1. The document provides information about several planets and objects in our solar system including Mercury, Venus, Earth, Mars, Jupiter, Saturn, and their moons and rings. 2. Key details include how Mercury has extreme temperature variations between day and night, Venus has the longest day length of any planet, and Earth is the only known planet to support life. 3. The gas giants Jupiter and Saturn are described as not having solid surfaces and having colorful atmospheric bands created by strong winds. Jupiter has the Great Red Spot storm and many moons, while Saturn is notable for its extensive ring system.

3. Solar System, the Sun and everything that orbits the
Sun, including the planets and their satellites; the dwarf
planets, asteroids, Kuiper Belt Objects, and comets

4. Our Sun produces most of
the neutrinos that pass
through Earth. The nuclear
reactions that fuel the Sun
produce so many neutrinos
that the small fraction of
neutrinos hitting Earth
amounts to 70 billion
neutrinos per square
centimeter per second.

5. 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. This
composite photograph was taken in
1974 by Mariner 10, the first probe to
study Mercury in detail.

6. It really cools off at night on Mercury. The temperature can drop as low as -290°
Fahrenheit (-180° Celsius) after the Sun goes down. So Mercury doesn’t just get
hotter than anywhere on Earth. It also gets colder! It gets so cold partly because
Mercury has almost no atmosphere. An atmosphere is the gases around a planet. On
Earth, the gases act like a blanket that holds in heat. Another reason it gets so cold is
that Mercury turns slowly. On Mercury, night lasts much longer than it does on Earth,
and all the heat leaks away into space.
TIME ON MERCURY
Daytime temperatures on Mercury can soar to 810° Fahrenheit (430° Celsius). That is
hot enough to melt some metals! Mercury gets so hot because it is so close to the
Sun. Mercury is 36 million miles (58 million kilometers) from the Sun, on average. Its
distance from the Sun changes somewhat throughout the year. Earth is about three
times farther from the Sun.

7. Not even the hottest day at
the hottest place on Earth
comes close to how hot it
gets on Mercury. Mercury is
one of the nine planets in
our solar system. Mercury is
the closest planet to the
Sun.

9. Days on Venus seem endless. Venus is the second planet from the Sun. One day on
Venus is as long as 243 days on Earth. A year on Venus is only 225 Earth days long. So a
day on Venus is longer than a year!
WHY DOES VENUS HAVE LONG DAYS?
Venus orbits, or goes around, the Sun just as all the planets do. It takes Venus 225 days to
go around the Sun. Earth goes around the Sun in 365 days. We call the time it takes
Earth to go around the Sun a year.
Venus also spins around on its axis. An axis is an imaginary line going through a planet
from top to bottom. Every planet spins on its axis. One day on Earth is the time it takes
for Earth to turn completely around on its axis. Earth turns once every 24 hours. Venus
turns much more slowly. It takes Venus 243 Earth days just to turn once.
Venus also spins backwards around its axis. It spins in the opposite direction that Earth
spins. On Venus, the Sun rises in the west and sets in the east.

10. Venus is more like Earth in some ways than any other planet. It is almost the same size
as Earth. It is a similar distance from the Sun compared to the other planets. It is made
mostly of rock and has an atmosphere (gases that surround a planet).
Venus has flat plains and high places, just like Earth. It has huge extinct (dead)
volcanoes and big craters. Meteorites crashing into the planet made the big craters. But
Venus has no moon.
In other ways, Venus is not at all like Earth. It is not a place you would like to visit. The
atmosphere is poisonous. It is made up mainly of a gas called carbon dioxide. The clouds
are filled with drops of powerful acid “rain” that would eat through your clothes—and
through you. The atmosphere is so thick that its weight would crush you. There is no
water on Venus.
It is very hot on Venus. The temperature on the surface is about 864° Fahrenheit (462°
Celsius). That’s more than four times as hot as boiling water. No plants or animals could
live in a place that hot .

11. 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. The Apollo 17
spacecraft took this snapshot in 1972 of the
Arabian Peninsula, the African continent,
and Antarctica (most of the white area near
the bottom).

12. HOW DOES EARTH MOVE IN SPACE?
Earth spins like a top on its axis. Earth’s axis is an imaginary line that goes
through Earth from the North Pole to the South Pole. Earth’s axis is slightly tipped
like a spinning top leaning to one side.
Earth travels around the Sun at about 67,000 miles per hour (about 107,000
kilometers per hour). One year is one trip around the Sun. Earth’s path around the
Sun is slightly oval-shaped. This oval shape causes Earth’s distance from the Sun
to change during the year.
WHAT MAKES DAY AND NIGHT?
The Sun seems to rise in the morning, cross the sky during the day, and set at
night. However, the Sun does not actually move around Earth. Earth’s turning on
its axis makes it look as if the Sun is moving.
Earth makes a complete turn on its axis every 24 hours. As Earth turns, half of
the planet faces the Sun, and the other half faces away. It is daytime on the half
facing the Sun. It is night on the half facing away from the Sun.

13. The most detailed information
available about Mars has come from
unpiloted spacecraft sent to the
planet by the United States. 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.

14. The moons of Mars,
Phobos (lower right) and
Deimos (lower left), appear
in this collage with the
asteroid Gaspra (top) for
comparison. Phobos and
Deimos may be asteroids
captured long ago by the
gravity of Mars. All three
are shown at the same
scale.

15. The Viking orbiters took more than 50,000
pictures of the surface of Mars. This
animation was created by making a mosaic
of Viking orbiter images and enhancing the
natural color to make features more
apparent. The path of the animation is along
Valles Marineris, a system of Martian
canyons over 4000 km (over 2400 mi) long
and over 7 km (over 4 mi) deep in some
places.

17. 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. The massive
planet, upper right, is shown here
with its four largest satellites: Io,
upper left, Ganymede, lower left,
Europa, center, and Callisto,
lower right.

18. WHAT’S IT LIKE ON JUPITER?
You could never land a spacecraft on Jupiter. Jupiter does not have a hard surface.
Astronomers (scientists who study space) call Jupiter a gas giant because it’s made almost
entirely of gas. From space, Jupiter looks striped. The stripes are actually bands of colored
clouds that circle the planet.
The clouds near the top of the atmosphere are bathed in deadly radiation. Jupiter's highest
clouds are also very cold. The clouds get hotter deeper down. Strong winds blow in opposite
directions in each band of clouds. In one band, the winds blow toward the east. In the next
band, they blow toward the west.
Big storms rage in the clouds around Jupiter. The biggest storm is called the Great Red Spot.
Three planets the size of Earth could fit across the Great Red Spot. This storm may have lasted
for hundreds of years.
Deeper into the planet, the gas gets thicker and heavier. It gets so heavy that some of it gets
squeezed into a layer of liquid hydrogen. Astronomers think that there might be some rock and
metal in the center, or core, of Jupiter.
JUPITER’S MOONS AND RINGS

19. 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.

20. Saturn’s Atmosphere
This infrared photo of the planet
Saturn has been color coded to
indicate the cloud level in Saturn’s
atmosphere. Violet and blue
represent areas in which Saturn’s
atmopshere is clear down to the main
cloud layer. Green and yellow show
layers of haze above the main cloud
layer (yellow represents thicker haze).
Red and orange indicate the highest
level of clouds, thicker than the haze.
White areas are areas of the
atmosphere with high levels of water
vapor. The bright dots at the upper
right and lower left of the picture are
Saturn’s satellites Tethys and Dione,
respectively. The Hubble Space
Telescope took this image in 1998.

21. WHAT IS SATURN LIKE?
Saturn is a huge ball of gas. Like the planets Jupiter, Neptune, and
Uranus, Saturn is called a gas giant. None of the gas giants have a
solid surface that you could land a spacecraft on.
The gases around Saturn are poisonous to people. You need to
breathe oxygen in order to live. Saturn’s atmosphere is mostly
hydrogen and helium gas. An atmosphere is the layer of gases
around a planet.
There are thick clouds in Saturn’s atmosphere. The clouds look
like colored stripes going around the planet. Strong winds and
storms make Saturn’s clouds whirl and swirl.
Saturn’s atmosphere blends into the center of the planet. The
gases get thicker and heavier the farther down you go. Finally,
the gas turns to liquid.
Astronomers think that the center, or core, of Saturn is very hot.
They think the temperature could be about 27,000° Fahrenheit
(15,000° Celsius). There are probably rocks and possibly iron in
the core of Saturn.
Saturn acts like a big magnet in space. Other planets, including
Earth, also act like big magnets.

22. Saturn’s rings are extremely wide,
but very flat, bands created by
orbiting fragments of rock, gas,
and ice. Close examination reveals
that there are more than 100,000
separate ringlets. Voyager 2
captured this enhanced view as it
flew by the planet in 1981.

23. 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. Scientists
compiled this view of Uranus from
images returned from Voyager 2 in 1986,
when the probe was 9.1 million km (5.7
million mi) away from the planet.

24. Uranus and Its Moons
The planet Uranus (the bright blue object) is
surrounded by its five largest satellites
clockwise from top left, Ariel, Umbriel,
Oberon, Titania, and Miranda, in this
collage created from photographs taken by
the United States Voyager 2 spacecraft in
1986.

25. 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.

26. The 1989 Voyager 2 mission
produced this false-color
image of Neptune showing
the different components of
Neptune’s atmosphere. The
red layer shows scattered
sunlight from a haze around
the planet, the blue/green
indicates methane, and the
white areas are high-level
clouds that reflect sunlight
above the atmosphere.

27. Kuiper Belt Beyond Neptune

28. WHAT IS IT LIKE ON NEPTUNE?
We could not breathe on Neptune, and the fierce winds would blow you away. Even
without the winds, you could not walk on Neptune because the planet has no solid
surface.
A thick layer of clouds surrounds Neptune. The clouds are part of the planet’s
atmosphere. An atmosphere is made of gases. Neptune’s atmosphere is made mostly of
hydrogen and helium gases. Some methane gas high in the atmosphere gives Neptune its
bluish color. You could not breathe the gases in Neptune’s atmosphere. You need to
breathe oxygen in order to live. There is no oxygen in Neptune’s atmosphere.
Blowing clouds make striped patterns around Neptune. Sometimes there are spots in the
clouds. The spots are storms. Neptune has the fastest winds in the solar system. The
winds on Neptune can blow at 1,200 miles per hour (2,000 kilometers per hour).
Scientists have made guesses about what the inside of Neptune is like. Scientists think
the planet’s thick atmosphere blends into an ocean of water. The core (center) of
Neptune may be made of ice and rock.

29. Asteroids are rocks in space that never quite
made it as planets. Astronomers think that
our solar system began as a cloud of gas and
dust. Gravity pulled parts of the cloud
together to make the Sun and the nine
planets. Astronomers think that the
asteroids formed in that cloud but never
grew large enough to be planets.
Asteroids go around, or orbit, the Sun just like planets. Most asteroids orbit in the
asteroid belt. The asteroid belt is farther out from the Sun than Earth’s orbit. It lies
between the orbits of the planets Mars and Jupiter.
Sometimes asteroids change orbits and move out of the asteroid belt. These
asteroids cross the orbits of planets as the planets go around the Sun. A few cross
Earth’s orbit.

30. Asteroid Impacts
Asteroids and comets sometimes hit Earth. In 1908, an
asteroid or comet flattened trees, left, over more than 400
square miles (1,000 square kilometers) in Russia. About
50,000 years ago, an asteroid carved out a huge crater,
right, in what is now Arizona.