Our Solar System

written by Mohammed Idrees Bhatti

There are nine planets that go around the sun. Some of the planets are small, some of them are large.

Remember the Order of the Planets: My Very Educated Mother Just Sent Us Nine Puzzles. Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

Mercury is the closest planet to the Sun and the eighth largest. Mercury is the second densest major body in the solar system, after Earth. It is 36m miles from the sun and the smallest of all the planets. Its diameter is 3,100 miles. It takes Mercury 88 days to go around the sun once(to revolve). Mercury rotates (spins) once in close to 59 days. One of the largest features on Mercury's surface is the Caloris Basin (right); it is about 1300 km in diameter. It is thought to be similar to the large basins (maria) on the Moon. Temperature variations on Mercury are the most extreme in the solar system ranging from 90 K to 700 K. Mercury is in many ways similar to the Moon: its surface is heavily cratered and very old; it has no atmosphere-- no air, rain, snow, clouds, or fog.

Venus is the second planet from the Sun and the sixth largest. It is 67.2m miles from the sun. It is the brightest object in the sky except for the Sun and the Moon. The diameter of Venus is 7,700 miles. Venus' orbit is the most nearly circular of that of any planet. Venus' rotation is somewhat unusual in that it is very slow (243 Earth days per Venus day, slightly longer than Venus' year). In addition, the periods of Venus' rotation and of its orbit are synchronized such that it always presents the same face toward Earth when the two planets are at their closest approach. The pressure of Venus' atmosphere at the surface is 90 atmospheres (about the same as the pressure at a depth of 1 km in Earth's oceans). It is composed mostly of carbon dioxide. There are several layers of clouds many kilometers thick composed of sulfuric acid. These clouds completely obscure our view surface. This dense atmosphere produces a run-away greenhouse effect that raises Venus' surface temperature by about 400 degrees to over 740 K (hot enough to melt lead). Venus' surface is actually hotter than Mercury's despite being nearly twice as far from the Sun. Most of Venus' surface consists of gently rolling plains with little relief. Data from Magellan's imaging radar shows that much of the surface of Venus is covered by lava flows. There are strong (350 kph) winds at the cloud tops winds at the surface are very slow, no more than a few kilometers per hour.

Earth is the third planet from the Sun and the fifth largest. This is the only planet where we know life exists. The diameter of the Earth is 7,918 miles. There are four planets larger than earth and there are four planets smaller than earth. The earth is 93m miles from the sun. This is just the right distance for the life to exist. Earth rotates once in about 24 hours. This rotation causes day and night. Earth takes about 365 days to complete a revolution around the sun. Earth has very good atmosphere. It has water, lakes, oceans, rivers, streams, and clouds and air. Earth may be called as the planet of water. Earth has a satellite revolving around it. We call it the moon. The moon is earth's natural satellite.

The Moon is the second brightest object in the sky after the Sun. The gravitational forces between the Earth and the Moon cause some interesting effects. The most obvious is the tides. Due to its size and composition, the Moon is sometimes classified as a terrestrial "planet" along with Mercury, Venus, Earth and Mars.

The fourth planet from the sun is Mars. This planet appears dull red when seen in the nighttime sky. We call it the red planet. When Mars is on one side of the Sun and Earth is on the other side, they are about 248m miles apart. When Mars and Earth are on the same side of the Sun, then they are only 25m miles apart. Mars has white polar caps. Mars rotates once in 24 hours 37 minutes-about same time it takes Earth to rotate. Mars goes around the sun once in 687 days. The year on Mars is much longer than a year on earth.

Two satellites revolve around Mars. They are very small--only 5 and 10 miles in diameter. The satellites are called Phobos and Deimos. Phobos and Deimos are widely believed to be captured asteroids. Phobos and Deimos may be composed of carbon-rich rock like C-type asteroids. But their densities are so low that they cannot be pure rock. They are more likely composed of a mixture of rock and ice. Both are heavily cratered. There is some speculation that they originated in the outer solar system rather than in the main asteroid belt. Phobos and Deimos may someday be useful as "space stations" from which to study Mars or as intermediate stops to and from the Martian surface; especially if the presence of ice is confirmed. Phobos ("FOH bus") is the larger and innermost of Mars' two moons. Phobos is closer to its primary than any other moon in the solar system, less than 6000 km above the surface of Mars. It is also one of the smallest moons in the solar system. The most prominent feature on Phobos is the large crater named Stickney, the maiden name of Hall's wife. Deimos ("DEE mos") is the smaller and outermost of Mars' two moons. It is the smallest known moon in the solar system. Discovered 1877 August 10 by Hall, photographed by Viking 1 in 1977.

Jupiter is the fifth planet from the Sun and by far the largest. Jupiter is more than twice as massive as all the other planets combined (318 times Earth). It is so big that over a thousand Earths could fit into one Jupiter. Jupiter radiates more energy into space than it receives from the Sun. Jupiter is 88,700 miles in diameter. Jupiter has faint rings like Saturn's, but much smaller. It also has large, reddish spot on the planet. The Great Red Spot (GRS) has been seen by Earthly observers for more than 300 years. The GRS is an oval about 12,000 by 25,000 km, big enough to hold two Earths. Other smaller but similar spots have been known for decades. Jupiter rotates faster than any other planet. Jupiter rotates once in 9 hours, 50 minutes. A day on Jupiter is very short indeed. Jupiter goes around the sun in a little less than 12 earth years. A year on Jupiter is 12 earth years long. If you were 12 years old on earth, you would be only one year old on Jupiter. It takes Jupiter 12 Earth years to go around the sun. Jupiter has an atmosphere. The vivid colors seen in Jupiter's clouds are probably the result of subtle chemical reactions of the trace elements in Jupiter's atmosphere, perhaps involving sulfur whose compounds take on a wide variety of colors, but the details are unknown. Jupiter's atmosphere is mostly hydrogen. The temperature is about 200 degrees below zero. Lots of Methane and Ammonia may be frozen solid near the surface of Jupiter.

Jupiter has 16 known satellites, the four large Galilean moons, Io, Europa, Ganyneede, and Callisto, and 12 small ones. Io ( "EYE oh") is the fifth of Jupiter's known satellites and the third largest; it is the innermost of the Galilean moons. Io is slightly larger than Earth's Moon. Io's surface is radically different from any other body in the solar system. It came as a very big surprise to the Voyager scientists on the first encounter. They had expected to see impact craters like those on the other terrestrial bodies and from their number per unit area to estimate the age of Io's surface. But there are very few, if any, impact craters on Io. Therefore, the surface is very young. It also has active volcano.

Europa ("yoo ROH puh") is the sixth of Jupiter's known satellites and the fourth largest; it is the second of the Galilean moons. Europa is slightly smaller than the Earth's Moon. The images of Europa's surface strongly resemble images of sea ice on Earth. It is possible that beneath Europa's surface ice there is a layer of liquid water, perhaps as much as 50 km deep, kept liquid by tidally generated heat. If so, it would be the only place in the solar system besides Earth where liquid water exists in significant quantities. Europa's most striking aspect is a series of dark streaks crisscrossing the entire globe. The latest theory of their origin is that they are produced by a series of volcanic eruptions or geysers.

Ganymede ("GAN uh meed") is the seventh and largest of Jupiter's known satellites. Ganymede is the third of the Galilean moons. Ganymede is the largest satellite in the solar system. It is larger in diameter than Mercury but only about half its mass. Ganymede is much larger than Pluto.

Callisto ("ka LIS toh") is the eighth of Jupiter's known satellites and the second largest. It is the outermost of the Galilean moons. Callisto is only slightly smaller than Mercury but only a third of its mass. Callisto's surface is covered entirely with craters. The surface is very old.

Saturn is the sixth planet from the Sun and the second largest. Saturn is the least dense of the planets. Saturn has faint dark bands on its surface very similar to those of Jupiter. Saturn also has beautiful rings around it. Though they look continuous from the Earth, the rings are actually composed of innumerable small particles each in an independent orbit. They range in size from a centimeter or so to several meters. A few kilometer-sized objects are also likely. They are made of separate little (tiny) particles. Tiny grams of sand, bits of dust, ad crystals of ice and snow appear to make up the rings of Saturn. Saturn's rings are extraordinarily thin: though they're 250,000 km or more in diameter they're no more than 1.5 kilometers thick. Despite their impressive appearance, there's really very little material in the rings -- if the rings were compressed into a single body it would be no more than 100 km across. The rings are very wide, 170,000 miles from one side to the other. Rings are very thin about 10 miles. Saturn's interior is similar to Jupiter's consisting of a rocky core, a liquid metallic hydrogen layer and a molecular hydrogen layer. Saturn is 886m miles from the Sun. Its diameter is over 75,100 miles. Almost nine Earths could fit into the diameter of Saturn. Saturn rotates in just a little over 10 hours. It takes Saturn 30 years to go around the Sun. Ten satellites revolve around Saturn. One of the largest satellites, Titan is larger than earth's satellite, the moon. All of the rest of the satellites are small. Saturn has 18 named satellites, more than any other planet. There may very well also be several small ones yet to be discovered. Of those moons for which rotation rates are known, all but Phoebe and Hyperion rotate synchronously.

Uranus is the seventh planet from the Sun and the third largest (by diameter). Careful pronounciation may be necessary to avoid embarassment; say"YOOR a nus". Uranus' blue color is the result of absorption of red light by methane in the upper atmosphere. Like the other gas planets, Uranus has rings. Like Jupiter's, they are very dark but like Saturn's composed of fairly large particles ranging up to 10 meters in diameter in addition to fine dust. There are 11 known rings, all very faint; the brightest is known as the Epsilon ring. Uranus is larger in diameter but smaller in mass than Neptune. Uranus is 1,783 miles from the sun and it rotates about 11 hours. Uranus takes 84 earth years to go around the sun once. Most of the planets spin on an axis nearly perpendicular to the plane of the ecliptic but Uranus' axis is almost parallel to the ecliptic. Uranus has 15 known moons. They form two distinct classes: the 10 small very dark inner ones discovered by Voyager 2 and the 5 large outer ones. They all have nearly circular orbits in the plane of Uranus' equator (and hence at a large angle to the plane of the ecliptic).

Neptune is the eighth planet from the Sun and the fourth largest (by diameter). Neptune is smaller in diameter but larger in mass than Uranus. Neptune's blue color is the result of absorption of red light by methane in the atmosphere. Neptune is 2,791m miles from the sun and it rotates in about 16 hours. Neptune takes almost 165 earth years to make the journey. It would be a long time between birthdays if you lived on Neptune. Neptune also has rings. Like Uranus and Jupiter, Neptune's rings are very dark but their composition is unknown. Neptune has 8 known moons; 7 small ones and Triton. Triton is about 2,300 miles in diameter and the Nereid is only about 200 miles across. Uranus, Neptune, Saturn, and Jupiter, make up the four major planets of the solar system.

Beyond Neptune is the ninth planet Pluto. Pluto is the farthest planet from the Sun (usually) and by far the smallest. Pluto is smaller than seven of the solar system's moons (the Moon, Io, Europa, Ganymede, Callisto, Titan and Triton). There are some who think Pluto would be better classified as a large asteroid or comet rather than as a planet. Some consider it to be the largest of the Kuiper Belt objects. It is a small cold planet with a small satellite which is half of its size. Pluto has a diameter of 3,600 miles and it is very far away-3,664 million miles from the sun. Pluto rotate in about 6 days and it takes about 250 earth years to go around the Sun only once-to revolve. It was the last planet ot be discovered.

So far as we know today, there are nine planets. The Sun and the nine planets are called the solar system. We still know little about planets. May be you will be an astronomer some day. Maybe you will make discoveries that we have never even dreamed about.