The solar system consists of the Sun and everything that orbits it, including eight planets and their natural satellites, as well as smaller objects like asteroids and comets. The four inner planets closest to the Sun are Mercury, Venus, Earth, and Mars. The four outer planets are Jupiter, Saturn, Uranus, and Neptune. Pluto, once considered the ninth planet, is now classified as a dwarf planet. Several large moons in the solar system are comparable in size to dwarf planets.

1. Solar System
The Sun and everything that orbits
the Sun, including the nine planets
and their satellites; the asteroids
and comets; and interplanetary dust
and gas.
02:50 Author: Tomas U. Ganiron Jr 1

2. MERCURY
• Mercury orbits closer to the Sun than any
other planet, making it dry, hot, and virtually
airless. Although the planet’s cratered surface
resembles that of the Moon, it is believed that
the interior is actually similar to Earth’s,
consisting primarily of iron and other heavy
elements.
02:50 Author: Tomas U. Ganiron Jr 2

3. VENUS
• Venus is the brightest object in our sky, after the
sun and moon. Swirling clouds of sulfur and
sulfuric acid obscure Venus’s surface and
inhibited study of the planet from Earth until
technology permitted space vehicles, outfitted
with probes, to visit it. These probes determined
that Venus is the hottest of the planets, with a
surface temperature of about 460° C (about 860°
F). Scientists believe that a greenhouse effect
causes the extreme temperature, hypothesizing
that the planet’s thick clouds and dense
atmosphere trap energy from the sun.
02:50 Author: Tomas U. Ganiron Jr 3

4. EARTH
• An oxygen-rich and protective atmosphere,
moderate temperatures, abundant water, and
a varied chemical composition enable Earth to
support life, the only planet known to harbor
life. The planet is composed of rock and metal,
which are present in molten form beneath its
surface.
02:50 Author: Tomas U. Ganiron Jr 4

5. MARS
• The most detailed information available about Mars
has come from unpiloted spacecraft sent to the planet
by the United States between 1964 and 1976. From
this data, scientists have determined that the planet’s
atmosphere consists primarily of carbon dioxide, with
small amounts of nitrogen, oxygen, water vapor, and
other gases. Because the atmosphere is extremely thin,
daily temperatures can vary as much as 100 Celsius
degrees (190 Fahrenheit degrees). In general, surface
temperatures are too cold and surface pressures too
low for water to exist in a liquid state on Mars. The
planet resembles a cold, high-altitude desert.
02:50 Author: Tomas U. Ganiron Jr 5

6. JUPITER
• Jupiter is the largest of the planets, with a
volume more than 1,300 times greater than
that of Earth. Jupiter’s colorful bands are
caused by strong atmospheric currents and
accentuated by a dense cloud cover.
02:50 Author: Tomas U. Ganiron Jr 6

7. SATURN
• Saturn, distinguished by its rings, is the second
largest planet in the solar system. This
processed Hubble Space Telescope image
shows the planet’s cloud bands, storms, and
rings as they would appear to the human eye.
02:50 Author: Tomas U. Ganiron Jr 7

8. URANUS
• Uranus’s blue-green color comes from the
methane gas present in its cold, clear
atmosphere. The dark shadings at the right
edge of the sphere correspond to the day-
night boundary on the planet. Beyond this
boundary, Uranus’s northern hemisphere
remains in a four-decade-long period of
darkness because of the way the planet
rotates.
02:50 Author: Tomas U. Ganiron Jr 8

9. NUPTUNE
• This image of Neptune, taken by the Voyager 2
spacecraft, shows the planet’s most
prominent features. The large, dark oval
surrounded by white clouds near the planet’s
equator is the Great Dark Spot, a storm similar
to Jupiter’s Great Red Spot. The smaller dark
oval with a bright core below and to the right
of the Great Dark Spot is another storm
known as Dark Spot 2.
02:50 Author: Tomas U. Ganiron Jr 9

10. PLUTO
• Pluto is farther from the Sun than the other
planets in the solar system, although it
occasionally moves in closer than Neptune
due to an irregular orbit. The small, rocky, and
cold planet takes 247.7 years to revolve
around the Sun. This artist's rendition depicts
Pluto, foreground; its moon, Charon,
background; and the distant Sun, upper right.
02:50 Author: Tomas U. Ganiron Jr 10

11. • Some of the largest
moons in the solar
system are as large as
or larger than the
smallest planets.
Depicted here to scale
are top row, from left
to right, Earth, Mars,
Mercury, and Earth's
moon; second row,
Jupiter’s satellites Io
and Europa; third row,
Jupiter’s moons
Ganymede and
Callisto; and bottom
row, Venus and
Saturn’s moon Titan.
02:50 Author: Tomas U. Ganiron Jr 11

12. SUN
02:50 Author: Tomas U. Ganiron Jr 12