Download Jupiter, the fifth planet from the sun and the largest planet in our

Jupiter
Jupiter, the fifth planet from the sun
and the largest planet in our solar
system, reigns over at least 63 moons
and a delicate, dark system of rings.
Jupiter is classified as a gas giant. Its
mass is a little less than onethousandth that of the sun, yet it is
more than two and a half times as
massive as all the other planets
combined.
One of Jupiter’s most famous
features is the Great Red Spot. The
Great Red Spot is a huge cyclonic
storm. It has persisted for at least
180 years and possibly since 1664. The storm varies in size, but is so big that
you could fit two or three Earth-sized planets inside it. The smaller white
spots are also storms.
Jupiter’s diameter is about eleven times the diameter of Earth. Despite its
huge size, it rotates incredibly fast making one complete rotation in just over
nine hours. At the equator, Earth is moving at about 1,600 km per hour (1000
miles per hour). Jupiter’s equatorial speed is about 45,300 km per hour
(28,150 miles per hour).
Jupiter is one of the five planets known since ancient times, but its four largest
moons were not discovered until Galileo trained his telescope on the sky in
1610. This discovery completely changed the way we thought of ourselves
and the Universe. Before this discovery, we believed we were the center of
the Universe and everything revolved around us. When we saw another
heavenly body out there with objects orbiting around it, we were forced to rethink a lot of things.
Saturn
Saturn, the sixth planet from the sun
and second largest in our solar
system, is famous for its rings. It has 61 known moons plus hundreds of
moonlets within the ring system.
Saturn’s ring system appears from Earth to be a few broad rings. It really
consists of more than 100,000 individual “ringlets.” They contain countless
icy particles. Most are the size of dust grains, but some are as big as houses,
each orbiting Saturn like a little moon. The ring system is wider than 20
Earths placed side-by-side, but only as thick as a football field is long.
Saturn is the second of the four gas giants. It is as massive as 95 Earths, but
its density is so low that it would float in water.
The winds on Saturn are even stronger than Jupiter’s, reaching up to 1,800 km
per hour (1,100 miles per hour).
Like Jupiter, despite its large size Saturn is rotating very fast. A day on Saturn
is 10 hours and 39 minutes compared to about 24 hours on Earth.
Saturn’s moon Titan is the second largest in the solar system (after Jupiter’s
moon, Ganymede) and is the only moon in the
solar system to have an atmosphere.
Two of Saturn’s moons are quite odd. Iapetus
is quite dark on one side and very bright on the
other. Mimas (at right) has a giant crater that
makes it look like the Death Star from the Star
Wars movies.
Saturn’s moon, Mimas
Uranus
Uranus (YUR uh nuhs), the seventh
planet from the sun, looks bland,
enshrouded by a haze that clouds our
view. Uranus is classified as a gas
giant and, like the other gas giants,
has a set of rings. However, Uranus’
rings are very thin and dark.
Uranus is the first planet discovered
since ancient times; a British
astronomer, William Herschel,
discovered it in 1781. Uranus has 21 known satellites. Miranda, the fifth
largest satellite, is a bizarre looking place with certain surface features that are
unique in our solar system (see picture below).
Uranus and Neptune both have very different compositions from the other gas
giants, Jupiter and Saturn. Astronomers sometimes refer to them as “ice
giants” because their atmospheres contain ices. Uranus’ atmosphere is the
coldest in the solar system,
As each planet orbits the sun, it spins like a top on an axis that stays tilted in a
particular direction. Earth is tipped 23.5°. Uranus is tilted more than any
other planet. Tipped at 98°, it spins almost on its
side. Its north and south poles are where most
planets have their equators. Its rings are also tilted.
Viewed from Earth, its ring system makes it look
like an archery target. Many astronomers think that
a collision with an Earth-sized planet may have
knocked Uranus on its side soon after it was
formed.
Uranus’ moon, Miranda
Orion
Nebula
The
The Orion Nebula is one of the brightest
nebulae and is visible to the naked eye. It
is the closest region of massive star
formation to Earth. Because of its
function as a stellar nursery – a birth place
and source of newly born stars – it is one of the most intensely studied
celestial objects. The nebula has revealed much about the process of how
stars and planets are formed.
The Orion Nebula contains a young cluster of stars called the Trapezium (the
four stars at the center of the picture above). Two of these stars are actually
binary systems – two stars that revolve around each other.
Betelgeuse
The Orion Nebula
Rigel
The Orion Nebula is part of
the sword in the constellation
Orion. This constellation,
shown at the left, is one of the
most easily recognized
constellations in the night sky
with it’s distinctive “belt”
formed by three bright stars in
a row, one shoulder formed
by Betelgeuse, and one foot
formed by Rigel. Betelgeuse
is the twelfth brightest star in
the sky and Rigel is the sixth
brightest.
Andromeda
Galaxy
The
The Andromeda Galaxy is a spiral galaxy
about 2.5 million light years away. On a
good night, it is visible as a faint smudge
making it one of the farthest objects
visible to the naked eye. Andromeda is
the nearest spiral galaxy to our own
Milky Way.
Andromeda is the largest galaxy in our
local group which consists of Andromeda, our Milky Way, the Triangulum
Galaxy and about 30 smaller galaxies. NASA’s Spitzer Telescope surveyed
Andromeda in 2006 and determined that it contains one trillion stars, several
times the 200-400 billion stars our Milky Way contains. Although
Andromeda is larger and has more stars, the Milky Way appears to have more
dark matter making it more massive.
Astronomers believe that all large galaxies
have a black hole at their center. Evidence was
found for this in Andromeda’s case.
Astronomers hypothesize a possible collision
between the Andromeda Galaxy and the Milky
Way. There is no way (yet) to know for sure if
this will happen but you still don’t need to worry for two reasons. First, it will
be about 4.5 billion years before it occurs. Second, if it does happen, there is
so much empty space between stars that the galaxies will merge with each
other with very little interaction. We probably wouldn’t even notice.
The
Moon
The Moon is Earth’s only natural satellite.
It is the fifth largest satellite in the solar
system. The Moon’s diameter is a little
more than a quarter that of Earth. The
pull of gravity at its surface is about 17%
(one-sixth) that of Earth.
The Moon is in synchronous rotation
about Earth which means that it rotates
about its axis in about the same time it takes to orbit Earth. This causes one
side of the moon to face Earth. Small variations (libration) in angles allow us
to see a total of about 59% of the Moon’s surface (but only 50% at any given
time). The side that faces Earth is called the near side and the opposite is
called the far side. The far side is often incorrectly called the “dark side” but
the sun shines on the far side just as often as it does on the near side.
The dark areas, maria, are solidified pools of basaltic lava. The majority of
these are associated with impact basins formed by meteors and comets. The
lighter colored areas, highlands, are usually mountain ranges and are believed
to be leftovers from the outer rims of the impact basins.
We have sent robotic vehicles to many other
bodies in the solar system, but the Moon is the
only place (other than Earth) on which humans
have landed. Between 1969 and 1972, twelve
humans landed on, explored and collected
samples from the Moon. These samples are
still undergoing intense study by scientists.
Astronaut Harrison Schmitt with a
boulder in the background and lunar
rover in the foreground.
In May 2009, NASA’s LCROSS mission
discovered proof of significant quantities of
water on the moon.
The
Sun
The Sun is the star at the center of our
solar system. Its diameter is more than
100 times that of Earth. By itself, it holds
about 99.9% of the mass of the entire solar
system – all the other planets, moons,
asteroids, comets, meteors and dust –
combined. About three-fourths of the
Sun’s mass is hydrogen and most of the rest is helium.
The Sun travels through the Local Interstellar Cloud within the inner rim of
the Orion Arm of the Milky Way Galaxy. The Sun is about 25,000 light years
from the center of the Milky Way and orbits the galactic center in about 225250 million years.
The Sun is about 150 million km (93 million miles) from Earth. It takes light
from the Sun about 8.3 minutes to reach Earth. The energy of sunlight
supports almost all life on Earth and powers Earth’s climate and weather. The
sunlight spans the electromagnetic spectrum – “light” is much more than what
we humans can see. To study the Sun, scientists take advantage of special
instruments that can measure the other forms of light radiated by the Sun.
Below are images of the Sun taken in increasing frequency of the
electromagnetic spectrum of light.
radio frequency
infrared
visible light
ultraviolet
x-ray
Mercury
Mercury is the closest planet to the sun.
It is classified as a terrestrial planet along
with Venus, Earth and Mars. Mercury is
an “extreme” planet. It is the smallest,
the most dense, it has the oldest surface
and the greatest daily variation in surface temperature. But, it is the least
explored of the inner planets.
Mercury is the smallest planet in our solar system (now that Pluto is not
considered a planet). It is only slightly larger than the Moon. Like the Moon,
it has almost no atmosphere to stop impacts so it is covered with craters.
During its day, the surface of Mercury is super heated by the sun to about
800°F. At night, the temperature will drop to a chilly 279°F below zero!
Only two spacecraft have visited Mercury. The first, Mariner 10, mapped
about 45% of the surface in 1974-1975. The second, MESSENGER, is on its
way and will settle into orbit around Mercury in 2011. During recent flybys,
MESSENGER mapped more of Mercury’s surface and revealed more of
Mercury than had ever been seen before.
Despite the generally high temperatures on Mercury, scientists think there may
be water there. The Moon was also thought to be a dry and barren place,
totally devoid of water until November 2009, when NASA’s LCROSS
mission provided conclusive evidence that water does exist inside the craters
at the lunar poles. Radar observations of Mercury provide astronomers with
strong evidence of ice. While ice is not the only explanation for the radar
data, scientists think it is the most likely cause because the floors of deep
craters near the poles are never exposed to sunlight and temperatures there
remain far below the freezing point of water.
Venus
Venus is the second closest planet to the
sun. After the Moon, Venus is the
brightest natural object in the sky. Because
it is between Earth and the Sun, from our
point of view, it never strays far from the
Sun and thus reaches its maximum
brightness shortly before sunrise or after
sunset. For this reason, it is often called the Morning Star or Evening Star.
Venus is sometimes called Earth’s “sister planet” because they are similar in
size, gravity and composition. A younger Venus is thought to have had Earthlike oceans but these evaporated as the temperature rose. Now, most of the
atmosphere is carbon dioxide. Venus is of interest to Earth scientists because
of these similarities and the differences.
Venus is now covered in an opaque layer of clouds of sulfuric acid which
prevents its surface from being seen in visible light. Scientists can show that
because of the small difference in distance from the Sun, Venus should be
only a few degrees warmer than Earth. However, Venus holds the dubious
honor of being the hottest planet in the solar system at 864°F, even hotter than
Mercury.
Because of the cloud cover, NASA sent the Magellan spacecraft to study
Venus using radar. The ground shows signs of recent volcanism but no signs
of lava flows, puzzling scientists. The image at the top of the page is a result
of that mission.
Venus is also different in how it rotates. All planets in our solar system orbit
around the sun in a counter-clockwise direction. Most of the planets also
rotate in a counter-clockwise direction. Venus’ rotation is retrograde which
means it rotates backwards – on Venus, the Sun would rise in the west and set
in the east.
Mars
Mars is the fourth planet from the Sun. Also
called the “Red Planet” because of its reddish
color, Mars has impact craters like Mercury and
the Moon alongside valleys and volcanoes, deserts
and ice caps like Earth. Mars has two moons,
Phobos and Deimos, which are probably captured
asteroids.
Mars is home to Olympus Mons, the largest volcano in the
solar system. It is about 27 km high, three times the height
of Mt. Everest. Mars also has Valles Marineris which, with
a length of 4000 km is the largest known canyon in the solar
system. The Grand Canyon is about 440 km long.
Phobos
Mars is midway in size between Earth and the Moon. The gravitational pull on the
surface of Mars is about one-third that of Earth. Mars’ rotational period and
seasonal cycles are also similar to Earth. A day on Mars is about forty minutes
longer than an Earth Day. Because of its greater distance from the Sun, a year on
Mars is about 687 Earth days.
In 1976, NASA’s Viking space craft took a picture of the Cydonia region on Mars
that looked like a face (Image 1). This caused a huge uproar in the SETI
community (Search for Extra-Terrestrial Intelligence). NASA scientists quickly
debunked the idea that the feature was a face, but it took 25 more years before
another successful flight to Mars, the Mars Global Surveyor would re-image the
same region (Image 2) showing that the “face” was actually the result of shadows
at just the right time of day and year.
Image 1
Image 2
Smiley Face on Mars
Pluto
Pluto used to be the ninth planet from the Sun but
in 2006 it was demoted to the status of Dwarf
Planet. Pluto is now considered the largest
member of a group called Kuiper Belt Objects.
Like other members of the Kuiper Belt, it is composed of rock and ice and is
relatively small. It has a highly eccentric and inclined orbit around the Sun which
makes it periodically come closer to the Sun than Neptune.
Pluto and its largest moon, Charon, are sometimes classified as a binary system.
Pluto has two smaller moons which were discovered in 2005.
Pluto was considered our ninth planet from its discovery in 1930 until 2006. But,
its status has been questioned since the 1970s with the discovery of minor planet
Chiron. As more objects similar to Chiron were discovered – including objects
larger than Pluto – the IAU (International Astronomical Union) defined “planet”
for the first time and Pluto didn’t fit the definition. The definition of a planet is:
1) it is in orbit around the Sun (yes for Pluto!), 2) it has enough mass to be round
(another yes for Pluto!!), and 3) it has “cleared” the neighborhood around its orbit.
The last part is where Pluto fails the definition. There is still a lot of controversy
over the definition.
In January 2006, NASA launched the New Horizons spacecraft to study Pluto and
the Kuiper Belt. After its last engine shut down, New Horizons left Earth with the
fastest launch speed ever, about 36,373 mph. Thirteen months after launch, it
passed Jupiter. Sixteen months after that, it passed
Saturn’s orbit. It is scheduled to reach Pluto in July 2015,
a nearly 9.5 year trip!
The Hubble Space Telescope operators recently compiled
four years worth of images to create the best picture yet
(until New Horizons arrives) of Pluto. The false colors
are used to show bright and dark areas (Pluto isn’t really
gold colored).
Hubble image of Pluto
Stars
A star is a huge ball of plasma. Stars are
held together by their own gravity. Their
gravity is so strong, that the atoms are
squeezed together until they fuse; this
releases tremendous amounts of energy
which is the source of their light. Our Sun
is a medium-sized star. Scientists believe
that the majority of stars are red dwarfs
which are smaller than our Sun.
Above: Relative sizes of some large stars: Sirius
is a blue giant, Pollux and Arcturus are orange
giants.
Below: red supergiants Betelgeuse and Antares
in comparison to the stars above.
Main sequence stars – stars in the prime
of their lives – are fusing hydrogen into
helium. Once they exhaust the hydrogen,
the size of the star determines what will
happen next. Stars about the size of our
sun will swell up and become red giants.
Small stars burn out and become white
dwarfs. Slightly larger stars will become red supergiants. Really big stars are
the most spectacular – they explode in a supernova which is so dazzling it may
temporarily outshine its entire galaxy.
In 1054, a supernova occurred which was
recorded by Chinese, Japanese, and
Persian/Arab astronomers. It was visible
during daylight for 23 days. We now see that
area as the Crab Nebula (right).
Almost all elements heavier than hydrogen and
helium are created in the fusion of stars or
during their death as supernovae. Most of the
material in your body was made inside a star!
Comets
Comets are small bodies that, when close
enough to the Sun exhibit a coma which makes
it look like a fuzzy blob. The comet may have
a tail caused by solar radiation. Comets are
often called “dirty snowballs” because they are
made of ice and dirt.
Comets are hypothesized to come from two
places. The Kuiper Belt is a region beyond the
orbit of Neptune. Comets from the Kuiper Belt
Comet Hale-Bopp in 1997
have a relatively short time to orbit the Sun and
will repeatedly appear in our sky. Halley’s Comet has been observed about
every 80 years, possibly since as early as 467 BCE.
The other source of comets is a debris cloud of ice, possibly left over from the
formation of the solar system, called the Oort Cloud. Scientists study comets
because it helps them learn about the origin of the Solar System.
Historically, comets have been considered omens of bad times such as the
death of a king, a coming catastrophe or even as an attack by heavenly beings
against humanity. The appearance of Halley’s Comet in 1066 was later
interpreted as the predictor of the Norman conquest of England.
There is an average of one comet per year in the
sky. However, most of these are not visible to the
naked eye. When we think of comets we usually
picture a brightly glowing ball with a long nebulous
tail. Surprisingly, the nucleus of a comet is one of
the darkest objects in the universe. It is the ices,
warmed to gaseous form by the Sun, boiling off and
reflecting the Sun’s light that creates the spectacular
coma and tail.
Comet Temple 1 imaged five
minutes before NASA’s Deep
Impact space craft crashed into it.
Meteoroids
Meteoroids are small bits of debris in the Solar System. They range in size
from particles of sand up to about 50 m across. If these objects enter Earth’s
atmosphere, they are called meteors (or shooting stars). If a meteor doesn’t
burn up entirely in the atmosphere, the part(s) that reach the ground are called
meteorites. Many meteors appearing seconds or minutes apart are called a
meteor shower.
There are three basic types of meteoroid: rocky, rocky-metal, and metal.
Rocky meteoroids are made of … rock! Metal meteoroids are primarily iron
or nickel-iron. Rocky-metals are a combination of rocks and nickel-iron.
As the result of Earth passing through the debris field of a defunct comet,
there are several meteor showers that are a regular event every year. Meteor
showers are named for the constellation from which they appear to radiate.
The best known of these annual showers are the Perseids (August – about 60
per hour), the Leonids (November – at the peak of their 33-year cycle you will
see 100s per hour) and the Geminids (December – known for their multi-color
display with about 26% yellow and 9% blue, red or green).
Meteors enter the atmosphere every day, but most are very tiny. It is rare for
the larger bodies to hit Earth. Approximately 50,000 years ago, a large
meteoroid about 45 m across hit the atmosphere and burned its way to the
ground. The result is still visible as Meteor Crater in Arizona. Meteor Crater
is almost 1 mile across and 550 ft deep. The Holsinger Meteorite is the largest
piece recovered from that event.
Meteor Crater, AZ
The Holsinger Meteorite
Asteroids
Asteroids are rocky and metallic bodies in orbit
around the sun. They are often called minor
planets or planetoids because they are smaller
than a planet but larger than meteoroids. There
are at least 16 known asteroids with a diameter of 240 km or greater (San
Francisco is about 150 km from Sacramento).
Most asteroids inhabit the Asteroid Belt between Mars and Jupiter. The
Asteroid Belt formed as the precursors to a planet, but the pull of gravity from
giant Jupiter prevented them from clumping together to make a planet.
Science fiction movies often depict passage through the Asteroid Belt as
dangerous, but the asteroid material is so spread out that multiple space craft
have passed through it without any incident.
The picture at the top of the page is Gaspra, the first asteroid to be imaged.
The picture was taken in 1991 by the Galileo probe on its way to Jupiter. It is
a small asteroid at about 18 km × 10.5 km. Below is Ida which is about 54 km
long. In the background of that picture is a small, 1.4 km “moon” named
Dactyl which orbits Ida. Galileo also imaged 50 km Mathilde.
Small asteroids, 1 km, strike Earth about every 500,000 years. Collisions with
5 km objects happen about every ten million years. The last known impact by
an asteroid of 10 km or more was an extinction event 65 million years ago.
Ida and Dactyl
Mathilde
Galaxies
A galaxy is a large, gravitationally bound system
made of stars, gas, dust, and something called dark
matter that is not yet understood. Earth and our Sun
are one of many solar systems in the Milky Way
Galaxy. Galaxies range in size from dwarfs with a
mere ten million stars up to giants with trillions of stars.
Elliptical galaxy M87
Galaxies are classified by their shape. An elliptical galaxy is one of the more
common forms. The image at the top of the page is an elliptical galaxy.
Spiral galaxies are flat and disk-shaped with curved arms. They usually have
a bulge in the center.
The Sombrero Galaxy
Spiral galaxy NGC1365
Galaxies with other, unusual shapes are classified as
irregular or peculiar galaxies and are thought to be
the result of disruptions by the gravitational pull of
nearby galaxies.
Most galaxies are separated by millions of light
years of space containing only one atom of gas for
every cubic meter. There are thought to be more
than 170 billion galaxies in the observable universe.
We live on a small planet orbiting a medium-sized
star in the outer spiral arm of one of those galaxies.
It’s humbling to think about.
An irregular galaxy
Earth
Earth is the third planet from the sun and
fifth largest in our solar system. It is also
the largest, most massive, and densest of
the four terrestrial planets. At present,
Earth is the only example of an
environment that has given rise to life.
Unlike the other planets in the solar system, Earth does not take its name from
an ancient Greek or Roman deity. The name “Earth” derives from an AngloSaxon word, erda, which means ground or soil. Even lacking a deity’s name,
Earth is often personified as a deity, usually a goddess.
Spaceflight has greatly changed our perspective of Earth. People used to think
of Earth as essentially infinite in resources. Perhaps the true legacy of the
space program is the environmental movement. After seeing the Earth from
afar Apollo 11 Command Module Pilot Mike Collins wrote, “I determined in
that moment that I would do all I could to let people know what a wonderful
home we have – before it’s too late.” When asked what we learned from
going to the moon, Dick Gordon of Apollo 12 replied, “We discovered the
Earth.”
The view from space showed us two things
of importance. First, our world is a tiny,
fragile place. That thin, blue line you seen
in the picture is all that keeps us alive.
Second, through our efforts to build and
operate the International Space Station,
we’ve learned the importance of
cooperation and friendship. The things that
we share in our world are far more valuable
than those which divide us.
STS-128 approaching the ISS with
Earth in the background.
Photo by Astronaut Jose Hernandez
Rockets
A rocket is a vehicle which creates thrust by ejecting a fast moving
fluid exhaust from its engine. Rockets rely on Newton’s Third
Law: the action of the exhaust against the inside of the combustion
chambers and exhaust nozzles exerts a large reactive thrust on the
rocket itself. Rockets do not push against the air or the ground.
Rockets date back at least to the 13th century, but there was little
progress until the 20th century. In the early 1900s, the theories
of rocketry were developed independently in Russia, Europe
and America. The “Father” of American Rocketry is Robert
Goddard who developed the ideas of a combustion chamber,
exhaust nozzles, and stages. He is shown at the top of the page
with the first liquid-fueled rocket.
World War II spurred development of rockets as weapons.
After the war, progress continued – military minds were still
thinking of weapons and capturing the high ground, but
scientists, engineers and pilots were anxious to push the
envelope and do things never done before. 1957 saw the launch
of the first artificial satellite, Sputnik, by the Soviet Union. We
soon saw more satellites and then, in 1961, Yuri Gagarin
became the first human in space. A month later, Alan Shepard became the first
American in space riding a rocket like that shown here.
Rocket development reached its peak with the Saturn V. The largest rocket ever
successfully flown, the Saturn V carried humans to land on the
moon.
Left: the Saturn V
is longer than a
football field at
363 ft.
Right: a single
first-stage engine
from the Saturn V
Galilean
Moons
The
The Galilean Moons are four moons of Jupiter discovered
by Galileo Galilei in 1610. They are the largest of
Jupiter’s many moons and are some of the most massive
objects in the Solar System (outside of the Sun and planets).
Io is the innermost of the Galilean Moons. It has over 400 active
volcanoes and hundreds of mountains, some of which are taller than
Mount Everest. Io’s multi-colored surface is caused by various sulfur
compounds. Volcanic plumes and lava flows create large-scale
changes in Io’s surface.
Europa is the second-closest of the four Galilean Moons and is the
smallest (it is slightly smaller than Earth’s Moon). It is one of the
smoothest objects in the Solar System. The surface is a layer of ice
and the bottom of the ice is theorized to be liquid water which could
possibly be the home of extraterrestrial life. It has a thin atmosphere
composed mainly of oxygen.
Ganymede is the third-closest Galilean Moon. It is the largest natural
satellite in the Solar System; it is larger than Mercury with only half
of Mercury’s mass. A salt-water ocean is believed to lie 200 km
below the surface.
Callisto is the most distant Galilean Moon. It is
Jupiter’s second largest and the third largest moon in the Solar
System. It is one of the most heavily cratered objects in the Solar
System. One major feature is an impact basin that is about 3000 km
wide.
Galileo’s discovery demonstrated the importance of the telescope as a
tool. It proved there were objects in space that were invisible to the naked eye. More
importantly, the discovery provided incontrovertible evidence that celestial bodies
existed that orbited something other than Earth.
The
ISS
The International Space
Station is an internationally
developed research facility in
low Earth orbit. The ISS
project began in 1994 with the
Shuttle-Mir program. The
first module, Zarya, was
launched by Russion in 1998.
The station consists of twelve
pressurize modules (as of Feb
2010) and a truss system to hold them together. Power is provided by 16 large solar
arrays and several smaller arrays.
The station’s sections are controlled by mission control centers operated by NASA, the
Russian Federal Space Agency, The Japan Aerospace Exploration Agency, the Canadian
Space Agency, and the European Space Agency. The ISS has been visited by astronauts
and cosmonauts from 15 different countries.
The ISS is primarily a research laboratory. It has the advantage over other space craft of
being a long-term platform. The ISS has been continuously staffed for over nine years.
Crews fly expeditions lasting several months during which they conduct scientific
experiments every day. They also practice replacement and repair procedures that will
be vital when operating space
craft farther from Earth, such as
voyages to Mars.
Left: fire under normal
gravity
Right: fire in microgravity