The Solar System
The solar system
consists of the Sun and its eight main planets, their satellites, asteroids,
comets, meteors and other dwarf planets. The Sun is at the one of the two
“centers” of the Solar system and the planets revolving around it in elliptical
orbits. Let us take a look at some quick facts about the Solar System:
- The closest planet to Sun is Mercury and the
farthest is Neptune.
- Pluto is a dwarf planet – relegated from its
status as the ninth planet.
- The eight planets of the solar system are
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
The Sun
The Sun is the
primary source of energy for life on Earth. It is the closest star to the
Earth, about 150 million kilometers from earth. The temperature of the Sun’s
visible surface (photosphere) is about 6000 degree Celsius. However, the outer
layer of Sun’s atmosphere, known as the Corona, is, on an average, about 2
million degree Celsius. The core of the sun is the center, and is about 15
million degree Celsius.
The Sun is made
up of 73% hydrogen and 25% helium. It also has trace amounts of oxygen, carbon,
iron and other elements. It is classified as a G-Type Main Sequence Star. It is
about 4.6 billion years old and will continue to shine for another 5 billion
years. After that it will grow into a Red Giant and then finally end its life
as a white dwarf.
The Planets
There are a
total eight planets in the solar system –
- The planets are divided in the two groups –
Inner planets and Outer planets.
- Inner planets – Mercury, Venus, Earth, Mars.
These are also known as terrestrial planets or rocky planets. These are
denser and have a shorter periods of revolution.
- Outer planets – Jupiter, Saturn, Uranus,
Neptune. These are also known as Gas Giants or Gaseous planets. They are
big in size and have a longer periods of revolution.
- Jupiter is the biggest planet in the Solar
System and Mercury is the smallest.
Mercury
- Closest planet to the Sun.
- Orbits the Sun the quickest.
- No significant atmosphere.
- Rotation period is longer than its orbital
(revolution) period.
- No natural satellites (moons).
- Spacecrafts to Mercury: Mariner 10, MESSENGER,
BepiColombo (upcoming).
- Can be seen from the earth only before sunrise
and after sunset.
Venus
- Known as Earth’s twin.
- Longest rotation period of any planet.
- Rotation period is longer than its orbital
(revolution) period.
- Hottest planet in the solar system.
- Dense atmosphere of gases and chemicals
including sulphuric acid clouds.
- Revolves around the sun in clockwise manner while most others are revolving in
anti-clockwise.
- Second brightest natural object in the night
sky (after Moon).
- Can be seen from the earth only before sunrise
(Morning Star) and after sunset (Evening Star).
- No natural satellites (moons).
- First planet visited by a spacecraft.
- Spacecrafts to Venus: Mariner 2, Venera 7,
Magellan etc.
Earth
- Only planet in the solar system to be known to
support life.
- Has water in all three states – liquid, solid
and gas.
- Gasses present in the earth’s atmosphere are
Nitrogen, Hydrogen, Oxygen, Carbon Dioxide etc
- It takes 23 hour 56 minutes 46 seconds to
rotate around its axis.
- It takes 365.26 days to revolve around the
Sun.
- The Ozone layer present in the Earth’s
atmosphere protects it from the ultra violet rays.
- Moon is the only natural satellite of the
Earth.
Mars
- Known as the ‘Red Planet’ due to presence of
iron-rich red soil.
- Despite its red colour, it is cold because it
has lost most of its atmosphere.
- Phobos and Deimos are the two moons of Mars.
- Has polar ice caps and traces of
sub-terrestrial liquid water has been found.
- Has the largest known volcano (and second
tallest mountain) in the solar system – Mons Olympus.
- Spacecrafts to Mars: Mariner 4, 2001 Mars
Odyssey, Mars Orbiter Mission (India), MAVEN etc.
- Rovers on Mars: Opportunity, Curiosity, Spirit
(decommissioned).
Jupiter
- Largest planet of the solar system.
- Has two and a half times the mass of all other
planets put together.
- Has the shortest rotation period.
- A gas giant, primarily composed of hydrogen
and helium with no discernible solid surface.
- Has a giant storm (three times the diameter of
earth) since 1831 called the ‘Great Red Spot’.
- Has a faint ring around it.
- Has 67 moons.
- 4 largest moons discovered by Galileo –
Ganymede (largest moon in the solar system – bigger than Mercury),
Callisto, Io (volcanic), Europa (has water-ice).
- Missions to Jupiter: Galileo, Juno (upcoming).
Saturn
- Second largest planet in the Solar system.
- Its density is less than the water.
- Has a band of concentric rings revolving
around it made up of tiny rocks and pieces of ice.
- Has 62 moons.
- Moons of Saturn: Titan is the largest (has a
major atmosphere, complex organic chemistry and ICE VOLCANOES), Rhea (may have its own ring system), Enceladus.
- Missions to Saturn: Cassini-Huygens.
Uranus
- Discovered by Sir William Herschel.
- Blue-green (cyan) in colour.
- Revolves around the sun in clockwise manner
- Third biggest planet of the solar system.
- Composed of Hydrogen, Helium, Water, Ammonia,
Methane.
- It is tilted sideways so that its poles lie
where most other planets have their equators.
- Has faint rings.
- Has 27 known moons (5 main – Miranda, Ariel,
Umbriel, Titania, Oberon).
- Spacecraft Flyby: Voyager 2.
Neptune
- Discovered by mathematical predictions and
disturbances in Uranus’ orbit.
- First proposed by Alexis Bouvard, and first
observed by Johann Galle.
- Farthest planet from the Sun.
- Primarily composed of hydrogen, helium,
nitrogen, water, ammonia, methane.
- Is blue in colour because of methane.
- Has a storm called ‘Great Dark Spot’.
- Has 14 known moons (Triton – largest)
- Spacecraft Flyby: Voyager 2.
Pluto
- Used to be the ninth planet.
- Demoted to status of “Dwarf Planet”.
- Icy and cold.
- Has five moons – Charon, Styx, Nix, Kerberos,
Hydra.
Asteroids
- Almost like planets but smaller in size.
- Not spherical in appearance.
- Revolve around the Sun.
- Most of them are found in a belt between Mars
and Jupiter.
- The largest asteroid in the Asteroid Belt is
Ceres.
Meteorites
- Meteoroids are formed due to the collisions
between asteroids.
- They are fragments of rocks floating about in
space.
- Sometimes they come across earth and fall into
the earth’s atmosphere. That’s when they become meteors or “shooting
stars”.
- Most of these meteors can’t reach earth’s
surface and burn up in the atmosphere due to the friction with air.
- The meteors that do reach the earth’s surface
are known as meteorites.
Comets
- Tiny icy and rocky bodies that travel in
highly elliptical orbits around the sun.
- When they pass close to the sun, they water
and gases heat up.
- This leads to the formation of a tail behind
the rocky core in the direction opposite to the sun.
- Most famous comet is Halley’s Comet which
reappears every 75-76 years.
- Last appeared: 1986. Next appearance: 2061.