3. Solar System
The Solar System comprises the Sun and the objects that orbit it,
whether they orbit it directly or by orbiting other objects that orbit it
Of those objects that orbit the Sun directly,
the largest eight are the planets that form the planetary system
while the remainder are significantly smaller objects,
such as dwarf planets and small Solar System bodies (SSSBs) such
as comets and asteroids.
The Sun is the star at the center of
the Solar System.
It is almost spherical and consists of
hot plasma interwoven with magnetic
It has a diameter of about 1,392,684
km, around 109 times that of Earth,
and its mass
accounts for about 99.86% of the
total mass of the Solar System.
Chemically, about three quarters of
the Sun's mass consists of hydrogen,
whereas the rest is mostly helium.
The remaining 1.69% consists of
heavier elements, including oxygen,
carbon, neon and iron.
Mercury is the closest to the Sun
of the eight planets in the Solar
with an orbital period of about 88
Earth days. Seen from Earth,
it appears to move around its orbit
in about 116 days,
which is much faster than any
other planet. It has no known
natural satellites. Because it has
almost no atmosphere to retain
heat, Mercury's surface
experiences the greatest
temperature variation of all the
planets, ranging from −173 °C to
427 °C. Mercury consists of
70% metallic and
30% silicate material.
The planet is named after the
Roman deity Mercury, the
messenger to the gods.
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days.
It has no natural satellite. It is named after the Roman goddess of love and beauty.
After the Moon, it is the brightest natural object in the night sky,
reaching an apparent magnitude of -4.6, bright enough to cast shadows. The
maximum temperature is 462°. It is the hottest planet in the Solar System. Venus
has the densest atmosphere of the four terrestrial planets, consisting of more than
96% carbon dioxide.
Earth, also known as the world, Terra, or Gaia, is the third planet from the Sun,
the densest planet in the Solar System. The only celestial body known to accommodate life.
It is home to over eight million species. 71% percent of Earth's surface is covered with water.
Earth gravitationally interacts with other objects in space, especially the Sun and the Moon. During one
orbit around the Sun, the Earth rotates about its own axis 366.26 times, creating 365.26 solar days, or
There are over 7.2 billion humans who depend upon its biosphere and minerals.
The Earth's human population is divided among about two hundred independent states that interact
through diplomacy, conflict, travel, trade, and media.
The Moon is Earth's only natural satellite.
Although not the largest natural satellite in the Solar System, it is, among the satellites
of major planets, the largest relative to the size of the object it orbits.
It is the second-densest satellite among those whose densities are known.
The Moon is similar to the Earth in that it has a crust, mantle, and core. The
composition of the two bodies is similar, which is part of why scientists think the Moon
may have formed from a large impact breaking off a piece of Earth when it was
forming. The crust consists of 43% oxygen, 20% silicon, 19% magnesium, 10% iron,
3% calcium, 3% aluminum.
Mars is the fourth planet from the Sun, named after the Roman god of war.
It is often described as the "Red Planet" because the iron oxide prevalent on its
surface gives it a reddish appearance. Mars is a terrestrial planet with a thin
atmosphere. Mars is the site of Olympus Mons,
the second highest known mountain within the Solar System. The smooth Borealis
basin in the northern hemisphere covers 40% of the planet and may be a giant
impact feature. Mars has two moons, Phobos and Deimos, which are small and
Jupiter is the fifth planet from
the Sun and the largest planet in
the Solar System. Jupiter's upper
atmosphere is composed of about 88–
92% hydrogen and 8–12% helium.
Jupiter's mass is 2.5 times that of all
the other planets in the Solar System
Saturn is the
sixth planet from the Sun.
Named after the Roman god
of agriculture, its astronomical
symbol (♄) represents the
Saturn's interior is probably
composed of a core
of iron, nickel and rock,
surrounded by a deep layer
of metallic hydrogen.
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 rocks and dust.
Uranus is the
seventh planet from
the Sun. Uranus is similar in
composition to Neptune.
Uranus's atmosphere contains
more "ices", such as
water, ammonia, and methane,
along with traces
of hydrocarbons. It is the
coldest planetary atmosphere in
the Solar System, with a
minimum temperature of
−224.2 °C, and has a complex,
layered cloud structure.
Neptune is the eighth and farthest planet from the Sun in the Solar System.
Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus.
Neptune orbits the Sun at an average distance of 30.1astronomical units. Named after the Roman
god of the sea, its astronomical symbol is ♆, a stylised version of the god Neptune's trident.
1. Upper atmosphere, top clouds
2. Atmosphere consisting of hydrogen, helium and methane gas
3. Mantle consisting of water, ammonia and methane ices
4. Core consisting of rock (silicates and nickel–iron)