Planet Earth 



Earth is the third planet from the Sun and is the largest of the terrestrial planets. The Earth is the only planet in our solar system not to be named after a Greek or Roman deity. The Earth was formed approximately 4.54 billion years ago and is the only known planet to support life.

Planet Profile

Mass: 5,972,190,000,000,000 billion kg
Equatorial Diameter: 12,756 km
Polar Diameter: 12,714 km
Equatorial Circumference: 40,030 km
Known Moons: 1
Notable Moons: The Moon
Orbit Distance: 149,598,262 km (1 AU)
Orbit Period: 365.26 Earth days
Surface Temperature: -88 to 58°C

Facts About The Earth

The Earth’s rotation is gradually slowing:
This deceleration is happening almost imperceptibly, at approximately 17 milliseconds per hundred years, although the rate at which it occurs is not perfectly uniform. This has the effect of lengthening our days, but it happens so slowly that it could be as much as 140 million years before the length of a day will have increased to 25 hours.

The Earth was once believed to be the centre of the universe:
Due to the apparent movements of the Sun and planets in relation to their viewpoint, ancient scientists insisted that the Earth remained static, whilst other celestial bodies travelled in circular orbits around it. Eventually, the view that the Sun was at the centre of the universe was postulated by Copernicus, though this is also not the case.

Earth distance from sun is 149.6 million km 

Earth has a powerful magnetic field:
This phenomenon is caused by the nickel-iron core of the planet, coupled with its rapid rotation. This field protects the Earth from the effects of solar wind.

There is only one natural satellite of the planet Earth:
As a percentage of the size of the body it orbits, the Moon is the largest satellite of any planet in our solar system. In real terms, however, it is only the fifth largest natural satellite.

Earth is the only planet not named after a god:
The other seven planets in our solar system are all named after Roman gods or goddesses. Although only Mercury, Venus, Mars, Jupiter and Saturn were named during ancient times, because they were visible to the naked eye, the Roman method of naming planets was retained after the discovery of Uranus and Neptune.

Of all the planets in our solar system, the Earth has the greatest density:
This varies according to the part of the planet; for example, the metallic core is denser than the crust. The average density of the Earth is approximately 5.52 grams per cubic centimeter.

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Planet Mercury


Mercury is the closest planet to the Sun and due to its proximity it is not easily seen except during twilight. For every two orbits of the Sun, Mercury completes three rotations about its axis and up until 1965 it was thought that the same side of Mercury constantly faced the Sun. Thirteen times a century Mercury can be observed from the Earth passing across the face of the Sun in an event called a transit, the next will occur on the 9th May 2016.

Planet Profile

Mass: 330,104,000,000,000 billion kg (0.055 x Earth)
Equatorial Diameter: 4,879
Polar Diameter: 4,879
Equatorial Circumference: 15,329 km
Known Moons: none
Notable Moons: none
Orbit Distance: 57,909,227 km (0.39 AU)
Orbit Period: 87.97 Earth days
Surface Temperature: -173 to 427°C
First Record: 14th century BC
Recorded By: Assyrian astronomers

Facts About Mercury

A year on Mercury is just 88 days long:
One solar day (the time from noon to noon on the planet’s surface) on Mercury lasts the equivalent of 176 Earth days while the sidereal day (the time for 1 rotation in relation to a fixed point) lasts 59 Earth days. Mercury is nearly tidally locked to the Sun and over time this has slowed the rotation of the planet to almost match its orbit around the Sun. Mercury also has the highest orbital eccentricity of all the planets with its distance from the Sun ranging from 46 to 70 million km.

Mercury is the smallest planet in the Solar System:
One of five planets visible with the naked eye a, Mercury is just 4,879 Kilometres across its equator, compared with 12,742 Kilometres for the Earth.

Mercury is the second densest planet:
Even though the planet is small, Mercury is very dense. Each cubic centimetre has a density of 5.4 grams, with only the Earth having a higher density. This is largely due to Mercury being composed mainly of heavy metals and rock.

Mercury has wrinkles:
As the iron core of the planet cooled and contracted, the surface of the planet became wrinkled. Scientist have named these wrinkles, Lobate Scarps. These Scarps can be up to a mile high and hundreds of miles long.

Mercury has a molten core: 
In recent years scientists from NASA have come to believe the solid iron core of Mercury could in fact be molten. Normally the core of smaller planets cools rapidly, but after extensive research, the results were not in line with those expected from a solid core. Scientists now believe the core to contain a lighter element such as sulphur, which would lower the melting temperature of the core material. It is estimated Mercury’s core makes up 42% of its volume, while the Earth’s core makes up 17%.

Mercury is only the second hottest planet:
Despite being further from the Sun, Venus experiences higher temperatures. The surface of Mercury which faces the Sun sees temperatures of up to 427°C, whilst on the alternate side this can be as low as -173°C. This is due to the planet having no atmosphere to help regulate the temperature.

Mercury Distance from the sun : 57.91 million km

Mercury is the most cratered planet in the Solar System:
Unlike many other planets which “self-heal” through natural geological processes, the surface of Mercury is covered in craters. These are caused by numerous encounters with asteroids and comets. Most Mercurian craters are named after famous writers and artists. Any crater larger than 250 kilometres in diameter is referred to as a Basin. The Caloris Basin is the largest impact crater on Mercury covering approximately 1,550 km in diameter and was discovered in 1974 by the Mariner 10 probe.

Only two spacecraft have ever visited Mercury:
Owing to its proximity to the Sun, Mercury is a difficult planet to visit. During 1974 and 1975 Mariner 10 flew by Mercury three times, during this time they mapped just under half of the planet’s surface. On August 3rd 2004, the Messenger probe was launched from Cape Canaveral Air Force Station, this was the first spacecraft to visit since the mid 1970’s.

Mercury is named for the Roman messenger to the gods:
The exact date of Mercury’s discovery is unknown as it pre-dates its first historical mention, one of the first mentions being by the Sumerians around in 3,000 BC.

Mercury has an atmosphere (sort of):
Mercury has just 38% the gravity of Earth, this is too little to hold on to what atmosphere it has which is blown away by solar winds. However while gases escape into space they are constantly being replenished at the same time by the same solar winds, radioactive decay and dust caused by micrometeorites

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Planet Venus


Venus is the second planet from the Sun and is the second brightest object in the night sky after the Moon. Named after the Roman goddess of love and beauty, Venus is the second largest terrestrial planet and is sometimes referred to as the Earth’s sister planet due the their similar size and mass. The surface of the planet is obscured by an opaque layer of clouds made up of sulfuric acid.

Planet Profile

Mass: 4,867,320,000,000,000 billion kg (0.815 x Earth)
Equatorial Diameter: 12,104 km
Polar Diameter: 12,104 km
Equatorial Circumference: 38,025 km
Known Moons: none
Notable Moons: none
Orbit Distance: 108,209,475 km (0.73 AU)
Orbit Period: 224.70 Earth days
Surface Temperature: 462 °C
First Record: 17th century BC
Recorded By: Babylonian astronomers

Facts About Venus

A day on Venus lasts longer than a year:
It takes 243 Earth days to rotate once on its axis. The planet’s orbit around the Sun takes 225 Earth days, compared to the Earth’s 365.

Venus is often called the Earth’s sister planet:
The Earth and Venus are very similar in size with only a 638 km difference in diameter, Venus having 81.5% of the Earth’s mass. Both also have a central core, a molten mantle and a crust.

Venus rotates counter-clockwise:
Also known as retrograde rotation. A possible reason might be a collision in the past with an asteroid or other object that caused the planet to alter its rotational path. It also differs from most other planets in our solar system by having no natural satellites.

Venus is the second brightest object in the night sky:
Only the Moon is brighter. With a magnitude of between -3.8 to -4.6 Venus is so bright it can be seen during daytime on a clear day.

Atmospheric pressure on Venus is 92 times greater than the Earth’s:
While its size and mass are similar to Earth, the small asteroids are crushed when entering its atmosphere, meaning no small craters lie on the surface of the planet. The pressure felt by a human on the surface would be equivalent to that experienced deep beneath the sea on Earth.

Venus is also known as the Morning Star and the Evening Star:
Early civilisations thought Venus was two different bodies, called Phosphorus and Hesperus by the Greeks, and Lucifer and Vesper by the Romans. This is because when its orbit around the Sun overtakes Earth’s orbit, it changes from being visible after sunset to being visible before sunrise. Mayan astronomers made detailed observations of Venus as early as 650 AD.

Venus is the hottest planet in our solar system:
The average surface temperature is 462 °C, and because Venus does not tilt on its axis, there is no seasonal variation. The dense atmosphere of around 96.5 percent carbon dioxide traps heat and causes a greenhouse effect.

Venus Distance from the Sun is 108.2 million km

A detailed study of Venus is currently underway:
In 2006, the Venus Express space shuttle was sent into orbit around Venus by the European Space Agency, and is sending back information about the planet. Originally planned to last five hundred Earth days, the mission has been extended several times. More than 1,000 volcanoes or volcanic centres larger than 20 km have been found on the surface of Venus.

The Russians sent the first mission to Venus:
The Venera 1 space probe was launched in 1961, but lost contact with base. The USA also lost their first probe to Venus, Mariner 1, although Mariner 2 was able to take measurements of the planet in 1962. The Soviet Union’s Venera 3 was the first man-made craft to land on Venus in 1966.

At one point it was thought Venus might be a tropical paradise:
The dense clouds of sulphuric acid surrounding Venus make it impossible to view its surface from outside its atmosphere. It was only when radio mapping was developed in the 1960s that scientists were able to observe and measure the extreme temperatures and hostile environment. It is thought Venus did once have oceans but these evaporated as the planets temperature increased.

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Planet Mars


Mars is the fourth planet from the Sun. Named after the Roman god of war, and often described as the “Red Planet” due to its reddish appearance. Mars is a terrestrial planet with a thin atmosphere composed primarily of carbon dioxide.

Mars Planet Profile

Mass:641 x 10^24 kg (0.107 x Earth)

Equatorial Diameter: 6,805 km

Polar Diameter:6,755 km

Equatorial Circumference:21,297 km

Known Moons: Phobos & Deimos

Orbit Distance: 227,943,824 km (1.38 AU)

Orbit Period: 686.98 Earth days (1.88 Earth years)

Surface Temperature:  -87 to -5 °C

First Record: 2nd millennium BC

Recorded By: Egyptian astronomers

Facts About Mars

Mars and Earth have approximately the same landmass:
Even though Mars has only 15% of the Earth’s volume and just over 10% of the Earth’s mass, around two thirds of the Earth’s surface is covered in water. Martian surface gravity is only 37% of the Earth’s (meaning you could leap nearly three times higher on Mars).

Mars is home to the tallest mountain in the solar system:
Olympus Mons, a shield volcano, is 21km high and 600km in diameter. Despite having formed over billions of years, evidence from volcanic lava flows is so recent many scientists believe it could still be active.

Only 18 missions to Mars have been successful
As of September 2014 there have been 40 missions to Mars, including orbiters, landers and rovers but not counting flybys. The most recent arrivals include the Mars Curiosity mission in 2012, the MAVEN mission, which arrived on September 22, 2014, followed by the Indian Space Research Organization’s MOM Mangalyaan orbiter, which arrived on September 24, 2014. The next missions to arrive will be the European Space Agency’s ExoMars mission, comprising an orbiter, lander, and a rover, followed by NASA’s InSight robotic lander mission, slated for launch in March 2016 and a planned arrival in September, 2016.

Mars has the largest dust storms in the solar system:
They can last for months and cover the entire planet. The seasons are extreme because its elliptical (oval-shaped) orbital path around the Sun is more elongated than most other planets in the solar system.

On Mars the Sun appears about half the size as it does on Earth:
At the closest point to the Sun, the Martian southern hemisphere leans towards the Sun, causing a short, intensely hot summer, while the northern hemisphere endures a brief, cold winter: at its farthest point from the Sun, the Martian northern hemisphere leans towards the Sun, causing a long, mild summer, while the southern hemisphere endures a lengthy, cold winter.

Mars Distance from the Sun is 227.9 million km

Pieces of Mars have fallen to Earth:
Scientists have found tiny traces of Martian atmosphere within meteorites violently ejected from Mars, then orbiting the solar system amongst galactic debris for millions of years, before crash landing on Earth. This allowed scientists to begin studying Mars prior to launching space missions.

Mars takes its name from the Roman god of war:
The ancient Greeks called the planet Ares, after their god of war; the Romans then did likewise, associating the planet’s blood-red colour with Mars, their own god of war. Interestingly, other ancient cultures also focused on colour – to China’s astronomers it was ‘the fire star’, whilst Egyptian priests called on ‘Her Desher’, or ‘the red one’. The red colour Mars is known for is due to the rock and dust covering its surface being rich in iron.

There are signs of liquid water on Mars:
For years Mars has been known to have water in the form of ice. The first signs of trickling water are dark stripes or stains on crater wall and cliffs seen in satellite images. Due to Mars’ atmosphere this water would have to be salty to prevent it from freezing or vaporising.

One day Mars will have a ring:
In the next 20-40 million years Mars’ largest moon Phobos will be torn apart by gravitational forces leading to the creation of a ring that could last up to 100 million years.

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Planet Jupiter


Jupiter is the fifth planet out from the Sun, and is two and a half times more massive than all the other planets in the solar system combined. It is made primarily of gases and is therefore known as a “gas giant”.

Jupiter Planet Profile

Mass: 1,898,130,000,000,000,000 billion kg (317.83 x Earth)
Equatorial Diameter: 142,984 km
Polar Diameter: 133,709 km
Equatorial Circumference: 439,264 km
Known Moons: 67
Notable Moons: Io, Europa, Ganymede & Callisto
Known Rings: 4
Orbit Distance: 778,340,821 km (5.20 AU)
Orbit Period: 4,332.82 Earth days (11.86 Earth years)
Surface Temperature: -108°C
First Record: 7th or 8th century BC
Recorded By: Babylonian astronomers

Facts About Jupiter

Jupiter is the fourth brightest object in the solar system:
Only the Sun, Moon and Venus are brighter. It is one of five planets visible to the naked eye from Earth.

The ancient Babylonians were the first to record their sightings of Jupiter:
This was around the 7th or 8th century BC. Jupiter is named after the king of the Roman gods. To the Greeks, it represented Zeus, the god of thunder. The Mesopotamians saw Jupiter as the god Marduk and patron of the city of Babylon. Germanic tribes saw this planet as Donar, or Thor.

Jupiter has the shortest day of all the planets:
It turns on its axis once every 9 hours and 55 minutes. The rapid rotation flattens the planet slightly, giving it an oblate shape.

Jupiter orbits the Sun once every 11.8 Earth years:
From our point of view on Earth, it appears to move slowly in the sky, taking months to move from one constellation to another.

Jupiter Distance from the Sun 778.5 million km

Jupiter has unique cloud features:
The upper atmosphere of Jupiter is divided into cloud belts and zones. They are made primarily of ammonia crystals, sulfur, and mixtures of the two compounds.

The Great Red Spot is a huge storm on Jupiter:
It has raged for at least 350 years. It is so large that three Earths could fit inside it.

Jupiter’s interior is made of rock, metal, and hydrogen compounds:
Below Jupiter’s massive atmosphere (which is made primarily of hydrogen), there are layers of compressed hydrogen gas, liquid metallic hydrogen, and a core of ice, rock, and metals.

Jupiter’s moon Ganymede is the largest moon in the solar system:
Jupiter’s moons are sometimes called the Jovian satellites, the largest of these are Ganymeade, Callisto Io and Europa. Ganymeade measures 5,268 km across, making it larger than the planet Mercury.

Jupiter has a thin ring system:
Its rings are composed mainly of dust particles ejected from some of Jupiter’s smaller worlds during impacts from incoming comets and asteroids. The ring system begins some 92,000 kilometres above Jupiter’s cloud tops and stretches out to more than 225,000 km from the planet. They are between 2,000 to 12,500 kilometres thick.

Eight spacecraft have visited Jupiter:
Pioneer 10 and 11, Voyager 1 and 2, Galileo, Cassini, Ulysses, and New Horizons missions. The Juno mission is its way to Jupiter and will arrive in July 2016. Other future missions may focus on the Jovian moons Europa, Ganymede, and Callisto, and their subsurface oceans.

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Planet Saturn


Saturn is the sixth planet from the Sun and the most distant that can be seen with the naked eye. It is best known for its fabulous ring system that was discovered in 1610 by the astronomer Galileo Galilei.

Planet Profile

Mass: 568,319,000,000,000,000 billion kg (95.16 x Earth)
Equatorial Diameter: 120,536 km
Polar Diameter: 108,728 km
Equatorial Circumference: 365,882 km
Known Moons: 62
Notable Moons: Titan, Enceladus, Iapetus, Mimas,  Tethys, Dione & Rhea.
Known Rings: 30+ (7 Groups)
Orbit Distance: 1,426,666,422 km (9.58 AU)
Orbit Period: 10,755.70 Earth days (29.45 Earth years)
Surface Temperature: -139 °C
First Record: 8th century BC
Recorded By: Assyrians

Facts About Saturn

Saturn can be seen with the naked eye:
It is the fifth brightest object in the solar system and is also easily studied through binoculars or a small telescope.

Saturn was known to the ancients, including the Babylonians and Far Eastern observers:
It is named for the Roman god Saturnus, and was known to the Greeks as Cronus.

Saturn is the flattest planet:
Its polar diameter is 90% of its equatorial diameter, this is due to its low density and fast rotation. Saturn turns on its axis once every 10 hours and 34 minutes giving it the second-shortest day of any of the solar system’s planets.

Saturn orbits the Sun once every 29.4 Earth years:
Its slow movement against the backdrop of stars earned it the nickname of “Lubadsagush” from the ancient Assyrians. The name means “oldest of the old”.

Saturn Distance from the Sun is 1.433 billion km

Saturn’s upper atmosphere is divided into bands of clouds:
The top layers are mostly ammonia ice. Below them, the clouds are largely water ice. Below are layers of cold hydrogen and sulfur ice mixtures.

Saturn has oval-shaped storms similar to Jupiter’s:
The region around its north pole has a hexagonal-shaped pattern of clouds. Scientists think this may be a wave pattern in the upper clouds. The planet also has a vortex over its south pole that resembles a hurricane-like storm.

Saturn is made mostly of hydrogen:
It exists in layers that get denser farther into the planet. Eventually, deep inside, the hydrogen becomes metallic. At the core lies a hot interior.

Saturn has the most extensive rings in the solar system:
The Saturnian rings are made mostly of chunks of ice and small amounts of carbonaceous dust. The rings stretch out more than 120,700 km from the planet, but are are amazingly thin: only about 20 meters thick.

Saturn has 150 moons and smaller moonlets:
All are frozen worlds. The largest moons are Titan and Rhea. Enceladus appears to have an ocean below its frozen surface.

Titan is a moon with complex and dense nitrogen-rich atmosphere:
It is composed mostly of water ice and rock. Its frozen surface has lakes of liquid methane and landscapes covered with frozen nitrogen. Planetary scientists consider Titan to be a possible harbour for life, but not Earth-like life.

Four spacecraft have visited Saturn:
Pioneer 11, Voyager 1 and 2, and the Cassini-Huygens mission have all studied the planet. Cassini continues to orbit Saturn, sending back a wealth of data about the planet, its moons, and rings.

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Planet Uranus


Uranus is the seventh planet from the Sun. It’s not visible to the naked eye, and became the first planet discovered with the use of a telescope. Uranus is tipped over on its side with an axial tilt of 98 degrees. It is often described as “rolling around the Sun on its side.

Uranus Planet Profile

Mass: 86,810,300,000,000,000 billion kg (14.536 x Earth)
Equatorial Diameter: 51,118 km
Polar Diameter: 49,946 km
Equatorial Circumference: 159,354 km
Known Moons: 27
Notable Moons: Oberon, Titania, Miranda, Ariel & Umbriel
Known Rings: 13
Orbit Distance: 2,870,658,186 km (19.22 AU)
Orbit Period: 30,687.15 Earth days (84.02 Earth years)
Surface Temperature: -197 °C
Discover Date: March 13th 1781
Discovered By: William Herschel

Facts About Uranus

Uranus was officially discovered by Sir William Herschel in 1781:
It is too dim to have been seen by the ancients. At first Herschel thought it was a comet, but several years later it was confirmed as a planet. Herscal tried to have his discovery named “Georgian Sidus” after King George III. The name Uranus was suggested by astronomer Johann Bode. The name comes from the ancient Greek deity Ouranos.

Uranus turns on its axis once every 17 hours, 14 minutes:
The planet rotates in a retrograde direction, opposite to the way Earth and most other planets turn.

Uranus makes one trip around the Sun every 84 Earth years:
During some parts of its orbit one or the other of its poles point directly at the Sun and get about 42 years of direct sunlight. The rest of the time they are in darkness.

Uranus Distance from the Sun 2.877 billion km

Uranus is often referred to as an “ice giant” planet:
Like the other gas giants, it has a hydrogen upper layer, which has helium mixed in. Below that is an icy “mantle, which surrounds a rock and ice core. The upper atmosphere is made of water, ammonia and the methane ice crystals that give the planet its pale blue color.

Uranus hits the coldest temperatures of any planet:
With minimum atmospheric temperature of -224°C Uranus is nearly coldest planet in the solar system. While Neptune doesn’t get as cold as Uranus it is on average colder. The upper atmosphere of Uranus is covered by a methane haze which hides the storms that take place in the cloud decks.

Uranus has two sets of rings of very thin set of dark coloured rings:
The ring particles are small, ranging from a dust-sized particles to small boulders. There are eleven inner rings and two outer rings. They probably formed when one or more of Uranus’s moons were broken up in an impact. The first rings were discovered in 1977 with the two outer rings being discovered in Hubble Space Telescope images between 2003 and 2005.

Uranus’ moons are named after characters created by William Shakespeare and Alaxander Pope:
These include Oberon, Titania and Miranda.  All are frozen worlds with dark surfaces. Some are ice and rock mixtures.  The most interesting Uranian moon is Miranda; it has ice canyons, terraces, and other strange-looking surface areas.

Only one spacecraft has flown by Uranus:
In 1986, the Voyager 2 spacecraft swept past the planet at a distance of 81,500 km. It returned the first close-up images of the planet, its moons, and rings.

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Planet Naptune 


Neptune is the eighth planet from the Sun making it the most distant in the solar system. This gas giant planet may have formed much closer to the Sun in early solar system history before migrating to its present position.

Planet Profile

Mass: 102,410,000,000,000,000 billion kg (17.15x Earth)
Equatorial Diameter: 49,528 km
Polar Diameter: 48,682 km
Equatorial Circumference: 155,600 km
Known Moons: 14
Notable Moons: Triton
Known Rings: 5
Orbit Distance: 4,498,396,441 km (30.10 AU)
Orbit Period: 60,190.03 Earth days (164.79 Earth years)
Surface Temperature: -201 °C
Discover Date: September 23rd 1846
Discovered By: Urbain Le Verrier & Johann Galle

Facts About Neptune

Neptune was not known to the ancients:
It is not visible to the naked eye and was first observed in 1846. Its position was determined using mathematical predictions. It was named after the Roman god of the sea.

Neptune spins on its axis very rapidly:
Its equatorial clouds take 18 hours to make one rotation. This is because Neptune is not solid body.

Neptune is the smallest of the ice giants:
Despite being smaller than Uranus, Neptune has a greater mass. Below its heavy atmosphere, Uranus is made of layers of hydrogen, helium, and methane gases. They enclose a layer of water, ammonia and methane ice. The inner core of the planet is made of rock.

Neptune Distance from the Sun 4.498 billion km

The atmosphere of Neptune is made of hydrogen and helium, with some methane:
The methane absorbs red light, which makes the planet appear a lovely blue. High, thin clouds drift in the upper atmosphere.

Neptune has a very active climate:
Large storms whirl through its upper atmosphere, and high-speed winds track around the planet at up 600 meters per second. One of the largest storms ever seen was recorded in 1989. It was called the Great Dark Spot. It lasted about five years.

Neptune has a very thin collection of rings:
They are likely made up of ice particles mixed with dust grains and possibly coated with a carbon-based substance.

Neptune has 14 moons:
The most interesting moon is Triton, a frozen world that is spewing nitrogen ice and dust particles out from below its surface. It was likely captured by the gravitational pull of Neptune. It is probably the coldest world in the solar system.

Only one spacecraft has flown by Neptune:
In 1989, the Voyager 2 spacecraft swept past the planet. It returned the first close-up images of the Neptune system. The NASA/ESA Hubble Space Telescope has also studied this planet, as have a number of ground-based telescopes.

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