Planets

Corinne Carbone
2/8/14
Environmental science

There are 8 planets in our solar system; these are divided into two types, large gas giants (Jupiter, Saturn, Uranus and Neptune) and smaller rocky terrestrial planets (Mercury, Venus, Earth and Mars). The order from closest to the Sun outwards is; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and finally Neptune. Until 2006 Pluto was also classed as a planet, however it is now classified as a dwarf planet (meeting the first two requirements of the definition but not the third).
A planet is currently defined by an IAU (International Astronomy Unit) as “a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.”
With the exception of Neptune and Uranus the other 6 planets can be seen unaided and all 8 are visible with a small telescope or binoculars. The largest planet in the solar system is Jupiter, followed by Saturn Uranus, Neptune, Earth, Venus, Mars with the smallest being Mercury.
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 and this was eventually shown to be the case. 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. Off all the planets 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 then the crust. The average density of the Earth is approximately 5.52 grams per cubic centimeter. Earth is the third planet from the Sun and is the largest of the terrestrial planets. Unlike the other planets in the solar system that are named after classic deities the Earth’s name comes from the Anglo-Saxon word erda which means ground or soil. The Earth was formed approximately 4.54 billion years ago and is the only known planet to support life.
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 Satellites: 1
Notable Satellites: The Moon
Orbit Distance: 149,598,262 km (1 AU)
Orbit Period: 365.26 Earth days
Surface Temperature: -88 to 58°Ch was formed approximately 4.54 billion years ago and is the only known planet to support life.
Jupiter:
It is not known when Jupiter was discovered – The earliest record of Jupiter is from Babylonian texts dating from the 7th or 8th century BC. Jupiter is named after the king of the Roman gods – Jupiter has also been known as Zeus the Greek god of thunder and Marduk the Mesopotamian god and patron of the city of Babylon. Jupiter’s most recognisable feature is the Great Red Storm – This is a storm that has been raging for at least 350 years and is large enough for two Earths to fit inside of. Jupiter’s larger moon Ganymede is the largest moon in the solar system – It’s has a diameter of 5,268 km making it larger than the planet Mercury. Jupiter had two rings – These are thought to be composed of material from it’s moons where they have been struck by meteorites. Jupiter is the third brightest object in the solar system – It is one of fJupiter is the fifth planet from the Sun and is the largest planet in the solar system, like the other four outer planets Jupiter is a gas giant.

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 Satellites: 67
Notable Satellites: Io, Europa, Ganymede, & Callisto
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
Saturn:
Saturn is the sixth planet from the Sun and is named after the Roman god of wealth. Saturn is the second largest planet in the solar system and is best known for its fabulous rings. The rings were not known to exist until Galileo first observed them in 1610.
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 Satellites: 62
Notable Satellites: Titan, Rhea & Enceladus
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
Mercury:
A year in Mercury is just 88 days long. One day on Mercury lasts the equivalent to 176 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 Kilometers across its equator, compared with 12,742 Kilometers for the Earth. Mercury is the second densest planet. Even though the planet is small, Mercury is very dense. Each cubic centimeter 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 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 is the most crated 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 extremely thin atmosphere. Mercury has just 38 percent 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 minds, radioactive decay and dust caused by micrometeorites. 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 Earth passing across the face of the Sun in an event called a transit, the next will occur on the 9th May 2016.
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 Satellites: none
Notable Satellites: 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
Mars:
Mars and Earth have approximately the same land mass. Even though Mars has only has 15% of the Earth’s volume and just over 10% of the Earth’s, around two thirds of the Earth’s surface is covered in water. Martian surface gravity is only 37% of 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 16 missions to mars have been successful. Including orbiters, landers and rovers there have been 39 missions to Mars, not including flybys or the attempt to return a sample of Phobos. Since the first, USSR’s Marsnik 1, was launched in1960. Europe’s Exobiology on Mars program (scheduled launch 2016) plans to: search for possible traces of Martian life; study the surface environment; map potential hazards to manned missions in the future and begin preparations for an eventual return flight. Mars has the largest gas storms in the Solar System. They can last for months and cover the entire planet on. 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 of the 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. Pieces of Mars have fallen from 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 ‘tMass: 641,693,000,000,000 billion kg (0.107 x Earth)

Equatorial Diameter: 6,805
Polar Diameter: 6,755
Equatorial Circumference: 21,297 km
Known Satellites: 2
Notable Satellites: 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 millenium BC
Recorded By: Egyptian astronomershe 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. 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.

Mercury:
A year in Mercury is just 88 days long:
One day on Mercury lasts the equivalent of 176 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 planets:
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 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 percent 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 minds, radioactive decay and dust caused by micrometeorites