ARE YOU READY FOR THE JOURNEY

OF A LIFETIME?

It’s going to be ASTRONOMICAL

Your name will go down in history explorer, for you are one of the lucky few to venture past the frontier of Earth and into the vast expanse of the solar system. An exciting challenge lays before you on the long journey, and you will experience sights unlike you have ever seen.

We’ve included this mission guide to get you up to speed on the basics of the solar system. Have a flick through before take off, but dont miss the sights on the way up! Don’t forget to keep track of your mission during the journey – we’ve included all the basic equipment you’ll need in the rest of this kit.

Good Luck!

MERCURY JUPITERVENUS

SATURN

MARS

URANUS

Page 8 Page 16 Page 24 Page 32

Page 40 Page 48

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NEPTUNE

Page 56

MAIN PLANETS

HAUMEA

136108

CERES

MAKEMAKE

136472

ERISPLUTO

Page 72

Page 74

Page 66 Page 68 Page 70

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MAIN PLANETS DWARF PLANETS

MISSION LOGPage 77

THEMAINPLANETS

OBJECTIVE 1Mercury is the closest planet to the sun in our solar system. It is also the smallest planet, with a radius of only 2439.7 km. This is smaller than the radius of some of the solar systems larger natural satellites. It orbits the sun at a much faster pace than the earth and its year lasts only 87.969 earth days. Because of its close proximity to the sun, it is one of the least studied planets in the solar system.

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Mercury is classed as a terrestrial planet, and has a rocky surface like that of the earth. It is also extremely dense, having a density only slightly lower than earths. It is Mercury’s large iron core which is responsible for its high density.

Mercury has the most eccentric orbit of all the planets of the solar system, its distance from the sun ranges from 46 to 70 million kilometres. One Mercury day is the same length as two mercury years (about 176 earth days)

In appearance, Mercury mostly resembles the moon; it has a heavily cratered surface and no atmosphere. The extent of the cratering and plains suggests that the planet has been geologically inactive for billions of years. The diversity of these craters is huge, they range from being only a few centimetres

9

MERCURY

10

– to hundreds of kilometres across. The largest of these craters is Caloris Basin, which has a diameter of 1550 km. This impact was so powerful that it’s left evidence of lava eruptions thousands of years later and a 2 km tall ring surrounds the impact crater.

Mercury has two distinct geographical plains; one being the heavily cratered areas of the surface, which are surrounded by the other, less severe plain comprised of rolling hills and the remains of much more ancient craters, most likely of volcanic origin.The first spacecraft to visit Mercury was Mariner 10 which completed its observations 1975. It provided the first close up images of the planets surface, but only managed to map 45% of the planets surface due to the length of its orbit. Eight days after its final approach, the probe ran out of fuel and was shut

down. It is thought to still be orbiting the sun, passing by Mercury every few months.

Mercury is one of the most difficult planets to reach in the solar system, due to its close proximity to the sun. Potential visitors have to travel the 91 million kilometres, into the suns gravitational well. As Mercury’s orbital velocity is greater than that of the earth, visitors will also have to undergo a large change in velocity to approach in an appropriate orbit. Because of this, the trip to Mercury requires more rocket fuel alone than would be needed to leave the solar system entirely.

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DAY LENGTH

1406EarthDays

A single day on Mercury last exactly two Mercury years, or about 176 Earth days.

Mercury has the most eccentric orbit of all the planets. It takes 88 days to complete an orbit.

YEAR LENGTH

88EarthDays

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PLANET STATS

Mercury is too small and hot for its gravity to retain any significant atmosphere over long periods of time; it does have a “tenuous surface-bounded exosphere” containing the above elements, but this is unstable.

Mercury is even smaller—albeit more massive—than the largest natural satellites in the Solar System, Ganymede and Titan.

ATMOSPHERE

HeK

Ar

NXe

Kr

Ne

4878 Km

DIAMETER

13

PLANET STATS

The mean surface temperature of Mercury is 442.5 K,[3] but it ranges from 100 K to 700 K[49] due to the absence of an atmosphere and a steep temperature gradient between the equator and the poles.

The surface of Mercury is heavily cratered due to thousands of impacts

during the planets life span.

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127°C

SURFACE TEMPERATURE

PLANET STATS

15

PLANET STATS

16

OBJECTIVE 2Venus is the second planet in the solar system. It one of the four terrestrial inner planets, and is very similar in size and composition to the earth, leading it to be known as earths sister planet. It is the brightest object in the sky after the sun and moon and can be seen be seen during the day on Earth when the skies are clear. Because of this, its existence has been known since ancient times and it was often referred to as the morning

or evening star. The first civilisation to recognise that these two ‘stars’ were the same object were the babylonians, who referred to the planet as the bright queen of the sky.

The atmosphere of Venus is immensely thick and dense, so much so that it is impossible to see the surface of the planet from space without resorting to using light beyond the visible spectrum. The atmosphere contains high levels of sulphur dioxide and carbon dioxide which create a huge greenhouse effect on the planet. This causes Venus to have a higher surface temperature than Mercury, despite being further away from the sun. This surface temperature stays constant throughout the planet, despite Venus’ slow rotation speed, regulated by the winds in its lower atmosphere.

17

VENUS

The surface of Venus is covered in vast volcanic plains, 167 of these volcanoes are over 100km across.

Venus’s rotation is unusual, as it spins in the opposite direction to its orbit around the sun. Every other planet has an anti-clockwise rotation orbital direction, whereas Venus spins in a clockwise direction. Is it believed that this was caused by a huge impact in the early solar system, this could explain the lack of moons and the unusually slow rotational speed of the planet.

Venus was host to the first ever robotic space probe mission which began in 1961 with the Soviet probe Venera 1. It took another two missions by the Soviet Union before the probe Venera 3 became the first man made object to strike the surface of another planet on March 1st 1966.

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DAY LENGTH

242EarthDays

DAY LENGTH

242EarthDays

A Venusian sidereal day lasts longer than a Venusian year, however because of its retrograde rotation the length of a solar day on Venus is significantly shorter than the sidereal day.

Venus orbits the Sun at an average distance of about 108 million kilometers (about 0.7 AU), and completes an orbit every 224.65 days. Although all planetary orbits are elliptical, Venus is the closest to circular, with an eccentricity of less than 0.01.

YEAR LENGTH

224EarthDays

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PLANET STATS

Venus has the densest atmosphere of all the terrestrial planets in the Solar System, consisting mostly of carbon dioxide. Venus has no carbon cycle to lock carbon back into rocks and surface features, nor does it seem to have any organic life to absorb it in biomass.

Venus is classified as a terrestrial planet and it is sometimes called Earth’s “sister planet” due to the similar size, gravity, and bulk composition.

ATMOSPHERE

N

ArCO

He

Ne

OCS

HCl

HF12,102 Km

DIAMETER

21

PLANET STATS

The Venusian surface is hotter than Mercury’s even though Venus is nearly twice Mercury’s distance from the Sun and thus receives only 25% of Mercury’s solar irradiance. The surface of Venus is often said to resemble Hell.

The surface of Venus is obscured by an immensely thick and dense

atmosphere.

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462 °C

SURFACE TEMPERATURE

PLANET STATS

PLANET STATS

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OBJECTIVE 3Mars is the fourth planet in our Solar system, and is the outermost terrestrial planet. It is often referred to as the Red Planet, due to the high levels of iron oxide dust in the atmosphere, however underneath this the planet is more yellow-orange in colour. It shares many features with the moon and Earth, its surface is heavily cratered, and it has numerous volcanoes, valleys and deserts. Mars is home to the highest

known Mountain in the solar system, Olympus Mons, and also has prominent ice caps at the poles, just like the Earth. It is believed that Mars had large quantities of liquid water on its surface at one point in its history, due to erosion patterns found across the surface, however atmospheric pressure at current times is too low to allow large quantities of liquid water to exist.

Mars is approximately half of the diameter of the Earth, but is much less dense. Its surface is composed largely of basalt, along with amounts of silica glass and iron oxide. Parts of this surface are magnetised, despite the planet not having a globalized magnetic field at the present time. This is believed to be evidence of plate tectonics on the Martian surface billions of years ago, when a younger Mars still had a

25

MARS

functioning magnetic field. The ceasing of the planets internal dynamo (the rotation of electrically conductive liquids) is believed to have caused the loss of this field. The loss of this magnetic field has had a dramatic effect on the planet. Without one, the planet has been unable to protect itself from the solar winds, which have stripped its atmosphere of its outer layers, reducing atmospheric density. The average surface pressure on mars is only 1% of that of the Earths.

Its surface features are not the only similarity Mars has with the earth. It is also the only planet in the Solar system with seasons like our own. This is due to its similar axial tilt of the two planets. It is theorised that Mars may have been much more habitable than it is today, and could have been very similar to the earth given the right conditions. However

the ceasing of the internal dynamo, lack of magnetic field and thin atmosphere have rendered the planet almost completely geologically dead. The thin atmosphere prevents heat transfer across the martian surface, the lack of magnetic field provides little insulation from the solar wind, and there is no apparent volcanic activity to regulate the recycling of minerals between the surface and interior of the planet.

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DAY LENGTH

242EarthDays

DAY LENGTH

1.029EarthDays

The solar day (or sol) on Mars is only slightly longer than an Earth day: 24 hours, 39 minutes, and 35.244 seconds.

A Martian year is equal to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours.

YEAR LENGTH

687EarthDays

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PLANET STATS

Mars lost its magnetosphere 4 billion years ago, so the solar wind interacts directly with the Martian ionosphere, lowering the atmospheric density by stripping away atoms from the outer layer. The surface pressure of Mars at its thickest is equal to the pressure found 35 km above Earth’s surface.

Mars has approximately half the radius of Earth. It is less dense than Earth, having about 15% of Earth’s volume and 11% of the mass.

ATMOSPHERE

N

Ar

O2

CO

NONe

Xe

Kr

HDO

H O2

CH4

H O2 2

H2

6,746 Km

DIAMETER

29

PLANET STATS

Of all the planets in the Solar System, the seasons of Mars are the most Earth-like, due to the similar tilts of the two planets’ rotational axes. Martian surface temperatures vary from lows of about -87 °C (-125 °F) during the polar winters to highs of up to -5 °C (23 °F) in summers.

The surface of Mars as imaged by the Viking 2 surfface probe

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-46°C

SURFACE TEMPERATURE

PLANET STATS

PLANET STATS

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OBJECTIVE 4Jupiter is the fifth planet from the sun. It is the largest planet in our solar system and has over the double the mass of all the other planets of the solar system combined. Jupiter’s mass is mainly composed of Hydrogen and Helium, leading to its classification as a Gas Giant. Jupiter has one of the most distinct appearances of all the solar systems planets. Its atmosphere is divided into vivid stripes, the result of turbulent

storms in the planets upper atmosphere. These stripes are composed of clouds of ammonia crystals, and its is the interaction between these clouds that causes the storms. The most prominent feature is the planets ‘Great Red Spot’ a giant storm larger than the diameter of the earth that has existed since at least since the 17th century when it was first observed. Some mathematical models suggest that the storm is stable and may be a permanent planetary feature.

While Jupiter’s outer atmosphere is over 90% Hydrogen, its interior contains a much more varied selection of elements, in both gaseous, liquid and solid form. It is believed that the composition of Jupiter’s outer atmosphere is very similar to that of a primordial solar nebula, due to its similarity to the elements found present in the Sun.

33

JUPITER

Jupiter’s mass is so immense that its barycentre, the central point at which the mass of two orbiting objects balance each other, isn’t centralised with the sun as with other planets. It is instead found above the suns surface. Despite this huge mass, Jupiter is actually less dense than the earth.

It is theorised that Jupiter does have a dense solid core, surrounded by liquid metallic hydrogen. The majority of the planet however is comprised of its atmosphere, and Jupiter has the largest planetary atmosphere of any body in the solar system, which reaches over 5000 km in altitude from the planets designated surface. The ability of Jupiter to keep such an immense atmosphere may be due to its immense magnetic field, which at fourteen times the strength of the Earth’s is the strongest in the solar system. Jupiter’s gravitational

well is also immense, and it has lead to Jupiter being referred to as the Solar systems Vacuum cleaner, as it tends to pull in and capture numerous comets and asteroids that would otherwise have been on a collision course with the terrestrial planets.

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DAY LENGTH

242EarthDays

DAY LENGTH

0.415EarthDays

Jupiter’s rotation is the fastest of all the Solar System’s planets, completing a rotation on its axis in slightly less than ten hours.

Jupiter is the only planet that has a centre of mass with the Sun that lies outside the volume of the Sun, though by only 7% of the Sun’s radius. It completes an orbit every 11.86 year.

YEAR LENGTH

4,332EarthDays

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PLANET STATS

Jupiter has the largest planetary atmosphere in the Solar System, spanning over 5000 km in altitude. As Jupiter has no surface, the base of its atmosphere is usually considered to be the point at which atmospheric pressure is equal to 10 bars, or ten times surface pressure on Earth.

Jupiter is composed primarily of gaseous and liquid matter. It is the largest of four gas giants as well as the largest planet in the solar system with a diameter of 142,984 km at its equator.

ATMOSPHERE

He

HDCH

H O2

NH SH4

4

C H62

NH3 142,984 Km

DIAMETER

37

PLANET STATS

The temperature and pressure inside Jupiter increase steadily toward the core.

Detailed image of Jupiter’s most distinguishing feature,

The Great Red Spot

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-148 °C

SURFACE TEMPERATURE

PLANET STATS

PLANET STATS

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OBJECTIVE 5Saturn is the sixth planet in the Solar System. A gas giant, it is the second largest planet after Jupiter. Its dense rocky core is surrounded by metallic hydrogen, liquid hydrogen and its 1000km thick gaseous atmosphere. Saturn has an extremely hot interior, despite its distance from the sun, and it radiates over twice as much energy into space as it receives from the sun.

The atmospheric composition of Saturn is very similar to that of Jupiter, with 93% of the outer atmosphere being composed of molecular hydrogen. One main difference however is the relative lack of Helium in comparison. Saturn’s atmosphere also displays banded patterns similar to those found on Jupiter, however they are much more feint. Instead, Saturn’s prominent feature is its rings. Although the other gaseous planets all have a ring system of some sort, Saturn’s are the most extensive, reaching as far as 120,700km from the planets equator. The rings are composed of millions of individual objects ranging from a few millimetres, to over 10 meters in diameter. Over 90% of these objects are composed of water ice. The exact origins of these rings is unknown, however theories suggest they could be the remains of a destroyed moon, or

41

SATURN

the original nebular material that came together to form the planet.

Saturn has been known since prehistoric times. In ancient times, it was the most distant of the five known planets in the solar system (excluding Earth) and thus a major character in various mythologies. Babylonian astronomers systematically observed and recorded the movements of Saturn. In ancient Roman mythology, the god Saturnus, from which the planet takes its name, was the god of the agricultural and harvest sector. The Romans considered Saturnus the equivalent of the Greek god Cronus. The Greeks had made the outermost planet sacred to Cronus, and the Romans followed suit.

Ptolemy, a Greek living in Alexandria, observed an opposition of Saturn, which was the basis for his determination of the

elements of its orbit. In Hindu astrology, there are nine astrological objects, known as Navagrahas. Saturn, one of them, is known as “Shani”, judges everyone based on the good and bad deeds performed in life. In the 5th century CE, the Indian astronomical text Surya Siddhanta estimated the diameter of Saturn as 73,882 miles, an error of less than 1% from the currently accepted value of 74,580 miles, for which there exist several possible explanations. Ancient Chinese and Japanese culture designated the planet Saturn as the earth star. This was based on Five Elements which were traditionally used to classify natural elements.

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DAY LENGTH

242EarthDays

DAY LENGTH

0.72EarthDays

DAY LENGTH

0.72EarthDays

The visible features on Saturn rotate at different rates depending on latitude and multiple rotation periods have been assigned to various region

With an average orbital speed of 9.69 km/s, it takes Saturn 10,759 Earth days (or about 29½ years), to finish one revolution around the Sun

YEAR LENGTH

10,747EarthDays

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PLANET STATS

Though there is no direct information about Saturn’s internal structure, it is thought that its interior is similar to that of Jupiter, having a small rocky core surrounded mostly by hydrogen and helium.

Due to a combination of its lower density, rapid rotation and fluid state, Saturn is an oblate spheroid; that is, it is flattened at the poles and bulges at the equator. Saturn is only 95 Earth masses, compared to Jupiter, which is 318 times the mass of the Earth but only about 20% larger than Saturn.

ATMOSPHERE

HeNH3

CH4

C H62

HD

NH SH4

120,536 Km

DIAMETER

45

PLANET STATS

-178 °C

SURFACE TEMPERATURE

Saturn has a very hot interior, reaching 11,700 °C at the core, and it radiates 2.5 times more energy into space than it receives from the Sun. Most of this extra energy is generated by the Kelvin–Helmholtz mechanism (slow gravitational compression), but this alone may not be sufficient to explain Saturn’s heat production

PLANET STATS

Detailed image of Saturn’s rings

46

PLANET STATS

48

OBJECTIVE 6Uranus is the seventh planet in the solar system. It was officially discovered in 1781 by Sir William Herschel, and was the first planet to be discovered by telescope, however numerous sightings are recorded prior to this, the earliest being in 1690. It was originally classified as a comet by Herschel, until fellow astronomers plotted the planets full orbit and Herschel was asked to officially give a name to his new planet 1983.

Uranus is unique in our solar system in terms of its rotation. Rather than its poles being perpendicular to its rotation around the sun, its axial tilt is 97.77 degrees, almost parallel with the plane of the solar system. This means the planet appears to spin sideways in comparison to the other planets. Its moons and rings still orbit the planets equator on this extreme tilt, looking like target rings around the planet when viewed from earth. The extreme tilt of the planet means its poles get more exposure to the sun than its equator, but due to the internal mechanisms of the planet, the equator is still its hottest area.

Although Uranus has almost 15 times the mass of the earth, it has the smallest mass of the giant outer planets. Because its solid mass is made up mainly of ices such as water and methane that

49

URANUS

surround a small iron silicate core, it is classified as an ‘Ice giant’. 90% of Uranus’ mass is comprised of this icy mantle layer, and its atmospheric mass is relatively small in comparison. This icy layer isn’t a solid mass like the ice found on earth. It is instead a highly conductive water-ammonia ocean. Above this, Uranus’ atmosphere consists manly of molecular hydrogen, helium and methane. It is this abundance of methane that gives Uranus it’s distinctive cyan colouring

Uranus has a complex planetary ring system. Its thirteen rings are made up of extremely small, dark particles and all but two of these rings are extremely narrow, being only a few kilometres wide. The objects that make up these rings are also extremely small, the largest being only a fraction of a meter wide. The rings are believed to be quite young

and were not formed at the same time as the planet. The most likely origin is that they are the remains of one or more moons that were destroyed by an impact.

The magnetic field of Uranus is also quite unusual. Rather than being close in alignment to the planets rotational axis, it its rotated 59° from this. This magnetic field also does not originate from the planets centre as with the other planets, and is displaced more towards the southern rotational pole of the planet. This gives the planet a very asymmetric magnetic field, which is much stronger in the northern hemisphere than in the south.

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DAY LENGTH

242EarthDays

DAY LENGTH

0.72EarthDays

DAY LENGTH

0.75EarthDays

The visible features on Saturn rotate at different rates depending on latitude and multiple rotation periods have been assigned to various region

Uranus revolves around the Sun once every 84 Earth years. Its average distance from the Sun is roughly 3 billion km.

YEAR LENGTH

30,685EarthDays

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PLANET STATS

Although there is no well-defined solid surface within Uranus’s interior, the outermost part of Uranus’s gaseous envelope that is accessible to remote sensing is called its atmosphere. The Uranian atmosphere can be divided into three layers: the troposphere, the stratosphere and the thermosphere.

Uranus’ north and south poles lie where most other planets have their equators. Seen from Earth, Uranus’s rings can sometimes appear to circle the planet like an archery target and its moons revolve around it like the hands of a clock.

ATMOSPHERE

NH3

HD

He

CH

H O

4

NH SH4

2

51,118 Km

DIAMETER

53

PLANET STATS

Uranus’s internal heat appears markedly lower than that of the other giant planets; in astronomical terms, it has a low thermal flux. Why Uranus’s internal temperature is so low is still not understood. Neptune, which is Uranus’s near twin in size and composition, radiates 2.61 times as much energy into space as it receives from the Sun

Early Hubble telescope image of Uranus with its rings

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-216 °C

SURFACE TEMPERATURE

PLANET STATS

PLANET STATS

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OBJECTIVE 7Neptune is the furthest planet from the sun and the eighth planet of the solar system. It was the first planet to be found my mathematical prediction rather than though a direct observation. Its effect on the orbit of Uranus lead to its prediction, and then discovery in 1846.

Neptune is one of the four giant outer planets. Like Jupiter and Saturn, its atmosphere is comprised mainly of

hydrogen and helium, however its icy mantle of a highly conductive water-ammonia ocean means it is classified as an ‘ice giant’ rather than a gas giant. It also contains a large proportion of methane in its atmosphere which, along with other atmospheric elements, is responsible for its vivid blue colouring. Its atmosphere is much more featured than that of Uranus, due to the abundance of visible weather patterns. Winds speeds can reach up to 600 meters a second and the majority of these move in the opposite direction to the planets rotation. It is believed that the active weather system is a result of the planets internal heat.

Despite Neptune being almost two billion miles further from the sun than Uranus is, the two planets have a similar surface temperature. It is believed that

57

NEPTUNE

reactions within the centre of the planet are responsible for the production of massive amounts of heat, leading to the convection currents that create weather systems.

Neptune was the farthest known planet for almost 100 years until the discovery of Pluto in 1930. It only regained this title in 2006, when the International Astronomical Union finally defined the word planet, and Pluto was reclassified as a dwarf planet.

Neptune’s size makes it an intermediate class of planet between the Earth and Jupiter. It has seventeen times the mass of the earth, and is 1/19th the mass of Jupiter.

The term ‘Neptunes’ is used to describe extrasolar planets that are similar in mass to the planet, just as the terms ‘Jupiters’

and ‘Earths’ are used to describe other sized planets. Neptune, along with Jupiter, is the only planet with a surface gravity higher than that of the Earth.

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PLANET STATS

DAY LENGTH

242EarthDays

DAY LENGTH

0.72EarthDays

DAY LENGTH

0.67EarthDays

The axial tilt of Neptune is 28.32°, which is similar to the tilts of Earth (23°) and Mars (25°). As a result, this planet experiences similar seasonal changes. The long orbital period of Neptune means that the seasons last for forty Earth years. Its sidereal rotation period (day) is roughly 16.11 hours

The average distance between Neptune and the Sun is 4.50 billion km (about 30.1 AU), and it completes an orbit on average every 164.79 years, subject to a variability of around ±0.1 years.

YEAR LENGTH

60,155EarthDays

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PLANET STATS

At high altitudes, Neptune’s atmosphere is 80% hydrogen and 19% helium. A trace amount of methane is also present. As with Uranus, this absorption of red light by the atmospheric methane is part of what gives Neptune its blue hue.

With a mass of 1.0243×1026 kg, Neptune is an intermediate body between Earth and the larger gas giants: its mass is seventeen times that of the Earth but just 1/19th that of Jupiter.

ATMOSPHERE

NH3

HD

HeCH

H O

4

NH SH4

2

C H62

49,532 Km

DIAMETER

61

Neptune’s weather is characterized by extremely dynamic storm systems, with winds reaching speeds of almost 600 m/s—nearly attaining supersonic flow. In 2007 it was discovered that the upper troposphere of Neptune’s south pole was about 10 °C warmer than the rest of Neptune, which averages approximately -200 °C (70 K)

Early Hubble telescope image of Neptune

-214 °C

SURFACE TEMPERATURE

62

PLANET STATS

PLANET STATS

THEDWARFPLANETS

OBJECTIVE 8Ceres, formally 1 Ceres, is the smallest identified dwarf planet in the Solar System and the only one in the asteroid belt. With a diameter of about 950 km, Ceres is by far the largest and most-massive asteroid, comprising about a third of the mass of the asteroid belt.Discovered on 1 January 1801 by Giuseppe Piazzi,it was the first asteroid to be identified. It is named after Cerës, the Roman goddess of growing plants, the

66

harvest, and motherly love.

The Cererian surface is probably a mixture of water ice and various hydrated minerals such as carbonates and clays. Ceres appears to be differentiated into a rocky core and icy mantle, and may harbour an ocean of liquid water under its surface.

From Earth, the apparent magnitude of Ceres ranges from 6.7 to 9.3, and hence even at its brightest it is still too dim to be seen with the naked eye except under extremely dark skies. On 27 September 2007, NASA launched the Dawn space probe to explore Vesta (2011–2012) and Ceres (2015).

67

CERES

OBJECTIVE 9Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System (after Eris) and the tenth-most-massive body observed directly orbiting the Sun. Originally classified as the ninth planet from the Sun, Pluto was recategorized as a dwarf planet and plutoid due to the discovery that it is one of several large bodies within the newly charted Kuiper belt.

From its discovery in 1930 until 2006, Pluto was classified as a planet. In the late 1970s, following the discovery of minor

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planet 2060 Chiron in the outer Solar System and the recognition of Pluto’s relatively low mass, its status as a major planet began to be questioned. In the late 20th and early 21st century, many objects similar to Pluto were discovered in the outer Solar System, notably the scattered disc object Eris in 2005, which is 27% more massive than Pluto. On August 24, 2006, the International Astronomical Union (IAU) defined what it means to be a “planet” within the Solar System. This definition excluded Pluto as a planet and added it as a member of the new category “dwarf planet” along with Eris and Ceres. After the reclassification, Pluto was added to the list of minor planets and given the number 134340. A number of scientists continue to hold that Pluto should be classified as a planet.

69

PLUTO

OBJECTIVE 10Eris, formal designation 136199 Eris, is the most massive known dwarf planet in the Solar System and the ninth most massive body known to orbit the Sun directly. It is estimated to be approximately 2300–2400 km in diameter, and 27% more massive than Pluto or about 0.27% of the Earth’s mass.

Eris was discovered in January 2005 by a Palomar Observatory-based team led by Mike Brown, and its identity was verified later that year. It is a trans-Neptunian object (TNO) and a member of a high-eccentricity population known as the scattered disc. It has one known moon, Dysnomia. As of 2011, its distance from the Sun is 96.6 AU, roughly three times that of Pluto. With the exception of some comets, Eris and Dysnomia are currently the most distant known natural objects in the Solar System.

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Because Eris appeared to be larger than Pluto, its discoverers and NASA initially described it as the Solar System’s tenth planet. This, along with the prospect of other similarly sized objects being discovered in the future, motivated the International Astronomical Union (IAU) to define the term planet for the first time. Under the IAU definition approved on August 24, 2006, Eris is a “dwarf planet” along with Pluto, Ceres, Haumea and Makemake.

In 2010, preliminary results from observations of a stellar occultation by Eris on November 6 suggested that its diameter may be only 2,326 km, which would make it essentially the same size as Pluto.[18] Given the error bars in the different size estimates, it is currently uncertain whether Eris or Pluto has the larger diameter.

71

ERIS

OBJECTIVE 11Haumea, formal designation 136108 Haumea, is a dwarf planet in the Kuiper belt. It is the fourth-largest dwarf planet in the Solar System, one-third the mass of Pluto. It was discovered in 2004 by a team headed by Mike Brown of Caltech at the Palomar Observatory in the United States and, in 2005, by a team headed by J. L. Ortiz at the Sierra Nevada Observatory in Spain, though the latter claim has been contested. On September 17, 2008, it was designated a dwarf planet by the International

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Astronomical Union (IAU) and named after Haumea, the Hawaiian goddess of childbirth.

Haumea’s extreme elongation makes it unique among known dwarf planets. Although its shape has not been directly observed, calculations from its light curve suggest it is an ellipsoid, with its major axis twice as long as its minor. Nonetheless, its gravity is believed sufficient for it to have relaxed into hydrostatic equilibrium, thereby meeting the definition of a dwarf planet. This elongation, along with its unusually rapid rotation, high density, and high albedo (from a surface of crystalline water ice), are thought to be the results of a giant collision, which left Haumea the largest member of a collisional family that includes several large trans-Neptunian objects (TNOs) and its two known moons.

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HAUMEA

136108

OBJECTIVE 12Makemake, formally designated (136472) Makemake, is the third-largest known dwarf planet in the Solar System and one of the two largest Kuiper belt objects (KBO) in the classical KBO population. Its diameter is roughly three-quarters that of Pluto. Makemake has no known satellites, which makes it unique among the largest KBOs. Its extremely low average temperature, about 30 K (-243.2 °C), means its surface is covered

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with methane, ethane, and possibly nitrogen ices.

Initially known as 2005 FY9 and later given the minor planet number 136472, it was discovered on March 31, 2005, by a team led by Michael Brown, and announced on July 29, 2005. Its name derives from the Rapanui god Makemake. On June 11, 2008, the International Astronomical Union (IAU) included Makemake in its list of potential candidates to be given “plutoid” status, a term for dwarf planets beyond the orbit of Neptune that would place the object alongside Pluto, Haumea and Eris. Makemake was formally classified as a plutoid in July 2008.

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MAKEMAKE

136472

This is your space to document your part in the story of the solar system.

Use the rest of this book to keep track of all the things you encounter on your journey, memories, and anything else you like. We’ve included a mini printer with your mission supplies so get documenting!

MISSIONLOG

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