Module 3: Solar System (Part 2)


Dwarf Planets

  • In 2006, the International Astronomical Union (IAU) created a new classification category for objects in solar system called ‘Dwarf Planets’.
  • A dwarf planet is a celestial body that:
    • Orbits the sun
    • Has enough mass to assume a nearly round shape
    • Has not cleared the neighborhood around its orbit
    • Is not a moon
  • IAU recognised five dwarf planets in our solar system. They are (1) Eris (2) Ceres (3) Pluto (4) Makemake and (5) Haumea.


  • Pluto was discovered by Clyde Tombaugh in 1930.
  • It was long considered the smallest and ninth planet in our solar system.
  • After the discovery of similar planets in Kuiper Belt, Pluto was expelled from planets and reclassified as dwarf planet in 2006.
  • Pluto takes 248 years for revolution and 156 hours for rotation.
  • Pluto has a thin atmosphere of nitrogen, methane and carbon monoxide.
  • The five known satellites of Pluto are Charon, Hydra, Nix, Kerberos and Styx.
  • The largest satellite, Charon, is so big that Pluto and Charon orbit each other like a double planet.
  • NASA launched first mission to Pluto named New Horizons in 2006 which passed close by in July 2015.
  • The name ‘Pluto’ was suggested by a 11 year old girl Venetia Burney of England. It is named after Roman God of underworld.


  • Eris is the second largest dwarf planet in the solar system.
  • It evolves around the sun beyond Pluto.
  • It was discovered by Mike Brown in 2005.
  • Dysnomia is the satellite of Eris.


  • Ceres is the only dwarf planet in the solar system located in the inner solar system (between Mars and Jupiter)
  • Ceres is also an asteroid and the largest object in the asteroid belt. It is now classified as a dwarf Planet.
  • While it is the smallest of the known dwarf planets, it is the largest object in the asteroid belt.
  • Ceres is named for the Roman goddess of corn and harvests.
  • Guiseppe Piazzi discovered the first and the largest asteroid Ceres, orbiting Mars and Jupiter.
  • ‘Dawn’ spacecraft of NASA was launched in 2007 to study about Ceres and Vesta, another object in asteroid belt. When Dawn arrived in 2015, Ceres became the first dwarf planet to receive a visit from a spacecraft.
  • It is the only dwarf planet with no satellites.


  • Makemake is the largest object in Kuiper Belt.
  • It was discovered in 2005 by a team led by Michael E. Brown.
  • The name was adopted from the mythology of Rapa Nui people of Easter Island.


  • Haumea is about one third mass of Pluto and was discovered in 2004.
  • It is the least spherical of all the dwarf planets.
  • It is named after Hawaiian Goddess of childbirth.
  • It is the third brightest object in the Kuiper belt, after the dwarf planets Pluto and Makemake. Haumea has a ring around it.
  • Haumea also has two moons named Hi’iaka and Namaka.


As of now, there are five artificial objects achieved the escape velocity that will allow them to leave the Solar System. These are Voyager-1, Voyager-2, New Horizons, Pioneer 10 and Pioneer 11. Voyager 1 was the first human-made object to leave our Solar System when it crossed into interstellar space in 2012. Voyager also made it to interstellar space in 2018. New Horizons is are still active and will eventually transition to the space between the stars. Pioneers 10 and 11 also have reached escape velocity, but both spacecraft have been inactive for many years.

Voyager -1 is the first space craft to leave solar system to reach interstellar space in 2012. It was launched in September 1977, flew past Jupiter in 1979 and Saturn in 1980, making a special close approach to Saturn’s moon Titan. The probe passed the heliosphere (the area of influence of sun) on 25 August 2012 to enter interstellar space and is still active.

Voyager-2 is the only spacecraft to study all the four outer planets of solar system at close range. It was launched in August 1977, flew past Jupiter in 1979, Saturn in 1981, Uranus in 1986, and Neptune in 1989. Voyager 2 left solar system and entered interstellar space on December 2018, making it second human made object to do so.

New Horizons: The Primary mission of this spacecraft was to study Pluto and a secondary mission to fly by and study one or more other Kuiper belt objects (KBOs). Launched in 2006, the probe flew past Jupiter in 2007 and Pluto on 14 July 2015. It is currently headed towards a Kuiper belt object (486958) 2014 MU69 (nick named Ultima Thule). The flyby will occur in January 2019, which will make it the farthest object in the Solar System ever to be visited by a spacecraft.


Also known as Kuiper – Edgeworth Belt, it is a disk-shaped region in the outer solar system, extending from the orbit of Neptune to around 50 Astronomical Unit from the sun. This region consists of bits of rock and ice, comets, and dwarf planets. These are also called Kuiper Belt Objects (KBOs). The Kuiper Belt is named after a scientist named Gerard Kuiper. In 1951 he proposed the idea that a belt of icy bodies might have existed beyond Neptune when the solar system formed. The dwarf planets Pluto, Makemake, Eris and Haumea are found in this region. Several dwarf planets within the Kuiper Belt have moons. The first mission to explore the Kuiper Belt is New Horizons. It flew past Pluto in 2015.

In 2018, a dwarf planet nicknamed the Goblin has been discovered well beyond Pluto. It is officially known as 2015 TG387 by the International Astronomical Union. Sedna and 2012 VP113 are the two other dwarf planets discovered recently.


Astronomers are searching for a possible planet that is suspected to be in orbit far beyond Pluto that might explain the strange orbits of several Kuiper Belt Objects.  It is given the nickname Planet 9 or Planet X.


The Oort Cloud is a theorised shell of icy objects that lie beyond the Kuiper Belt, in the outermost reaches of the solar system. It is a predicted, but undiscovered region of space. It is named after astronomer Jan Oort, who first theorised its existence. The Oort Cloud is roughly spherical. Objects in the Oort Cloud are also referred to as Trans-Neptunian objects. This name also applies to objects in the Kuiper Belt.

Astronomers think that long-period comets (which take more than 200 years to orbit the Sun) have their origins in the Oort Cloud. Also the most short-period comets (which take 200 years or less to orbit the sun) have their origins in the Kuiper Belt.


  • Asteroids are small rocky celestial bodies revolving around the sun in elliptical orbit. Most of the asteroids are found between the orbits of Mars and Jupiter.
  • Asteroids do not have rings.
  • The largest asteroid is Ceres, which has a diameter of about 1000 km. It was discovered by Giuseppe Piazzi. It is now classified as Dwarf Planet.
  • Ceres encompasses over one-third of the estimated total mass of all the asteroids in the asteroid belt.
  • Asteroids that pass close to Earth are called Near-Earth Objects, or NEOs.
  • The first discovery of an asteroid-moon system was of asteroid Ida and its moon Dactyl in 1993.
  • Galileo was the spacecraft that visited two asteroids – Gaspra in 1991 and Ida in 1993.
  • Near-Earth Asteroid Rendezvous (NEAR – Shoemaker) mission studied asteroids Mathilde and Eros.
  • The Rosetta mission encountered Steins in 2008 and Lutetia in 2010.
  • Dawn spacecraft of NASA was launched in 2007. It orbited and explored the asteroid Vesta for over one year and then headed towards Ceres, another asteroid and a dwarf planet. Dawn entered the orbit of Ceres on 23 April 2015. It was the first mission to explore a dwarf planet. Dawn is the first spacecraft to orbit two extraterrestrial bodies. It was retired on 1 November 2018.
  • In 2003, Japanese robotic spacecraft Hayabusa landed on near-Earth asteroid Itokawa. On June 3, 2010, Hayabusa successfully returned to Earth with a small amount of asteroid dust now being studied by scientists.
  • The spacecraft Hayabusa2 of Japan landed two robotic rovers, collectively named MINERVA II1 on the surface of the asteroid Rygu on Spetember 21, 2018. MINERVA-II1 is world’s first rover to land on the surface of an asteroid.


  • Natural satellites are celestial bodies that orbit a planet or a minor planet.
  • Natural satellites are sometime referred to as ‘moons’.
  • There are more than 150 known moons in our solar system and several more awaiting confirmation of discovery.
  • Johannes Kepler was the first person to use the term ‘satellite’.
  • They are generally solid bodies and few have atmospheres.
  • Out of 8 planets in solar system, six have their own satellites.
  • Mercury and Venus does not have any satellites. Earth has one satellite and Mars has two. Jovian planets have numerous satellites.
  • Jupiter has most number of satellites (67) Saturn has second highest number of satellites (62)
  • Ganymede is the largest satellite in solar system. It is the satellite of Jupiter.
  • Titan, the satellite of Saturn is the second largest satellite in solar system. It was discovered by Christian Huygens (1655).
  • Titan is the only satellite in the solar system with an atmosphere of its own. Nitrogen is the main component in Titan’s atmosphere.
  • The satellites of Saturn are named after Greek mythical characters.
  • The satellites of Uranus are named after characters created by William Shakespeare and Alexander Pope.
  • The largest satellite of Neptune is Triton. It revolves around Neptune in the opposite direction.
  • Charon is the largest satellite of Pluto.
Jupiter 67 (12 more discovered, making it 79) Ganymede, Io, Europa, Callisto, Himalia Lysithea, Thebe, Elara
Saturn 62 Titan, Prometheus, Pandora, Atlas, Helan, Thethys Phoebe
Uranus 27 Umbriel, Miranda, Ariel, Titania, ophelia,Oberon
Neptune 14 Triton, Nereid, Proteus, Larissa, Despina, Thalassa
Mars 2 Phobos, Deimos
Earth 1 Moon


  • Moon is the only natural satellite of the Earth.
  • It is fifth largest satellite in solar system and has a size of about 27% of the earth
  • Over 59% of Moon’s surface is visible from the earth.
  • The study of moon is called Selenology.
  • The highest point on the surface of moon is Mount Leibnitz (35000 ft), situated on the south pole of the moon
  • The volume of moon is only 2% of volume of earth and the mass of moon is 1.2% of that of earth
  • The escape velocity from the surface of moon is 2.376 km/sec.
  • The period of rotation and revolution of moon are almost same, meaning the same side is always taking the earth.
  • The force due to gravity at the surface of moon is only about one sixth of that on Earth (If an object weigh 60 kg on the surface of earth, it will weigh only 10 kg at the lunar surface.
  • The sky always appears black in moon due to the absence of atmosphere. No sound can be heard on the surface of moon and is unprotected from meteorites and solar winds.
  • Most abundant elements found on lunar surface are Oxygen, Silicon, Iron, Magnesium, Calcium and Titanium.
  • Ilmenite, the ore of titanium is found abundantly on the surface of moon.
  • The light will reach from moon to earth in 1.3 seconds.
  • The moon has a very thin and tenuous (weak) atmosphere, called an exosphere.
  • More than 100 spacecrafts have been launched to explore the moon. It is the only celestial body beyond Earth that has been visited by human beings.
  • The first space craft to reach the surface of moon was Luna – 2 (Russia). It is the first man-made object to land on another celestial body.
  • The first spacecraft to orbit the moon successfully was Luna -10 (the first artificial satellite of moon).
  • Apollo 11 mission of NASA carried three astronauts to moon in 1969. It was launched by Saturn V rocket from Kennedy space station, Florida.
  • Twelve human beings have walked on the surface of the moon.
  • Neil Armstrong was the first astronaut to land on the moon. He was followed by Edwin Aldrin.
  • Neil Armstrong described this as: “one small step for a man, a giant leap for mankind”.
  • The lunar module which they used to land on the moon was called Eagle. They landed on an area called ‘Sea of Tranquility’.
  • Eugene Cernan was the last man to have walked on Moon (1972).


  • Distance from Earth 384400 km
  • Orbital Velocity 3680.5 km/h
  • Density 3.344 g/cm3
  • Diameter 3475 km
  • Mass 7.35 × 1022 kg
  • Circumference 11000 km
  • Maximum distance from earth (Apogee) 406000 km
  • Minimum distance from Earth (Perigee) 364000 km


  • Government of India approved ISRO’s proposal for the first Indian Moon Mission, called Chandrayaan-1 in November 2003.
  • Chandrayaan-1, India’s first mission to Moon, was launched successfully on October 22, 2008 from Sathish Dhavan Space Centre, Sriharikota.
  • The rocket used to launch Chandrayan-1 was PSLV C-11. Vikram Sarabhai Space Centre, Thiruvananthapuram designed and developed PSLV-C11.
  • The spacecraft was orbiting around the Moon at a height of 100 km from the lunar surface
  • The spacecraft carried 11 scientific instruments built in India, USA, UK, Germany, Sweden and Bulgaria.
  • The payload (instrument) in Chandrayaan spacecraft that separated from it and hit on the surface of moon was Moon Impact Probe (MIP). Moon Impact Probe landed on Shackleton crater on the South Pole of Moon .
  • The payload in Chandrayaan spacecraft that detected the presence of water in lunar surface was Moon Mineralogy Mapper.
  • ISRO Chairman at the time of Chandrayaan launching was G. Madhavan Nair.
  • The mission was concluded when the communication with the spacecraft was lost on August 29, 2009
  • ISRO is planning to launch Chandrayaan – 2, the country’s second mission to moon. It is expected to launch before October 2018.
  • The total cost of the Chandrayaan – 2 Mission will be about Rs 800 crore.

Lunar Mare (singular: lunar maria) are large, dark plains on the surface of the moon. These basaltic plains are formed as the result of volcanic eruptions in the ancient period. Sea of Tranquility, Ocean of Storms etc. are some of the lunar mare.


  • The first artificial satellite in the world – Sputnik I (4th October 1957)
  • Sputnik I was launched by – Russia
  • The first animal sent to space – The dog name ‘Leika’
  • The first man in space – Yuri Gagarin (Russia)
  • The spacecraft in which Yuri Gagarin travelled – Vostok – 1
  • Yuri Gagarin went to space on – 12thApril 1961
  • The person who was known as ‘Columbus of the space’ – Yuri Gagarin
  • The first woman in space – Valentina Tereshkova (Russia, 1963)
  • The first American space traveler – Alan Shepard
  • The first American woman in space – Sally K Ride
  • The oldest man in space – John Glenn (77 years) [He died on December 8, 2016)
  • The first person to walk in space – Alexi Leonov (USSR, 1965)
  • The first woman to walk in space – Svetlana Savitskaya
  • The first Indian in space – Rakesh Sharma (1984 – Soyuz T11)(138th space traveler in the world)
  • The space agency of America – NASA
  • The year in which NASA was established – 1958
  • The rocket launching station of NASA – Cape Canaveral
  • The first satellite of America – Explorer – I
  • The first space station in the world – Salyut – I (Russia)
  • The first space shuttle in the world – Colombia (USA)
  • The first woman of Indian origin in space is – Kalpana Chawla (1997)
  • The whole universe is my Native Land” words of – Kalpana Chawla
  • Kalpana Chawla was killed in the space shuttle Columbia disaster on – 1st February 2003
  • The first Indian satellite to study about weather – Metsat (2002)
  • The Metsat was renamed as – Kalpana I
  • The second woman of Indian origin in space is – Sunitha Williams
  • The woman who holds the record of maximum number of space walks (8) – Peggy Whitson [Peggy Whitson breaks Sunitha Williams record of maximum number of space walks (7)]
  • The oldest woman to reach space Peggy Whitson (56 years, NASA)
  • First marathon in space was run by Sunitha Williams
  • Japan’s communication satellite launched by space X þ JCSAT 14
  • The largest space station in the world – International Space Station
  • World’s largest radio telescope – FAST (Five hundred meter Aperture Spherical Telescope), China
  • The robotic spacecraft of NASA to be launched in 2020 to perform in – orbit satellite servicing in low Earth orbit – Restore L. Mission
List of Space Agencies
Names Full Form Nation
NASA National Aeronautics and Space Administration USA
ROSCOSMOS Russian Federal Space Agency Russia
ESA European Space Agency EU
CNES French Space Agency France
JAXA Japan Aerospace Exploration Agency Japan
DLR German Aerospace Centre Germany
ISRO Indian Space Research Organization India
CNSA China National Space Administration China
ASI Italian Space Agency Italy
ISA Iranian Space Agency Iran
UKSA UK Space Agency United Kingdom
SUPARCO Space and Upper Atmosphere Research Commission Pakistan


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