Our solar system was formed around 4.6 billion years ago. It is a part of Milkyway's Orion Star Cluster. The Milky Way galaxy contains hundreds of solar systems and was formed 13.2 billion years ago, making it as old as the Universe itself.
The Solar System consists of the Sun, 8 planets, 8 planets, 180 satellites, comets, meteors, asteroids, the Kuiper Belt, and the Oort Cloud. The diameter of the solar system is estimated as approx 1170 Crore Kms.
Our Sun's nearest neighbor in the Milkyway is nearly is 4.3 light-years away and it is the triple star system known as Alpha and Proxima Centauri.
Heliocentric, Geocentric Theories & Laws of Planetary Motion
Astronomers of the past believed that the Earth was flat and was at the center of the Solar System. Every other celestial body including Sun revolves around it. This theory put forward by Greek astronomer and mathematician Ptolemy is called the Geocentric model of the solar system.
Whereas in the Heliocentric model of the solar system, Copernicus (1543) believed that the Sun is at the center of the Solar System and all other planets including Earth orbit around it at a uniform speed.
Later in 1609, Johannes Kepler modified Copernicus' Heliocentric model and put forward 3 planetary laws. They are as follows:
- The orbit of a planet is an ellipse with the Sun at one of the two foci.
- A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
- The square of a planet's orbital period is proportional to the cube of the length of the semi-major axis of its orbit.
Then again, Sir Issac Newton based his laws of gravity and laws of motion on Kepler's laws.
Classification of Planets
The planets in the solar system are classified into two depending on their proximity with the sun & the structure of the planets. They are as follows:
- Inner Planets / Terrestrial Planets – Mercury, Venus, Earth & Mars.
- Outer Planets / Jovian Planets – Jupiter, Saturn, Uranus & Neptune.
Sun & the 8 Planets of the Solar System
Sun
- Most abundant gas on Sun – Hydrogen.
- Composition – 73% Hydrogen & 25% Helium.
- Age – Approx. 4.6 billion years.
- Diameter – 1,392,684 km (108 times that of Earth).
- Surface Temperature – 5,800 kelvins (K)
- Core Temperature – 15,000,000 K (approx. 27 million degrees Fahrenheit).
- G-Type Main Sequence Star (Dwarf Star).
- The galaxy to which the Sun belongs – Milky Way.
- Rotation – 27 days.
- The time taken by the sun to complete one revolution around the center of the Milky Way is termed as – Cosmic Year.
- The sun makes up more than 99 percent of the solar system's mass.
- Layers of Sun –
- The outer layer of the Sun's Atmosphere – Corona (visible during the eclipse).
- Photosphere – Glowing Surface of Sun.
- Chromosphere – The inner reddish region.
- The energy created by the Sun’s core is – Thermo Nuclear fusion.
- Sunspots – darker regions on the surface of the Sun, follows an 11-year cycle.
- Sunflares – Huge explosions that occur when there is a change in the magnetic fields near the sunspots and produces electromagnetic radiation, x-rays, ultraviolet radiation, visible light, and radio waves.
- The position of the Sun nearest to the earth is known as – Perihelion.
- The position of the Sun farthest from the earth is known as – Aphelion.
- Time taken by Sun's rays to reach Earth – 8 minutes.
- Skylab – First manned spacecraft to study the Sun (February 1974).
Mercury
- Nearest Planet to the Sun.
- Smallest & Fastest Planet.
- No Moons (Satellites).
- No significant atmosphere.
- Rotation – 58.65 days.
- Revolution – 88 days.
- The planet with the shortest revolution.
- Mercury has the shortest year of all the planets in the solar system.
- Second densest Planet in the Solar System.
- The planet with the highest temperature variation.
- Space Missions – Mariner 10 (1970), Messenger (2004), BepiColombo.
Venus
- Epithets – Morning Star, Evening Star, Lucifer, Sun's Pet & Earth's Twin.
- Hottest Planet in the Solar System (up to 463.889°C).
- Brightest Planet on the Earth's Sky.
- The planet that reflects sunlight the most.
- The only planet which takes more time to complete rotation (243 days) than a revolution (224.7 days).
- The planet with Longest Rotation.
- The planet with most no. of volcanoes (more than 1600).
- No satellites.
- The direction of spin opposite to that of Earth ie rotates in the clockwise direction: East to west.
- The first planet to be visited by a spacecraft from Earth.
- Space Missions – Mariner 2, Venera 7, Magellan, Akatsuki (Japan) etc
- The first robotic space probe mission to Venus, and the first to any other planet – Venera 1.
Earth
- Epithets – Blue Planet, Watery Planet.
- Only known planet that supports life.
- Mass of the Earth – 5.98 x 1024 kg.
- Diameter – 12,756 km.
- Orbital Speed – 29.8 km/sec.
- The planet with the highest density (5.514 g/cm³).
- Escape Velocity – 11,200 m/s.
- The time taken by the sunlight to reach the Earth – 8 minutes 18 seconds.
Mars
- Epithets – Red Planet, Fossil Planet.
- Prevalence of Iron oxide in its atmosphere.
- Rotation – 24 hours 37 minutes 30 seconds.
- Revolution – 687 days.
- Approx the same landmass as Earth.
- Less density than Earth.
- Has 2 permanent polar ice caps.
- The sunset on Mars appears blue.
- Largest known Volcano in the Solar System – Olympus Mons (22km).
- Tallest Mountain in the Solar System – Olympus Mons (22km).
- Moons/Satellites – Phobos (meaning fear) & Deimos (meaning terror).
- Discovered by – Asaph Hall (1877).
- Space Missions – Viking-1.
Jupiter
- Largest planet.
- Epithet – Lord of Heavens.
- The planet with the lowest escape velocity.
- The planet with the shortest Rotation period.
- Rotation – 9 hours 50 minutes 30 seconds.
- Revolution – 12 years.
- Orbital speed – 13.1 km/sec.
- Giant Storm – Great Red Spot.
- Spins faster on its axis than any other planet, hence have shortest days ie, fastest rotation.
- Jupiter’s rings were discovered by Voyager 1 in 1979.
- Jupiter’s rings are identified as – Halo ring, Main ring, Amalthea gossamer ring & Thebe gossamer ring.
- Moons/Satellites – 79 (Europa, Callisto, Ganymede, etc).
- Ganymede – Largest satellite in the solar system.
- Satellites discovered by Gallileo (1610) – Europa, Callisto, Ganymede & lo.
- Space Missions – Pioneer 10.
- First spacecraft to visit Jupiter – Pioneer 10 (March 1972).
Saturn
- Epithet – The Ringed Planet.
- Discovered by – Galileo Galilei (1610).
- Second Largest Planet in the Solar System.
- The planet with the lowest density (lower than that of water).
- Band of concentric rings made up of ice and rocks.
- nine continuous main rings and three discontinuous arcs.
- Rotation – 10 hours 14 minutes.
- Revolution – 30 years.
- Moons/Satellites – 82 (Titan, Rhea, Enceladus, Phoebe, etc).
- Titan – Biggest Satellite of Saturn,
- – discovered by Christiaan Huygens (1655).
- The planet whose satellites are named after Greek mythological characters.
- Mimas, the moon of Saturn is one of the most heavily cratered objects in the Solar System and resembles the Death Star from the film Star Wars of 1977.
- Space Missions – Pioneer 11, Voyager 1 & 2 & the Cassini-Huygen.
- Pioneer 11 – First spacecraft to reach Saturn (1979).
Uranus
- Epithet – The Ice Giant, Rolling Planet & Lying Planet.
- First identified by William Herschel in 1781.
- Third Largest Planet in the Solar System.
- Greenish blue color.
- Rotation – 16 hours.
- Revolution – 34 years.
- Orbital speed – 6.6 km/sec.
- Rotates in the clockwise direction.
- Axial tilt is 98 degree, so it appears to be flat.
- Moons/Satellites – 27 (Titania, Oberon, Ariel, etc).
- Space Missions – Voyager 2.
Neptune
- First planet located through mathematical predictions.
- The Discovery of Neptune is contributed to Berlin scientist Johann Gottfried Galle along with Urbain Jean Joseph Le Verrier, & John Couch Adams in 1846.
- Farthest & Coolest planet.
- The Windiest Planet because of raging dense, methane-rich clouds
- Storm – Small Dark Spot / Dark Spot 2 / The Wizard's Eye.
- Discovered by the Voyager 2 (1989).
- Rotation – 18 hours.
- Revolution – 165 years.
- Moons/Satellites – 14 (Triton – largest, Neso, Proteus, etc).
- Triton follows a retrograde orbit ie, its orbits in the opposite direction to Neptune's rotation.
- Space Missions – Voyager 2 (1989).
Other Celestial Bodies
Pluto
- Discovered by – Tombaugh (1930).
- The previously smallest planet in the Solar System, now considered a dwarf planet.
- Colder than Neptune.
- Rotation – 6.4 days, second slowest rotation in the Solar System after Venus.
- Revolution – 248 Earth years.
- Moons/Satellites – 5 (Charon, Styx, Nix, Kerberos & Hydra).
- Charon – Largest.
- – discovered by James Christy (1978).
Pluto is the second most contrast body in the Solar System.
Moon
- Only Natural Satellite of the Earth.
- Fifth Largest Satellite in our Solar System.
- No atmosphere.
- Diameter – 2160 miles (3476 km).
- Distance to Earth – 384,400 km.
- Rotation – 27 days, 7 hours, 43 minutes & 11.47 seconds.
- Revolution – 27 days, 7 hours, 43 minutes & 11.47 seconds.
- Same periods of rotation and revolution making only one side of the Moon is visible at all times.
- Blue Moon – Two full Moons in the same month.
- First person to make use of a telescope for lunar observation – Galileo Galilei (1610).
- First Man to Land on Moon – Neil Armstrong (July 20, 1969, Apollo 11).
The average distance between the Earth and the Moon varies because the lunar orbit is not a perfect circle.
Asteroids
- Also known as Small planets or Planetoids.
- Rocky debris found between the planets, Mars and Jupiter.
- The term 'Asteroid' was coined by – William Herschel.
- Ceres – Largest Asteroid.
- Brightest asteroid visible from Earth – Vesta.
- Asteroids with Moons – 243 Ida, 45 Eugenia, 617 Patroclus, 1999 KW4, etc.
- First Asteroid with Moon observed was – 243 Ida (1993).
The central peak of the crater Rheasilvia of Asteroid Vesta is believed to be equal or bigger than that of the tallest mountain in the Solar System, Olympus Mons. But due to the lack of data, comparisons are now impossible.
Meteors
- Epithet – Shooting Star, Falling Star.
- Small rocky or metallic bodies.
- Smaller than asteroids.
- Size ranges from small grains to 1-meter-wide objects.
A meteorite is any solid substance such as a comet, asteroid, or meteoroid that originates from interplanetary space and survives the Earth's atmosphere.
The Allende meteorite is the largest carbonaceous chondrite crashed into Earth over Mexico on February 8, 1969.
Comets
Halley's Comet is a periodic comet that passes by the Earth in every 75 years, last seen in 1986.
Kuiper Belt
Similar to the asteroid belt, beyond the terrestrial planets there is the Edgeworth–Kuiper belt. It is 20 times wider and 200 times massive than the asteroid belt. Pluto and the other dwarf planets are present in the Kuiper belt.
- Dwarf Planets – Haumea, Ceres, Eris, Makemake & Pluto.
Oort cloud
Beyond the Kuiper Belt is the Oort Cloud. It is a vast, spherical trillion of icy debris and is up to 2,000 times farther from the sun. The gravitational and magnetic field of the Sun extends up to the Oort Cloud, so is considered the edge of the solar system.
This is a brief summary of our solar system where we live. With ever increasing technology, robotics and man's thirst for knowledge new discoveries are being made every day. In the future, we will continue to explore more and someday, we will unravel the mysteries of the Universe.
Image sources: Astronomy.com, wikipedia.com
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📝SideNotes:
- Father of Big Bang Theory – Georges Lemaitre (Belgium; Catholic priest; 1927),
- Propounded by Edwin Hubble (1929).
- The Steady State Theory was put forward by – Sir Hermann Bondi, Thomas Gold & Sir Fred Hoyle (1948).
Thanks for reading!!!
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