Neptune

Neptune is the furthest planet from the sun,in the solar system.It is situated at an average distance of about 4,500 million kilometres.It is a gas giant and is thought to consist of a small rocky core surrounded by a mixture of liquids and gases. The atmosphere contains several prominant features of clouds. The largest of these are the Great Dark Spot,and the Scooter.The Great and Small Dark Spots are huge storms that are swept around the planet by winds of about 2,000 kilometres per hour. The Scooter is a large area of cirrus cloud. Neptune is an ice giant that has the same deep, blue color like Uranus. Neptune gets its color from the methane in the atmosphere. The dark spots on Neptune are from the storms that happen on the planet. Neptune has the same seasons as Earth, but Neptune's spring lasts for 40 years.  Most of Neptune's energy lies inside the planet. The chemicals change into a different form of energy when deep beneath the surface. It releases a ton of heat when the change occurs. The atmosphere contains about 80% hydrogen, 19% helium and 1% methane. Neptune's length of day is 16.11 hours and the year length is 169.9 Earth days. Neptune weighs about 105 669 X 10 to the power of 19kg. That weighs heavier then Earth right? Neptune's cloud gravity is 1.13g and the diameter from the middle of the planet is 49,532km. The distance from Neptune to Earth is 248 light minutes away.(Distance used in space) The most dangerous thing about Neptune is that it has extreme winds in the atmosphere. Neptune was thought to have no rings but in 1989, rings were discovered by Voyager 2 spacecrafts. The discovery of Neptune was made from a person named Galileo Galilei. He made his first drawing of Neptune on December 28, 1612. Thinking it was a fixed star when it appeared to the eye. During the period of Galileo first observation, Neptune was stationary in the sky because it turned retrogradethat day. This appeared in a backward motion when the orbit of Earth takes it path out of order. However, in 2009 University of Melbourne, David Jamieson got proof and told everyone his new evidence saying that Galileo was not aware of the fixed star. It was actually a planet, Neptune. 
Once Uranus was discovered, astronomers set about charting its orbit. The figures we have just listed do indeed describe Uranus's orbital motion, but eighteenth-century astronomers quickly discovered a small discrepancy between the planet's predicted position and where they actually observed it. Try as they might, astronomers could not find an elliptical orbit that fit the planet's trajectory to within the accuracy of their measurements. Half a century after Uranus's discovery, the discrepancy had grown to a quarter of an arc minute, far too big to be explained away as observational error. The logical conclusion was that an unknown body must be exerting a gravitational force on Uranus--much weaker than that of the Sun, but still measurable. But what body could this be? Astronomers realized that there had to be another planet in the solar system perturbing Uranus's motion.
In the 1840s, two mathematicians independently solved the difficult problem of determining this new planet's mass and orbit. A British astronomer, John Adams, reached the solution in September 1845; in June of the following year, the French mathematician Urbain Leverrier came up with essentially the same answer. British astronomers seeking the new planet found nothing during the summer of 1846. In September, a German astronomer named Johann Galle began his own search from the Berlin Observatory, using a newly completed set of more accurate sky charts. He found the new planet within one or two degrees of the predicted position--on his first attempt. After some wrangling over names and credits, the new planet was named Neptune, and Adams and Leverrier (but not Galle!) are now jointly credited with its discovery.
Neptune orbits the Sun with a semi-major axis of 30.1 A.U. (4.5 billion km) and an eccentricity of just 0.01. Since its sidereal orbital period is 164.8 years, it has not yet completed one revolution since its discovery. Unlike Uranus, Neptune cannot be seen with the naked eye, although it can be seen with a small telescope--in fact, Galileo may actually have seen Neptune, although he had no idea what it really was at the time. Through a large telescope, Neptune appears as a bluish disk, with a maximum angular diameter of 2.4´´ at opposition.
Neptune is so distant that surface features are virtually impossible to discern. Even under the best observing conditions, only a few markings can be seen. These are suggestive of multicolored cloud bands--light bluish hues seem to dominate. With Voyager 2's arrival, much more detail emerged, at least, Neptune resembles a blue-tinted Jupiter, with atmospheric bands and spots clearly evident. From Earth, we can see only two moons orbiting Neptune. William Lassell discovered the inner moon, Triton, in 1846. The outer moon, Nereid, was located by Gerard Kuiper in 1949. Voyager 2 discovered six additional moons, all less than a few hundred kilometers across and all lying within Nereid's orbit. 
In its moons we find Neptune's contribution to our list of solar system peculiarities. Unlike the other jovian worlds, Neptune has no regular moon system. The larger moon, Triton, is 2800 km in diameter and occupies a circular retrograde orbit 354,000 km (14.2 planetary radii) from the planet, inclined at about 20° to Neptune's equatorial plane. It is the only large moon in our solar system to have a retrograde orbit. The other moon visible from Earth, Nereid, is only 200 km across. It orbits Neptune in the prograde sense, but on an elongated trajectory that brings it as close as 1.4 million km to the planet and as far away as 9.7 million km. Nereid is probably similar in both size and composition to Neptune's small inner moons.
Voyager 2 approached to within 24,000 km of Triton's surface, providing us with essentially all that we now know about that distant, icy world. Astronomers redetermined the moon's radius (which was corrected downward by about 20 percent) and measured its mass for the first time. Along with Saturn's Titan and the four Galilean moons of Jupiter, Triton is one of the six large moons in the outer solar system. Triton is the smallest of them, with about half the mass of the next smallest, Jupiter's Europa.
Lying 4.5 billion km from the Sun, and with a fairly reflective surface, Triton has a surface temperature of just 37 K. It has a tenuous nitrogen atmosphere, perhaps a hundred thousand times thinner than Earth's, and a surface that most likely consists primarily of water ice. The moon's low temperatures produce a layer of nitrogen frost that forms and evaporates over the polar caps, a little like the carbon dioxide frost responsible for the seasonal caps on Mars. Overall, there is a marked lack of cratering on Triton, presumably indicating that surface activity has obliterated the evidence of most impacts. There are many other signs of an active past. Triton's face is scarred by large fissures similar to those seen on Ganymede, and the moon's odd cantaloupe-like terrain may indicate repeated faulting and deformation over the moon's lifetime. In addition, Triton has numerous frozen "lakes" of water ice which are believed to be volcanic in origin. Triton's surface activity is not just a thing of the past. As Voyager 2 passed the moon, its cameras detected two great jets of nitrogen gas erupting from below the surface, rising several kilometers into the sky. it is thought that these "geysers" result when liquid nitrogen below Triton's surface is heated and vaporized by some internal energy source, or perhaps even by the Sun's feeble light. Vaporization produces high pressures, which force the gas through cracks and fissures in the crust, creating the displays Voyager 2 saw. Scientists conjecture that nitrogen geysers may be very common on Triton and are perhaps responsible for much of the moon's thin atmosphere.
The event or events that placed Triton on a retrograde orbit and Nereid on such an eccentric path are unknown, but they are the subject of considerable speculation. Triton's peculiar orbit and surface features suggest to some astronomers that the moon did not form as part of the Neptune system but instead was captured, perhaps not too long ago. Other astronomers, basing their views on Triton's chemical composition, maintain that it formed as a "normal" moon but was later kicked into its abnormal orbit by some catastrophic event, such as an interaction with another similar-sized body. It has even been suggested that the planet Pluto may have played a role in this process, although no really convincing demonstration of such an encounter has ever been presented. The surface deformations on Triton certainly suggest fairly violent and relatively recent events in the moon's past. However, they were most likely caused by the tidal stresses produced in Triton as Neptune's gravity circularized its orbit and synchronized its spin, and they give little indication of the processes leading to the orbit in the first place.

Whatever its past, Triton's future is fairly clear. Because of its retrograde orbit, the tidal bulge Triton raises on Neptune tends to make the moon spiral toward the planet rather than away from it (as our Moon moves away from Earth). Thus, Triton is doomed to be torn apart by Neptune's tidal gravitational field, probably in no more than 100 million years or so, the time required for the moon's inward spiral to bring it inside Neptune's Roche limit. By that time, it is conceivable that Saturn's ring system may have disappeared, so that Neptune will then be the planet in the solar system with spectacular rings.

Pluto

Pluto

Pluto was first discovered in 1930 by Clyde W. Tombaugh at the Lowell Observatory in Flagstaff Arizona. Astronomers had long predicted that there would be a ninth planet in the Solar System, which they called Planet X. Only 22 at the time, Tombaugh was given the laborious task of comparing photographic plates. These were two images of a region of the sky, taken two weeks apart. Any moving object, like an asteroid, comet or planet, would appear to jump from one photograph to the next.
After a year of observations, Tombaugh finally discovered an object in the right orbit, and declared that he had discovered Planet X. Because they had discovered it, the Lowell team were allowed to name it. They settled on Pluto, a name suggested by an 11-year old school girl in Oxford, England (no, it wasn’t named after the Disney character, but the Roman god of the underworld).The Solar System now had 9 planets.Astronomers weren’t sure about Pluto’s mass until the discovery of its largest moon Charon, in 1978. And by knowing its mass (0.0021 Earths), they could more accurately gauge its size. The most accurate measurement currently gives the size of Pluto at 2,400 km (1,500 miles) across. Although this is small, Mercury is only 4,880 km (3,032 miles) across. Pluto is tiny, but it was considered larger than anything else past the orbit of Neptune.Over the last few decades, powerful new ground and space-based observatories have completely changed previous understanding of the outer Solar System. Instead of being the only planet in its region, like the rest of the Solar System, Pluto and its moons are now known to be just a large example of a collection of objects called the Kuiper Belt. This region extends from the orbit of Neptune out to 55 astronomical units (55 times the distance of the Earth to the Sun).
Astronomers estimate that there are at least 70,000 icy objects, with the same composition of Pluto, that measure 100 km across or more in the Kuiper Belt. And according to the new rules, Pluto is not a planet. It’s just another Kuiper Belt object.Here’s the problem. Astronomers had been turning up larger and larger objects in the Kuiper Belt. 2005 FY9, discovered by Caltech astronomer Mike Brown and his team is only a little smaller than Pluto. And there are several other Kuiper Belt in that same classification.Pluto is the only world named by an 11 year old girl, Venetia Burney of Oxford, England, who suggested to her grandfather that it get its name from the Roman god of the underworld. Her grandfather then passed the name on to Lowell Observatory. The name also honours Percival Lowell, whose initials are the first two letters of Pluto.
Since Pluto is so far from Earth, little is known about the planet’s size or surface conditions. Pluto has an estimated diameter less than one-fifth that of Earth or only about two-thirds as wide as Earth's moon. The planets’ surface conditions probably consist of a rocky core surrounded by a mantle of water ice, with more exotic ices such as methane and nitrogen frost coating its surface.Unfortunately, this uncertainty may persist for some time--there is no present or proposed space mission that might suddenly and radically improve our understanding of these distant worlds.

Pluto's orbit is highly eccentric, or far from circular, which means its distance from the sun can vary considerably and at times, Pluto’s orbit will take within the orbit of the planet Neptune. When Pluto is closer to the sun, its surface ices thaw and temporarily form a thin atmosphere, mostly of nitrogen, with some methane. Pluto's low gravity, which is a little more than one-twentieth that of Earth's, causes this atmosphere to extend much higher in altitude than Earth's. When  traveling farther away from the Sun, most of Pluto's atmosphere is thought to freeze and all but disappear. Still, in the time that it does have an atmosphere, Pluto can apparently experience strong winds.
 Pluto is so far away that little is known of its physical nature. Until the late 1970s, studies of its reflected light variations suggested a rotation period of nearly a week, but measurements of its mass and diameter were very uncertain. All this changed in July 1978, when astronomers at the U.S. Naval Observatory discovered that Pluto has a satellite. It is now named Charon, after the mythical boatman who ferried the dead across the river Styx into Hades, Pluto's domain. Charon is the small bump near the top of the image.Knowing the moon's orbital period of 6.4 days, astronomers could determine the mass of Pluto to much greater accuracy. It is 0.0025 Earth masses (1.5 × 10²² kg), far smaller than any earlier estimate--more like the mass of a moon than of a planet.The improved resolution of that instrument clearly separates the two bodies and allowed even more accurate measurements of their properties.Before Charon was discovered, Pluto's radius was also poorly known. Pluto's angular size is much less than 1´´, so its true diameter is blurred by the effects of Earth's turbulent atmosphere. But Charon's orbital orientation has given astronomers new insight into the system. By pure chance, Charon's orbit over the 6-year period from 1985 to 1991 (less than 10 years after the moon was discovered) has produced for Earth viewers a series of eclipses. Pluto and Charon repeatedly passed in front of one other, as seen from our vantage point. With more good fortune, these eclipses took place while Pluto was closest to the Sun, making for the best possible Earth-based observations.Basing their calculations on the variations in light as Pluto and Charon periodically hid each other, astronomers have computed their masses and radii and have determined their orbit plane. Additional studies of sunlight reflected from Pluto's surface indicate that the two objects are tidally locked as they orbit each other. Pluto's diameter is 2250 km, about one-fifth the size of the Earth. Charon is about 1300 km across and orbits at a distance of 19,700 km from Pluto. If planet and moon have the same composition (probably a reasonable assumption), Charon's mass must be about one-sixth that of Pluto, giving the Pluto-Charon system by far the largest satellite-to-planet mass ratio in the solar system. Charon's orbit is inclined at an angle of 118° to the plane of Pluto's orbit around the Sun. Since the spins of both planet and moon are perpendicular to the plane of Charon's orbit around Pluto, the geographic "north" poles of both bodies lie below the plane of Pluto's orbit. Thus, Pluto is the third planet in the solar system found to have retrograde rotation.The known mass and radius of Pluto allow us to determine its average density, which is 2300 kg/m³--too low for a terrestrial planet, but far too high for a mixture of hydrogen and helium of that mass. Instead, the mass, radius, and density of Pluto are just what we would expect for one of the icy moons of a jovian planet. In fact, Pluto is quite similar in mass and radius to Neptune's large moon, Triton. The planet is almost certainly made up mostly of water ice. In addition, spectroscopy reveals the presence of frozen methane as a major surface constituent. Pluto is the only planet in the solar system on which methane exists in the solid state, implying that the surface temperature on Pluto is no more than 50 K. Pluto may also have a thin methane atmosphere, associated with the methane ice on its surface. Recent computer studies indicate that Charon may have bright polar caps, but their composition and nature are as yet unknown.Because Pluto is neither terrestrial nor jovian in its makeup, and because of its similarity to the ice moons of the outer planets, some researchers suspect that Pluto is not a "true" planet at all. Pluto may be an escaped planetary moon or a large icy chunk of debris left over from the formation of the solar system. This idea is bolstered by Pluto's eccentric, inclined orbit, which is quite unlike the orbits of the other known planets. Since 1978, the explanation of Pluto's origin has been greatly complicated by the presence of Charon. It was much easier to suppose that Pluto was an escaped moon before we learned that it had a moon of its own. There is still no clear or easy answer to the puzzle of Pluto's origin.

Pluto may be just what it seems--a planet that formed in its current orbit, possibly even with its own moon right from the outset. Because we know so little about the environment in the outer solar system, we cannot rule out the possibility that planets beyond Neptune should simply look like Pluto. There is evidence for large chunks of ice circulating in interplanetary space beyond the orbits of Jupiter or Saturn , and some researchers have even suggested that there might have been thousands of Pluto-sized objects initially present in the outer solar system. The capture of a few of these objects by the giant planets would explain the strange moons of the outer worlds, especially Triton. And if there were enough moon-sized chunks originally orbiting beyond Neptune, it is quite plausible that Pluto could have captured Charon following a collision (or near-miss) between the two. At present, our scant knowledge of the compositions of the two bodies does not allow us to confirm or disprove either the coformation or the capture theory of the Pluto-Charon system. 

Asteroids,Comets,and Meteoroids

.   Asteroid 951    

                      Asteroids,comets,and meteoroids are all debris remaining from the nebula in which the Solar System formed 4.6 billion years ago. Asteroids are rocky bodies up to about 1,000 kilometres in diameter,although most are much smaller. Most of them orbit the Sun in the asteroid belt,which lies between the orbit of Mars and Jupiter. Comets may originate in a huge cloud (called the Oort cloud) that is thought to surround the Solar System. They are made of frozen gases and dust,and a few kilometres in diameter. Occasionally,a comet is deflected from the Oort cloud Sun in a long,elliptical path   As the comet approaches the Sun,the comet's surface starts  to vaporize in the heat,producing a brightly shining coma (a huge sphere of gas and dust around the nucleus),a gas tail,and a dust tail. Meteoroids are small chunks of stone or stone and iron,some of which are fragments of asteroid or comets. Meteoroids range in size from tiny dust particles to objects tens of metres across. If a meteoroid enters the Earth's atmosphere,it is heated by friction and appears as a glowing streak of light called a meteor (also known as a shooting star).Meteor showers occur when the Earth passes through the trail of dust particles left by a comet. Most meteor burn up in the atmosphere. The few tht are large enough to reach the Earth's surface are termed meteorites. As we see about the comets its tail is the most distinctive feature. As a comet approaches the Sun it develops an enormous tail of luminous material that extends for millions of kilometers away from the Sun. When far from the Sun, a comet's nucleus is very cold and its material is frozen. Water ice, as well as other compounds such as carbon dioxide and carbon monoxide ice, may be found in the nucleus. This icy nucleus changes radically when a comet approaches the Sun. The intense solar wind from the Sun transforms the solid nucleus directly into a vapor, bypassing the liquid phase. This process is called sublimation. The vapor helps stir things up in the nucleus, forcing the core to form a cloud-like mixture of gas and dust around it, called the coma. There, sunlight and the solar wind interact with the ingredients, creating the tails. The ingredients in the coma determine the types and number of tails. 

Some comets may appear to have no tails, but they really do. They are simply very faint. Scientists can identify these tails by using special filters that are sensitive to dust or gas emissions. Other comets, like Hale-Bopp, which could be seen from Earth in 1997, have very prominent tails. Although Hale-Bopp's tails could be seen visibly from Earth, scientists using sensitive cameras identified a much more complicated tail structure. One of these images revealed a long, curving dust tail. Other pictures showed dust and gas ion tails. There was even an image of a dust tail and two gas ion tails. The different tails provide scientists with important information about the internal chemistry and structure of a comet's nucleus.

Stony Meteorite

Stony-Iron meteorite

Halley's comet

structure of comet

structure of a comet

parts of a comet

Development of a comet tail

false color of Hally's comet