Diameter as seen from Earth: 86,375 miles (1,390,000 km)
Composition: hydrogen, helium
Surface Temperature: 9,940°F (5,505°C)
Core Temperature: 27,000,000°F (15,000,000°C)
Period
of Rotation: 25 days at the equator, 36 days at the poles
Our Sun, named Sol, is at the center of our solar system, and even gives our planetary system its name.
The Sun is an ordinary star, one of about 100 billion in our galaxy, the Milky Way.
The Sun is about 4.5 billion years old, and will continue to put out heat and light for about 5 billion more years.
The Sun is made entirely of gasses, mainly hydrogen and helium, but it contains 99.8 percent of the mass of the entire solar system.
The Sun produces its energy through a process called fusion. The Sun's immense gravity squeezes it inside, creating so much heat that is actually fuses hydrogen atoms together, forming helium. This releases tremendous amounts of energy to the Sun's surface and out into space.
For more information about Earth, its satellite, and our nearest star, see the Morehead Planetarium show Earth, Moon, and Sun and the many accompanying activities and links.
Activity Idea: visit www.solarviews.com/eng/edu/convect.htm and learn how to make a soup that illustrates heat convection, a process that occurs on the surface of the Sun. Convection functions because heated fluids, due to their lower density, rise and cooled fluids fall. A heated fluid will rise to the top of a column, radiate heat away and then fall to be re-heated, rise and so on. A high resolution image of the Sun shows a pattern that looks something like rice grains. Very large convection cells cause this granulation.
Comets are made of ice and dust -- just dirty snowballs in space, with a nucleus only a few miles across.
Comets normally stay in the cold outer parts of the solar system, beyond Pluto. Sometimes a comet nucleus gets nudges by the gravity of another object, and it begins a really lopsided orbit that carries it in toward the sun.
When the comet's nucleus gets close to the Sun, the ice on its surface gets heated and begins spewing off gasses and dust into space, forming a long, beautiful tail. The tail always points away from the Sun, because the Sun sends out a "wind" of charged particles into space in all directions, blowing the tail with it. The tail can stretch millions of miles into space.
Near the Sun, comets travel at about 100,000 miles per hour.
Activity Idea: visit www.solarviews.com/eng/edu/comets.htm to learn how to make a comet nucleus with dry ice, ammonia, dirt, corn starch, and a few other common household items.
About 100,000 asteroids orbit the Sun between Mars and Jupiter in what is called the Asteroid Belt.
Most asteroids are very small, but some are hundreds of miles across.
Asteroids are made of rock and metals, probably material that never formed a complete planet. They are often covered with craters.
Activity Idea: learn.jpl.nasa.gov/crater.htm The Educator's Guide to Impact Craters by the Jet Propulsion Laboratory describes a crater-making exercise, with well-explained background information and vocabulary.
Activity Idea: www.smv.org/jims/crater/crater2.htm includes detailed instructions for a crater-making activity and helpful photographs of the process.
Activity Idea: quest.arc.nasa.gov/mars/teachers/tg/program3/3.2ws.html includes student worksheets on which to record all data and observations.
Diameter: 3,032 miles (4,879 km)
Average Distance from Sun: 36,000,000 miles (57,900,000 km)
Planet Composition: rock surrounding a dense metallic core
Atmosphere: virtually none
Average Temperature: 333°F (167°C)
Number of Moons: 0
Orbital Period: 88 days
Period of Rotation: 59 days
Mercury is just under half the size of Earth, and has no moon.
Mercury looks much like Earth's moon, since mountains, craters, and flat lava plains cover its surface.
Because it is so close to the Sun, intense solar radiation bombards Mercury's surface. Mercury has no atmosphere to protect it from this radiation, which includes dangerous ultraviolet, X-rays, and gamma rays.
Mercury orbits the sun quickly, but it spins slowly on its axis. This means that the long days are very hot, and the long nights are very cold.
Diameter: 7,521 miles (12,104 km)
Average Distance from Sun: 67,200,000 miles (108,200,000 km)
Planet Composition: rock surrounding an iron core
Atmosphere: dense carbon dioxide
Average Temperature: +867°F (464°C)
Number of Moons: 0
Orbital Period: 224.7 days
Period of Rotation: 243 days
retrograde
Venus is the hottest planet in the solar system. It is even hotter than Mercury, which is closer to the Sun. It is hotter because it has a thick carbon dioxide atmosphere that acts like a huge greenhouse, trapping heat from the Sun.
The atmosphere on Venus is so dense that is would crush you. It presses down with 90 times more pressure than Earth's atmosphere.
Venus is completely covered by clouds of sulfuric acid droplets -- the same chemical that is in a car battery. It corrodes metal and burns skin instantly. Repeated volcanic eruptions created and continue to replenish the sulfuric acid clouds. The photo above shows only the dense, swirling cloud tops that always hide this planet.
Venus has a bizarre surface. Using radar, we can see that its rocky surface is covered with impact craters, vast lava plains, and numerous volcanoes.
Venus moves strangely through space. It rotates in the opposite direction from the other planets (retrograde rotation), and it rotates more slowly than it orbits the sun. It takes longer for Venus to turn around its axis once than it does to go around the Sun once. Because of the speed and direction of rotation, an observer on Venus would see the sun rise, set, and rise again in 117 days, although a complete planetary rotation takes 243 days.
Venus is only slightly smaller than Earth, is made from similar rocky materials, and orbits about three fourths of Earth's distance from the Sun. It is Earth's closest planetary neighbor. Because of these similarities, it has been called Earth's sister planet.
Venus cannot compete with the Sun's gravity to hold onto a moon, so it has no natural satellites.
Diameter: 7,926 miles (12,756 km)
Average Distance from Sun: 93,000,000 miles (149,600,000 km)
Planet Composition: rock surrounding a nickel-iron core
Atmosphere: nitrogen, oxygen
Average Temperature: +59°F (15°C)
Number of Moons: 1
Orbital Period: 365.2 days (1 year)
Period of Rotation: 23 hours 56
minutes
Earth is probably the only planet in our solar system with liquid water on its surface. Water covers over 70% of the Earth's surface, and white clouds of water vapor often hide large parts of Earth.
Earth is quite colorful from space. The oceans, land and clouds easily show up as blue, brown, and white.
The abundant water and oxygen-rich atmosphere support a a wide variety of complex life forms. Life has not been found anywhere else in the solar system.
The 23.5° tilt of the Earth's axis cause the changes in the seasons as the planet orbits the Sun.
Although the atmosphere shields the planet from hazardous radiation and the huge temperature extremes of space, it is only a few miles thick. The moderate temperature on Earth is not only caused by its distance from the Sun, but also the composition of the atmosphere. Even a slight change in the amount of different gasses or dust in the air could turn Earth into either a frigid ice planet or a scorching hot world.
Earth's one moon, Luna, has no protective atmosphere. If you faced the Sun, your front would be boiling hot while your back would be 270 below zero!
The moon is only about 1/4 Earth's diameter.
The dark spots on the moon were caused long ago when meteorites collided with the moon. The impacts melted huge amounts of rock that flowed like lava, and later hardened.
The moon is covered with mountains, valleys, and craters. It has more craters than the Earth because there is no wind or water to wear them away. Features on the moon, including the footprints left by the Apollo astronauts, last for millions of years.
For more information about our planet, its moon, and its motions through space, see the Morehead Planetarium show Earth, Moon, and Sun and the many accompanying activities and links.
Diameter: 4,222 miles (6,794 km)
Average Distance from Sun: 141,600,000
miles (227,900,000 km)
Planet Composition: rock and metal
Atmosphere: thin carbon dioxide
Average Temperature: -85°F (-65°C)
Number of Moons: 2
Orbital Period: 687 days
Period of Rotation: 24 hours 37
minutes
The red color of Mars is caused by iron oxide, or rust, in the soil. In the picture above, a cloudy haze makes the atmosphere a slight blue color, and the frozen water and carbon dioxide at the polar icecaps appears white.
Mars has a gigantic canyon five miles deep and almost 2,000 miles long. That could stretch across most of the United States!
Mars has the largest volcano in the solar system. Olympus Mons is 15 miles high and nearly as big as the state of Texas.
Mars is more like Earth than any other planet in the solar system. It is about half Earth's size, and its rotation and axis tilt are nearly identical. However, it is much colder, and its thin atmosphere has almost no oxygen for us to breathe. There is no liquid water on the surface, but there is ice frozen underground and in the polar ice caps.
If there is any life on Mars today, it is probably just simple bacteria buried in the soil.
Mars probably had a thicker atmosphere in the past, allowing liquid water to form rivers and lakes on its surface. Perhaps it had complex life forms long ago that died out when the environment changed.
Mars has two tiny moons that are probably captured asteroids: Phobos and Deimos.
quest.arc.nasa.gov/mars/background/ The Mars Team Online provides facts about Mars and lots of links to information about Mars probes, missions, and research projects.
Activity Idea: teachspacescience.stsci.edu/graphics/pdf/10000273.pdf the Destination: Mars activity packet encourages students to learn about scientific exploration on Mars. It includes lessons on navigation and trajectory, soils, making and mapping volcanoes, and understanding geological sequence of events while mapping craters and river channels. This guide is available free for download in PDF format.
Activity Idea: www.thursdaysclassroom.com/index_02dec99.html has information about looking for extraterrestrial life, especially on Mars. It includes stories about an imaginary Mars Vacation, Martian Math, a bar graph exercise, and activities about planning for human exploration and colonization of the Red Planet.
Diameter: 88,846 miles (142,984 km)
Average Distance from Sun: 483,800,000 miles (778,600,000 km)
Planet Composition: liquid hydrogen and helium surrounding a rocky core
Atmosphere: hydrogen, helium
Average Temperature: -166°F (-110°C)
Number of Moons: 4 large, 12 small, and 12 or more newly discovered and unnamed
Orbital Period: 4331 days (11.87 years)
Period of Rotation: 9 hours 55 minutes
Jupiter, the largest planet in the solar system, could fit over 1,000 Earth's inside it. It contains most of the solar system's mass that is not part of our Sun.
Jupiter is a massive planet with lots of gravity. A 100 pound person on Earth would weigh 240 pounds here!
Jupiter's radiation belt is composed of energetic particles trapped in the planet's powerful magnetic field. It is 1,000 percent stronger than the radiation belt surrounding Earth.
Jupiter is covered with colorful clouds and storms. The colors are caused by different chemicals in the clouds. Wind speeds here measure up to 300 miles per hour.
The Great Red Spot, a huge, hurricane-like storm big enough to swallow three Earth's, is over 300 years old!
Jupiter rotates rapidly, giving it a flattened appearance like Saturn.
Jupiter has faint rings composed of fine, rocky particles.
Ganymede is the largest moon in the solar system. It is made of ice and rock, with mountains, valleys, and craters all over the surface.
Europa looks like it has been painted with brown, criss-crossing lines. The lines are where liquid water inside Europa breaks through cracks in the surface ice. The dirty water then flows out of the cracks and freezes, forming the brown ridges.
Europa, Ganymede, and another moon, Callisto, might have slushy, salt water oceans beneath their surfaces. Maybe primitive life might be found in some of these oceans!
Io is a very colorful moon, and even looks like a big round pizza.
Io is caught in a gravity tug-of-war between Jupiter and Jupiter's other three large moons. This squeezes Io and heats up the inside. The heat and pressure forces molten rock to erupt from volcanoes all over the surface. A full ton of the moon is blasted out into space every second, and the material is swept away into Jupiter's magnetic field.
www.jpl.nasa.gov/galileo/ The Galileo Project is a NASA unmanned mission to explore the planet Jupiter and its surrounding moons and magnetosphere. The spacecraft started its journey on October 18, 1989 with the launch of the Space Shuttle Atlantis. The Galileo Mission consisted of an atmospheric entry probe (Galileo Probe) designed to enter Jupiter's atmosphere, and an orbiter (Galileo Orbiter) designed to orbit the planet and observe Jupiter, its moons, and radiation belts.
This homepage: ccf.arc.nasa.gov/galileo_probe/is devoted to background information and scientific results from the Galileo atmospheric entry probe portion of the mission.
The story of the Galileo Mission to Jupiter told with humor and illustrated with cartoons at eis.jpl.nasa.gov/~skientz/galileo/.
www.jpl.nasa.gov/sl9/ From July 16 through July 22, 1994, pieces of an object designated as Comet P/Shoemaker-Levy 9 collided with Jupiter. This is the first collision of two solar system bodies ever to be observed, and the effects of the comet impacts on Jupiter's atmosphere have been simply spectacular and beyond expectations.
Diameter: 74,897 miles (120,536 km)
Average Distance from Sun: 890,800,000 miles (1,433,500,000 km)
Planet Composition: liquid hydrogen and helium surrounding a small rocky core
Atmosphere: hydrogen, helium
Average Temperature: -220°F (-140°C)
Number of Moons: 18 named and 12 or more newly discovered and unnamed
Orbital Period: 10,747 (29.44 years)
Period of Rotation: 10 hours 40 minutes
Saturn is the second largest planet in the solar system, and is nine times the diameter of Earth.
Because Saturn rotates so quickly, it bulges out around the equator and looks flattened at the poles.
Because Saturn is made mostly of hydrogen, it is lighter than water. It would float in a bathtub!
Ammonia and sulfur in the cloud tops color the planet white and yellow.
Saturn has a stormy atmosphere with winds up to a thousand miles per hour.
The beautiful rings (Saturn may have up to a thousand separate ringlets) are 170,000 miles across, but less than a mile thick. These rings are made of rock and chunks of ice as small as bits of dust and as large as house-sized boulders. They may have come from a moon that was pulverized during a collision or shattered by Saturn's massive gravity.
Saturn's moon Mimas has a huge crater that reminds many people of the Death Star from the Star Wars movies.
Titan is the second largest moon in the solar system -- it is even larger than Mercury or Pluto!
Titan has a nitrogen atmosphere that is thicker than Earth's, with an orange smog that completely hides a rocky, icy surface.
Pools and lakes of liquid ethane are scattered across Titan's surface. Ethane is highly flammable substance that is usually a gas on Earth. On Titan, it is so cold that ethane is liquid like water -- but water on Titan is frozen solid.
Activity Idea: teachspacescience.stsci.edu/graphics/pdf/10000265.pdf the Saturn Educator Guide has detailed background information and lessons about Saturn's rings and moons, the history of Saturn's discovery, the Cassini-Huygens mission, and art, language, and mythological enrichment activities. This guide is available free for download in PDF format.
Diameter: 31,763 miles (51,118 km)
Average Distance from Sun: 1,784,800,000 miles (2,872,500,000 km)
Planet Composition: methane ice and rock
Atmosphere: helium, hydrogen, methane
Average Temperature: -320°F (-195°C)
Number of Moons: 5 large and 16 or more small
Orbital Period: 30,589 days (83.8 years)
Period of Rotation: 17 hours 14 minutes retrograde
Uranus rotates strangely. It rolls around the sun on its side, instead of the more "upright" rotation of the other planets. It also rotates the opposite direction of most of the rest of the solar system, so its rotation is called retrograde. Perhaps this strange orientation was caused by a collision with a planet-sized object long ago. This would have blown Uranus apart, and when the material reassembled, it spun in a different direction.
We cannot see storms on Uranus because a thick fog at the top of the atmosphere hides the planet. It does have strong winds, which have been recorded at between 90 and 360 miles per hour.
The surface of Miranda, one of Uranus's moons, has a twisted, jumbled-up collection of fault canyons, grooves, and ridges on the surface. Astronomers theorize that collision with other moons or asteroids broke Miranda apart as many as five separate times. Each time, the gravity of the remaining pieces reassembled the moon in a different way, creating the unusual patterns.
Diameter: 30,775 miles (49,528 km)
Average Distance from Sun: 2,793,100,000 miles (4,497,100,000 km)
Planet Composition: liquids surrounding a rocky core
Atmosphere: hydrogen, helium, methane, water vapor
Temperature: -330°F (-200°C)
Number of Moons: 8
Orbital Period: 59,800 days (163.8 years)
Period of Rotation: 16 hours 3 minutes
Neptune is four times larger than the planet Earth, but it is the smallest of the gas giants.
Neptune's blue color is caused by methane gas in the atmosphere. The streaks and bands on Neptune are caused by storms and clouds that may travel at up to 1,300 miles per hour -- the fastest measured on any planet in the solar system.
Neptune has thin rings that are not visible from Earth. Although scientists had suspected that rings existed, we did not know for sure until Voyager 2 photographed them when it flew past in August 1989.
Triton is Neptune's largest moon -- it is even bigger than the planet Pluto.
Triton is made of rock and ice with a thin atmosphere. Its surface is covered with patterns where the ice melted and refroze. Underground heat and pressure cause geysers that blast material, such as liquid nitrogen, through cracks on the moon's surface.
Diameter: 1,485 miles (2,390 km)
Average Distance from Sun:
3,647,200,000 miles (5,870,000,000 km)
Planet Composition: rock and ice
Atmosphere: virtually none
Surface Temperature: -375°F (-225°C)
Number of Moons: 1
Orbital Period: 90,588 (248 years)
Period of Rotation: 6 days 9 hours
Pluto is the smallest planet in the solar system, and is usually the farthest from the Sun. It is about 39 times farther from the Sun than the Earth is!
Pluto has a lopsided orbit with large eccentricity. Occasionally Pluto travels inside Neptune's orbit, and is the 8th planet from the Sun.
Pluto is the only planet in our solar system that has not been visited by a spacecraft. Even the best photographs taken by the Hubble Space Telescope are fuzzy with few details, like the one above. We know very little about this distant planet, and scientists are only guessing about its composition and atmosphere.
In Pluto's low gravity, a 100 pound person would weigh only 7 pounds.
The moon Charon is half Pluto's diameter, so Pluto and Charon are sometimes called a double planet.
Some astronomers do not consider Pluto a planet due to its small size, lack of atmosphere, unusual orbit, and large moon.
All the terrestrial planets are close to the Sun, so they are sometimes called the inner planets.
These planets are all small.
Terrestrial planets are made mostly of rock and metal.
These planets have thin atmospheres and solid surfaces.
Spacecraft can land on them.
The gas giants, are farther from the Sun, so they are sometimes called the outer planets.
Gas giants are also called the Jovian planets. "Jove" is another name for the god Jupiter, and these planets are like the planet Jupiter.
These planets are all large.
The gas giants are made mostly of gasses, liquids, and ice around small rocky cores.
Gas giants have no solid surface, just layers of liquids and gasses. If you tried to stand on one, you would slowly sink down into the planet, and the high pressures inside would crush you.
The many storms on the gas giants are caused by heat deep inside the planet. Although all the giant planets are cold, gravity squeezes their interiors, making the centers very hot.
These planets have many moons and rings.
Pluto is a tiny planet that is far from the Sun.
It is made of ice and rock.
Pluto has an odd, eccentric orbit that is very different from any other planet.
Some astronomers do not consider Pluto a true planet.
Pluto has hardly any atmosphere.