The aurora borealis, are beautiful dancing waves of light whose occurrence is due to energized particles from the Sun, called the solar wind, slamming into Earth's upper atmosphere, or ionosphere, at speeds of up to 45 million mph (72 million kph).
The planet's magnetic field protects it from the onslaught. In the Northern Hemisphere, the phenomenon is called the northern lights (aurora borealis), while in the Southern Hemisphere, it's called the southern lights (aurora australis).
Italian astronomer Galileo Galilei gave them the name "aurora borealis" in 1619 — after the Roman goddess of dawn, Aurora, who travelled from east to west announcing the coming of the sun. And the Greek god of the north wind, Boreas. In Roman mythology, Auster is the god of the south wind.
Norwegian scientist Kristian Birkeland theorized that electrons emitted from sunspots produced the atmospheric lights after being guided toward the poles by Earth's magnetic field. The theory would eventually prove correct.
The earth's magnetic field is weaker at either pole and therefore some particles enter the earth's atmosphere and collide with gas particles. These collisions emit light that we perceive as the dancing lights. The lights of the Aurora generally extend from 80 km (50 miles) to as high as 640 km (400 miles) above the earth's surface.
Every type of atom or molecule, whether it's atomic hydrogen or a molecule like carbon dioxide, absorbs and radiates its own unique set of colors. Some of the dominant colors seen in aurorae are red, a hue produced by the nitrogen molecules, and green, which is produced by oxygen molecules.
The best places to watch the lights are in the northwestern parts of Canada, particularly the Yukon, Nunavut, Northwest Territories and Alaska. Auroral displays can also be seen over the southern tip of Greenland and Iceland, the northern coast of Norway and over the coastal waters north of Siberia. Southern auroras are not often seen as they are concentrated in a ring around Antarctica and the southern Indian Ocean.
Auroras have been seen in the atmospheres of all the gas giant planets, these planets all have robust magnetic fields. Auroras have also been discovered on both Venus and Mars, both of which have very weak magnetic fields.
Planet Type: Terrestrial
Moons: 1
Average Orbital Distance: 1 AU | 93 million miles | 150 million kilometers
Orbital Period: 365.25 days
Day: 23.9 hours
Average Surface Temperature: 59 °F | 15 °C
Equatorial Circumference: 24,873.6 mi | 40,030.2 km
Surface Gravity: 32.041ft/s2 | 9.80665 m/s2
Escape Velocity: 25,031 mph | 40,284 km/h
Atmospheric Constituents: Nitrogen, Oxygen
Third planet orbiting the Sun. The fifth largest planet in the solar system. Our home planet. Earth is a rocky planet with a solid and dynamic surface of mountains, canyons, plains and more. The only world in our solar system with liquid water on the surface. 70% of the planet is covered in water.
Except for Earth, all the planets were named after Greek and Roman gods and goddesses. However, the name Earth is a Germanic word, which simply means “the ground.”
Earth's atmosphere is 78% nitrogen, 21% oxygen and 1% other ingredients. The atmosphere protects the planet from incoming meteoroids, most of which break up in the atmosphere before they can strike the surface. The atmosphere shields the planet from much of the harmful radiation coming from the Sun.
One astronomical unit (AU) away from the Sun. Earth's axis of rotation is tilted 23.4 degrees with respect to the plane of Earth's orbit around the Sun. This tilt causes the yearly cycle of seasons. When spring and fall begin, both northern and southern hemispheres receive roughly equal amounts of heat from the Sun.
The only planet in the solar system with a single moon. The moon stabilizes the planet's wobble, which has made the climate less variable over thousands of years. Earth's oceans provided a place for life to begin about 3.8 billion years ago.
Earth is composed of four main layers, starting with an inner core at the planet's center, enveloped by the outer core, mantle, and crust.
The inner core is a solid sphere made of iron and nickel metals, with a temperature as high as 9,800 °F | 5,400 °C. The outer core is made of iron and nickel fluids, and is surrounded by the mantle, the thickest layer, a hot viscous mixture of molten rock. The outermost layer, Earth's crust, goes about 19 miles (30 km) deep on average on land. At the bottom of the ocean, the crust is thinner and extends about 3 miles (5 km) from the seafloor to the top of the mantle.
Earth's lithosphere, composed of the crust and the upper mantle, is divided into huge plates that are constantly moving, roughly at a rate equal to the growth of our fingernails. Earthquakes result when plates grind past one another, ride up over one another, collide to make mountains, or split and separate.
Planet Type: Gas Giant
Moons: 80
Average Orbital Distance: 5.1 AU | 483,638,564 miles | 778,340,821 kilometers
Orbital Period: 4,333 Earth days | 11.8 Earth years
Day: 9.93 hours
Average Surface Temperature: -160 °F | -110 °C
Equatorial Circumference: 272,945.9 mi | 439,263.8 km
Surface Gravity: 81.3 ft/s2 | 24.79 m/s2
Escape Velocity: 134,664 mph | 216,720 km/h
Atmospheric Constituents: Hydrogen, Helium
Jupiter gets its name from the king of the ancient Roman gods. The Fifth planet from the sun, Jupiter is a gas giant and the largest planet in the solar system. It is more than twice as large as all of the other planets combined. Its iconic Great Red Spot is a giant storm bigger than Earth that has raged for hundreds of years. Eleven Earths could fit across Jupiter's equator. If Earth were the size of a grape, Jupiter would be the size of a basketball.
Being a gas giant, Jupiter lacks a solid surface. If it has a solid inner core at all, it is likely only about the size of Earth. Jupiter's observed stripe and swirl patterns are cold, windy clouds of ammonia and water floating in an atmosphere of hydrogen (H2) and helium (He).
Jupiter's equator is tilted with respect to its orbital path around the Sun by 3 degrees. This means that Jupiter spins nearly upright and does not have seasons as extreme as other planets do. A day in Jupiter is a Jovian day. Jupiter has a short day, it rotates once about every 10 hours, making that the shortest day in the solar system. A year in Jupiter is a Jovian year. Jupiter has a long year, it takes Jupiter about 12 Earth years to complete one orbit around the Sun.
All four giant planets in our solar system have ring systems. Jupiter's rings are composed of small, dark particles and are difficult to see except when backlit by the Sun. Jupiter's very faint ring system may be formed by dust kicked up as interplanetary meteoroids smash into the giant planet's small innermost moons.
Jupiter cannot support life as we know it. The temperatures, pressures, and materials that characterize this planet are most likely too extreme and volatile for organisms to adapt, but some of Jupiter's moons have oceans beneath their crusts that might support life. The moon Europa is one of the likeliest places, there is evidence of a vast ocean just beneath its icy crust, where life could possibly be supported. With four large moons and many smaller moons, Jupiter forms a kind of miniature solar system. Jupiter has 80 moons. The International Astronomical Union (IAU) has given 57 moons official names, another 23 moons are awaiting names.
Jupiter's four largest moons - Io, Europa, Ganymede, and Callisto - were first observed by the astronomer Galileo Galilei in 1610 using an early version of the telescope. These four moons are known today as the Galilean satellites, and they're some of the most fascinating destinations in our solar system.
Of Jupiter's moons, Io is the most volcanically active body in the solar system, with hundreds of volcanoes, some erupting lava fountains dozens of miles, or kilometers high. Ganymede is the largest moon in the solar system, it is bigger than the planet Mercury, and it's the only moon with its own magnetic field. Callisto is the most heavily cratered object in our solar system, its very few small craters indicate a small degree of current surface activity. Europa is thought to have an iron core, a rocky mantle, and beneath its frozen crust may lie a salty liquid-water ocean with the ingredients for life. It may be one of the best places to look for life beyond Earth in our solar system, making it a tempting place to explore.
Jupiter took shape when the rest of the solar system formed about 4.5 billion years ago when gravity pulled swirling gas and dust in to become this gas giant. Jupiter took most of the mass left over after the formation of the Sun, ending up with more than twice the combined material of all the other bodies in the solar system. Jupiter has the same ingredients as a star - mostly hydrogen and helium, but it did not grow massive enough to ignite.
Deep in its 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. At depths halfway to the planet's center, perhaps the pressure becomes so great that electrons are squeezed off the hydrogen atoms, making the liquid electrically conducting like metal. Jupiter's fast rotation is thought to drive electrical currents in this region, generating the planet's powerful magnetic field. It's unclear if deeper down, Jupiter has a central core of solid material, or a thick super-hot dense soup. Temperatures could be up to 90,032 °F | 50,000 °C in its core, made mostly of iron and silicate minerals, similar to quartz.
As a gas giant, Jupiter doesn't have a true surface. The planet is mostly swirling gases and liquids. The extreme pressures and temperatures deep inside the planet crush, melt, and vaporize objects trying to fly inside. Jupiter's appearance is a tapestry of colorful cloud bands and spots. The gas planet likely has 3 distinct cloud layers in its "skies" that together, span about 44 mi | 71 km. The top layer is probably made of ammonia ice, while the middle layer is likely made of ammonium hydrosulfide crystals. The innermost layer may be made of water ice and vapor. The vivid colors in thick bands across Jupiter may be plumes of sulfur and phosphorus-containing gases rising from the planet's warmer interior.
Jupiter's fast rotation creates strong jet streams, separating its clouds into dark belts and bright zones across long stretches. Stormy Jupiter is swept by over a dozen prevailing winds, some reaching up to 335 mph | 539 km/h at the equator. 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.
Jupiter's cyclones are warmer on top, with lower atmospheric densities, while they are colder at the bottom, with higher densities. Anticyclones, which rotate in the opposite direction, are colder at the top but warmer at the bottom. These storms are far taller than expected, with some extending 60 mi | 100 km below the cloud tops and others, including the Great Red Spot, extending over 200 mi | 350 km. These vortices cover regions beyond those where water condenses and clouds form, below the depth where sunlight warms the atmosphere.
Jupiter is known for its distinctive belts and zones - white and reddish bands of clouds that wrap around the planet. Strong east-west winds moving in opposite directions separate the bands. These winds, or jet streams, reach depths of about 2,000 mi | 3,200 km.
Jupiter has Polygonal arrangements of giant cyclonic storms at both of its poles - eight arranged in an octagonal pattern in the north and five arranged in a pentagonal pattern in the south. These atmospheric phenomena are extremely resilient, remaining in the same location. Like hurricanes on Earth, these cyclones want to move poleward, but cyclones located at the center of each pole push them back. This balance explains where the cyclones reside and the different numbers at each pole. The sizes of these cyclones range from 1,500 mi | 2,400 km to 1,740 mi | 2,800 km across.
The Jovian magnetosphere is the region of space influenced by Jupiter's powerful magnetic field. It balloons 600,000 to 2 million mi | 1 to 3 million km toward the Sun - seven to 21 times the diameter of Jupiter itself - and tapers into a tadpole-shaped tail extending more than 600 million mi | 1 billion km behind Jupiter, as far as Saturn's orbit. Jupiter's enormous magnetic field is 16 to 54 times as powerful as that of the Earth. It rotates with the planet and sweeps up particles that have an electric charge. Near the planet, the magnetic field traps swarms of charged particles and accelerates them to very high energies, creating intense radiation that bombards the innermost moons. Jupiter's magnetic field also causes some of the solar system's most spectacular aurorae at the planet's poles.
Planet Type: Terrestrial
Moons: 2
Average Orbital Distance: 1.5 AU | 141,637,725 miles | 227,943,824 kilometers
Orbital Period: 669.6 sols | 687 Earth days | 1.8 Earth years
Day: 24.6 hours
Average Surface Temperature: -85 °F | -65 °C
Equatorial Circumference: 13,233.3 mi | 21,296.9 km
Surface Gravity: 12.2 ft/s2 | 3.71 m/s2
Escape Velocity: 11,252 mph | 18,108 km/h
Atmospheric Constituents: Carbon Dioxide, Nitrogen, Argon
Fourth planet from the Sun. Mars is about half the size of Earth. A dusty, cold, desert world with a very thin atmosphere. Mars is also a dynamic planet with seasons, polar ice caps, canyons, extinct volcanoes, and evidence that it was even more active in the past. Its surface has nearly the same area as Earth's dry land.
Mars was named by the ancient Romans for their god of war because its reddish color was reminiscent of blood. In the night sky it looks like a bright red point of light. Today, it is frequently called the "Red Planet" because iron minerals in the Martian dirt oxidize, or rust, causing the surface to look red.
Martian days are called sols - short for "solar day." Mars' axis of rotation is tilted 25 degrees with respect to the plane of its orbit around the Sun. Mars has distinct seasons, but they last longer than seasons on Earth and vary in length because of Mars' elliptical, egg-shaped and more distant orbit around the Sun.
Spring in the northern hemisphere (autumn in the southern) is the longest season at 194 sols. Autumn in the northern hemisphere (spring in the southern) is the shortest at 142 sols. Northern winter/southern summer is 154 sols, and northern summer/southern winter is 178 sols.
Mars has evidence of ancient river valley networks, deltas, and lakebeds, as well as rocks and minerals on the surface that could only have formed in liquid water. Some features suggest that Mars experienced huge floods about 3.5 billion years ago. Water on Mars is found in the form of water-ice just under the surface in the polar regions as well as in briny (salty) water, which seasonally flows down some hillsides and crater walls. The Martian atmosphere is too thin for liquid water to exist for long on the surface.
Mars has a thin atmosphere, and heat from the Sun easily escapes this planet. To our eyes, the sky would be hazy and red because of suspended dust. Mars' sparse atmosphere doesn't offer much protection from impacts by such objects as meteorites, asteroids, and comets. Occasionally, winds on Mars are strong enough to create dust storms that cover much of the planet. After such storms, it can be months before all of the dust settles.
The temperature on Mars can be as high as 70 °F | 20 °C or as low as about -225 °F | -153 °C. Because the atmosphere is so thin, if you were to stand on the surface of Mars on the equator at noon, it would feel like spring at your feet 75 °F | 24 °C and winter at your head 32 °F | 0 °C.
Mars has two small moons, Phobos and Deimos, that may be captured asteroids. They're potato-shaped because they have too little mass for gravity to make them spherical. The moons get their names from the horses that pulled the chariot of the Greek god of war, Ares. Phobos, the innermost and larger moon, is slowly moving towards Mars and will crash into the planet or break apart in about 50 million years.
Mars has a dense core at its center between 930 and 1,300 mi (1,500 to 2,100 km) in radius. It's made of iron, nickel, and sulfur. Surrounding the core is a rocky mantle between 770 and 1,170 mi (1,240 to 1,880 km) thick, and above that, a crust made of iron, magnesium, aluminum, calcium, and potassium. This crust is between 6 and 30 mi (10 to 50 km) deep. Mars has no global magnetic field today, but areas of the Martian crust in the southern hemisphere are highly magnetized.
Despite being inhospitable to humans, an international team of robotic explorers are serving as pathfinders to eventually get humans to the surface of the Red Planet.
Planet Type: Terrestrial
Average Orbital Distance: 0.4 AU | 35,983,125 miles | 57,909,227 kilometers
Orbital Period: 88 Earth days
Day: About 59 Earth days
Average Surface Temperature: 333 °F | 167 °C
Equatorial Circumference: 9,525.1 miles | 15,329.1 kilometers
Surface Gravity: 12.1 ft/s2 | 3.7 m/s2
Escape Velocity: 9,507 mph | 15,300 km/h
Atmospheric Constituents: Near vacuum
The smallest planet in our solar system and the planet that orbits closest to the Sun. Mercury is about 2.6x smaller than Earth, and only slightly larger than Earth's Moon. The planet Mercury is named after the Roman God of speed. Mercury's highly eccentric, egg-shaped orbit takes the planet as close as 29 million mi (47 million km) and as far as 43 million mi (70 million km) from the Sun. The closer a planet is to the Sun, the faster it travels. This makes Mercury the fastest planet in our solar system as it travels through space at nearly 29 mi (47 km) per second, and orbits around the Sun every 88 Earth days.
Mercury is a terrestrial planet, with a rocky cratered surface, much like the Earth's moon. Mercury has no moons, and no rings around its orbit. From Its surface, the Sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be about seven times brighter. Despite being nearest to the Sun, Mercury is not the hottest planet in our solar system — the hottest being Venus, due to its dense atmosphere.
It is unlikely that life, as we know it, could survive on Mercury due to solar radiation, and extreme temperatures. Mercury's surface temperatures are both extremely hot and cold. Day temperatures can reach highs of 800°F (430°C), and without an atmosphere to retain that heat at night, temperatures can drop as low as -290°F (-180°C). Mercury's thin unbreathable atmosphere, or exosphere, is composed mostly of oxygen (O2), sodium (Na), hydrogen (H2), helium (He), and potassium (K).
Mercury spins slowly on its axis and completes one rotation every 59 Earth days. When Mercury is closest to the Sun, and moving fastest in its elliptical orbit, each rotation is not accompanied by sunrise and sunset like it is on most other planets. The morning Sun appears to rise briefly, set, and rise again from some parts of the planet's surface. The same thing happens in reverse at sunset for other parts of the surface. One Mercury solar day, meaning one full day-night cycle, equals 176 Earth days - is equal to two years on Mercury. Mercury's axis of rotation spins nearly perfectly upright in its orbit around the Sun and so does not experience seasons like many other planets do.
Like its fellow terrestrial planets, Mercury has a central core, a rocky mantle, and a solid crust. Mercury is the second densest planet, after Earth. It has a large metallic core with a radius of about 1,289 mi (2,074 km), about 85 percent of the planet's radius. There is evidence that it is partly molten or liquid. Mercury's outer shell, comparable to Earth's outer shell (called the mantle and crust), is only about 400 km (250 mi) thick.
Though Mercury's magnetic field at the surface has just 1% the strength of Earth's, it interacts with the magnetic field of the solar wind to sometimes create intense magnetic tornadoes that funnel the fast, hot solar wind plasma down to the surface of the planet. When the ions strike the surface, they knock off neutrally charged atoms and send them on a loop high into the sky. Instead of an atmosphere, Mercury possesses a thin exosphere made up of atoms blasted off the surface by the solar wind and striking meteoroids. Mercury's exosphere is composed mostly of oxygen, sodium, hydrogen, helium, and potassium.
Moon Type: Terrestrial
Average Orbital Distance from Earth: 238,855 miles | 384,400 kilometers
Orbital Period: 27.3 Earth days
Day: 29.5 Earth days
Average Surface Temperature: -10 °F | -23 °C
Equatorial Circumference: 6,783.5 miles | 10,917 kilometers
Surface Gravity: 5.328 ft/s2 | 1.624 m/s2
Escape Velocity: 5,314 mph | 8,552 km/h
Atmospheric Constituents: Near vacuum
The fifth largest of the 200+ moons orbiting planets and asteroids in our solar system. The Moon is less than a third of the width of Earth. Earth's only natural satellite, simply called "the Moon”, because until Galileo Galilei discovered four moons orbiting Jupiter in 1610, people didn't know other moons existed.
The brightest and largest object in our night sky. The Moon makes Earth a more livable planet by moderating our home planet's wobble on its axis, leading to a relatively stable climate. The Moon was likely formed after a Mars-sized body collided with Earth. Long ago the Moon had active volcanoes, but today they are all dormant and have not erupted for millions of years. The Moon is slowly moving away from Earth, by about an inch every year.
Tidally locked, the Moon is rotating at the same rate that it revolves around Earth (synchronous rotation). The rotations are so in sync that we only see one side of the Moon. We didn't see the lunar far side until a Soviet spacecraft flew past in 1959. An international law written in 1967 prevents any nation from owning planets, stars, or any other natural objects in space.
The Moon has a solid, rocky surface cratered and pitted from impacts by asteroids, meteorites, and comets. Its atmosphere, called an exosphere, is very thin, does not provide any protection from the Sun's radiation, and is not breathable. 24 astronauts have traveled to the Moon, of those, 12 have walked on its surface. More than 105 robotic spacecraft have been launched to explore the Moon. Nearly the entire Moon is covered by a charcoal-gray, powdery dust, and rocky debris called the lunar regolith. Beneath is a region of fractured bedrock referred to as the megaregolith. Apollo astronauts brought back a total of 842 pounds (382 kg) of lunar rocks and soil to Earth, that are still being studied.
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 compositions and ages, which provide evidence for how the early crust may have crystallized from a lunar magma ocean.
The first definitive discovery of water was made in 2008 by the Indian mission Chandrayaan-1, which detected hydroxyl molecules spread across the lunar surface and concentrated at the poles. Missions such as Lunar Prospector, LCROSS, and Lunar Reconnaissance Orbiter, have not only shown that the surface of the Moon has global hydration but there are actually high concentrations of ice water in the permanently shadowed regions of the lunar poles. This makes the Moon a little more hospitable for future human colonists.
The temperature on the Moon reaches about 260 degrees Fahrenheit (127 degrees Celsius) when in full Sun, but in darkness, the temperatures plummet to about -280 degrees Fahrenheit (-173 degrees Celsius).
The Moon's solid iron-rich inner core is 149 mi (240 km) in radius, surrounded by a liquid iron shell 56 mi (90 km) thick, surrounded by a partial molten layer with a thickness of 93 mi (150 km). The mantle extends from the top of the partially molten layer to the bottom of the Moon's crust. It is most likely made of minerals like olivine and pyroxene, which are made up of magnesium, iron, silicon, and oxygen atoms. The crust has a thickness of about 43 mi (70 km) on the Moon's near-side hemisphere and 93 mi (150 km) on the far-side. It is made of oxygen, silicon, magnesium, iron, calcium, and aluminum, with small amounts of titanium, uranium, thorium, potassium, and hydrogen.
Planet Type: Ice Giant
Moons: 16 [known] moons
Average Orbital Distance: 30 AU | 2,795,083,500 miles | 4,498,250,000 kilometers
Orbital Period: 60,190 Earth days | 165 Earth years
Day: 16 hours
Average Surface Temperature: -353 °F | -214 °C
Equatorial Circumference: 96,129 mi | 154,705 km
Surface Gravity: 36.678 ft/s2 | 3.41 m/s2
Escape Velocity: 52,583 mph | 84,600 km/h
Atmospheric Constituents: Hydrogen, Helium, Methane
Planet Type: Gas Giant
Moons: 83
Average Orbital Distance: 9.5 AU | 886,489,415 miles | 1,426,666,422 kilometers
Orbital Period: 10,759 Earth days | 29 Earth years
Day: 10.7 hours
Average Surface Temperature: -220 °F | -140 °C
Equatorial Circumference: 235,298 mi | 378,675 km
Surface Gravity: 34.3 ft/s2 | 10.4 m/s2
Escape Velocity: 80,731 mph | 129,924 km/h
Atmospheric Constituents: Hydrogen, Helium
The sixth planet from the Sun, and the second largest planet in our solar system. Adorned with thousands of spectacular beautiful ringlets orbiting the planet - made of chunks of ice and rock, Saturn's complex ring system consists of seven rings and several gaps and divisions between them. Saturn is unique and perhaps the most iconic of all the planets in our solar system. A gas giant, Saturn is a massive ball made mostly of hydrogen and helium, lacking a solid surface, with a possible solid core at its center. Like a mini solar system, Saturn has 53 known moons with an additional 29 moons awaiting confirmation of their discovery and official naming by the International Astronomical Union (IAU) - totaling 82 moons. Saturn cannot support life as we know it, but some of Saturn's moons have conditions that might support life.
The farthest planet from Earth discovered by the unaided human eye, Saturn has been known since ancient times. The planet is named for the Roman god of agriculture and wealth, who was also the father of Jupiter. Saturn is 9 times wider than Earth. If Earth were the size of a nickel, Saturn would be about as big as a volleyball. Saturn has the second shortest day in the solar system. One day on Saturn takes only 10.7 hours, and Saturn makes a complete orbit around the Sun in about 29.4 Earth years. Its axis is tilted by 26.73 degrees with respect to its orbit around the Sun, which is similar to Earth's 23.5 degree tilt. This means that, like Earth, Saturn experiences seasons. The temperatures, pressures, and materials that characterize this planet are most likely too extreme and volatile for organisms to adapt. While planet Saturn is an unlikely place for living things to take hold, the same is not true of some of its many moons. Moons like Enceladus and Titan, are home to internal oceans, and could possibly support life.
Saturn's rings are thought to be pieces of comets, asteroids, or shattered moons that broke up before they reached the planet, torn apart by Saturn's powerful gravity. They are made of billions of small chunks of ice and rock coated with other materials such as dust. The ring particles mostly range from tiny, dust-sized icy grains to chunks as big as a house. A few particles are as large as mountains. The rings would look mostly white if you looked at them from the cloud tops of Saturn, and interestingly, each ring orbits at a different speed around the planet.
Saturn's ring system extends up to 175,000 mi | 282,000 km from the planet, yet the vertical height is typically about 30 ft | 10 m in the main rings. Named alphabetically in the order they were discovered, the rings are relatively close to each other, with the exception of a gap measuring 2,920 mi | 4,700 km in width called the Cassini Division that separates Rings A and B. The main rings are A, B, and C. Rings D, E, F, and G are fainter and more recently discovered. Starting from Saturn and moving outward, there is the D ring, C ring, B ring, Cassini Division, A ring, F ring, G ring, and finally, the E ring. Much farther out, in the orbit of Saturn's moon Phoebe, there is the very faint Phoebe ring.
Saturn took shape when the rest of the solar system formed about 4.5 billion years ago when gravity pulled swirling gas and dust in to become this gas giant. About 4 billion years ago, Saturn settled into its current position in the outer solar system, where it is the sixth planet from the Sun. Like Jupiter, Saturn is mostly made of hydrogen and helium, the same two main components that make up the Sun. At Saturn's center is a dense core of metals like iron and nickel surrounded by rocky material and other compounds solidified by intense pressure and heat. It is enveloped by liquid metallic hydrogen inside a layer of liquid hydrogen - similar to Jupiter's core but considerably smaller. It's hard to imagine, but Saturn is the only planet in our solar system with an average density that is less than water. The giant gas planet could float in a bathtub if such a colossal thing existed. As a gas giant, Saturn doesn't have a true surface. The planet is mostly swirling gases and liquids deeper down. While a spacecraft would have nowhere to land on Saturn, it wouldn't be able to fly through unscathed either. The extreme pressures and temperatures deep inside the planet would crush, melt, and vaporize any spacecraft trying to fly into the planet.
Saturn is blanketed with clouds that appear as faint stripes, jet streams, and storms. The planet is many different shades of yellow, brown, and gray. Winds in the upper atmosphere reach 1,600 ft per second | 500 m per second in the equatorial region. In contrast, the strongest hurricane-force winds on Earth top out at about 360 ft per second | 110 m per second. Its pressure - the same kind felt in a deep underwater dive - is so powerful it squeezes gas into a liquid. Saturn's north pole has an interesting atmospheric feature - a six-sided jet stream. This hexagon shaped pattern spanning about 20,000 mi | 30,000 km across, is a wavy jet stream of 200 mph winds | about 322 kph with a massive, rotating storm at the center. There is no weather feature like it anywhere else in the solar system.
Saturn's magnetic field is smaller than Jupiter's but still 578 times as powerful as Earth's. Saturn, the rings, and many of the satellites lie totally within Saturn's enormous magnetosphere, the region of space in which the behavior of electrically charged particles is influenced more by Saturn's magnetic field than by the solar wind. Aurorae occur when charged particles spiral into a planet's atmosphere along magnetic field lines. On Earth, these charged particles come from the solar wind. Cassini showed that at least some of Saturn's aurorae are like Jupiter's and are largely unaffected by the solar wind. Instead, these aurorae are caused by a combination of particles ejected from Saturn's moons and Saturn's magnetic field's rapid rotation rate. But these "non-solar-originating" aurorae are not completely understood yet.
Star Type: G2 V, yellow dwarf main-sequence star
Age: 4.5 billion years
Orbital Distance: 26,000 light years from galactic center
Orbital Period: 230 million years around the Milky Way
Atmospheric Temperature: 3.5 million °F | 2 million °C
Surface temperature (Photosphere): 10,000 °F | 5,500 °C
Equatorial Circumference: 2,715,395.6 mi | 4,370,005.6 km
Surface Gravity: 899 ft/s2 | 274 m/s2
Escape Velocity: 1,381,756 mph | 2,223,720 km/h
A hot glowing ball of hydrogen and helium at the center of our solar system. The Sun, and its solar system, orbits the galactic center of the Milky Way Galaxy, at an average velocity of 450,000 mph | 720,000 kph, in a spiral arm called the Orion Spur that extends outward from the Sagittarius arm.
The Sun is about 93 million mi | 150 million km from Earth, or one astronomical unit (AU). The largest object in our solar system. Its volume would need 1.3 million Earths to fill it. Its gravity holds everything from the biggest planets to tiny debris in its orbit. Orbited by eight planets, at least five dwarf planets, tens of thousands of asteroids, and three trillion comets and icy bodies.
The planets in its orbit are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The dwarf planets Pluto, Ceres, Makemake, Haumea, and Eris.
The Sun has been called by many names. The Latin word for Sun is “sol,” which is the main adjective for all things Sun-related: solar. Helios, the Sun god in ancient Greek mythology, lends his name to many Sun-related terms as well, such as heliosphere and helioseismology.
Our Sun is an average star in terms of its size. Stars up to 100 times larger have been found. And many solar systems have more than one star. By studying our Sun, scientists can better understand the workings of distant stars.
The Sun formed about 4.6 billion years ago in a giant, spinning cloud of gas and dust called the solar nebula. As the nebula collapsed under its own gravity, it spun faster and flattened into a disk. Most of the nebula's material was pulled toward the center to form our Sun, which accounts for 99.8% of our solar system's mass. Much of the remaining material formed the planets and other objects that now orbit the Sun.
Like all stars, the Sun will eventually run out of energy. When it starts to die, the Sun will expand into a red giant star, becoming so large that it will engulf Mercury and Venus, and possibly Earth as well. Scientists predict the Sun is a little less than halfway through its lifetime and will last another 5 billion years or so before it becomes a white dwarf.
Made of super-hot, electrically charged gas called plasma. This plasma rotates at different speeds on different parts of the Sun. At its equator, the Sun completes one rotation in 25 Earth days. At its poles, the Sun rotates once on its axis every 36 Earth days. The hottest part of the Sun is its core, where temperatures top 27 million °F | 15 million °C. Hot enough to sustain nuclear fusion. This creates outward pressure that supports the star's gigantic mass, keeping it from collapsing.
The Sun generates magnetic fields, solar radiation, that extend out into space to form the interplanetary magnetic field - the magnetic field that pervades our solar system. The field is carried through the solar system by the solar wind - a stream of electrically charged gas blowing outward from the Sun in all directions. The vast bubble of space dominated by the Sun's magnetic field is called the heliosphere.
Its nearest stellar neighbor is the Alpha Centauri triple star system: red dwarf star Proxima Centauri is 4.24 light-years away, and Alpha Centauri A and B - two sunlike stars orbiting each other - are 4.37 light-years away. A light-year is the distance light travels in one year, which equals about 6 trillion miles | 9.5 trillion kilometers).
Planet Type: Ice Giant
Moons: 27
Average Orbital Distance: 19.8 AU | 1,783,744,300 miles | 2,870,658,186 kilometers
Orbital Period: 30,687 Earth days | 84 Earth years
Day: 17 hours and 14 minutes
Average Surface Temperature: -320 °F | -195 °C
Equatorial Circumference: 99,018.1 miles | 159,354.1 kilometers
Surface Gravity: 29.1 ft/s2 | 8.87 m/s2
Escape Velocity: 47,826 mph | 76,968 km/h
Atmospheric Constituents: Hydrogen, Helium, Methane
The seventh planet from the Sun, Uranus has the third-largest diameter in our solar system. Named after the Greek god of the sky. Uranus is the source of more than a few jokes. About four times wider than Earth. If Earth were a large apple, Uranus would be the size of a basketball. Discovered in 1781 by astronomer William Herschel, it was the first new planet discovered since ancient times, found with the aid of a telescope. The radioactive element uranium was named after Uranus when the element was discovered in 1789. Uranus cannot support life as we know it.
Uranus is an ice giant. Most of its mass is a hot, dense fluid of "icy" materials - water, methane and ammonia - above a small rocky core. Very cold and windy, its atmosphere is made mostly of molecular hydrogen and atomic helium, with a small amount of methane. Uranus is orbited by 27 known small moons, while most of the satellites orbiting other planets take their names from Greek or Roman mythology, Uranus' moons are unique in being named after characters from the works of William Shakespeare and Alexander Pope. Uranus is surrounded by 13 known faint rings. The inner rings are narrow and dark and the outer rings are brightly colored. Like Venus, Uranus rotates east to west. But Uranus is unique in that it rotates on its side at a nearly 90-degree angle from the plane of its orbit. This unique tilt makes Uranus appear to spin sideways, orbiting the Sun like a rolling ball. Uranus' tilt causes the most extreme seasons in the solar system. For nearly a quarter of each Uranian year, the Sun shines directly over each pole, plunging the other half of the planet into a 21-year-long, dark winter. The temperatures, pressures, and materials that characterize this planet are most likely too extreme and volatile for organisms to adapt to.
Uranus has two sets of rings. The inner system of nine rings consists mostly of narrow, dark grey rings. There are two outer rings: the innermost one is reddish like dusty rings elsewhere in the solar system, and the outer ring is blue like Saturn's E ring. In order of increasing distance from the planet, the rings are called Zeta, 6, 5, 4, Alpha, Beta, Eta, Gamma, Delta, Lambda, Epsilon, Nu, and Mu. Some of the larger rings are surrounded by belts of fine dust. All of Uranus' inner moons appear to be roughly half water ice and half rock. The composition of the outer moons remains unknown, but they are likely captured asteroids. Here are some names of a few of the Uranian moons: Ariel, Cupid, Mab, Miranda, Oberon, Titania, and Umbriel.
Uranus took shape when the rest of the solar system formed about 4.5 billion years ago - when gravity pulled swirling gas and dust in to become this ice giant. Like its neighbor Neptune, Uranus likely formed closer to the Sun and moved to the outer solar system about 4 billion years ago. One of two ice giants in the outer solar system, the other one being Neptune. As an ice giant, Uranus doesn't have a true surface. The planet is mostly swirling fluids. While a spacecraft would have nowhere to land on Uranus, it wouldn't be able to fly through its atmosphere unscathed either. The extreme pressures and temperatures would destroy a metal spacecraft. More than 80% of Uranus' mass is made up of a hot dense fluid of "icy" materials - water, methane, and ammonia - near the planet's small rocky core, this fluid heats up to 9,000 °F | 4,982 °C. Uranus is slightly larger in diameter than its neighbor Neptune, yet smaller in mass. It is the second least dense planet; Saturn is the least dense of all.
Uranus' atmosphere is mostly hydrogen and helium, with a small amount of methane and traces of water and ammonia. The methane gas in the atmosphere gives Uranus its signature blue-green color. Sunlight passes through the atmosphere and is reflected back out by Uranus' cloud tops. Methane gas absorbs the red portion of the light, resulting in a blue-green color. Recent observations reveal that Uranus exhibits dynamic clouds as it approaches equinox, including rapidly changing bright features. Uranus' planetary atmosphere, with a minimum temperature of -371.56 °F | -224.2 °C makes it even colder than Neptune in some places. Wind speeds can reach up to 560 mph | 900 kph on Uranus. Winds are retrograde at the equator, blowing in the reverse direction of the planet's rotation. But closer to the poles, winds shift to a prograde direction, flowing with Uranus' rotation.
Uranus has an unusual, irregularly shaped magnetosphere. Magnetic fields are typically in alignment with a planet's rotation, but Uranus' magnetic field is tipped over: the magnetic axis is tilted nearly 60° from the planet's axis of rotation, and is also offset from the center of the planet by one-third of the planet's radius. Auroras on Uranus are not in line with the poles -like they are on Earth, Jupiter, and Saturn- due to the lopsided magnetic field. The magnetosphere tail behind Uranus opposite the Sun extends into space for millions of miles. Its magnetic field lines are twisted by Uranus' sideways rotation into a long corkscrew shape.
Planet Type: Terrestrial
Average Orbital Distance: 0.7 AU | 67,238,251 miles | 108,209,475 kilometers
Orbital Period: 225 Earth days
Day: About 243 Earth days
Average Surface Temperature: 900 °F | 475 °C
Equatorial Circumference: 23,627.4 miles | 38,024.6 kilometers
Surface Gravity: 29.1 ft/s2 | 8.87 m/s2
Escape Velocity: 23,175 mph | 37,296 km/h
Atmospheric Constituents: Carbon Dioxide, Nitrogen
The second planet from the Sun and Earth's closest planetary neighbor. Venus is one of the four inner, terrestrial planets, and it's often called Earth's twin due to its similarity in size and density. The ancient Romans could easily see seven bright objects in the sky: the Sun, the Moon, and the five brightest planets; Mercury, Venus, Mars, Jupiter, and Saturn. They named the objects after their most important gods. Venus, the third brightest object after the Sun and Moon, was named after the Roman goddess of love and beauty.
Venus' solid surface is a rusty color, covered in dome-like volcanoes, rifts, and mountains, with expansive volcanic plains and vast, ridged plateaus. It is possible some volcanoes are still active. The average surface of Venus is less than a billion years old, and possibly as young as 150 million years old —which is relatively young from a geological perspective. It is not known exactly what happened that made Venus completely resurface itself. Venus has no moons, and no rings in its orbit.
Venus has a crushing air pressure at its surface —more than 90 times that of Earth— similar to the pressure you'd encounter a mile below the ocean on Earth. It has a dense toxic atmosphere filled with carbon dioxide, and it's perpetually shrouded in yellowish clouds of sulfuric acid that trap heat, causing a runaway greenhouse effect. A view of the Sun from the surface of Venus, would appear as a smear of light. Even though Mercury is closer to the Sun, Venus' extreme surface heat makes it the hottest planet in our solar system. Surface temperatures on Venus are about 900 °F | 475 °C —hot enough to melt lead. The greenhouse effect makes Venus roughly 700 °F | 390 °C hotter than it would be without a greenhouse effect.
Venus slowly rotates on its axis backward. Meaning that, on Venus, the Sun rises in the west and sets in the east, opposite to what we experience on Earth. Due to Venus' extremely slow rotation —sunrise to sunset would take 117 Earth days, one day and night cycle on Venus lasts about 243 Earth days, one year on Venus takes about 225 Earth days to complete. Making a Venusian day last longer than a Venusian year. Venus lacks any semblance of seasons, the tilt on its spin axis is only three degrees.
Venus might once have been a habitable ocean world, like Earth, but that was at least a billion years ago. The runaway greenhouse effect turned all surface water into vapor, which then leaked slowly into space. It is an unlikely place for life as we know it, yet, it is theorized that microbes might exist high in the clouds of Venus where the temperature is cooler and the pressure is similar to Earth's surface. These clouds whip around the planet at about 200 mph (100 meters per second), circling Venus in about four and a half Earth days. Phosphine, a possible indicator of microbial life, has been observed in the clouds.
A catastrophic planet wide resurfacing is theorized to have happened between 350 and 750 million years ago. In other words, Venus appears to have completely erased most traces of its early surface. The causes: volcanic and tectonic forces, which could include surface buckling and massive eruptions. The average age of surface features could be as young as 150 million years, with some older surfaces mixed in. Notably, except for Earth, Venus has by far the fewest impact craters of any rocky planet, revealing a young surface.
If we could slice Venus and Earth in half, pole to pole, and place them side by side, they would look remarkably similar. Each planet has an iron core enveloped by a hot-rock mantle; the thinnest of skins forms a rocky, exterior crust. On both planets, this thin skin changes form and sometimes erupts into volcanoes in response to the ebb and flow of heat and pressure deep beneath.
Venus does not have its own internally generated magnetic field. Instead, Venus has what is known as an induced magnetic field. This weak magnetic field is created by the interaction of the Sun's magnetic field and the planet's outer atmosphere. Ultraviolet light from the Sun excites gases in Venus' outermost atmosphere; these electrically excited gases are called ions, and thus this region is called the ionosphere (Earth has an ionosphere as well). The solar wind —a 1,000,000 mph gale of electrically charged particles streaming continuously from the Sun— carries with it the Sun's magnetic field. When the Sun's magnetic field interacts with the electrically excited ionosphere of Venus, it creates or induces, a magnetic field there. This induced magnetic field envelops the planet and is shaped like an extended teardrop, or the tail of a comet, as the solar wind blows past Venus and outward into the solar system.