1.Jupiter was the first. Giant lies just beyond the frost line. As the frost line accumulated great amounts of water via evaporation from infalling icy material, it created a zone of lower pressure that increased the speed of orbiting dust particles and halted their motion toward the Sun. As a result , the frost line acted as a barrier whice lead material to accumulate. This excess material coalesced into a huge embryo of around 10 Earth masses, which then began to grow rapidly by swallowing hydrogen from the surrounding disc, reaching 150 Earth masses in only another 1000 years and finally topping out at 318 Earth masses,proving Saturn may owe its substantially lower mass simply to having formed a few million years after Jupiter, when there was less gas available to consume.
2. In 1950 Jan Oort noticed that 1)no comet has been observed with an orbit that indicates that it came from interstellar space; 2)there is a strong tendency for aphelia of long period comet orbits to lie at a distance of about 50,000 AU; 3)there is no preferential direction from which comets come. From this he proposed that comets reside in a vast cloud at the outer reaches of the solar system. This has come to be known as the Oort Cloud. The statistics imply that it may contain as many as a trillion comets. Unfortunately, since the individual comets are so small and at such large distances, we have no direct evidence about the Oort Cloud. Its objects were formed closer to Sun than the Kuiper Belt objects. Small objects formed near the giant planets would have been ejected from the solar system by gravitational encounters. Those that didn't escape entirely formed the distant Oort Cloud. Small objects formed farther out had no such interactions and remained as the Kuiper Belt objects. The Kuiper Belt objects are extremely primitive remnants from the early accretional phases of the solar system. The inner, dense parts of the pre-planetary disk condensed into the major planets, approximately few millions to tens of millions of years. The outer parts are not so dense, and accretion progressed slowly. Alex Parker examined binary objects in the cold classical Kuiper belt, a region on the edge of the Solar System, 6 to 7 billion kilometres from the Sun. Traditional theory finds it hard to explain how these objects formed there because, that far out, their accretion would have been too slow to have been finished during the known life of the solar system. Thus, in a theory known as the Nice model, scientists suggested that these objects formed closer to the Sun, where faster growth was possible. (http://nineplanets.org/kboc.html)
3. 1) Thermosphere extends from the top of the mesosphere to over 640 km. Within the thermosphere temperatures rise continually to well beyond 1000 degrees Celsius . Those few molecules that are present in the thermosphere get enormous amounts of energy from the Sun, leading the layer to warm extremely. Lower part of the thermosphere, from 80 to 550 km above the Earth's surface, contains the ionosphere. Beyond the ionosphere extending out to perhaps 10,000 km is the exosphere or outer thermosphere, which gradually merges into space.Temperature increases with height up to 1,500 C'.
2) Mesosphere. It is the third highest layer, occupying the region above the stratosphere and below the thermosphere. It extends from the top of the stratosphere to the range of 80 to 85 km. Temperatures here drop with increasing altitude to about -100 C'. Layer is the coldest one — enough to freeze water vapor into ice clouds which called Noctilucent Clouds (NLC). NLCs are most readily visible when the Sun is from 4 to 16 degrees below the horizon.
3) Stratosphere lies above the troposphere and is separated from it by the tropopause. It extends from the top of the troposphere to about 50 km. Contains relatively high concentrations of ozone. The stratosphere defines a layer in which temperatures rises with increasing altitude. This rise in temperature is caused by the absorption of ultraviolet (UV) radiation from the Sun by the ozone layer. This creates very stable atmospheric conditions, and the stratosphere lacks the air turbulence that is so prevalent in the troposphere.
4) Troposphere is the lowest layer,extending from Earth's surface up to 7 km at the poles, and around 17-18 km at the equator. Bounded above by the tropopause, a boundary marked by stable temperatures. Although variations do occur, temperature usually declines with increasing altitude in the troposphere. Contains up to 75% of the mass of the atmosphere. Fifty percent of the total mass of the atmosphere is located in the lower 5.6 km part. It is primarily composed of nitrogen (78%) and oxygen (21%) with only small concentrations of other trace gases. Nearly all atmospheric water vapor or moisture is found in the troposphere. The troposphere is the layer where most of the world's weather takes place.(http://airs.jpl.nasa.gov/maps/satellite_feed/atmosphere_layers/ )
4. When the gravitational force on one side of the planet is different from that on the other side, it is called a tidal force. Tides are due to the gravitational attraction of one massive body on another. The net result of this is that the Earth gets deformed into a slightly squashed, ellipsoidal shape due to these tidal forces. We commonly think of the tides as being a phenomenon that we see in the sea. Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon, the Sun and the rotation of the Earth. Most places in the ocean usually experience two high tides and two low tides each day (semidiurnal tide), but some locations experience only one high and one low tide each day (diurnal tide). The tidal bulge, when it is over an ocean, presents itself as a rise in sea level. 90° later in revolution, when the bulge is at right angle to the ocean, a reduced sea level is experienced (Moore).
5. The main component of the atmosphere of Mars is carbon dioxide (CO2) at 95.9%. Each pole is in continual darkness during its hemisphere's winter, and the surface gets so cold that as much as 25% of the atmospheric CO2 condenses at the polar caps into solid CO2 ice (dry ice). When the pole is again exposed to sunlight during summer, the CO2 ice sublimates back into the atmosphere. This process leads to a significant annual variation in the atmospheric pressure and atmospheric composition around the Martian poles. The atmospheric pressure on the Martian surface averages 600 pascals (0.087 psi), about 0.6% of Earth's mean sea level pressure of 101.3 kilopascals. The Martian atmosphere is about 95%carbon dioxide, 3% nitrogen, 1.6% argon, and traces of free oxygen, carbon monoxide, water and methane. Compared to other planets,most close to Earth atmosphere.( http://abyss.uoregon.edu/~js/ast121/lectures/lec10.html).
6. Most of the craters formed in the early years of the solar system, around 4.5 billion years ago, when meteors bombarded all the planets and their moons. We can still see the craters on Mercury and the Moon, because neither has weather systems to erode them or a biosphere to cover them. Mercury's surface is less cratered than the Moon, because Mercury is larger with higher gravity, reducing the number of secondary impacts. Scientists believe large, flat areas on Mercury's surface to be ancient, solidified lava fields, also found on the Moon. There is evidence of water ice, found in the shadow of crater rims, on both. Another similarity is that neither Mercury nor the Moon is seismologically active.
However they are very different worlds. Mercury’s density is almost the same as Earth's at about 5.4 grams per cubic centimeter as opposed to the moon's 3.3 grams. Mercury is about 70 percent iron and associated metals by mass, while the moon is severely depleted of iron and elements that bind to it such as nickel. Mercury's core is in fact as big as the moon and at least a thin shell must still be molten because it has a magnetic field. The moon at best has an iron core that can be no more than 300 miles or so across, and has no magnetic field. The entire surface of Mercury is in fact made of erupted lava, while most of the moon's crust is rock that floated to the surface when the moon at least partially if not completely melted, causing denser rocks and it's meager amount of iron to sink to the center. Mercury's heavy iron core also contracted at it started to solidify, cause the crust to crack and buckle all over the planet, leaving vertical walls of rock up to 2 miles high. Both the moon and Mercury have huge impact scars when other planetesimals crashed into them, but Mercury's largest scar caused shock waves to go to the far side and push up gigantic blocks or rock several miles, leaving a large region of weird terrain.
7.Constituents of many of the minerals that make up the continental plates on Earth have been converted to gas (e.g., carbonates have been destroyed and much of the carbon appears as carbon dioxide instead). This is consistent with the lack of evidence for continental plates.The surface of Venus appears to be geologically young. The most obvious indication is the small number of impact craters. Surface of the planet was renewed some 300 - 500 million years ago. The most likely event to cause this resurfacing is a planet-wide episode of elevated volcanic activity producing massive lava flows that might have lasted for millions of years. Venus has erased most of its craters by covering them with magma. Like Earth,Venus has continent-like plateaus and ocean-bottom-like lowlands. Venus contains very little water compared Earth because it is so hot that it has evaporated surface water into its atmosphere,and water in its interior has probably been mostly ejected through volcanoes or when the surface periodically melts
8.Mars does not have ring due to the fact that it formed too close into the Sun for it to have icy rings. In fact, none of the rocky inner planets in our solar system has rings. Saturn has the most prominent rings, but astronomers have discovered rings around all the gas giants, including Jupiter.
Mars is orbited by two moons, Phobos and Deimos, which are small and irregular in shape, indicating that they may be captured asteroids. Astronomers know that Phobos is slowly spiraling inward towards Mars. Sometime in the next 50 million years, Phobos will either collide with Mars or disintegrate to form a rocky ring around Mars. Also, scientists have not ruled out the existence of dust rings trailing in the wake of Phobos and Deimos. However, these rings would be incredibly faint, and to date no such rings have been discovered.
9.Metallic hydrogen is a state of hydrogen in which it behaves as an electrical conductor. This state was predicted theoretically in 1935, but has not been reliably produced in laboratory experiments due to the requirement of high pressures, on the order of hundreds of kilobars. At these pressures, hydrogen might exist as a liquid rather than solid. Liquid metallic hydrogen is thought to be present in large amounts in the gravitationally compressed interiors of Jupiter, Saturn, and in some of the newly discovered extrasolar planets.
10.Spectroscopic studies of sunlight reflected from Uranus's and Neptune's dense clouds indicate that the two planets' outer atmospheres (the parts we actually measure spectroscopically) are similar to those of Jupiter and Saturn. The most abundant element is molecular hydrogen (84%), followed by helium (about 14 %) and methane, which is more abundant on Neptune (about 3%) than on Uranus (2 percent). Ammonia, which plays such an important role in the Jupiter and Saturn systems, is not present in any significant quantity in the outermost jovian worlds. The abundances of gaseous ammonia and methane vary systematically among the jovian planets. Jupiter has much more gaseous ammonia than methane, but moving outward from the Sun, we find that the more distant planets have steadily decreasing amounts of ammonia and relatively greater amounts of methane. The reason for this variation is temperature. Ammonia gas freezes into ammonia ice crystals at about 70 K. This is cooler than the cloud-top temperatures of Jupiter and Saturn but warmer than those of Uranus (58 K) and Neptune (59 K). Thus, the outermost jovian planets have little or no gaseous ammonia in their atmospheres, so their spectra (which record atmospheric gases only) show just traces of ammonia. The increasing amounts of methane are largely responsible for the outer jovian planets' blue coloration. Methane absorbs long-wavelength red light quite efficiently, so sunlight reflected from the planets' atmospheres is deficient in red and yellow photons and appears blue-green or blue. As the concentration of methane increases, the reflected light should appear bluer. This is just the trend observed: Uranus, with less methane, looks blue-green, while Neptune, with more, looks distinctly blue.
11.Comet is a name for space debris that is a roughly equal mix of rock and ice.
12. A comet generally has two tails. One tail is due to the comet's dust particles, the other is due to ionized gas from the comet coma. Dust particles form the first tail. This comet tail generally points back along the comet path (so if the comet is traveling right, the dust tail extends to the left).
Lons (electrically charged particles), which first come from the nucleus as (neutral) gaseous particles, are swept into the second comet tail. Because of the special interaction with the Sun's magnetic field, this tail always points directly away from the Sun. As the ices of the comet nucleus evaporate, they expand rapidly into a large cloud around the central part of the comet. This cloud, called the coma, is the atmosphere of the comet and can extend for millions of miles. The neutral particles that are in the coma can actually become excited by the solar wind causing the particles to become ions. A continual stream of neutral particles is produced as long as the nucleus is evaporating, and these neutral particles are continually converted to ions. These ions are what help form another comet tail. (http://www.windows2universe.org/comets/coma.html ).
13.Each time a comet swings by the Sun in its orbit, some of its ice vaporizes and a certain amount of meteoroids will be shed. The meteoroids spread out along the entire orbit of the comet to form a meteoroid stream, also known as a "dust trail" (as opposed to a comet's "dust tail" caused by the very small particles that are quickly blown away by solar radiation pressure). Recently, Peter Jenniskens (Jenniskens P. 2006). has argued that most of our short-period meteor showers are not from the normal water vapor drag of active comets, but the product of infrequent disintegrations, when large chunks break off a mostly dormant comet. Examples are the Quadrantidsand Geminids, which originated from a breakup of asteroid-looking objects 2003 EH1 and 3200 Phaethon, respectively, about 500 and 1000 years ago. The fragments tend to fall apart quickly into dust, sand, and pebbles, and spread out along the orbit of the comet to form a dense meteoroid stream, which subsequently evolves into Earth's path.
In other words, comets are dirty snow balls. Over their lives ice will evaporate from the comet at every passage in the inner solar system. This liberates the dust. As the dust has more or less the same speed as the comet it will continue the same orbit as the comet, and only very slowly spread out. When the Earth moves through this cloud of dust the result is a meteor shower. Isolated meteors where born in collisions, between asteroids and planetesimals during the formation of the solar system. The violence of the collisions, makes the debris scatter in random directions: no two fragments stay close together over time.
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