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The Planets

Mercury

• Mercury is a small rock planet composed of 70% metallic and 30% silicate minerals, with deep ice pockets. It's dense iron core is larger than Earth's.
• What little atmosphere exists is almost a vacuum, made up of atoms blasted off its surface by the solar wind which has less than a million-billionths the pressure of Earth's atmosphere at sea level. It is composed chiefly of oxygen, sodium, and helium.
• Mercury is the closest planet to the sun, therefore hard to see from Earth except during twilight.
• Mercury is the fastest planet, and speeds around the Sun in a wildly elliptical (non-circular) orbit that takes it as close as 47 million km and as far as 70 million km from the Sun.
• Because it is so close to the Sun, with little atmosphere and very long days, extremes of temperature occur, from 750 to 800 degrees F. during the day to -330 degrees F at night.
• As Mercury has virtually no atmosphere to scatter light, the sky would be black, even though Mercury is the closest planet to the Sun, whose disc would appear over twice as large as what we observe from the Earth.
• Mercury completes three rotations for every two orbits around the Sun. If you wanted to stay up for a Mercury day, you'd have to stay up for 176 Earth days.

Venus

• Venus is a rock planet composed of an iron core covered metal and silicon composites.
• Its atmosphere consists mainly of carbon dioxide (the same gas that produces fizzy sodas), droplets of sulphuric acid, and virtually no water vapour.
• This thick atmosphere of swirling clouds allows the Sun's heat in but does not allow it to escape, resulting in surface temperatures over 450 °C, hotter than the surface of the planet Mercury, which is closest to the Sun.
• These clouds reflect a great deal of sunlight too, so Venus it is usually the brightest planet in the sky.
• In the upper layers, the clouds move faster than hurricane- force winds on Earth.
• Is similar to Earth in size, mass, and composition. However Venus has no ocean.
• Venus rotates retrograde, or "backwards," spinning in the opposite direction of its orbit around the Sun. From its surface, the Sun would seem to rise in the west and set in the east.
• Venus has temperatures hot enough to melt lead and pressure so intense that standing on Venus would feel like the pressure felt 900 meters deep in Earth's oceans.
• This pressure, caused by the high density of the atmosphere, results in a surface pressure 90 times that of Earth, which is why probes that have landed on Venus have only survived several hours before being crushed.
• Venus sluggishly rotates on its axis once every 243 Earth days, while it orbits the Sun every 225 days - its day is longer than its year!

Earth

• Earth is a gas/rock/ice planet composed of a molten iron core, carbonaceous chondrites, basalts, silicates, alkali metals, and hydrogen. It is the only planet known to harbour life.
• All of the things we need to survive are provided under a thin layer of atmosphere made mostly of oxygen and nitrogen. This separates us from the uninhabitable void of space.
• The spinning molten iron core creates a strong magnetic field, which keeps the atmosphere in place. Without this nothing would survive on earth.
• The magnetic field also protects life from deadly cosmic radiation, by drawing it away to the magnetic poles and funnelling it out into space again.
• The four seasons are a result of Earth's axis of rotation being tilted more than 23 degrees.
• The temperature of Earth increases about 20 degrees Celsius for every kilometre down. Near the centre, it is thought to be at least 3,870 Celsius.
• Earth is more than 4.5 billion years old, just 10 billion years younger than the Sun.
• 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.
• Earth is 2/3 water. but all the fresh water streams only represent one hundredth of one percent.
• 1,000 tons of material enters the earths atmosphere from outer space every year and makes its way to Earth’s surface.
• The distance from the surface of Earth to the centre is about 6,378 kilometres.
• Much of Earth is fluid. The mostly solid skin of the planet is only 66 kilometres thick.

Mars

• Mars is a small rock/ice planet composed of metal, mostly iron oxide, silicates, and hydrogen.
• Its atmosphere is made up of carbon dioxide and argon but is too thin to trap enough heat to allow the ice to melt.
• It has polar ice caps that grow and recede with the change of seasons.
• 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.
• Mars has some remarkable geological characteristics, including the largest volcanic mountain in the solar system, Olympus Mons (27 km high and 600 km across); volcanoes in the northern region that are so huge they deform the planet's roundness; and a gigantic equatorial rift valley, the Valles Marineris. This canyon system is the largest and deepest known in the solar system. It extends more then 4,000 km and reaches depths of 5 to 10 km below the surface, stretching a distance equivalent to the distance from New York to Los Angeles. Arizona's Grand Canyon could easily fit into one side of it!
• 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.
•  The month of March was named after Mars and was considered to be a month of war and bloodshed by ancient peoples.

Jupiter

• Jupiter is a gas planet composed of hydrogen and helium with traces of methane, water, and ammonia. Jupiter's core is not solid but a dense, hot liquid with a consistency like thick soup. The pressure inside Jupiter may be 30 million times greater than the pressure at Earth's surface.
• Jupiter’s atmosphere is a magnetosphere, the most deadly radiation environment of any of the planets, both for humans and for electronic equipment.
• Jupiter is the most volcanically active body in our solar system.
• Jupiter now officially has 63 moons - by far the most in the solar system, and more are being discovered all the time. Many of the outer moons are probably asteroids captured by the giant planet's gravity.
• If Earth were the size of a person, Jupiter would be as tall as a six story building.
• When it is in the night-time sky, Jupiter is often the brightest "star" in the sky (it is second only to Venus, which is seldom visible in a dark sky). Four of its Galilean moons are easily visible with binoculars; a few bands and the Great Red Spot can be seen with a small astronomical telescope.
• Jupiter is very gradually slowing down due to the tidal drag produced by these Galilean moons. Also, the same tidal forces are changing the orbits of the moons, very slowly forcing them farther from Jupiter.

Saturn

• Saturn is a gas giant composed of mostly hydrogen and helium, with some methane and ammonia. It may have a very small rock core.
• At the top of the clouds surrounding Saturn it is so cold that the ammonia freezes right out.
• It has a thick magnetosphere which attracts 46 moons, which have a very wide variety of shapes, sizes, colours, and geography.
• Winds in the upper atmosphere reach 500 meters per second in the equatorial region. (In contrast, the strongest hurricane-force winds on Earth top out at about 110 meters per second.) These super-fast winds, combined with heat rising from within the planet's interior, cause the yellow and gold bands visible in its atmosphere.
• Saturn’s rings would just fit in the distance between Earth and the Moon.
• Saturn is lighter than water and would float in a bathtub if you had one big enough.
• The effect of Saturn's low density and high rotation speed is that it actually "flattens out" at it's equator.
• Saturn’s ring system is very complex and is made up of many, many separate rings, including one ring that appears to be "braided" The appearance of the rings can change and the reason for that is not known.
• Saturn has 33 moons. The largest one is Titan, which is the only satellite in the solar system known to have an atmosphere, consisting of nitrogen and methane.

Uranus

• Uranus is classified as a "gas giant" planet because it has no solid surface. Methane gas above the deeper cloud layers causes its blue-green colour (methane absorbs red light and reflects blue light).
• 80 percent of its mass is contained in an extended liquid core consisting primarily of the "icy" materials water (hydrogen), methane, helium, and ammonia, with higher-density material at depth.
• Uranus has the brightest clouds in the outer solar system.
• Uranus' magnetic field is unusual in that the magnetic axis is tilted 60 degrees from the planet's axis of rotation and is offset from the centre of the planet by one-third of the planet's radius.
• The temperature differences on the summer and winter sides of the planet do not differ that greatly. Near the cloud-tops, the temperature of Uranus is near -215 °C.
• Uranus takes 84 years to complete an orbit.
• Uranus has 11 rings. Like Jupiter's, they are very dark but like Saturn's they are composed of fairly large particles ranging up to 10 meters in diameter in addition to fine dust.
• Uranus lies on its "side", and there is no adequate explanation as to why. The extreme axial tip of Uranus is 98° as it revolves around the sun.
• Many of Uranus' 27 known moons are 'icy moons' which means they have no atmosphere.

Neptune

• Neptune is a gas planet composed ofHydrogen (80.0%), Helium (18.5%), Methane (1.5%) with no solid surfaces and several rings.
• Neptune's atmosphere extends to great depths, gradually merging into water and other "melted ices" over a heavier, approximately Earth-sized liquid core.
• Neptune was the first planet located through mathematical predictions rather than through regular observations of the sky. When Uranus didn't travel exactly as astronomers expected it to, two mathematicians, working independently of each other, proposed the position and mass of another, as yet unknown planet that could account for Uranus' orbit. Although "the establishment" ignored the predictions, a young astronomer decided to look for the predicted planet. Thus, Neptune was discovered in 1846. Seventeen days later, its largest moon, Triton, was also discovered.
• Neptune is invisible to the naked eye because of its extreme distance from Earth. Interestingly, due to Pluto's unusual elliptical orbit, Neptune is actually the farthest planet from the Sun for a 20-year period out of every 248 Earth years.
• Neptune has 13 known moons.
• Neptune is well known for its "Great Dark Spot" (about the size of Earth,) which is similar to Jupiter's "Great Red Spot." Both of them are massive hurricanes. The strange thing about this spot is it seems to have disappeared around 1994. It has either slowed down or is hidden by atmospheric components.
• The wind on Neptune can blow as fast as 2000 km an hour, and are nine times stronger than Earth's.
• It takes Neptune about 165 years to orbit the sun. It still hasn't made a full circle around the sun since it was discovered!
• Its two seasons last an incredible 41 years each.
• Black holes occur in the solar system when a giant star explodes. The outer layers of the star are spewed out into space and the core of that giant star is left behind. The core then collapses inward making a very small ball. This small ball is called a neutron star, and becomes a black hole. It is very dense and VERY heavy, and contains a great gravitational pull. Everything near this ball is sucked right to it even light rays, that’s why the “black holes” are so dark.

Pluto

• Pluto is an ice planet composed of a rocky core surrounded by a mantle of water ice. It appears to have a bright layer of frozen methane, nitrogen, and carbon monoxide on its surface. While it is close to the Sun, these ices thaw, rise, and temporarily form a thin atmosphere, with a pressure one one-millionth that of Earth's atmosphere.
• When Pluto is near the Sun, it has a thin atmosphere, but when Pluto travels to the outer regions of its orbit, the atmosphere freezes and collapses to the planet's surface. In that way, Pluto acts like a comet.
• Pluto's low gravity (about 6 percent of Earth's) causes the atmosphere to be much more extended in altitude than our planet's. Because Pluto's orbit is so elliptical, Pluto grows much colder during the part of each orbit when it is travelling away from the Sun. During this time, the bulk of the planet's atmosphere freezes.
• Pluto is tough to see even with the best telescopes. Between 1979 and 1999, Pluto's highly elliptical orbit brought it closer to the Sun than Neptune, providing rare opportunities to study this small, cold, distant world.
• Pluto turns on it’s own axis every 6 days and 9 minutes, so on this planet time practically stands still!
• Pluto takes 248 Earth years to orbit the Sun, and its most recent close approach to the Sun was in 1989.
• Pluto has only one moon.

Sun

• The Sun is a huge bright gas planet composed mostlyof ionized Hydrogen and Helium.
• Its two outer layers consist of the photosphere and the chromosphere. The surface, known as the photosphere, is the visible 500-km-thick layer from which most of the Sun's radiation and light finally escape and is the place where sunspots are found.
• Above the photosphere lies the chromosphere ("sphere of colour") that may be seen briefly during total solar eclipses as a reddish rim, caused by hot hydrogen atoms, around the Sun.
• The Sun has inspired mythology in almost all cultures, since the beginning of time.
• The Sun is about 4.5 billion years old. There are millions of similar stars in the Milky Way Galaxy (and billions of galaxies in the universe).
• Our Sun supports life on Earth. It powers photosynthesis in green plants and is ultimately the source of all food and fossil fuel.
• The connection and interaction between the Sun and the Earth drive the seasons, currents in the ocean, weather, and climate.
• The Sun is some 333,400 times more massive than Earth and contains 99.86 percent of the mass of the entire solar system. It is held together by gravitational attraction, producing immense pressure and temperature at its core (more than a billion times that of the atmosphere on Earth, with a density about 160 times that of water).
• At the core, the temperature is 16 million degrees Kelvin (K), which is sufficient to sustain thermonuclear fusion reactions. The released energy prevents the collapse of the Sun and keeps it in gaseous form. The total energy radiated is 383 billion trillion kilowatts, which is equivalent to the energy generated by 100 billion tons of TNT exploding each second.

Astronomical Data

	Distance from the Sun (km) (Semimajor axis of orbit)	Mean Equatori al Radius (km)	Mean Equatori al Radius (x Earth)	Volume (km3)	Volum e (x Earth)	Mass (kg)	Densit y (g/cm 3)	Equatori al Surface Gravity (m/s2)	Escape Velocit y (km/h)
Mercury	57,909,175	2,439.70	0.3825	6.08272 x 1010	0.054	3.3022 x 1023	5.427	3.7	15,300
Venus	108,208,930	6,051.80	0.9488	9.284 x 1011	0.88	4.8685 x 1024	5.24	8.87	37,300
Earth	149,597,890	6,378.14	1	1.0832 x 1012	1	5.9737 x 1024	5.515	9.766	40,248
Mars	227,936,640	3,397	0.5326	1.6314 X 1011	0.15	6.4185 x 1023	3.94	3.693	18,072
Jupiter	778,412,020	71,492	11.209	1.4255 x 1015	1316	1.8987 x 1027	1.33	20.87	214,300
Saturn	1,426,725,400	60,268	9.449	8.2713 x 1014	763.6	5.6851 x 1026	0.7	7.207	127,760
Uranus	2,870,972,200	25,559	4.007	5.9142 x 1013	63.1	8.6849 x 1025	1.3	8.43	76,640
Neptun e	4,498,252,900	24,764	3.883	6.2526 x 1013	57.7	1.0244 x 1026	1.76	10.71	85,356
Pluto	5,906,380,000	1,151	0.18	6.39 x 109	0.0059	1.3 x 1022	2	0.81	4,570

	Rotation Period (Earth days)	Orbit Period (Earth years)	Mean Orbit Velocity (km/h)	Orbit Eccentricity	Orbit Inclination to Ecliptic	Inclination of Equator to Orbit
Mercury	58.646	0.241	172,341	0.20563069	7°	0°
Venus	-243	0.615	126,077	0.0068	3.39°	177.3°
Earth	0.99726968	1.000017	107,229	0.01671022	0.00005°	23.45°
Mars	1.026	1.8807	86,871	0.0934	1.8°	25.19
Jupiter	0.41354	11.8565	47,051	0.04839	1.305°	3.12°
Saturn	0.44401	29.4	34,821	0.0541506	2.484°	26.73°
Uranus	-0.7196	84.02	24,607	0.047168	0.770°	97.86°
Neptune	0.67125	164.79	19,720	0.00859	1.769°	29.58°
Pluto	6.387	247.92	17,096	0.2488	17.14°	119.61°

	Major Atmospheric Constituents	Composition	Moon s	Rings	Minimum Surface Temperature	Maximum Surface Temperature
Mercury	Potassium, Sodium	70% Metallic and 30% Silicate	None	No	-173	427
Venus	Carbon Dioxide, Nitrogen	Iron, Metallic, Silicate	None	No	462
Earth	Nitrogen, Oxygen		1	No	-88	58
Mars	Carbon Dioxide, Nitrogen, Argon		2	No	-87	-5
Jupiter	Hydrogen, Helium		63	Yes
Saturn	Hydrogen, Helium		46	Yes
Uranus	Hydrogen, Helium, Methane		27	Yes
Neptune	Hydrogen, Helium, Methane		13	Yes
Pluto	Nitrogen, Methane, Carbon Monoxide		1	No	-233	-223

Links

http://www.solarviews.com/eng/
Summary of planetary facts with illustrations.

http://solarsystem.jpl.nasa.gov/planets/
Details about many aspects of the solar system.

http://nssdc.gsfc.nasa.gov/planetary/
Info and photos of space exploration for education.

http://nssdc.gsfc.nasa.gov/planetary/education/schoolyard_ss/
Contains great specific educational resources.

http://www.nineplanets.org/
A ‘multimedia’ tour of the solar system

http://teacher.scholastic.com/researchtools/articlearchives/space/planets.htm
Includes Lesson Plans.

http://en.wikipedia.org/wiki/Planet
Is a detailed encyclopaedia for all aspects of planets. Has resources with animation and interaction for children.

http://seds.lpl.arizona.edu/billa/tnp
Detailed information about all planets.

www.crh.noaa.gov/fsd/astro
Up to date and detailed facts about the planets.

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