Mercury The first planet
Temperatures on Mercury's surface can reach 800 degrees Fahrenheit (430
degrees Celsius). Because the planet has no atmosphere to retain that heat,
night time temperatures on the surface can drop to -280 degrees Fahrenheit (-170
degrees Celsius).
Because Mercury is so close to the sun, it is hard to directly observe from
Earth except during twilight.
No Atmosphere
Rather than an atmosphere, Mercury possesses a thin
exosphere made up of atoms blasted off its surface by solar
wind and striking micro meteoroids. Because of the planet's extreme surface
temperature, the atoms quickly escape into space. With the thin exosphere, there
has been no wind erosion of the surface and meteorites do not burn up due to
friction as they do in other planetary atmospheres.
Mercury is the second smallest planet in the solar system, larger than
Pluto which is now not a member of the solar system. Mercury is the second densest planet
after Earth, with a large iron core having a radius of 1,100 to 1,200 miles
(1,800 to 1,900 kilometers), about 75 percent of the planet's radius. Mercury's
outer shell, comparable to Earth's outer shell (called the mantle), is only 300
to 400 m to 600 m thick
degrees Celsius). Because the planet has no atmosphere to retain that heat,
night time temperatures on the surface can drop to -280 degrees Fahrenheit (-170
degrees Celsius).
Because Mercury is so close to the sun, it is hard to directly observe from
Earth except during twilight.
No Atmosphere
Rather than an atmosphere, Mercury possesses a thin
exosphere made up of atoms blasted off its surface by solar
wind and striking micro meteoroids. Because of the planet's extreme surface
temperature, the atoms quickly escape into space. With the thin exosphere, there
has been no wind erosion of the surface and meteorites do not burn up due to
friction as they do in other planetary atmospheres.
Mercury is the second smallest planet in the solar system, larger than
Pluto which is now not a member of the solar system. Mercury is the second densest planet
after Earth, with a large iron core having a radius of 1,100 to 1,200 miles
(1,800 to 1,900 kilometers), about 75 percent of the planet's radius. Mercury's
outer shell, comparable to Earth's outer shell (called the mantle), is only 300
to 400 m to 600 m thick
Venus; Planet of eruptions
Venus and Earth are similar in size, mass, density, composition, and distance from the sun. There, however, is where the similarities end.
Venus is covered by a thick, rapidly spinning atmosphere, creating a scorched world with temperatures hot enough to melt lead and a surface pressure 90 times that of Earth. Because of its proximity to Earth and the way its clouds reflect sunlight, Venus appears to be the brightest planet in the sky.
Toxic Atmosphere
Venus's atmosphere consists mainly of carbon dioxide, with clouds of sulfuric acid droplets. Only trace amounts of water have been detected in the atmosphere. The thick atmosphere traps the sun's heat, resulting in surface temperatures over 880 degrees Fahrenheit (470 degrees Celsius). Probes that have landed on Venus have not survived more than a few hours before being destroyed by the incredibly high temperatures.
The Venusian year (orbital period) is about 225 Earth days long, while the planet's rotation period is 243 Earth days, making a Venus day about 117 Earth days long. Venus rotates retrograde (east to west) compared with Earth's pro grade (west to east) rotation. Seen from Venus, the sun would rise in the west and set in the east. As Venus moves forward in its solar orbit while slowly rotating "backwards".
About 90 percent of the surface of Venus appears to be recently solidified basalt lava; it is thought that the planet was completely resurfaced by volcanic activity 300 million to 500 million years ago.
Venus is covered by a thick, rapidly spinning atmosphere, creating a scorched world with temperatures hot enough to melt lead and a surface pressure 90 times that of Earth. Because of its proximity to Earth and the way its clouds reflect sunlight, Venus appears to be the brightest planet in the sky.
Toxic Atmosphere
Venus's atmosphere consists mainly of carbon dioxide, with clouds of sulfuric acid droplets. Only trace amounts of water have been detected in the atmosphere. The thick atmosphere traps the sun's heat, resulting in surface temperatures over 880 degrees Fahrenheit (470 degrees Celsius). Probes that have landed on Venus have not survived more than a few hours before being destroyed by the incredibly high temperatures.
The Venusian year (orbital period) is about 225 Earth days long, while the planet's rotation period is 243 Earth days, making a Venus day about 117 Earth days long. Venus rotates retrograde (east to west) compared with Earth's pro grade (west to east) rotation. Seen from Venus, the sun would rise in the west and set in the east. As Venus moves forward in its solar orbit while slowly rotating "backwards".
About 90 percent of the surface of Venus appears to be recently solidified basalt lava; it is thought that the planet was completely resurfaced by volcanic activity 300 million to 500 million years ago.
Earth the Big blue marble
Earth, our home planet, is the only planet in our solar system known to harbor life. All of the things we need to survive are provided under a thin layer of atmosphere that separates us from the uninhabitable void of space. Earth is made up of complex, interactive systems that are often unpredictable. Air, water, land, and life—including humans—combine forces to create a constantly changing world that we are striving to understand.
Viewing Earth from the unique perspective of space provides the opportunity to see Earth as a whole. Scientists around the world have discovered many things about our planet by working together and sharing their findings.
Some facts are well known. For instance, Earth is the third planet from the sun and the fifth largest in the solar system. Earth's diameter is just a few hundred kilometers larger than that of Venus. The four seasons are a result of Earth's axis of rotation being tilted more than 23 degrees.
Oceans at least 2.5 miles (4 kilometers) deep cover nearly 70 percent of Earth's surface. Fresh water exists in the liquid phase only within a narrow temperature span (32 to 212 degrees Fahrenheit/ 0 to 100 degrees Celsius). This temperature span is especially narrow when contrasted with the full range of temperatures found within the solar system. The presence and distribution ofwater vapor in the atmosphere is responsible for much of Earth's weather.
Protective Atmosphere
Near the surface, an ocean of air that consists of 78 percent nitrogen, 21 percent oxygen, and 1 percent other ingredients envelops us. This atmosphere affects Earth's long-term climate and short-term local weather; shields us from nearly all harmful radiation coming from the sun; and protects us from meteors as well. Satellites have revealed that the upper atmosphere actually swells by day and contracts by night due to solar activity.
Viewing Earth from the unique perspective of space provides the opportunity to see Earth as a whole. Scientists around the world have discovered many things about our planet by working together and sharing their findings.
Some facts are well known. For instance, Earth is the third planet from the sun and the fifth largest in the solar system. Earth's diameter is just a few hundred kilometers larger than that of Venus. The four seasons are a result of Earth's axis of rotation being tilted more than 23 degrees.
Oceans at least 2.5 miles (4 kilometers) deep cover nearly 70 percent of Earth's surface. Fresh water exists in the liquid phase only within a narrow temperature span (32 to 212 degrees Fahrenheit/ 0 to 100 degrees Celsius). This temperature span is especially narrow when contrasted with the full range of temperatures found within the solar system. The presence and distribution ofwater vapor in the atmosphere is responsible for much of Earth's weather.
Protective Atmosphere
Near the surface, an ocean of air that consists of 78 percent nitrogen, 21 percent oxygen, and 1 percent other ingredients envelops us. This atmosphere affects Earth's long-term climate and short-term local weather; shields us from nearly all harmful radiation coming from the sun; and protects us from meteors as well. Satellites have revealed that the upper atmosphere actually swells by day and contracts by night due to solar activity.
mars the big red planet
The Red Planet
Mars is a small rocky body once thought to be very Earthlike. Like the otherterrestrial planets—Mercury, Venus, and Earth—its surface has been changed by volcanism, impacts from other bodies, movements of its crust, and atmospheric effects such as dust storms. It has polar ice caps that grow and recede with the change of seasons; areas of layered soils near the Martian poles suggest that the planet's climate has changed more than once, perhaps caused by a regular change in the planet's orbit.
Martian tectonism, the formation and change of a planet's crust, differs from Earth's. Where Earth tectonics involve sliding plates that grind against each other or spread apart in the seafloors, Martian tectonics seem to be vertical, with hot lava pushing upwards through the crust to the surface.
Periodically, great dust storms engulf the entire planet. The effects of these storms are dramatic, including giant dunes, wind streaks, and wind-carved features.
Water on Mars?
Scientists believe that 3.5 billion years ago, Mars experienced the largest known floods in the solar system. This water may even have pooled into lakes or shallow oceans. But where did the ancient floodwater come from, how long did it last, and where did it go?
At present, Mars is too cold and its atmosphere is too thin to allow liquid water to exist at the surface for long. There's water ice close to the surface and more water frozen in the polar ice caps, but the quantity of water required to carve Mars's great channels and flood plains is not evident on—or near—the surface today. Images from NASA's Mars Global Surveyor spacecraft suggest that underground reserves of water may break through the surface as springs. The answers may lie deep beneath Mars's red soil.
Mars is a small rocky body once thought to be very Earthlike. Like the otherterrestrial planets—Mercury, Venus, and Earth—its surface has been changed by volcanism, impacts from other bodies, movements of its crust, and atmospheric effects such as dust storms. It has polar ice caps that grow and recede with the change of seasons; areas of layered soils near the Martian poles suggest that the planet's climate has changed more than once, perhaps caused by a regular change in the planet's orbit.
Martian tectonism, the formation and change of a planet's crust, differs from Earth's. Where Earth tectonics involve sliding plates that grind against each other or spread apart in the seafloors, Martian tectonics seem to be vertical, with hot lava pushing upwards through the crust to the surface.
Periodically, great dust storms engulf the entire planet. The effects of these storms are dramatic, including giant dunes, wind streaks, and wind-carved features.
Water on Mars?
Scientists believe that 3.5 billion years ago, Mars experienced the largest known floods in the solar system. This water may even have pooled into lakes or shallow oceans. But where did the ancient floodwater come from, how long did it last, and where did it go?
At present, Mars is too cold and its atmosphere is too thin to allow liquid water to exist at the surface for long. There's water ice close to the surface and more water frozen in the polar ice caps, but the quantity of water required to carve Mars's great channels and flood plains is not evident on—or near—the surface today. Images from NASA's Mars Global Surveyor spacecraft suggest that underground reserves of water may break through the surface as springs. The answers may lie deep beneath Mars's red soil.
Jupiter the king of the solar system
Jovian Giant
The most massive planet in our solar system, with four planet-size moons and many smaller satellites, Jupiter forms a kind of miniature solar system. Jupiter resembles a star in composition. In fact, if it had been about eighty times more massive, it would have become a star rather than a planet.
On January 7, 1610, using his primitive telescope, astronomer Galileo Galilei saw four small "stars" near Jupiter. He had discovered Jupiter's four largestmoons, now called Io, Europa, Ganymede, and Callisto. Collectively, these four moons are known today as the Galilean satellites.
Galileo would be astonished at what we have learned about Jupiter and its moons in the last 30 years. Io is the most volcanically active body in our solar system. Ganymede is the largest planetary moon and is the only moon in the solar system known to have its own magnetic field. A liquid ocean may lie beneath the frozen crust of Europa. Icy oceans may also lie deep beneath the crusts of Callisto and Ganymede. In 2003 alone, astronomers discovered 23 new moons orbiting the giant planet, giving Jupiter a total moon count of 49, the most in the solar system. The numerous small outer moons may be asteroids captured by the giant planet's gravity.
Jupiter's appearance is a tapestry of beautiful colors and atmospheric features. Most visible clouds are composed of ammonia. Water exists deep below and can sometimes be seen through clear spots in the clouds. The planet's "stripes" are dark belts and light zones created by strong east-west winds in Jupiter's upper atmosphere. Within these belts and zones are storm systems that have raged for years. The Great Red Spot, a giant spinning storm, has been observed for more than 300 years.
Atmosphere
The composition of Jupiter's atmosphere is similar to that of the sun—mostly hydrogen and helium. Deep in the atmosphere, the pressure and temperature increase, compressing the hydrogen gas into a liquid. At depths about a third of the way down, the hydrogen becomes metallic and electrically conducting. In this metallic layer, Jupiter's powerful magnetic field is generated by electrical currents driven by Jupiter's fast rotation. At the center, the immense pressure may support a solid core of ice-rock about the size of Earth.
The most massive planet in our solar system, with four planet-size moons and many smaller satellites, Jupiter forms a kind of miniature solar system. Jupiter resembles a star in composition. In fact, if it had been about eighty times more massive, it would have become a star rather than a planet.
On January 7, 1610, using his primitive telescope, astronomer Galileo Galilei saw four small "stars" near Jupiter. He had discovered Jupiter's four largestmoons, now called Io, Europa, Ganymede, and Callisto. Collectively, these four moons are known today as the Galilean satellites.
Galileo would be astonished at what we have learned about Jupiter and its moons in the last 30 years. Io is the most volcanically active body in our solar system. Ganymede is the largest planetary moon and is the only moon in the solar system known to have its own magnetic field. A liquid ocean may lie beneath the frozen crust of Europa. Icy oceans may also lie deep beneath the crusts of Callisto and Ganymede. In 2003 alone, astronomers discovered 23 new moons orbiting the giant planet, giving Jupiter a total moon count of 49, the most in the solar system. The numerous small outer moons may be asteroids captured by the giant planet's gravity.
Jupiter's appearance is a tapestry of beautiful colors and atmospheric features. Most visible clouds are composed of ammonia. Water exists deep below and can sometimes be seen through clear spots in the clouds. The planet's "stripes" are dark belts and light zones created by strong east-west winds in Jupiter's upper atmosphere. Within these belts and zones are storm systems that have raged for years. The Great Red Spot, a giant spinning storm, has been observed for more than 300 years.
Atmosphere
The composition of Jupiter's atmosphere is similar to that of the sun—mostly hydrogen and helium. Deep in the atmosphere, the pressure and temperature increase, compressing the hydrogen gas into a liquid. At depths about a third of the way down, the hydrogen becomes metallic and electrically conducting. In this metallic layer, Jupiter's powerful magnetic field is generated by electrical currents driven by Jupiter's fast rotation. At the center, the immense pressure may support a solid core of ice-rock about the size of Earth.
Saturn the king of the ring
The Ringed Planet
Saturn was the most distant of the five planets known to the ancients. In 1610, Italian astronomer Galileo Galilei was the first to gaze at Saturn through a telescope. To his surprise, he saw a pair of objects on either side of the planet. He sketched them as separate spheres and wrote that Saturn appeared to be triple-bodied. In 1659, Dutch astronomer Christiaan Huygens, using a more powerful telescope than Galileo's, proposed that Saturn was surrounded by a thin, flat ring.
In 1675, Italian-born astronomer Jean-Dominique Cassini discovered a "division" between what are now called the A and B rings. It is now known that the gravitational influence of Saturn's moon Mimas is responsible for theCassini Division, which is 3,000 miles (4,800 kilometers) wide.
Like Jupiter, Saturn is made mostly of hydrogen and helium. Its volume is 755 times greater than that of Earth. Winds in the upper atmosphere reach 1,600 feet (500 meters) per second in the equatorial region. (In contrast, the strongest hurricane-force winds on Earth top out at about 360 feet, or 110 meters, per second.) These superfast winds, combined with heat rising from within the planet's interior, cause the yellow and gold bands visible in the atmosphere.
Saturn's ring system is the most extensive and complex in the solar system, extending hundreds of thousands of kilometers from the planet. In the early 1980s, NASA's two Voyager spacecraft revealed that Saturn's rings are made mostly of water ice. They also found "braided" rings, ringlets, and "spokes," dark features in the rings that circle the planet at different rates from that of the surrounding ring material. Material in the rings ranges in size from a few micrometers to several tens of meters. Two of Saturn's small moons orbit within gaps in the main rings.
Many Moons
Saturn has 52 known natural satellites, or moons, and there are probably many more waiting to be discovered. Saturn's largest satellite, Titan, is a bit bigger than the planet Mercury. (Titan is the second-largest moon in the solar system; only Jupiter's moon Ganymede is bigger.) Titan is shrouded in a thick, nitrogen-rich atmosphere that might be similar to what Earth's was like long ago. Further study of this moon promises to reveal much about planetary formation and, perhaps, about the early days of Earth. Saturn also has many smaller "icy" satellites. From Enceladus, which shows evidence of recent (and ongoing) surface changes, to Iapetus, with one hemisphere darker than asphalt and the other as bright as snow, each of Saturn's satellites is unique.
Saturn was the most distant of the five planets known to the ancients. In 1610, Italian astronomer Galileo Galilei was the first to gaze at Saturn through a telescope. To his surprise, he saw a pair of objects on either side of the planet. He sketched them as separate spheres and wrote that Saturn appeared to be triple-bodied. In 1659, Dutch astronomer Christiaan Huygens, using a more powerful telescope than Galileo's, proposed that Saturn was surrounded by a thin, flat ring.
In 1675, Italian-born astronomer Jean-Dominique Cassini discovered a "division" between what are now called the A and B rings. It is now known that the gravitational influence of Saturn's moon Mimas is responsible for theCassini Division, which is 3,000 miles (4,800 kilometers) wide.
Like Jupiter, Saturn is made mostly of hydrogen and helium. Its volume is 755 times greater than that of Earth. Winds in the upper atmosphere reach 1,600 feet (500 meters) per second in the equatorial region. (In contrast, the strongest hurricane-force winds on Earth top out at about 360 feet, or 110 meters, per second.) These superfast winds, combined with heat rising from within the planet's interior, cause the yellow and gold bands visible in the atmosphere.
Saturn's ring system is the most extensive and complex in the solar system, extending hundreds of thousands of kilometers from the planet. In the early 1980s, NASA's two Voyager spacecraft revealed that Saturn's rings are made mostly of water ice. They also found "braided" rings, ringlets, and "spokes," dark features in the rings that circle the planet at different rates from that of the surrounding ring material. Material in the rings ranges in size from a few micrometers to several tens of meters. Two of Saturn's small moons orbit within gaps in the main rings.
Many Moons
Saturn has 52 known natural satellites, or moons, and there are probably many more waiting to be discovered. Saturn's largest satellite, Titan, is a bit bigger than the planet Mercury. (Titan is the second-largest moon in the solar system; only Jupiter's moon Ganymede is bigger.) Titan is shrouded in a thick, nitrogen-rich atmosphere that might be similar to what Earth's was like long ago. Further study of this moon promises to reveal much about planetary formation and, perhaps, about the early days of Earth. Saturn also has many smaller "icy" satellites. From Enceladus, which shows evidence of recent (and ongoing) surface changes, to Iapetus, with one hemisphere darker than asphalt and the other as bright as snow, each of Saturn's satellites is unique.
uranus; the mysterious planet
Once considered one of the blander-looking planets, Uranus has been revealed as a dynamic world with some of the brightest clouds in the outer solar system and 11 rings. The first planet found with the aid of a telescope, Uranus was discovered in 1781 by astronomer William Herschel. The seventh planet from the sun is so distant that it takes 84 years to complete one orbit.
Uranus, with no solid surface, is one of the gas giant planets. (The others are Jupiter, Saturn, and Neptune.) Its atmosphere is composed primarily of hydrogen and helium, with a small amount of methane and traces of water and ammonia. Uranus gets its blue-green color from methane gas. Sunlight is reflected from Uranus's cloud tops, which lie beneath a layer of methane gas. As the reflected sunlight passes back through this layer, the methane gas absorbs the red portion of the light, allowing the blue portion to pass through and resulting in the blue-green color that we see.
The planet's atmospheric details are very difficult to see in visible light. The bulk (80 percent or more) of the mass of Uranus is contained in an extended liquid core consisting primarily of "icy" materials (water, methane, and ammonia), with higher-density material at depth.
Uranus, with no solid surface, is one of the gas giant planets. (The others are Jupiter, Saturn, and Neptune.) Its atmosphere is composed primarily of hydrogen and helium, with a small amount of methane and traces of water and ammonia. Uranus gets its blue-green color from methane gas. Sunlight is reflected from Uranus's cloud tops, which lie beneath a layer of methane gas. As the reflected sunlight passes back through this layer, the methane gas absorbs the red portion of the light, allowing the blue portion to pass through and resulting in the blue-green color that we see.
The planet's atmospheric details are very difficult to see in visible light. The bulk (80 percent or more) of the mass of Uranus is contained in an extended liquid core consisting primarily of "icy" materials (water, methane, and ammonia), with higher-density material at depth.
Neptune; invisible to the naked eye
The eighth planet from the sun, Neptune was the first planet located through mathematical predictions rather than through regular observations of the sky. (Galileo had recorded it as a fixed star during observations with his small telescope in 1612 and 1613.)
When Uranus didn't travel exactly as astronomers expected it to, a French mathematician, Urbain Joseph Le Verrier, proposed the position and mass of another as yet unknown planet that could cause the observed changes to Uranus's orbit. After being ignored by French astronomers, Le Verrier sent his predictions to Johann Gottfried Galle at the Berlin Observatory, who found Neptune on his first night of searching in 1846. Seventeen days later, its largest moon, Triton, was also discovered.
Nearly 2.8 billion miles (4.5 billion kilometers) from the sun, Neptune orbits the sun once every 165 years. It is invisible to the naked eye because of its extreme distance from Earth.
The main axis of Neptune's magnetic field is "tipped over" by about 47 degrees compared with the planet's rotation axis. Like Uranus, whose magnetic axis is tilted about 60 degrees from the axis of rotation, Neptune's magnetosphere undergoes wild variations during each rotation because of this misalignment. The magnetic field of Neptune is about 27 times more powerful than that of Earth.
Neptune's atmosphere extends to great depths, gradually merging into water and other "melted ices" over a heavier, approximately Earth-size solid core. Neptune's blue color is the result of methane in the atmosphere. Uranus's blue-green color is also the result of atmospheric methane, but Neptune is a more vivid, brighter blue, so there must be an unknown component that causes the more intense color that we see.
When Uranus didn't travel exactly as astronomers expected it to, a French mathematician, Urbain Joseph Le Verrier, proposed the position and mass of another as yet unknown planet that could cause the observed changes to Uranus's orbit. After being ignored by French astronomers, Le Verrier sent his predictions to Johann Gottfried Galle at the Berlin Observatory, who found Neptune on his first night of searching in 1846. Seventeen days later, its largest moon, Triton, was also discovered.
Nearly 2.8 billion miles (4.5 billion kilometers) from the sun, Neptune orbits the sun once every 165 years. It is invisible to the naked eye because of its extreme distance from Earth.
The main axis of Neptune's magnetic field is "tipped over" by about 47 degrees compared with the planet's rotation axis. Like Uranus, whose magnetic axis is tilted about 60 degrees from the axis of rotation, Neptune's magnetosphere undergoes wild variations during each rotation because of this misalignment. The magnetic field of Neptune is about 27 times more powerful than that of Earth.
Neptune's atmosphere extends to great depths, gradually merging into water and other "melted ices" over a heavier, approximately Earth-size solid core. Neptune's blue color is the result of methane in the atmosphere. Uranus's blue-green color is also the result of atmospheric methane, but Neptune is a more vivid, brighter blue, so there must be an unknown component that causes the more intense color that we see.