the report however, which makes this a Low Excellence. For a more secure Excellence, full evidence of the justification of the astronomical aspects linked to the key science is required. Crown 2012

3 Student 1: Low Excellence Finding dwarf planets What is a Dwarf Planet? A dwarf planet is a celestial body that orbits around the Sun, is massive enough for its own gravity to make it round and is not a satellite, i.e. a moon. But, unlike a planet, it has not cleared the neighbourhood around its orbit. This means that there are bodies of a similar size in the orbit of the dwarf planet. For example, Pluto doesn t have enough mass and hence enough gravity to either consume smaller objects or fling them out of its orbit. It shares its orbit with other large objects called plutinos and these may cross Pluto s path. There are currently five dwarf planets Pluto, Ceres, Eris, Makemake and Haumea. Ceres is located in the asteroid belt, a region of millions of rocky, irregularly shaped objects found between the orbits of Mars and Jupiter. Ceres is the only round asteroid and is about 950km in diameter. It was discovered in 1801 and was considered a planet for about 50 years before becoming an asteroid and then a dwarf planet in The asteroid belt can be easily observed and searched from Earth and it is highly unlikely that there are any more dwarf planets in this region of the solar system. Eris, Makemake and Haumea are all located in the Kuiper Belt and were discovered in 2005, 2006 and 2004 respectively. Eris is larger than Pluto and this discovery started the debate as to whether Pluto was a planet or a dwarf planet. Eris orbits the sun every 560 years and has a moon is called Dysnomia. The Kuiper Belt The Kuiper belt extends from Neptune s orbit which is at 30 AU from the Sun, to about 55 AU. It contains possibly up to 70,000 icy and rocky bodies called Kuiper Belt Objects (KBO) or trans-neptunian objects (TNOs). Many of these may be similar or even larger than Pluto and, when discovered, will be classified as dwarf planets. Since 1992 over 1000 KBOs have been discovered. The reason that more dwarf planets haven t already been discovered it that KBOs are very hard to find. There are several reasons for this. Firstly, they are very small and are a great distance away, up to 55 AU from the Sun. Secondly; they have highly erratic orbits which mean that the whole sky has to be searched, rather than just the plane that the planets and asteroid belt are in. Such small objects are not so easily seen with current day telescopes and their actual size can be very difficult to find out. Thirdly, whether they can actually be seen or not depends on how bright, or reflective, their surface is. This is called albedo and the albedo of an object depends on how shiny the surface is. An object with a dark surface (albedo about 0) is much harder to see than an object with a bright, white surface (albedo about 1). For example, Pluto may have methane ice on its surface which makes it very reflective. However a rocky KBO would absorb more light so that the KBO would have a lower albedo and would not be so easy to see.

4 The diameters of KBOs are very difficult to measure and have to be done by the estimation of their brightness and how far away they are from the Sun. Also important is the direction that the light is reflecting off the KBO relative to the observing telescope. Direct reflection is obviously going to make the planet seem brighter than it may actually be. This may also make the diameter seem greater than it actually is. This makes it very difficult to measure the size of the objects found. Eris is the most massive known dwarf planet and has a diameter of about 2326 km in diameter. It is 27% more massive than Pluto. It is nearly 97 AU from the Sun and with its moon Dysnomia is the most distant known natural object in the Solar System. Because Eris is so far away, but very bright, originally it was thought to be bigger than it actually is. However, further astronomical observation put it at a similar size to Pluto. This makes Eris very bright indeed, reflecting about 86% of light falling on it (compared with 60% in the case of Pluto). Eris s orbit is highly erratic, and in its 560 year long orbit around the Sun comes as close as 38 AU and as far away as 98 AU. Pluto was first discovered in 1930 by Clyde W. Tombaugh and was found by using a blink comparator. Photographs of the night sky were taken at certain time intervals using optical telescopes and then the blink comparator would rapidly switch from one photograph to the other. The object that had moved in that time would appear to be jumping back and forth and could be identified as a new planet (as Pluto was at that time). These days, KBOs are looked for by computer controlled telescopes. Each day the computers locate different moving objects that then are looked at by astronomers. The distant stars and galaxies appear stationary in sky so that anything that moves could be either a satellite, dwarf planet, asteroid or comet. The objects that are found to be moving are then be looked at and analysed until they are identified. Eris was discovered using the Spitzer Space Telescope and because no heat was detected it was assumed that the size of Eris was 3300km. When heat was measured with another telescope Eris was estimated to be about 3000km. However, measurements with Hubble put it at close to Pluto s size. The part of the Kuiper belt that is visible from the Earth's Northern Hemisphere has been well observed but, until recently, the area visible from the Southern Hemisphere hadn t been very well explored at all. In KBOs were discovered in Pluto's neighbourhood, 3 of which may be new dwarf planets. The biggest object is about 620 kilometres wide. Pluto and Eris are both approximately 2,333 kilometres wide. Ceres, which is the smallest dwarf planet, is about 490 kilometres wide. Because of the fact that these new objects are not very big and are so distant, the astronomers cannot say for sure at the moment whether they are round and can be classified as dwarf planets. However, it shows that there more swarf planets out there to be found.

5 Exemplar for internal assessment resource Earth and Space Science 3.6B for Achievement Standard Grade Boundary: High Merit For Merit the student needs to investigate in depth an aspect of astronomy. This involves explaining the key science relevant to the astronomical aspect. The student has produced a report with the astronomical aspects and the key science explained, but without the integrated links needed for Excellence. A wide range of reliable information was selected and processed related to the astronomical aspect and the relevant science and sighted by the teacher. Examples: A dwarf planet is a celestial body that is in orbit around the Sun, is massive enough for its own gravity to make it round, is not a moon but has not cleared the neighbourhood around its orbit. The latter point means that there are bodies of a similar size in the orbit of the dwarf planet. For example, Pluto shares its orbit with Kuiper Belt objects of a similar size called plutinos. This is an example of an astronomical aspect explained. They are mostly very small their diameters are very difficult to measure and have to be done by the estimation of their brightness and how far away they are form the Sun. This makes it very difficult to classify the objects found. Science related to the astronomical aspect has been explained at a Merit level. To reach Excellence full evidence of the justification of the astronomical aspects linked to the key science is required. Crown 2012

6 Discovering Dwarf Planets Student 2: High Merit Dwarf Planets A dwarf planet is a celestial body that is in orbit around the Sun, is massive enough for its own gravity to make it round, is not a moon but has not cleared the neighbourhood around its orbit. The latter point means that there are bodies of a similar size in the orbit of the dwarf planet. For example, Pluto shares its orbit with Kuiper Belt objects of a similar size called plutinos. There are currently five dwarf planets Pluto, Ceres, Eris, Makemake and Haumea, all of which meet the above criteria. Ceres is located in the asteroid belt between the orbits of Mars and Jupiter and is about 950km in diameter. It was discovered in 1801 and was called a planet for about 50 years before becoming an asteroid and then a dwarf planet in Eris, Makemake and Haumea are all located in the Kuiper Belt and were discovered in 2005, 2006 and 2004 respectively. Eris is larger than Pluto and this discovery started the debate as to what was a planet and what was a dwarf planet. Eris orbits the sun every 560years and its moon is called Dysnomia. The Asteroid Belt The asteroid belt has more rocky objects compared with the Kuiper s belts icier and larger objects. The asteroid belt is found between Mars and Jupiter and has several million asteroids - lumps of irregular shaped rock much smaller than planets. These are sometimes known as minor planets and are not visible from Earth by the naked eye. Anything above 50km in diameter is an asteroid and anything smaller is a meteoroid. The four largest objects are Ceres, Pallas, Vespa and Hygiea but only Ceres is considered a dwarf planet. No more large asteroids are liable to be found and so any more dwarf planets will be found in the Kuiper Belt. The Kuiper Belt The Kuiper belt extends from about 30 to 55 AU and contains thousands of icy and rocky bodies, many of which may become dwarf planets and may even be bigger than Eris. The Kuiper belt is similar to the asteroid belt but a lot larger. In 1992 the first Kuiper Belt object (KBO) was discovered. Since then, over 1000 KBOs have been discovered and there may be as many as 70,000 KBOs. KBOs are hard to find though for several reasons. They are mostly very small. They are all a long way away, up to 55 AU. Only the very biggest telescopes can see that far. They have highly erratic orbits which means that the whole sky has to be searched, rather than just the plane that the planets and asteroid belt are in. Their ability to be seen depends on how reflective the surface is. This is called albedo. An object with a dark surface is much harder to see than an object with a bright, white surface.

7 their diameters are very difficult to measure and have to be done by the estimation of their brightness and how far away they are form the Sun. This makes it very difficult to classify the objects found. Pluto was first discovered in 1930 by Clyde W. Tombaugh. It has a diameter of 2400 km across. At that time the Kuiper belt had not been discovered and Pluto was thought to be at the edge of the Solar System. When the first KBO was discovered in 1992 astronomers then realised that Pluto was probably part of the Kuiper Belt. One of Pluto s moons, Charon, is half Pluto s size and some astronomers believe that the pair should be treated as a binary system rather than a planet and satellite. Pluto has an erratic orbit that is at a 17 degree angle to the ecliptic and crosses Neptune s orbit. These are just some of the facts that have contributed to a long running debate as to if Pluto is to be considered a planet or not. Pluto was considered a planet until 2009 when it was officially downgraded to a dwarf planet by the International Astronomical Union. This happened because more and more objects were starting to be discovered in the Kuiper Belt that were only slightly smaller than Pluto, or in Eris s case, larger. If Pluto remained as a planet many other subjects would have to be declared planets as well, including Ceres. The only eight planets that meet these requirements are the ones from Mercury to Neptune. In July 2005 a group of astronomers have discovered a KBO that is vaguely larger than Pluto. It was temporarily named 2003 UB313 and later named Eris. Its orbit around the sun takes 560 year with its distance stretching from 38 to 98 AU. It also has a tiny moon called Dysnomia. Pluto was originally found by using a blink comparator. Photographs of the night sky would be taken using optical telescopes and then the blink comparator would rapidly switch from one photograph to the other. The moving object would appear to be jumping back and forth and so could be identified. These days, KBOs are looked for by robotically controlled telescopes taking pictures of the same section of sky at different time intervals. Each day the computers locate different moving objects that then need to be looked at by astronomers. The billions of stars and galaxies always appear stationary in sky, which means that anything that moves could be either a satellite, dwarf planet, asteroid or comet. The objects that are found to be moving are then be looked at and analysed until they are identified. In the future even more KBOs will be found. I wonder how many will become dwarf planets. Our Solar System will keep on growing for a while yet.

8 Exemplar for internal assessment resource Earth and Space Science 3.6B for Achievement Standard Grade Boundary: Low Merit For Merit the student needs to investigate in depth an aspect of astronomy. This involves explaining the key science relevant to the astronomical aspect. The student has produced a report with the astronomical aspects and key science explained, but without a lot of detail. A wide range of reliable information was selected and processed related to the astronomical aspect and the relevant science and sighted by the teacher. Examples: The part of the Kuiper belt that is visible from the Earth's Northern Hemisphere These were found in a small section of the Kuiper belt that was studied by astronomers using a 1.3-meter Warsaw University Telescope in Chile. The astronomical aspect is well explained at a Merit level. KBOs are difficult to find because they are so far away and because they have erratic orbits Brighter planets are more easily seen but it is still hard to tell exactly how far away they are. The science has been explained, although the explanation is lacking in detail and therefore the response is at Low Merit level. For a more secure Merit the science needs to be fully explained. Crown 2012

9 Student 3: Low Merit Finding Dwarf planets With modern day technology more and more celestial bodies are being found in the Kuiper Belt, a region that stretches from the orbit of Neptune at 30 AU to 50 AU from the Sun. This has led to a reclassification of some celestial objects such as Pluto. What is a dwarf planet? In our Solar System, we have 8 planets. In order from the sun they are Mercury, Venus, Earth, Mars (the rocky planets) and Jupiter, Saturn, Uranus and Neptune (the gas giants). For something to be classified as a planet it must have the following characteristics: It must also be big enough to be round due to the force of its own gravity. It must orbit the sun. Finally, it must dominate and clear its neighbourhood around its orbit. This means that it has a planet is the biggest in its orbit and has the most gravity. It may have moons but no other large bodies will be in the same orbit. Dwarf planet was a category made in 2006 due to the realisation that there may be numerous objects like Pluto in our Solar System. Dwarf planets share the first two characteristics but not the third. Pluto is no longer classified as a planet but is now a dwarf planet in our Solar System. Pluto that orbits the sun and is massive enough to be round because of the force of its own gravity. But, the main reason that Pluto was demoted to a dwarf planet is because it doesn t dominate its neighbourhood around its orbit. Pluto s moon Charon is about half of Pluto s size compared to the other eight planets which are a lot bigger than their moons. Pluto even happens to be a lot smaller than our moon. Also, Pluto has a very untidy orbit, not clearing a path along it. Therefore, it is now deemed a dwarf planet. Currently, there are 4 other known and classified dwarf planets not including Pluto. They are Haumea, Makemake, Eris and Ceres. Haumea, Makemake and Eris are bits of ice and rock that orbit out beyond Neptune. Ceres (which is also the Solar System s largest asteroid) lies in the main belt in between Mars and Jupiter. Eris has a single moon that is called Dysnomia. Haumea has two moons that are called Hi iaka and Namaka. Ceres and Makemake do not have any moons. Discovering dwarf planets Ceres is the closest dwarf planet to the sun and earth because it lies in the Asteroid Belt between Mars and Jupiter. Objects in the asteroid belt are easy to find so it is highly unlikely that there are any other dwarf planets there. However, Pluto, Eris, Makemake and Haumea lie in the Kuiper Belt beyond Neptune. Pluto is the most well-known dwarf planet and Eris is the biggest. They are all said to be smaller than Earth s moon (Pluto is about a fifth of its mass and about a third of its volume). Eris, was one time referred to as a 10 th planet, sharing a lot of similarities to Pluto and it is even bigger than Pluto. The Kuiper Belt was discovered in 1951 by a Dutch-American astronomer named Gerard Kuiper. It is a disc of icy objects that orbit the sun beyond Neptune and extends 50 AU from the Sun, and is part of the Solar System. Objects found in the Kuiper Belt are referred to as KBOs (Kuiper Belt objects). The largest KBOs, Pluto being one of them, are the ones that are called dwarf planets. It is estimated that there are over 70,000 KBOs in the Kuiper Belt. Many of these may be larger than Pluto.

10 The part of the Kuiper belt that is visible from the Earth's Northern Hemisphere has been well observed but, until recently, a shortage of the appropriate instruments meant that the area visible from the Southern Hemisphere hadn t been very well explored. In KBOs were discovered in Pluto's neighbourhood, 3 of which may be new dwarf planets. These were found in a small section of the Kuiper belt that was studied by astronomers using a 1.3-meter Warsaw University Telescope in Chile. By estimation, the biggest object is probably 620 kilometres wide. Pluto and Eris are both approximately 2,333 kilometres wide. Ceres, which is the smallest dwarf planet, is about 487 kilometres wide. Because of the fact that these new objects are not very big and are so distant, the astronomers cannot say for sure at the moment whether they are actually spherical and therefore able to be classified as dwarf planets. The Kuiper belt is definitely filled with objects that are about the same size or the same brightness of these three new bodies. There are actually 37 other objects that lie in the Kuiper Belt that are at least as bright as the newfound possible dwarfs. The Southern skies still need to be searched to get a wider view on filling our Solar System, though. It is always possible that more objects will be found in the next region that is beyond the Kuiper Belt. This is where Sedna is (another possible dwarf planet) which approximately orbits at about 14.3 billion kilometres from the sun. KBOs are difficult to find because they are so far away and because they have erratic orbits, that is, they are very tilted relative to the plane the planets orbit on. This makes looking for them quite hard. Also, the brightness, or albedo affects how easily they are found. Brighter planets are more easily seen but it is still hard to tell exactly how far away they are. The Kuiper Belt part of the Solar System may have tens or even hundreds of dwarf planets. Who knows how many will join Pluto and the other dwarf planets over the next few years.

11 Exemplar for internal assessment resource Earth and Space Science 3.6B for Achievement Standard Grade Boundary: High Achieved In order to Achieve the student needs to investigate an aspect of astronomy. This involves selecting and processing a wide range of reliable information related to the astronomical aspect and the relevant science and explaining the astronomical aspect. The student has produced a report with the astronomical aspects explained, but with the key science only briefly mentioned. A wide range of reliable information was selected and processed related to the astronomical aspect and the relevant science and sighted by the teacher. Examples: Dwarf planets also orbit the sun and are round but they have not cleared their neighbourhood and often orbit with other similar sized bodies because their gravity is not great enough. The key science is not fully explained which is a requirement of achievement. A description is not enough at level 3. The moving object which is recognised by the telescopes only appears as a dot of light Though this gives us a result it is not always reliable, as it has to look through objects in our atmosphere. Again the key science is not fully explained as required. Another factor which makes these planets hard to discover is their distance away from earth, they are a very far way away and incredibly small, which does not make the process any easier. Key astronomical aspect has not been fully explained as required for achievement. To reach Merit the science needs to be fully explained. Crown 2012

12 Student 4: High Achieved Finding dwarf planets What is a planet? A planet is a body orbiting around the sun with enough mass and therefore gravity to be round. A planet has also cleared its neighbourhood, orbit by sucking in small bodies or deflecting them away from their orbit. There are eight planets within our Galaxy: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. What is a dwarf planet? The International Astronomical Union (IAU) adopted the term dwarf planet in 2006 for objects in the solar system that were not quite planets but bigger than the other objects in the solar system such as comets and asteroids. Dwarf planets also orbit the sun and are round but they have not cleared their neighbourhood and often orbit with other similar sized bodies because their gravity is not great enough. Dwarf planets can often be called the in-between sized planets. The official dwarf planets are: Pluto, Ceres, Eris, Makemake and Haumea What is the Asteroid Belt? The asteroid belt is the region of the Solar System located between the orbits of the planets Mars and Jupiter. It is occupied by many irregularly shaped bodies called asteroids, primarily composed of rock and metal. These asteroids orbit the sun, the time in which it takes for an object to orbit the sun in the asteroid bet varies from about three to six years. The asteroid belt is home to the dwarf planet of Ceres, this is the belt s only dwarf planet and the largest object in its orbit. What is the Kuiper Belt? The Kuiper Belt is a region of the Solar System beyond the planets extending from the orbit of Neptune. It is similar to the asteroid belt, but is far larger, being 20 times as wide and times as massive. The Kuiper belt consists mainly of small rock, icy bodies and is home to three dwarf planets, Pluto, Haumea and Makemake. DWARF PLANETS PLUTO: Pluto is the best known dwarf planet because of its demotion from a planet to a dwarf planet in 2006, Pluto is the second biggest dwarf planet (Eris is the biggest) and is considered one of the largest member of a distinct population known as the Kuiper belt objects (KBOs). Pluto was found in 1930 when Clyde Tombaugh was using a blink comparator to compare photographic plates taken over a series of days. He discovered that there one tiny object was moving relative to the background stars. Pluto has three moons; its main moon is Charon was discovered in The smaller less significant moons, Nix and Hydra, were discovered in 2005 and sice then 3 more tiny moons have been found. WHY IS PLUTO NOT A PLANET?

13 In 2006 the IAU decided on a new class, dwarf planets, for objects such as Pluto. This meant that any new KBOs discovered of a similar size would also become dwarf planets, without needing to consider whether they were planets or not. DISCOVERING DWARF PLANETS Dwarf Planets have been discovered in a number of ways. Unlike most planets which can be easily found through looking through a telescope, dwarf planets are much harder to find. This is because of their positions in the solar system. Most of the dwarf planets can be located in the Kuiper Belt and are also incredibly small in comparison to other Planets. Dwarf planets used to be found by taking pictures of the same section of sky at different time intervals (eg. every few days or hours). The billions of stars and galaxies always appear stationary in sky, which means that anything that moves could be either a satellite, dwarf planet, asteroid or comet. The objects that are found to be moving would then be looked at and analysed until they are identified. For any astronomer this is a lot of time and work, therefore most of the work is done by computer. Once the images are taken using a robotically controlled telescope 10 computers at the observatory search the images. Each day the computers locate different moving objects that then need to be looked at by astronomers. Sometimes the images just show flaws in the photo but they are often successful in finding new dwarf planets. The moving object which is recognised by the telescopes only appears as a dot of light, therefore it is necessary to research further in order to find out exactly what it is and what size. The size of an object can be determined by heat radiating from the object, and this can be done using a high-tech telescope, the Hubble Space Telescope. Though this gives us a result it is not always reliable, as it has to look through objects in our atmosphere. WHAT MAKES DWARF PLANETS SO HARD TO FIND? The most prominent factor in the difficulty of discovering Dwarf Planets is their size. As they are much smaller than normal planets, and usually in the Kuiper belt (surrounded by thousands of other objects) they are harder to detect. It takes a lot of time, money and patience to discover. Another factor which makes these planets hard to discover is their distance away from earth, they are a very far way away and incredibly small, which does not make the process any easier.

14 Exemplar for internal assessment resource Earth and Space Science 3.6B for Achievement Standard Grade Boundary: Low Achieved In order to Achieve the student needs to investigate an aspect of astronomy. This involves selecting and processing a wide range of reliable information related to the astronomical aspect and the relevant science and explaining the astronomical aspect. The student has produced a report with the astronomical aspects explained, but with not a lot of detail. A wide range of reliable information was selected and processed related to the astronomical aspect and the relevant science and sighted by the teacher. Examples: Eris is the largest of the dwarf planets being approximately 2400km in diameter Eris s orbit is highly tilted and it takes 557 earth years to orbit around the sun. Eris has one moon. These details are more description than explanation. New dwarf planets in the Kuiper Belt are hard to find for many reasons KBOs have very tilted orbits which means that they are hard to see in the sky. Not much detail but enough to reach Low Achieved. Explanations are required for higher grades. To Achieve more securely the science needs to be described and explained. Crown 2012

15 Student 5: Low Achieved What s the difference between a planet and a dwarf planet? Modern land and space observatories have meant that much more is known about the solar system today. New objects in the outer solar system are often being identified. In our solar system Pluto has always been the odd one out, mainly because that it has a tilted orbit which for 20 years comes inside of Neptune and for the rest of the 248 years orbits outside Neptune, and also because it is a very small rocky object near to an enormous gas giant. In 2005 a team of astronomers discovered an object further out than the orbit of Pluto which was probably the same size or larger than Pluto. This object was named Eris and it is in fact larger than Pluto. A debate began as to whether it was another planet or not and what exactly was a planet anyway. Astronomers decided they would need to make some sort of final decision about how to classify objects in the solar system. At the 2006 General Assembly of the International Astronomers Union (IAU) astronomers debated how to classify objects that may or may not be planets. They decided on three categories: planets, dwarf planets and small solar system bodies. Although not everyone agreed the outcome was that the IAU has defined a planet as having to meet the following criteria:- 1. It is in orbit around the sun 2. It needs to have enough gravity to pull itself into a round shape 3. It needs to orbit in a clear path around the sun i.e.; it needs to have cleared the neighbourhood of similar sized objects. This means that the largest object in an orbit, and therefore the one with the most gravity, either consumes smaller objects or flings them out of the orbit. A dwarf planet is defined by the IAU as a body that:- 1. It is in orbit around the sun 2. Has enough gravity to pull itself into a spherical shape 3. Has not cleared the neighbourhood around its orbit, and therefore hasn t consumed smaller objects or flung them out of the orbit. 4. Is not a satellite (a moon) The final category defined by the IAU is Small Solar System Bodies and these are all other objects, except satellites, orbiting the sun. This includes asteroids, comets and most Trans Neptunian Objects (TNOs) or as they are often called, Kuiper Belt Objects (KBOs). Pluto is different to the 8 planets of our Solar System: Pluto was discovered in 1930 and it is located in an area in the outer solar system called the Kuiper Belt which extends from the orbit of Neptune out to 55 astronomical units which is 55 times the distance from earth to the sun. Since 2006 Pluto has been called a dwarf planet. It is only approximately 2390 km in diameter and its largest moon, Charon, is large in comparison to Pluto. Charon is approximately half the size of Pluto where as other planet s moons are proportionally much smaller than them. Pluto has a tilted orbit which is at an angle from the plane of

16 the eight planets. Pluto has five known moons which shows that Pluto hasn t cleared its neighbourhood. Other Dwarf Planets: Currently the IAU recognises five dwarf planets; Pluto, Eris, Ceres, Makemake and Haumea. The IAU designates dwarf planets that orbit the sun beyond Neptune as Plutoids. Other dwarf planets that are Plutoids are Eris, Makemake and Haumea. Ceres is a dwarf planet that orbits in the main asteroid belt between Mars and Jupiter. Ceres is the smallest of the dwarf planets, having a diameter of about 950km. It is the only dwarf planet in the asteroid belt. Ceres was first discovered in 1801 and its orbit around the sun takes 4.6 earth years. Eris is the largest of the dwarf planets being approximately 2400km in diameter. It is roughly three times further out in the solar system than Pluto and may even be beyond the Kuiper Belt and in the start of the Oort Cloud. Eris s orbit is highly tilted and it takes 557 earth years to orbit around the sun. Eris has one moon. After Eris and Pluto, Makemake is the third largest dwarf planet and it is also located in the Kuiper Belt. It was discovered in 2005 and takes 310 earth years to orbit the sun. Haumea was first noticed in the Kuiper Belt in 2004 and recognised by the IAU in 2008 as a dwarf planet. Its orbit around the sun takes 285 earth years and it has two moons. It has an unusual oval shape which may be due to a collision or rapid spinning but it does have enough mass to be a dwarf planet. Further discoveries in the Kuiper Belt: Astronomers and scientists now know that the Kuiper Belt is home to a large collection of objects, maybe up to KBOs. It is estimated this may include 20 or more further dwarf planets of similar composition to Pluto. Further observations will determine their size, shape and properties allowing their status to be classified. Studies are conducted through powerful telescopes on land and also in space. Space probes, spectroscopes and space crafts also collect valuable information. In 2005 NASA launched the spacecraft New Horizons and this will reach Pluto in 2015 providing new insights. New dwarf planets in the Kuiper Belt are hard to find for many reasons. They are a long distance away and they can be very hard to detect. Even when they are seen it may be hard to find out much about them or even to tell how big they are. Also, KBOs have very tilted orbits which means that they are hard to see in the sky.

17 Exemplar for internal assessment resource Earth and Space Science 3.6B for Achievement Standard Grade Boundary: High Not Achieved In order to Achieve the student needs to investigate an aspect of astronomy. This involves selecting and processing a wide range of reliable information related to the astronomical aspect and the relevant science and explaining the astronomical aspect. The student has produced a report with the astronomical aspect mostly explained, but it is lacking in adequate explanations on key points. Examples: sufficient mass to have the right amount of gravity to be round. This is an inaccurate statement, showing a lack of careful checking. This is because Pluto isn t the dominant gravitational body in its orbit. This concept is not adequately explained, just described. The range of information in this response was not wide enough; only 3 resources that didn t adequately cover the topic were used. To Achieve the science needs to be described and explained and a valid ranges of resources is required. Crown 2012

18 Student 6: High Not Achieved Finding dwarf planets: A range of reliable information was selected and processed related to the astronomical aspect and the relevant science and sighted by the teacher. Images have been deleted because of copyright and paragraphs not directly relevant to the task removed. There are 8 planets in our Solar System, but lots of smaller bodies that are now being called dwarf planets. Examples of dwarf planets are Pluto, Ceres and Eris. Astronomers used to think that the Solar System ended at Pluto but in 1992 the Kuiper Belt was discovered beyond Neptune. Many dwarf planets are being discovered in the Kuiper Belt. Planets and dwarf planets are similar in two ways but different in one other way. Planets and dwarf planets both orbit the Sun and are round. This means that they have sufficient mass to have the right amount of gravity to be round. Planets also dominate their orbits which means that they have cleared their neighbourhood of smaller objects. Dwarf planets haven t cleared their neighbourhood. The dwarf planets do not dominate their orbit as they are not the main gravitational body in the orbit. Many objects in our solar system have been classified as dwarf planets, the main ones being Pluto, Ceres and Eris. Pluto was discovered on February 18 th 1930 by Clyde Tombaugh. Pluto is usually the farthest from the sun out of any of the main planets, however, due to its erratic orbit, it sometimes comes inside Neptune. Since Pluto is so far from Earth, little is known about the planet s size or surface conditions. Ceres is the smallest identified dwarf planet in the solar system and the only one in the asteroid belt. The asteroid belt sits between the planets Mars and Jupiter. It is a region where millions of rocks can be found circling the sun. Some rocks are huge like Ceres itself but some only as small as a baseball. The surface of Ceres is a mixture of water, ice and various minerals such as carbonates and clays. The mass of Ceres is small, but it is large enough to give it a shape with is nearly spherical. No other asteroids are dwarf planets because none of them have enough mass to be round. The Kuiper Belt is like the asteroid belt except that the objects are icier. There are many objects in the Kuiper belt, many of which may be larger than Pluto. Eris is the largest dwarf planet as is the ninth biggest body known to orbit the sun directly. Because Eris is bigger than Pluto, it was initially considered to be a tenth planet but as the definition for a planet changed, both Pluto and Eris became known as dwarf planets. Eris s surface is described as icy and rocky and is similar to Pluto s surface.

19 Pluto is the only dwarf planet to once have been considered a major planet. Once thought of as the ninth planet and the one most distant from the sun, Pluto is now seen as one of the largest known objects of the Kuiper belt though a number of other objects were almost as large. The Kuiper belt is a region beyond the orbit of Neptune that contains hundreds of icy objects. Detecting these objects is difficult because they are very faint and have very erratic orbits. Modern telescopes are revealing a lot more of these objects in the Kuiper belt as the technology is becoming a lot more powerful. Pluto is considered for one main reason. Objects still remain in Pluto s path which means Pluto does not have a cleared neighbourhood. The new definition of a planet is an object that orbits the sun and is large enough to overcome the force of its own gravity. In addition to this the object must clear its neighbourhood around its orbit. Under this definition, Pluto is not considered one of the planets in our solar system. This is because Pluto isn t the dominant gravitational body in its orbit. In the future telescopes may discover even more dwarf planets in the Kuiper Belt. It will be interesting to see if any of these are even bigger than Pluto and Eris.