ball of hydrogen and helium gases. It
constantly changes the hydrogen in its
core into helium. This process gives out
huge amounts of energy. Living things
on Earth depend on light and heat from
the sun.
The SolarWind
The gases that surround the sun shoot
out a stream of tiny particles called the
solar wind. It flows outward through the
whole solar system. The solar wind is
what causes auroras, or displays of colored
light in the night sky in parts of
Earth.
The Planets
After the sun, the largest objects in the
solar system are the planets. In order
from closest to the sun, these planets are
Mercury, Venus, Earth, Mars, Jupiter,
Saturn, Uranus, and Neptune. Most of
them orbit the sun in paths shaped like
The Oort Cloud is part of the solar system. It consists of countless small, icy objects. Many
comets were once part of the Oort Cloud.
BRITANNICA STUDENT ENCYCLOPEDIA Solar System 127
circles. Most of the planets have at least
one moon. Scientists used to call Pluto
the ninth planet. But in 2006 scientists
decided to call Pluto a dwarf planet
instead.
Asteroids
Millions of small chunks of metal and
rock called asteroids also orbit the sun.
Most asteroids are found in a ring
between Mars and Jupiter. Small asteroids
regularly fall to Earth or burn up in
the sky as glowing meteors.
Comets
Comets are small chunks of dirt and ice.
Billions of them orbit the sun in very
long paths shaped like ovals. Most comets
are too small or too distant to ever be
seen from Earth. Comets come from
two parts of the outer solar system: the
Kuiper Belt and the Oort Cloud.
Outer Regions
Beyond Neptune lies the Kuiper Belt, a
flat ring of millions of small, icy
objects. These objects orbit the sun at a
very great distance. They are mostly 30
to 50 times farther from the sun than
Earth is.
At the outer reaches of the solar system
is the Oort Cloud. It is a huge cloud of
countless small, icy objects. The Oort
Cloud surrounds the rest of the solar
system.
How the Solar SystemWas
Formed
The solar system formed about 4.7 billion
years ago. It probably started as a
loose cloud of gas and dust. Scientists
think that a force called gravity pulled
parts of the cloud together into clumps.
The largest clump was squeezed together
so tightly that it got very hot. This
clump eventually became the sun. Over
millions of years the other clumps
became the planets. The sun’s strong
gravity eventually pulled the planets into
their orbits. Over time some of the leftover
clumps became asteroids, comets,
and other small, icy objects.
#More to explore
Asteroid • Comet • Galaxy • MilkyWay
• Planets • Sun • Universe
Some Facts About the Planets
Period of Period of Orbit
Rotation Around Sun
Date Diameter (Length of Day) (Length of Year)
Name Discovered (approximate) in Earth Days in Earth Years
Mercury ancient times 3,000 mi (4,900 km) 58.6 0.24
Venus ancient times 7,500 mi (12,100 km) 243 0.62
Earth 7,940 mi (12,780 km) 0.997 1
Mars ancient times 4,200 mi (6,800 km) 1.03 1.88
Jupiter ancient times 89,000 mi (143,000 km) 0.41 11.86
Saturn ancient times 74,900 mi (120,600 km) 0.44 29.4
Uranus 1781 32,000 mi (51,000 km) 0.72 84
Neptune 1846 31,000 mi (50,000 km) 0.67 164
128 Solar System BRITANNICA STUDENT ENCYCLOPEDIA
Solomon Islands
The Solomon Islands is a country in the
southwestern Pacific Ocean. The capital,
Honiara, is on the country’s largest
island, Guadalcanal.
The islands lie east of Papua New
Guinea, in the region called Oceania.
The country includes eight main islands
and hundreds of small islands. The main
islands have many mountains and volcanoes.
Many of the small islands are
made of coral. The country’s climate is
hot, humid, and rainy.
Thick rain forests cover most of the
land. Mangroves and coconut trees grow
along the coasts. Many flowering plants,
including orchids, also grow on the
islands. The country has a wide variety
of birds, butterflies, fish, and reptiles.
Most of the country’s people are
Melanesians, or people native to the
southwestern Pacific islands. There are
many local languages. The different
groups communicate using Pijin, a language
based on English. Most of the
people live in small villages.
The economy is based on farming, logging,
and fishing. Farmers grow coconuts,
sweet potatoes, taro, yams, and
fruits. They raise pigs, cattle, and chickens.
The Solomon Islands produces
palm oil and cocoa.
People have lived on the Solomon
Islands for at least 4,000 years. Spanish
explorers visited the islands in 1568.
Great Britain gained control of the
islands by 1899.
In 1978 the Solomon Islands became
independent from Britain. Since independence,
violence between different
groups has been a serious problem.
..More to explore
Honiara • Oceania
Coral reefs surround some of the
small islands in the Solomon
Islands group.
Facts About
SOLOMON
ISLANDS
Population
(2008 estimate)
517,000
Area
10,954 sq mi
(28,370 sq km)
Capital
Honiara
Form of
government
Constitutional
monarchy
Major towns
Honiara, Noro,
Gizo, Auki,
Tulagi
BRITANNICA STUDENT ENCYCLOPEDIA Solomon Islands 129
Somalia
The country of Somalia in northeastern
Africa is a hot and dry land. Many of
