Our solar system consists of an average star we call the Sun, the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. It includes: the satellites of the planets; numerous comets, asteroids and meteoroids; and the interplanetary medium. The Sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system. The Sun's nearest known stellar neighbor is a red dwarf star called Proxima Centauri, at a distance of 4.3 light years away.
The whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy, a spiral disk of 200 billion stars we call the Milky Way. The Milky Way has two small galaxies orbiting it nearby, which are visible from the southern hemisphere. They are called the Large Magellanic Cloud and the Small Magellanic Cloud. The nearest large galaxy is the Andromeda Galaxy. It is a spiral galaxy like the Milky Way but is 4 times as massive and is 2 million light years away. Our galaxy, one of billions of galaxies known, is traveling through intergalactic space.
The planets, most of the satellites of the planets and the asteroids revolve around the Sun in the same direction, in nearly circular orbits. When looking down from above the Sun's north pole, the planets orbit in a counter-clockwise direction. The planets orbit the Sun in or near the same plane, called the ecliptic. Pluto is a special case in that its orbit is the most highly inclined (18 degrees) and the most highly elliptical of all the planets. Because of this, for part of its orbit, Pluto is closer to the Sun than is Neptune. The axis of rotation for most of the planets is nearly perpendicular to the ecliptic. The exceptions are Uranus and Pluto, which are tipped on their sides.
Composition of The Solar System:
The Sun contains 99.85% of all the matter in the Solar System. The planets, which condensed out of the same disk of material that formed the Sun, contain only 0.135% of the mass of the solar system. Jupiter contains more than twice the matter of all the other planets combined. Satellites of the planets, comets, asteroids, meteoroids, and the interplanetary medium constitute the remaining 0.015%. The following table is a list of the mass distribution within our Solar System.
The sun is a star, a hot ball of glowing gases at the heart of our solar system. Its influence extends far beyond the orbits of distant Neptune and Pluto. Without the sun's intense energy and heat, there would be no life on Earth. And though it is special to us, there are billions of stars like our sun scattered across the Milky Way galaxy.
1.The sun is a star. A star does not have a solid surface, but is a ball of gas (92.1 percent hydrogen (H2) and 7.8 percent helium (He)) held together by its own gravity.
2. The sun is the center of our solar system and makes up 99.8% of the mass of the entire solar system
3. If the sun were as tall as a typical front door, Earth would be about the size of a nickel.
4. Since the sun is not a solid body, different parts of the sun rotate at different rates. At the equator, the sun spins once about every 25 Earth days, but at its poles the sun rotates once on its axis every 36 days.
5. The solar atmosphere is where we see features such as sunspots and solar flares on the sun. The sun's outer atmosphere - the corona - extends beyond the orbit of dwarf-planet Pluto.
6. The sun is orbited by eight planets, at least five dwarf planets, tens of thousands of asteroids, and hundreds of thousands to three trillion comets and icy bodies.
7. The sun does not have any rings.
8. Spacecraft are constantly increasing our understanding of the sun - from Genesis (which collected samples of the solar wind and returned the particles to Earth) to SOHO, STEREO THEMIS, and many more, which are examining the sun's features, its interior and how it interacts with our planet.
9. Without the sun's intense energy there would be no life on Earth.
10.The temperature at the sun's core is about 15 million degrees Celsius (27 million degrees Fahrenheit).
Sun-scorched Mercury is only slightly larger than Earth's moon. Like the moon, Mercury has very little atmosphere to stop impacts and it is covered with craters. Mercury's dayside is super-heated by the sun, but at night temperatures drop hundreds of degrees below freezing. Ice may even exist in craters. Mercury's egg-shaped orbit takes it around the sun every 88 days.
Need-to-know things about Mercury:
1. Mercury is the smallest planet in our solar system - only slightly larger than the Earth's moon.
2. It is the closest planet to the sun at a distance of about 58 million km or 0.39 AU.
3. One day on Mercury (the time it takes for Mercury to rotate or spin once) takes 59 Earth days. Mercury makes a complete orbit around the sun (a year in Mercury time) in just 88 Earth days.
4. Mercury is a rocky planet, also known as a terrestrial planet. Mercury has a solid, cratered surface, much like Earth's moon.
5. Mercury's thin atmosphere, or exosphere, is composed mostly of oxygen (O2), sodium (Na), hydrogen (H2), helium (He), and potassium (K). Atoms that are blasted off the surface by the solar wind and micrometeoroid impacts create Mercury's exosphere.
6. Mercury has no moons.
7. There are no rings around Mercury.
8. Only two spacecraft have visited this rocky planet: Mariner 10 in 1974 - 75 and MESSENGER, which flew past Mercury three times before going into orbit around Mercury in 2011.
9. No evidence for life has been found on Mercury. Daytime temperatures can reach 800 degrees Fahrenheit (430 degrees Celsius) and drop to -290 degrees Fahrenheit (-180 degrees Celsius) at night. It is unlikely life (as we know it) could survive on this planet.
10. Standing on Mercury's surface at its closest point to the sun, the sun would appear more than three times larger than it does on Earth.
Mercury's eccentric orbit takes the small planet as close as 47 million km and as far as 70 million km from the sun. If one could stand on the scorching surface of Mercury when it is at its closest point to the sun, the sun would appear more than three times as large as it does when viewed from Earth. Temperatures on Mercury's surface can reach 800 degrees Fahrenheit (430 degrees Celsius). Because the planet has no atmosphere to retain that heat, nighttime temperatures on the surface can drop to -290 degrees Fahrenheit (-180 degrees Celsius).
Because Mercury is so close to the sun, it is hard to directly observe from Earth except during dawn or twilight. Mercury makes an appearance indirectly 13 times each century, observers on Earth can watch Mercury pass across the face of the sun, an event called a transit. These rare transits fall within several days of 8 May and 10 November. The first two transits of Mercury in the 21st century occurred 7 May 2003, and 8 November 2006. The next are 9 May 2016, and 11 November 2019.
Mercury speeds around the sun every 88 days, traveling through space at nearly 50 km (31 miles) per second faster than any other planet. One Mercury solar day equals 175.97 Earth days.
Instead of an atmosphere, Mercury possesses a thin exosphere made up of atoms blasted off the surface by the solar wind and striking micrometeoroids. Because of solar radiation pressure, the atoms quickly escape into space and form a tail of neutral particles. Though Mercury's magnetic field at the surface has just one percent the strength of Earth's, it interacts with the magnetic field of the solar wind to episodically create intense magnetic tornadoes that funnel the fast, hot solar wind plasma down to the surface. When the ions strike the surface, they knock off neutrally charged atoms and send them on a loop high into the sky.
Venus is a dim world of intense heat and volcanic activity. Similar in structure and size to Earth, Venus' thick, toxic atmosphere traps heat in a runaway 'greenhouse effect.' The scorched world has temperatures hot enough to melt lead. Glimpses below the clouds reveal volcanoes and deformed mountains. Venus spins slowly in the opposite direction of most planets.
Need-to-know things about Venus:
1. Venus is only a little smaller than Earth.
2. Venus is the second closest planet to the sun at a distance of about 108 million km (67 million miles) or 0.72 AU.
One day on Venus lasts as long as 243 Earth days (the time it takes for Venus to rotate or spin once). Venus makes a complete orbit around the sun (a year in Venusian time) in 225 Earth days.
4. Venus is a rocky planet, also known as a terrestrial planet. Venus' solid surface is a cratered and volcanic landscape.
5. Venus' thick and toxic atmosphere is made up mostly of carbon dioxide (CO2) and nitrogen (N2), with clouds of sulfuric acid (H2SO4) droplets.
6. Venus has no moons.
7. There are no rings around Venus.
8. More than 40 spacecraft have explored Venus. The Magellan mission in the early 1990s mapped 98 percent of the planet's surface.
9. No evidence for life has been found on Venus. The planet's extreme high temperatures of almost 480 degrees Celsius (900 degrees Fahrenheit) make it seem an unlikely place for for life as we know it.
10. Venus spins backwards (retrograde rotation) when compared to the other planets. This means that the sun rises in the west and sets in the east on Venus.
Venus and Earth are similar in size, mass, density, composition, and gravity. There, however, the similarities end. Venus is covered by a thick, rapidly spinning atmosphere, creating a scorched world with temperatures hot enough to melt lead and surface pressure 90 times that of Earth (similar to the bottom of a swimming pool 1 - 1/2 miles deep). Because of its proximity to Earth and the way its clouds reflect sunlight, Venus appears to be the brightest planet in the sky.
We cannot normally see through Venus' thick atmosphere, but NASA's Magellan mission during the early 1990s used radar to image 98 percent of the surface, and the Galileo spacecraft used infrared mapping to view both the surface and mid-level cloud structure as it passed by Venus on the way to Jupiter. In 2010, infrared surface images by the European Space Agency's Venus Express provided evidence for recent volcanism within the past several hundred thousand years. Indeed, Venus may be volcanically active today.
Like Mercury, Venus can be seen periodically passing across the face of the sun. These "transits" of Venus occur in pairs with more than a century separating each pair. Transits occurred in 1631, 1639; 1761, 1769; and 1874, 1882. On 8 June 2004, astronomers worldwide watched the tiny dot of Venus crawl across the sun; and on 6 June 2012, the second in this pair of transits occurred. The next transit is 11 December 2117. Observing these transits helps us understand the capabilities and limitations of techniques used to find and characterize planets around other stars.
Venus' 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 higher than 470 degrees Celsius (880 degrees Fahrenheit). The few probes that have landed on Venus have not survived longer than 2 hours in the intense heat. Sulfur compounds are abundant in Venus' clouds; the corrosive chemistry and dense, moving atmosphere cause significant surface weathering and erosion.
Earth, our home planet, is the only planet in our solar system known to harbor life - life that is incredibly diverse. All the things we need to survive exist under a thin layer of atmosphere that separates us from the cold, airless void of space.
1. If the sun were as tall as a typical front door, Earth would be the size of a nickel.
2. Earth is the third planet from the sun at a distance of about 150 million km (93 million miles) or one AU.
3. One day on Earth takes 24 hours (this is the time it takes the Earth to rotate or spin once). Earth makes a complete orbit around the sun (a year in Earth time) in about 365 days.
4. Earth is a rocky planet, also known as a terrestrial planet, with a solid and dynamic surface of mountains, valleys, canyons, plains and so much more. What makes Earth different from the other terrestrial planets is that it is also an ocean planet: 70 percent of the Earth's surface is covered in oceans.
5. The Earth's atmosphere is made up of 78 percent nitrogen (N2), 21 percent oxygen (O2) and 1 percent other ingredients -the perfect balance for us to breathe and live. Many planets have atmospheres, but only Earth's is breathable.
6. Earth has one moon. Another name for a moon is satellite.
7. Earth has no rings.
8. Many orbiting spacecraft study the Earth from above as a whole system and together aid in understanding our home planet.
9. Earth is the perfect place for life.
10. Earth's atmosphere protects us from incoming meteoroids, most of which break up in our atmosphere before they can strike the surface as meteorites.
11. Earth, our home planet, is the only planet in our solar system known to harbor life - life that is incredibly diverse. All the things we need to survive exist under a thin layer of atmosphere that separates us from the cold, airless void of space.
12. Earth is made up of complex, interactive systems that create a constantly changing world that we are striving to understand. From the vantage point of space, we are able to observe our planet globally, using sensitive instruments to understand the delicate balance among its oceans, air, land, and life. NASA satellite observations help study and predict weather, drought, pollution, climate change, and many other phenomena that affect the environment, economy, and society.
13. Earth is the thrid 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 23.45 degrees with respect to the plane of Earth's orbit around the sun. During part of the year, the northern hemisphere is tilted toward the sun and the southern hemisphere is tilted away, producing summer in the north and winter in the south. Six months later, the situation is reversed. When spring and fall begin, both hemispheres receive roughly equal amounts of solar illumination.
14. Earth's global ocean, which covers nearly 70 percent of the planet's surface, has an average depth of about 4 kilometers. Fresh water exists in the liquid phase only within a narrow temperature span - 0 to 100 degrees Celsius (32 to 212 degrees Fahrenheit). This span is especially narrow when contrasted with the full range of temperatures found within the solar system. The presence and distribution of water vapor in the atmosphere is responsible for much of Earth's weather.
Our moon makes Earth a more livable planet by moderating our home planet's wobble on its axis, leading to a relatively stable climate, and creating a tidal rhythm that has guided humans for thousands of years. The moon was likely formed after a Mars-sized body collided with Earth and the debris formed into the most prominent feature in our night sky.
Need-to-know things about Earth's Moon:
1. If the sun were as tall as a typical front door, Earth would be the size of a nickel and the moon would the size of a green pea.
2. The moon is Earth's satellite and orbits the Earth at a distance of about 384 thousand km or 0.00257 AU.
3.The moon makes a complete orbit around Earth in 27 Earth days and rotates or spins at that same rate, or in that same amount of time. This causes the moon to keep the same side or face towards Earth during the course of its orbit.
4. The moon is a rocky, solid-surface body, with much of its surface cratered and pitted from impacts.
5. The moon has a very thin and tenuous (weak) atmosphere, called an exosphere.
6. The moon has no moons.
7. The moon has no rings.
8. More than 100 spacecraft been launched to explore the moon. It is the only celestial a body beyond Earth that has been visited by human beings (The Apollo Program).
9. The moon's weak atmosphere and its lack of liquid water cannot support life as we know it.
10. Surface features that create the face known as the "Man in the moon" are impact basins on the moon that are filled with dark basalt rocks.
The regular daily and monthly rhythms of Earth's only natural satellite, the moon, have guided timekeepers for thousands of years. Its influence on Earth's cycles, notably tides, has been charted by many cultures in many ages. The moon moderates Earth's wobble on its axis, leading to a relatively stable climate over billions of years. From Earth, we always see the same face of the moon because the moon is spinning on its axis at the same speed that it is going around Earth (that is, it is in synchronous rotation with Earth).
The light areas of the moon are known as the highlands. The dark features, called maria (Latin for seas), are impact basins that were filled with lava between 4.2 and 1.2 billion years ago. These light and dark areas represent rocks of different composition and ages, which provide evidence for how the early crust may have crystallized from a lunar magma ocean. The craters themselves, which have been preserved for billions of years, provide an impact history for the moon and other bodies in the inner solar system.
The leading theory of the moon's origin is that a Mars-sized body collided with Earth approximately 4.5 billion years ago, and the resulting debris from both Earth and the impactor accumulated to form our natural satellite. The newly formed moon was in a molten state. Within about 100 million years, most of the global "magma ocean" had crystallized, with less-dense rocks floating upward and eventually forming the lunar crust. The early moon may have developed an internal dynamo, the mechanism for global magnetic fields for terrestrial planets.
Mars is a cold desert world. It is half the diameter of Earth and has the same amount of dry land. Like Earth, Mars has seasons, polar ice caps, volcanoes, canyons and weather, but its atmosphere is too thin for liquid water to exist for long on the surface. There are signs of ancient floods on Mars, but evidence for water now exists mainly in icy soil and thin clouds.
Need-to-know things about Mars
1. If the sun were as tall as a typical front door, Earth would be the size of a nickel, and Mars would be about as big as an aspirin tablet.
2. Mars orbits our sun, a star. Mars is the fourth planet from the sun at a distance of about 228 million km or 1.52 AU.
3. One day on Mars takes just a little over 24 hours (the time it takes for Mars to rotate or spin once). Mars makes a complete orbit around the sun (a year in Martian time) in 687 Earth days.
4. Mars is a rocky planet, also known as a terrestria palanet. Mars solid surface has been altered by volcanoes, impacts, crustal movement and atmospheric effects such as dust storms.
5.Mars has a thin atmosphere made up mostly of carbon dioxide (CO2), nitrogen (N2) and argon (Ar).
6. Mars has two moons named Phobos and Deimos.
7. There are no rings around Mars.
8. More than 40 spacecraft have been launched for Mars, from flybys and orbiters to rovers and landers that touched surface of the Red Planet. The first true Mars mission success was Mariner 4 in 1965.
9. At this time in the planet's history, Mars' surface cannot support life as we know it. A key science goal is determining Mars' past and future potential for life.
10. Mars is known as the Red Planet because iron minerals in the Martian soil oxidize, or rust, causing the soil - and the dusty atmosphere - to look red.
Mars is a rocky body about half the size of Earth. As with the other terrestrial planets - Mercury, Venus, and Earth - volcanoes, impact craters, crustal movement, and atmospheric conditions such as dust storms have altered the surface of Mars.
Mars has two small moons, Phobos and Deimos, that may be captured asteroids. Potato-shaped, they have too little mass for gravity to make them spherical. Phobos, the innermost moon, is heavily cratered, with deep grooves on its surface.
Like Earth, Mars experiences seasons due to the tilt of its rotational axis. Mars' orbit is about 1.5 times farther from the sun than Earth's and is slightly elliptical, so its distance from the sun changes. That affects the length of Martian seasons, which vary in length. The polar ice caps on Mars grow and recede with the seasons. Layered areas near the poles suggest that the planet's climate has changed more than once. Volcanism in the highlands and plains was active more than 3 billion years ago. Some of the giant shield volcanoes are younger, having formed between 1 and 2 billion years ago. Mars has the largest volcano in the solar system, Olympus Mons, as well as a spectacular equatorial canyon system, Valles Marineris.
Asteroids are rocky, airless worlds that orbit our sun, but are too small to be called planets. Tens of thousands of these minor planets are gathered in the main asteroid belt, a vast doughnut-shaped ring between the orbits of Mars and Jupiter. Asteroids that pass close to Earth are called near-earth objects.
Need-to-know things about Asteroids:
1. If all of the asteroids were combined into a ball, they would still be much smaller than Earth's moon. If the sun was as tall as a typical front door, Earth would be the size of a nickel, the moon would be about as big as a green pea and Ceres (the largest object in the main asteroid belt) would be as small as a sesame seed.
2. Most Asteroids orbit our sun, a star, in a region of space between the orbits of Mars and Jupiter known as the Asteroid Belt.
3. Days and years vary by asteroid. A day on asteroid Ida, for example, takes only 4.6 hours (the time it takes to rotate or spin once). Ida makes a complete orbit around the sun (a year in this asteroid's time) in 4.8 Earth years.
4. Asteroids are solid, rocky and irregular bodies.
5. Asteroids do not have atmospheres.
6. More than 150 asteroids are known to have a small companion moon (some have two moons). The first discovery of an asteroid-moon system was of asteroid Ida and its moon Dactyl in 1993.
7. One asteroid, named Chariklo, is known to have two dense and narrow rings.
8. More than 10 spacecraft have explored asteroids. NEAR Shoemaker even landed on an asteroid (Eros). The Dawn mission is the first mission to orbit (2011) a main belt asteroid (Vesta).
9. Asteroids cannot support life as we know it.
10. Ceres, the first and largest asteroid to be discovered (1801 by Giuseppe Piazzi) and the closest dwarf planet to the sun, encompasses over one-third of the estimated total mass of all the asteroids in the asteroid belt.
Meteors and Meteorites
Little chunks of rock and debris in space are called meteoroids. They become meteors - or shooting stars - when they fall through a planet's atmosphere; leaving a bright trail as they are heated to incandescence by the friction of the atmosphere. Pieces that survive the journey and hit the ground are called meteorites.
Need-to-know things about Meteors and Meteorites:
1.Meteoroids become meteors - or shooting stars - when they interact with a planet's atmosphere and cause a streak of light in the sky. Debris that makes it to the surface of a planet from meteoroids are called meteorites.
2. Meteorites may vary in size from tiny grains to large boulders. One of the largest meteorite found on Earth is the Hoba meteorite from southwest Africa, which weighs roughly 54,000 kg (119,000 pounds).
3.Meteor showers are usually named after a star or constellation which is close to the radiant (the position from which the meteor appears to come).
4. Meteors and meteorities begin as meteoroids, which are little chunks of rock and debris in space.
5. Most meteorites are either iron, stony or stony-iron.
6.Meteorites may look very much like Earth rocks, or they may have a burned appearance. Some may have depressioned (thumbprint-like), roughened or smooth exteriors.
7. Many of the meteor showers are associated with comets. The Leonids are associated with comet Tempel-Tuttle; Aquarids and Orionids with comet Halley, and the Taurids with comet Encke.
8. When comets come around the sun, they leave a dusty trail. Every year the Earth passes through the comet trails, which allows the debris to enter our atmosphere where it burns up and creates fiery and colorful streaks (meteors) in the sky.
9. Leonid MAC (an airborne mission that took flight during the years 1998 - 2002) studied the interaction of meteoroids with the Earth's atmosphere.
10. Meteoroids, meteors and meteorites cannot support life. However, they may have provided the Earth with a source of amino acids: the building blocks of life.
The most massive planet in our solar system - with dozens of moons and an enormous magnetic field - Jupiter forms a kind of miniature solar system. It resembles a star in composition, but did not grow big enough to ignite. The planet's swirling cloud stripes are punctuated by massive storms such as the Great Red Spot, which has raged for hundreds of years.
Need-to-know things about Jupiter:
1. If the sun were as tall as a typical front door, the Earth would be the size of a nickel and Jupiter would be about as big as a basketball.
2. Jupiter orbits our sun, a star. Jupiter is the fifth planet from the sun at a distance of about 778 million km or 5.2 AU.
3. One day on Jupiter takes about 10 hours (the time it takes for Jupiter to rotate or spin once). Jupiter makes a complete orbit around the sun (a year in Jovian time) in about 12 Earth years (4,333 Earth days).
4. Jupiter is a gas-giant planet and therefore does not have a solid surface. However, it is predicted that Jupiter has an inner, solid core about the size of the Earth.
5. Jupiter's atmosphere is made up mostly of hydrogen (H2) and helium (He).
6. Jupiter has 50 known moons, with an additional 17 moons awaiting confirmation of their discovery - that is a total of 67 moons.
7. Jupiter has a faint ring system that was discovered in 1979 by the Voyager 1 mission.
8. Many missions have visited Jupiter and its system of moons. The Juno mission will arrive at Jupiter in 2016.
9. Jupiter cannot support life as we know it. However, some of Jupiter's moons have oceans underneath their crusts that might support life.
10. Jupiter's Great Red Spot is a gigantic storm (bigger than Earth) that has been raging for hundreds of years.
Jupiter is the largest and most massive planet in our solar system, containing more than twice the amount of material of the other bodies orbiting our sun combined. Most of the material left over after the formation of the sun went to Jupiter, forming a type of planet called a gas giant.
Jupiter's appearance is a tapestry of colorful cloud bands and spots. Most visible clouds are composed of ammonia and ammonia compounds, with unknown chemicals providing color. Jupiter's fast rotation - spinning once every 10 hours - creates strong jet streams, smearing its clouds into bands across the planet.
With no solid surface to slow them down, Jupiter's spots can persist for many years. The Great Red Spot, a swirling oval of clouds twice as wide as Earth, has been observed on the giant planet for more than 300 years. More recently, three smaller ovals merged to form the Little Red Spot, about half the size of its larger cousin. Scientists do not yet know if these ovals and planet-circling bands are shallow or deeply rooted to the interior.
The composition of Jupiter's atmosphere is similar to that of the sun - mostly hydrogen and helium. Deep in the atmosphere, pressure and temperature increase, compressing the hydrogen gas into a liquid. This gives Jupiter the largest ocean in the solar system - an ocean made of hydrogen instead of water. Scientists think that, at depths perhaps halfway to the planet's center, the pressure becomes so great that electrons are squeezed off the hydrogen atoms, making the liquid electrically conducting. Jupiter's fast rotation is thought to drive electrical currents in this region, generating the planet's powerful magnetic field. It is still unclear if, deeper down, Jupiter has a central core of solid material.
Adorned with thousands of beautiful ringlets, Saturn is unique among the planets. All four gas giant planets have rings - made of chunks of ice and rock - but none are as spectacular or as complicated as Saturn's. Like the other gas giants, Saturn is mostly a massive ball of hydrogen and helium.
Need-to-know things about Saturn:
1. If the sun were as tall as a typical front door, the Earth would be the size of a nickel and Saturn would be about as big as a basketball.
2. Saturn orbits our sun, a star. Saturn is the sixth planet from the sun at a distance of about 1.4 billion km or 9.5 AU.
3. One day on Saturn takes 10.7 hours (the time it takes for Saturn to rotate or spin once). Saturn makes a complete orbit around the sun (a year in Saturnian time) in 29 Earth years.
4. Saturn is a gas-giant planet and does not have a solid surface.
5. Saturn's atmosphere is made up mostly of hydrogen (H2) and helium (He).
6. Saturn has 53 known moons with an additional 9 moons awaiting confirmation of their discovery.
7. Saturn has the most spectacular ring system of all our solar system's planets. It is made up of seven rings with several gaps and divisions between them.
8. Five missions have been sent to Saturn. Since 2004, Cassini has been exploring Saturn, its moons and rings.
9. Saturn cannot support life as we know it. However, some of Saturn's moons have conditions that might support life.
10. When Galileo Galilei looked at Saturn through a telescope in the 1600s, he noticed strange objects on each side of the planet and drew in his notes a triple-bodied planet system and then later a planet with arms or handles. The handles turned out to be the rings of Saturn.
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, thinking that Saturn was triple-bodied. Continuing his observations over the next few years, Galileo drew the lateral bodies as arms or handles attached to Saturn. 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 the Cassini Division, which is 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 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 the atmosphere.
Uranus is the only giant planet whose equator is nearly at right angles to its orbit. A collision with an Earth-sized object may explain the unique tilt. Nearly a twin in size to Neptune, Uranus has more methane in its mainly hydrogen and helium atmosphere than Jupiter or Saturn. Methane gives Uranus its blue tint.
Need-to-know things about Uranus:
1. If the sun were as tall as a typical front door, Earth would be the size of a nickel and Uranus would be about as big as a baseball.
2. Uranus orbits our sun, a star. Uranus is the seventh planet from the sun at a distance of about 2.9 billion km or 19.19 AU.
3. One day on Uranus takes about 17 hours (the time it takes for Uranus to rotate or spin once). Uranus makes a complete orbit around the sun (a year in Uranian time) in about 84 Earth years.
4. Uranus is an ice giant. Most (80 percent or more) of the planet's mass is made up of a hot dense fluid of "icy" materials – water (H2O), methane (CH4). and ammonia (NH3) – above a small rocky core.
5. Uranus has an atmosphere which is mostly made up of hydrogen (H2) and helium (He), with a small amount of methane (CH4).
6. Uranus has 27 moons. Uranus' moons are named after characters from the works of William Shakespeare and Alexander Pope.
7. Uranus has faint rings. The inner rings are narrow and dark and the outer rings are brightly colored.
8. Voyager 2 is the only spacecraft to have visited Uranus.
9. Uranus cannot support life as we know it.
10. Like Venus, Uranus has a retrograde rotation (east to west). Unlike any of the other planets, Uranus rotates on its side, which means it spins horizontally
The first planet found with the aid of a telescope, Uranus was discovered in 1781 by astronomer William Herschel, although he originally thought it was a comet or star. The seventh planet from the Sun is so distant that it takes 84 years to complete one orbit.
Like Venus, Uranus rotates east to west. Uranus' rotation axis is tilted almost parallel to its orbital plane, so Uranus appears to be rotating on its side. This situation may be the result of a collision with a planet-sized body early in the planet's history, which apparently radically changed Uranus' rotation. Because of Uranus' unusual orientation, the planet experiences extreme variations in sunlight during each 20-year-long season.
Voyager 2, the only spacecraft to visit Uranus, imaged a bland-looking sphere in 1986. When Voyager flew by, the south pole of Uranus pointed almost directly at the sun because Uranus was near its southern summer solstice, with the southern hemisphere bathed in continuous sunlight and the northern hemisphere radiating heat into the blackness of space.
Uranus reached equinox in December 2007, when it was fully illuminated as the sun passed over the planet's equator. By 2028, the north pole will point directly at the sun, a reversal of the situation when Voyager flew by. Equinox also brings ring-plane crossing, when Uranus' rings appear to move more and more edge-on as seen from Earth.
The Hubble Space Telescope and the Keck Observatory in Hawaii captured detailed images of Uranus as the planet approached equinox. While Voyager 2 saw only a few discrete clouds, more recent observations reveal that Uranus exhibits dynamic clouds as it approaches equinox, including rapidly evolving bright features and a new Great Dark Spot like those seen on Neptune.
Dark, cold and whipped by supersonic winds, Neptune is the last of the hydrogen and helium gas giants in our solar system. More than 30 times as far from the sun as Earth, the planet takes almost 165 Earth years to orbit our sun. In 2011 Neptune completed its first orbit since its discovery in 1846.
Need-to-know things about Neptune:
1. If the sun were as tall as a typical front door, the Earth would be the size of a nickel and Neptune would be about as big as a baseball.
2. Neptune orbits our sun, a star. Neptune is the eighth planet from the sun at a distance of about 4.5 billion km or 30.07 AU.
3. One day on Neptune takes about 16 hours (the time it takes for Neptune to rotate or spin once). Neptune makes a complete orbit around the sun (a year in Neptunian time) in about 165 Earth years (60,190 Earth days).
4. Neptune is a sister ice giant to Uranus. Neptune is mostly made of a very thick, very hot combination of water (H2O), ammonia (NH3), and methane (CH4) over a possible heavier, approximately Earth-sized, solid core.
5. Neptune's atmosphere is made up mostly of hydrogen (H2), helium (He) and methane (CH4).
6. Neptune has 13 confirmed moons (and 1 more awaiting official confirmation of discovery). Neptune's moons are named after various sea gods and nymphs in Greek mythology.
7. Neptune has six rings
8. Voyager 2 is the only spacecraft to have visited Neptune.
9. Neptune cannot support life as we know it.
10. At times during the course of Neptune's orbit, dwarf planet Pluto is actually closer to the sun, and us, than Neptune. This is due to the unusual elliptical (egg) shape of Pluto's orbit.
The ice giant 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' 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 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. Interestingly, the highly eccentric orbit of the dwarf planet Pluto brings Pluto inside Neptune's orbit for a 20-year period out of every 248 Earth years. Pluto can never crash into Neptune, though, because for every three laps Neptune takes around the Sun, Pluto makes two. This repeating pattern prevents close approaches of the two bodies.
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' 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.
Comets are cosmic snowballs of frozen gases, rock and dust roughly the size of a small town. When a comet's orbit brings it close to the sun, it heats up and spews dust and gases into a giant glowing head larger than most planets. The dust and gases form a tail that stretches away from the sun for millions of kilometers.
Need-to-know things about Comets:
1. If the sun were as tall as a typical front door, Earth would be the size of a nickel, dwarf planet Pluto would be the size of a head of a pin and the largest Kuiper Belt comet (about 100 km across, which is about one twentieth the size of Pluto) would only be about the size of a grain of dust.
2. Short-period comets (comets that orbit the sun in less than 200 years) reside in the icy region known as the Kuiper Belt beyond the orbit of Neptune from about 30 to 55 AU. Long-period comets (comets with long, unpredictable orbits) originate in the far-off reaches of the Oort Cloud, which is five thousand to 100 thousand AUs from the sun.
3. Days on comets vary. One day on comet Halley varies between 2.2 to 7.4 Earth days (the time it takes for comet Halley to rotate or spin once). Comet Halley makes a complete orbit around the sun (a year in this comet's time) in 76 Earth years.
4. Comets are cosmic snowballs of frozen gases, rock and dust.
5. A comet warms up as it nears the sun and develops an atmosphere, or coma. The coma may be hundreds of thousands of kilometers in diameter
6. Comets do not have moons.
7. Comets do not have rings.
8. More than 20 missions have explored comets from a variety of viewpoints.
9. Comets may not be able to support life themselves, but they may have brought water and organic compounds - the building blocks of life - through collisions with Earth and other bodies in our solar system.
10. Comet Halley makes an appearance in the Bayeux Tapestry from the year 1066, which chronicles the overthrow of King Harold by William the Conqueror at the Battle of Hastings.
Dwarf planets are round and orbit the Sun just like the eight major planets. But unlike planets, dwarf planets are not able to clear their orbital path so there are no similar objects at roughly the same distance from the Sun. A dwarf planet is much smaller than a planet (smaller even than Earth's moon), but it is not a moon. Pluto is the best known of the dwarf planets.
Need-to-know things about Dwarf Planets:
1. If the sun were as tall as a typical front door, Earth would be the size of a nickel and dwarf planets Pluto and Eris. For example, would each be about the size of the head of a pin.
2. Dwarf planets orbit our sun, a star. Most are located in the Kuiper Belt, a region of icy objects beyond the orbit of Neptune. Pluto, one of the largest and most famous dwarf planets, is about 5.9 billion km or 39.48 AU away from the sun. Dwarf planet Ceres is in the main asteroid belt between Mars and Jupiter.
3. Days and years vary on dwarf planets. One day on Ceres. For example, takes about nine hours (the time it takes for Ceres to rotate or spin once). Ceres makes a complete orbit around the sun (a year in Ceresian time) in about 4.60 Earth years
4. Dwarf planets are solid rocky and/or icy bodies, The amount of rock vs. ice depends on their location in the solar system.
5. Many, but not all dwarf planets have moons.
6. There are no known rings around dwarf planets.
7. Dwarf planets Pluto and Eris have tenuous (thin) atmospheres that expand when they come closer to the sun and collapse as they move farther away. It is possible dwarf planet Ceres has an atmosphere.
8. The first mission to a dwarf planet is Dawn (to Ceres).
9. Dwarf planets cannot support life as we know it.
10. Pluto was considered a planet until 2006. The discovery of a similar-sized worlds deeper in the distant Kuiper Belt sparked a debate that resulted in a new official definition of a planet that did not include Pluto.