planets

The Solar System formed billion years ago from the gravitational collapse of a region within a large molecular cloud. This initial cloud was likely several light-years across and probably birthed several stars. As is typical of molecular clouds, this one consisted mostly of hydrogen, with some helium, and small amounts of heavier elements fused by previous generations of stars. As the region that would become the Solar System.

Our solar system consists of an average star we call the Sun, the planets Mercury,   Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It includes the satellites of the planets; numerous comets, asteroids, and meteoroids; and the interplanetary medium.

Ancient astronomers observed points of light that appeared to move among the stars. They called these objects “planets,” meaning wanderers, and named them after Roman deities—Jupiter, king of the gods; Mars, the god of war; Mercury, messenger of the gods; Venus, the goddess of love and beauty, and Saturn, father of Jupiter and god of agriculture. The stargazers also observed comets with sparkling tails, and meteors or shooting stars apparently falling from the sky.

The four planets closest to the sun—Mercury, Venus, Earth, and Mars—are called the terrestrial planets because they have solid rocky surfaces. Jupiter, Saturn, Uranus, and Neptune are known as the Jovian (Jupiter-like) planets, because they are all gigantic compared with Earth, and they have a gaseous nature like Jupiter’s. The Jovian planets are also referred to as the gas giants, although some or all of them might have small solid cores.

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Nearly every planet—and some of the moons—has an atmosphere. Earth’s atmosphere is primarily nitrogen and oxygen. Venus has a thick atmosphere of carbon dioxide, with traces of poisonous gases such as sulfur dioxide. Mars’s carbon dioxide atmosphere is extremely thin. Jupiter, Saturn, Uranus, and Neptune are primarily hydrogen and helium.

The Sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system. The Sun’s nearest known stellar neighbour is a red dwarf star called Proxima Centauri, at a distance of 4.3 light years away. The whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy, a spiral disk of 200 billion stars we call the Milky Way.

The Milky Way has two small galaxies orbiting it nearby, which are visible from the southern hemisphere. They are called the Large Magellanic Cloud and the Small Magellanic Cloud. The nearest large galaxy is the Andromeda Galaxy. It is a spiral galaxy like the Milky Way but is 4 times as massive and is 2 million light years away. Our galaxy, one of the billions of galaxies known, is travelling through intergalactic space.

Mercury

  • Mercury is the closest and second smallest in the Solar System.
  • Mercury is the second densest planet after Earth.
  • The only visit to Mercury was a flyby made by the Mariner 10 spacecraft in 1974.
  • Mercury speeds around the sun every 88 days, traveling through space at nearly 50 km (31 miles) per second
  • Galileo first observed Mercury during the 17th century.

Venus

  • Venus is the second closest and sixth largest planet in the Solar System
  • The orbital speed of Venus is 35 km per second.
  • Venus is the hottest planet in the Solar System.
  • Venus appears to be the brightest planet in the sky.
  • It takes 244.7 days for Venus to rotate on its axis.
  • The first robotic space probe mission to Venus and the first to any planet began on 12 February 1961, with the launch of the Venera 1 probe

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Earth

  • Earth formed approximately 4.54 billion years ago, and life appeared on its surface within one billion years.
  • The Earth is the densest planet in the Solar System.
  • Earth is the fifth largest planet in the Solar System.
  • The Diameter of the Earth is 12,756 km (7,926 miles)
  • The earth’s orbital speed is 29.8 km per second.
  • Earth atmosphere consists of 78 percent nitrogen, 21 percent oxygen, and 1 percent other ingredients.
  • Earth rotates about its own axis 366.26 times, creating 365.26 solar days

Mars

Mars is the fourth planet from the Sun and the second smallest planet in the Solar System.

  • Iron oxide prevalent on its surface gives it a reddish appearance, often described as “ Red Planet”
  • A Mars year is equal to 686.98 Earth Days
  • A day on Mars is equal to 24.6 Earth Hours
  • Like Earth, Mars experiences seasons because of the tilt of its rotational axis
  • Asaph Hall discovered both of Mars’ moons, Phobos, and Deimos, in August 1877.
  • Mariner 4 – first successful flyby mission to Mars. Launched on November 28, 1964, and arrived at Mars on July 14, 1965.
  • Viking 1 – Successful orbit and landing on the surface of Mars. Launched August 20, 1975, and arrived on Mars July 20, 1976.

Jupitar

Jupiter, the largest planet in our solar system, is 318 times larger than Earth.

  • The orbital speed of Jupiter is 13.1 km/sec
  • A year on Jupiter is equal to 11.9 Earth Years
  • Jupiter has 67 natural satellites. 105 Of these, 51 are less than 10 kilometres in diameter and have only been discovered since 1975.
  • Galileo Galilei had discovered Jupiter’s four largest moons, now called Io, Europa, Ganymede, and Callisto. These four moons are known today as the Galilean satellites.
  • In 1610, Galileo Galilei makes the first detailed observations of Jupiter.
  • Jupiter’s moon Ganymede is the biggest satellite in solar system
  • Jupiter has rings, the third planet discovered to have a ring system in our Solar System.
  • Jupiter’s rings are identified as  Halo ring, Main ring, Amalthea gossamer ring, and Thebe gossamer ring.
  • Jupiter’s rings were discovered by Voyager 1 in 1979.

Saturn

Saturn is the sixth planet from the Sun and the second largest.

  • Saturn has 62 known moons, fifty-three have been named. Most of them are small in size.
  • Names of some of Saturn’s moons: the largest is Titan, discovered in 1655; Tethys, Dione, Rhea, & Iapetus, discovered from 1671 to 1672; Mimas & Enceladus, discovered in 1789; and Hyperion, discovered in 1848.
  • A year on Saturn is equal to 29.5 Earth Years
  • Pioneer 11 is the first spacecraft to reach Saturn, in 1979
  • Saturn has a prominent ring system that consists of nine continuous main rings and three discontinuous arcs, composed mostly of ice particles with a smaller amount of rocky debris and dust.

Uranus

The orbital speed of Uranus is 6.6 km/sec

  • Uranus takes 84 Earth years to complete one orbit.
  • Uranus is the third largest planet in the Solar System.
  • Voyager 2, the only spacecraft to visit Uranus,
  • A day on Uranus is equal to a little more than 17 hours on Earth.
  • Uranus has 27 known moons, named for characters from the works of William Shakespeare or Alexander Pope
  • Uranus was discovered by Sir William Herschel in 1781

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Neptune

Neptune is the fourth largest planet and the coolest planet in the Solar System.

  • Neptune was the first planet located through mathematical predictions rather than through regular observations of the sky.
  • Neptune was discovered by Urbain Le Verrier, John Couch Adams, and Johann Galle on September 23, 1846.
  • The only spacecraft ever to visit Neptune was Voyager 2 in 1989.
  • The magnetic field of Neptune is about 27 times more powerful than that of Earth.
  • One Neptune year is equal to 164.83 Earth Years
  • Neptune has six known rings.
  • In 2011, Neptune completes its first 165-year orbit of the sun since its discovery in 1846.
  • Neptune has 13 moons, the largest of which is named Triton. The other moons are Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, Nereid, Halimede, Sao, Laomedeia, Neso, and Psamathe.

Pluto

Pluto is the smallest planet in the Solar System, now consider as dwarf planet

  • Pluto is colder than Neptune.
  • Pluto’s journey around the Sun takes 248 Earth years.
  • Pluto is the second most contrast body in the Solar System
  • Pluto has not yet been visited by a spacecraft.
  • Pluto has a satellite, Charon, which was discovered (in 1978). The distance between them is 19,640 km (12,200 miles). The other 3 are Nix, Hydra, and newly discovered S/2011 P 1 on July of 2011.
  • Pluto rotation (a Pluto day) takes 6.4 Earth days, meaning that it has the second slowest rotation in the Solar System after Venus
  • Pluto was discovered by Tombaugh in 1930

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