Scattered disc- The home for minor planets

Scattered disc objects are the most distant objects of our solar system till date, they are located as much as from 35AU to 1000AU from Sun. Due to their far distances from Sun they are also the coldest objects of our solar system with temperatures being only 35k to 55k. The other effect of distance on these objects is that they are really hard to be observed form earth. All the objects of scattered disc are relatively small and are hard to observe with normal earth based optical telescopes. They were first observed in 1980's using CCD(charged-coupled device in  telescopes. This led to many more new discoveries of scattered disc objects(SDO) in very less time between 1992 to 2006.

Image here shows the largest known scattered disc object Eris and it's moon Dysnomia (the object on left)

     The scattered disc lies immediately behind the kuiper belt, and the difference between kuiper belt and scattered disc is mainly the shape and the minor objects population. The shape of kuiper belt is a torus (or doughnut) whereas the scattered disc is in the shape of an irregular disc. And coming to the population, the kuiper belt is thickly populated and the scattered disc is sparsely populated with minor planets or asteroids. The outer part of kuiper belt known as the classical kuiper belt remains unaffected by the Neptune, in contrast to this the scattered disc population can be disturbed by the Neptune. Scattered disc objects come within the gravitational range of Neptune at their closest approaches(~30AU) but their farthest distances may reach many more times of this.

 Image showing few large known SDO's









     The trans-Neptunium objects are often divided into three sub-categories, they are: Kuiper belt, Scattered disc and the Oort cloud. Many of the oort cloud objects are believed to be oce the scattered disc objects. The scattered disc is spreadarther above and below the elliptic than the belt. As this disc is unstable in nature, now the SDO's are considered to be the place for the origin of comets.

 An artistic image of comet











      During the early ages of our solar system, when our sun entered its T-Tauri phase, that is, whenthe sun starts blowing out the solar winds for the first time with a very high speed in all the directions around sun. At this phase, most of the planetesimals where blown away far from the sun, this is though to be the origin for the kuiper belt, scattered disc and the hypothetical oort cloud. The reason for distorted orbit of these SDO's is still unknown but the orbital migration of Neptune and Uranus at the time of formation of solar system is thought to be the reason for throwing SDO's into elliptical orbit.

              Do you know?
The comets have an elliptical orbit around sun (as shown in this image) with a revolution period being for few hundred years.












      The scattered disc is very dynamic in nature, this is because they are still capable of being perturbed by Neptune, SDO's orbits are always are in danger of disruption, either of being sent outward to the oort cloud or inward into the centaur family and finally into the family of comets.

Do you know?

  The white spot inside the Oort cloud is the kuiper belt, inside kuiper belt is outer solar system, inside outer solar system is asteroid belt, inside asteroid belt is inner solar system and inside inner solar system is Sun.

  This whole together is known as the complete "SOLAR SYSTEM".

               Do you know?

The sun's gravity holds all these objects which means it got a very massive gravitational field of 274m/s²

Kuiper belt- The reason why Pluto is no more a planet

      In the year 1951, Gerard Kuiper an astronomer, said that some kinds of comets might come from the distant regions that are even far beyond the planets. Hence after the dicovery of that region it is named as "The Kuiper Belt"  after Gerard Kuiper.The Kuiper belt otherwise known as the Edgeworth–Kuiper belt is a region of our solar system that extends beyond the orbit of Neptune and is 30 to 50 AU from the Sun. 

The dots in this image show the Kuiper belt region in solar system.
 
   
The orbit of Pluto, a Kuiper belt object passing through the Neptune's orbit is shown here.


    Do you know?
Objects that can be found in the Kuiper belt (KBOs) can also be referred to as trans-Neptunian objects (TNOs).







      As we read earlier that the unexpected changes in the orbit of Uranus led the astronomers to deduce that its orbit was affected by other forces, most probably the gravitational forces of some other massive object that existed beyond the orbit of Uranus. This led to the discovery of planet Neptune. Similarly, the orbit of Neptune is also observed to be subjected to some gravitational perturbation at a smaller level. This again led the astronomers to a conclusion that their exists another planet beyond Neptune which is affecting the Neptune's orbit and for this continuous observations were made for its discovery.


 

Comparison of Pluto with Earth.




                 Do you know?
Pluto's volume is just 0.6% of Earth's volume.










 
     Pluto was discovered in 1930. For causing perturbations in orbits of a giant planets such as Uranus and Neptune, the planet beyond it should be at least as massive as Neptune, but the size and relatively low mass of Pluto left astronomers with many unanswerable questions. This led to continue observations beyond the Neptune's orbit. Many other objects with similar composition and mass to that of Pluto were found which subsequently led to the discovery of Kuiper belt in 1992. From its discovery in 1930 to the discovery of Kuiper belt in 1992, Pluto was considered to be a planet. In 2006, IAU redefined it as a dwarf planet rather than a main planet.

Image of the hypothesized Oort cloud and the Kuiper belt.


             Do you know?
Pluto is given the number 134340 and reclassified in the category "minor planets". Therefore, from now Pluto is officially called as-
134340-Pluto.











      When the solar system was formed,the planets of the system swept most of the remaining debris into the sun or out of the solar system. But bodies farther out remained safe from gravitational pulls of massive , and so managed to stay safe as they slowly orbited the sun. The Kuiper Belt is assumed to contain the leftover remnants from the beginning of the solar system and can provide valuable insights into its birth. The most crowded section of the Kuiper Belt lies between 42-48 AU from the sun, and this region is called the classical Kuiper Belt.

The relative sizes of few KBOs in comparison to Earth is shown.




Because of their small size and distant location, Kuiper Belt Objects are a challenge to spot from Earth.







 

Two of the moons in our solar system Neptune’s Triton and Saturn’s Phoebe are thought to have come originally from the Kuiper belt.


 

               Do you know?
Triton, the moon of  Neptune has similar composition to that of KBOs and is the only moon in the solar system to have retrograde orbit. This indicates that this is captured from Kuiper belt.










 


     In order to catch a better glimpse of these remote leftovers from the birth of the solar system, NASA has launched the "New Horizons" mission. Set to reach Pluto in 2015, the mission is to perform the observations of the most famous dwarf planet, the Pluto before continuing on with an aim to examine multiple KBOs.

Neptune- The farthest planet from sun

     The fourth-largest planet by diameter and the third-largest by mass, Neptune got its name from the Greek god- Poseidon, the god of the Sea.  Neptune is 17 times the mass of Earth and is somewhat more massive than its near-twin Uranus, which is 15 times the mass of Earth but not as dense.

                      Do you know?
Because of its great distance from the Sun, Neptune's outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching −218 °C.









   
     Neptune was the first planet found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus led to deduce that its orbit was subject to gravitational perturbation by an unknown planet behind it. Neptune was subsequently observed on 23 September 1846.

     More than four centuries earlier, in 1613, Galileo observed Neptune when it happened to be very near Jupiter, but he thought it was just a star. On two successive nights he actually noticed that it moved slightly with respect to another nearby star. But on the subsequent nights it was out of his field of view. Had he seen it on the previous few nights, Neptune's motion would be obvious to him and Galileo would have discovered it. But, alas, cloudy skies prevented observations on those few critical days.

   

        Do you know?
The axial tilt of Neptune is 28.32°, which is similar to the tilts of Earth (23°) and Mars (25°). As a result, this planet experiences similar seasonal changes. The long orbital period of Neptune means that the seasons last for forty Earth years.




The image here shows the size of Neptune in comparison to Earth.





      Neptune has 13 known moons. The largest by far, comprising more mass in orbit around Neptune and the only one massive enough to be spheroidal, is Triton, Unlike all other large planetary moons in the Solar System, Triton has a retrograde orbit, which indicates that it was captured rather than forming in place; it was probably once a dwarf planet in the Kuiper belt. It is close enough to Neptune to be locked into a synchronous rotation, and it is slowly spiraling inward because of tidal acceleration.

            



        Do you know?
   Dark spot on Neptune similar in appearance to Jupiter's Great Red Spot, Like Jupiter's spot, they are anticyclonic storms. However, the interiors of Great Dark Spots are relatively cloud-free, and unlike Jupiter's spot, which has lasted for hundreds of years, their lifetimes appear to be much shorter.










     Neptune is never visible to the naked eye, having a brightness between magnitudes +7.7 and +8.0. Neptune's orbit has a profound impact on the region directly beyond it, known as the Kuiper belt, extending from Neptune's orbit at 30 AU out to about 55 AU from the Sun. Much in the same way that Jupiter's gravity dominates the asteroid belt, shaping its structure, so Neptune's gravity dominates the Kuiper belt.



  Few other characteristics of Neptune:

Escape velocity                    : 23.5 km/s
Equatorial rotation velocity  : 2.68 km/s 
Equatorial radius                  : 24,764 km
Axial tilt                                  : 23.38°
Gravitational acceleration
on surface                             : 11.15 m/s²
 

Uranus- The rolling planet

     The seventh planet from sun in our solar system. Uranus got a different composition than the larger gas giants of which we have discussed earlier- Jupiter and Saturn. The same composition of Uranus is shared by the other gas giant- Neptune. Because of their very large distance from Sun, Uranus and Neptune contains more ice of ammonia and methane, therefore, sometimes planets are termed as "Ice giants' rather than "Gas giants". Uranus is named after the ancient Greek deity of the sky - Uranus, the father of Cronus (Saturn) and grandfather of Zeus (Jupiter). 

   Do you know?
The intensity of sunlight on Uranus is about 1/400 that on Earth, due to this the faint blue disk of Uranus appears to be exceptionally dull and lifeless.




 



     Are you amazed to see the ring system around Uranus? Are you tilting our head side ways to look at the image shown above?
     You really do not need to do that, this is how Uranus looks like if your a standing before it with your head towards the Sun's (or earth's) north. Yes, Uranus has got a very unique feature, it got an unusual axis tilt of 97.77 degrees making it literally look like, as if it is rolling in its orbit. And, coming back to its ring system as mentioned in my previous posts, all the Jovian planets show a common feature- the planetary rings. Though, Saturn alone is famous for its ring system.

     Uranus's mass is roughly 14.5 times that of the Earth, making it the least massive of the giant planets. Its diameter is slightly larger than Neptune's at roughly four times Earth's. A resulting density of 1.27 g/cm³ makes Uranus the second least dense planet, after Saturn. Uranus's internal heat appears markedly lower than that of the other giant planets; in astronomical terms, it has a low thermal flux. Why Uranus's internal temperature is so low is still not understood and astronomers are working on this topic. Neptune, which is Uranus's near twin in size and composition, radiates 2.61 times as much energy into space as it receives from the Sun.

     The gravity on Uranus is 8.69 m/s² which almost 91% of the gravity on Earth (earth's gravity=9.81 m/s² ), this is because it is such a large planet that has got a radius which is around 4 times the radius of earth and since the gravity is inversely proportional to square times the radius, therefore though the mass of Uranus is larger than Earth because of it's radius it got slightly lesser gravitational acceleration than on the surface of Earth.

The image here shows the size of Uranus in comparison to Earth.






                Do you know?
Unlike Jupiter or Saturn, does not seem to have a solid core of any kind. The planet does contain some rocky material, but the planet is almost all gas, with the outer layer of methane providing the blue color.

Uranus's magnetosphere contains charged particles: protons and electrons with small amount of H₂⁺ ions. No heavier ions have been detected. Many of these particles probably derive from the hot atmospheric corona.

This image is taken from Wikipedia. Here it shows another interesting fact about Uranus, its magnetic field.















 
      The magnetic field is peculiar, both because it does not originate from the planet's geometric center, and because it is tilted at 59° from the axis of rotation. In fact the magnetic dipole is shifted from the center of the planet towards the south rotational pole by as much as one third of the planetary radius.


 

                        Do you know?
From 1995 to 2006, Uranus's apparent magnitude fluctuated between +5.6 and +5.9, placing it just within the limit of naked eye visibility at +6.5.



                       Do you know?
 Uranus has got 27 moons orbiting around it.








     A day on Uranus only takes 17 hours 14 minutes and 24 seconds.Because of its fast rotation, equatorial bulge can be easily observed. Uranus is 19.19AU or 1.79 billion miles away from Sun & 18.19AU from earth (as earth is exactly 1AU from Sun), hence it takes 84 years to complete one revolution.




  Few other characteristics of Uranus:

Escape velocity                   : 21.3 km/s
Equatorial rotation velocity : 2.59 km/s 
Equatorial radius                 : 25,559 km
Axial tilt                                  : 97.77°
Gravitational acceleration
on surface                             : 8.69 m/s²

Saturn- The visually unique planet

Named after the Roman God Saturn (Greek God-Cronus), the father of Zeus(Jupiter). Saturn has been known since prehistoric times. Galileo was the first to observe it with a telescope in 1610.

                   Do you know?
Saturn has at least 62 moons, of which 53 have formal names.









     When it is in the nighttime sky, Saturn is easily visible to the unaided eye. Though it is not nearly as bright as Jupiter, it is easy to identify as a planet because it doesn't "twinkle" like the stars do. The rings and the larger satellites are visible with a small astronomical telescope.

     Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is a gas giant with an average radius about nine times that of Earth. While only one-eighth the average density of Earth, with its larger volume Saturn is just over 95 times more massive than Earth.

The image here is, comparing the sizes of Saturn and Earth.














     Saturn has a prominent ring system that consists of nine continuous main rings and three discontinuous arcs, composed mostly of ice particles with a smaller amount of rocky debris and dust. The origin of the rings of Saturn (and the other Jovian planets) is unknown. Though they may have had rings since their formation, the ring systems are not stable and must be regenerated by ongoing processes, perhaps the breakup of larger satellites. The current set of rings may be only a few hundred million years old. 

         Do you know?
A persisting hexagonal wave cloud pattern around the north polar vortex in the atmosphere at about 78°N.


It was first noted in the Voyager images, North polar hexagonal cloud feature, discovered by Voyager 1 and confirmed in 2006 by Cassini.








     Saturn is termed a gas giant, but it is not entirely gaseous. The planet primarily consists of hydrogen, which becomes a non-ideal liquid when the density is above 0.01 g/cm³. This density is reached at a radius containing 99.9% of Saturn's mass. Standard planetary models suggest that the interior of Saturn is similar to that of Jupiter, having a small rocky core surrounded by hydrogen and helium with trace amounts of various volatiles. This core is similar in composition to the Earth, but more dense.

     The outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium. It takes approximately 29½ years to make a complete circuit of the ecliptic against the background constellations of the zodiac.

   The image here shows an amateur telescopic view




Most people will require optical aid (large binoculars or a telescope) magnifying at least 20× to clearly resolve Saturn's rings.





      Saturn is 9.53AU, that is, 886 million miles or 1426 million kilometers from Sun. Due to this distance, for a year to complete on Saturn (a complete revolution around Sun) it takes 29.14 earth years or 29 years, 54 days. And, similar to Jupiter, Saturn also rotates on its axis at a faster rate. The length of a day on Saturn is extremely difficult to determine. It is always harder to determine the length of a day of a gas giant than it is to determine the length of a day of a terrestrial planet, but the astronomers can find this to an approximate value of 10 hours, 47 minutes to complete a day. This makes Saturn the second fastest spinning planet in our solar system.






  Few other characteristics of Saturn:

Escape velocity                   :35.5 km/s
Equatorial rotation velocity : 9.87 km/s 
Equatorial radius                 : 60 268 km
Axial tilt                                 : 26.73°
Gravitational acceleration
on surface                            : 10.44 m/s²

Jupiter- Solar system's vacuum cleaner

     The fifth planet from the sun, Jupiter is known since early 17th century and is always a very fascinating object is the night sky for most of the year. In 1610 when Galileo first pointed a telescope at the sky he discovered Jupiter's four large moons Io, Europa, Ganymede and Callisto (now known as the Galilean moons) and recorded their motions back and forth around Jupiter. This was the first discovery of a center of motion not apparently centered on the Earth. It was a major point in favor of Copernicus's heliocentric theory of the motions of the planets (along with other new evidence from his telescope: the phases of Venus and the mountains on the Moon).

                Do you know?
Few Jupiter things:-
1)Biggest planet of our solar system
2)Planet with more number of moons
3)Planet with huge magnetosphere
4)Most massive planet of our solar system  
5)The only planet that has a center of mass
    with the Sun that lies outside the volume of
    the Sun
6)Fastest rotating planet in the entire solar
    system
7)Jupiter also got immense gravitational field
    of all other planets





     Jupiter has rings like Saturn's, but much fainter and smaller, unlike Saturn's, Jupiter's rings are dark (albedo about .05). They're probably composed of very small grains of rocky material. There are mainly three rings, unlike Saturn's rings, they seem to contain no ice, and they are named Gossamer, Main and Halo.

          True image of Jupiter.


               Do you know?
Under Jupiter's atmosphere is a large liquid ocean of hydrogen and water. What lies in between that ocean and the atmosphere? Actually, there is no in between. The atmosphere slowly gets thicker and thicker until it becomes part of the ocean.







     Jupiter is the fastest rotating planet in our solar system with a rotational period almost equal to 10 hours. Therefore a day on Jupiter (if you can manage to stay on its surface) is just 9 hours 54 minutes. Due to this fast rotation the planet gets bulged at its equator and the region near the poles become flat. This massive planet is 5.2AU away from sun, hence it got a revolution period (time to orbit around Sun) is approximately 12 years, that is, 11.84 years or 11 years, 306 days, 19 hours. This makes Jupiter and Earth almost look like the hour's hand and minute's hand respectively of a clock, for every ~12 revolutions of Earth around sun, Jupiter completes its one revolution, just like a minute's hand making its 12 revolutions to complete get back the hour's hand back to its initial position.

    Jupiter is a very stormy planet. There are storms found throughout the atmosphere, and most of the storms seem to never end. The many different cloud formations and storms in the atmosphere also make Jupiter a very colorful planet.

     Jupiter has been called the Solar System's vacuum cleaner, because of its immense gravity well and location near the inner Solar System. It receives the most frequent comet impacts of the Solar System's planets.

            Do you know?
Jupiter's great red spot, visible in the picture, is where a giant storm has been raging for at least 300 years. This red spot is also called "The Eye of Jupiter" because of its shape. This storm's super hurricane winds blow across an area larger than the Earth.












 Few other characteristics of Jupiter:

Escape velocity                   : 59.5 km/s
Equatorial rotation velocity : 12.6 km/s
Surface pressure                 : 20-200 kPa
Equatorial radius                 : 71,492 km
Axial tilt                                  : 3.13°
Gravitational acceleration
on surface                             : 24.79 m/s²