The asteroids

Most of the thousands of known asteroids, or minor planets, move in a belt on the large gap between Mars and Jupiter. The largest, Ceres, the first to be discovered, is only 930 Kms across, and only 200 are more than 100Kms across. They are too small for their own gravity to pull them into a spherical shape. They fall into types that match the meteorite types.

 The asteroids are probably debris left over from the birth of the Solar System, debris that failed to coalesce into a full sixed planet because of the disturbing gravitational pull of Jupiter. Some of them were deflected by collisions or close encounters into orbits outside the main asteroid belt. The so called Earth grazers come within Earth’s orbit. Other asteroids have been observed moving beyond the orbit of Saturn, and there may be more. Two groups of asteroids share the orbit of Jupiter, one 60^. Ahead of the planet and another 60^. Behind.

Unknown Planet in the known Solar System

Could there be a tenth planet beyond Pluto?  Neptune was “discovered” on paper in 1846, a year before it was seen; its orbit was calculated from its gravitational effect on the orbit of Uranus. But it did not seem to explain all the disturbance of Uranus that was observed and the search for other planet began. It was not until 1930 that Clyde Tombaugh discovered Pluto. Pluto does not seem to be massive enough to be responsible for all the gravitational disturbance of Uranus and Neptune that has been observed, and at least one more planet may lie beyond Pluto.

Computer analysis of the orbits of Uranus and Neptune gives some “best bets” for the distance and mass of possible planets, some predictions indicate a planet up to five times the mass of the Earth, several times as far from the Sun as Neptune, and possibly in a tilt orbit.

The existence of Charon was not suspected until 1978, when a small bump was noticed on Pluto’s image on a photographic. From 1985 to 1990, Charon’s orbit was positioned so that the satellite passed repeatedly in front of and behind Pluto. This revealed a great deal about both bodies. They both revolve about their common centre of gravity, a point in space between them. Likewise there is definitely more chances for another planet in the Solar System.

Solar System

The solar system is dominated by the gravitation of the Sun. About 99.85 percent of the mass of the system resides in the sun, 0.14 percent in the planets and the rest in satellites, asteroids, comets and meteoric matter that also circle the central star.

The planets all circle the sun in the same direction, and almost exactly the same plane. Viewed from “above” that is the side on which the Earth’s Northern Hemisphere lies, the direction of the planetary motion is counter clockwise. The asteroids, or minor planets, do the same. But the orbits of the comets are oriented randomly. They can approach the sun, and recede from it, at any angle.

The furthest planet from the Sun, normally, is Pluto, which at its maximum reaches 7,375 million Km from the Sun. but the furthest members of the sun’s group are believed to be an enormous group of unseen comets which form Oort’s Cloud, named after the Dutch astronomer who deduced their presence. The comets spend most of their time in the outermost reaches of their orbits, at a distance of about two light years from the Sun. They mark the true outer limit of the Solar System, the region in which the Sun’s gravity becomes feebler than that of its neighboring stars

The Suns Life Cycle

The sun has billions of years behind and ahead of it. About 4.6 billion years ago it began like other stars, as a cold mass of hydrogen and helium – the solar nebula left over from the big bang. The gas cloud began to shrink under its own gravity and, as it collapsed, the temperature of the core rise from frictional heating as gas molecules collided. When the temperature reached about 10 million ^.C the thermo nuclear reaction began.

The sun has about another five billion years of life ahead of it, as it turns hydrogen into helium in its core. When the hydrogen fuels runs low, it will burn some of the helium nuclei, fusing those into heavier nuclei. But at the same time it will swell into a giant red star, whereupon the Earth will be destroyed. Only a few million years after that, the sun will puff off some of its out layers and then shrink into a white dwarf, with an intensely hot surface, but so small that it gives out little light. It will then cool off for the rest of time.

The Sun Radiation

The Sun puts out its maximum radiation in the yellow part of the optical spectrum but it radiates substantially in the ultra violet and infrared and to a lesser extent at the X-ray and radio wavelengths. These make up the electromagnetic spectrum of transverse waves which all have the same velocity in space.

 The source of this energy is the conversion of mass into energy caused by nuclear fusion reactions that occur within the core. This reaction will only occur at extremely high temperatures and pressures, when gas turns to plasma. In this reaction hydrogen nuclei fuse together to form helium.  Each helium nucleus produced has slightly less mass than the hydrogen nuclei that went into it, and this difference is converted into energy, in accordance with Einstein’s famous principle of the equivalence of mass and energy  E=mc²,where C represents the speed of light and m represents mass. The heat produced by this reaction is sufficient to activate further reactions and so it is self sustaining. Four million tons of matters are converted to energy each second in the Sun and will continue to do so for the next five billion years.  

The Solar Cycles

The sun’s activity follows an 11- years cycle, during with sunspot numbers build to a maximum and then decline again. After a time of sunspot minimum, when the surface many be completely unblemished, the first spots of the new cycle appear in mid latitudes. These gradually migrate towards the equator, while further spots continue to appear in the higher latitudes. At the same time flares and prominences become more numerous; prompted by the same fluctuation in the magnetic field, and the corona grows bigger. This continues for five or six years, after which the rate at which new spots appear        gradually drops, and other forms of activity decline.

This characteristic movement of the sunspots across the Sun is positive proof that it spins. The cycle is caused by the progressive tangling and untangling of magnetic fields within the Sun, owing to the differential rates of rotation, with regions which are near to the poles taking a few days to complete their rotation than the equatorial areas. Unlike the planets, the whole mass does not spin at the same rate

The birth of Solar System

When the Sun was born about 4.6 billion years ago, it was encircled by a disc of matter, left over from the parent cloud. Such a cloud would consist of gas, mostly hydrogen and helium, mixed with solid grains. In the cooler outer regions of the cloud, the grains would consist of rock matter and of –“ices’-frozen water, carbon dioxide, methane and ammonia. The ices could relatively easily be turned into vapour, so in the inner regions of the cloud only the rock material condensed as it was warmed by the newly born star.

Grains of dust in the disc collided, accumulated and built up into small bodies called planetoids. These rapidly swept the surrounding space clear of the remaining dust. The inner planetoids consisted of rock, and were fairly small: in the outer system, the planetoids also included the icy materials. Because they were more massive, the outer planetoids gathered large atmospheres of hydrogen and helium around them. The smaller inner planetoids could not retain atmospheres: the warmth from the central star also helped to drive off these light gases. The process of planetoid formation was repeated in miniature around the larger outer planets, which formed systems of numerous satellites, or moons.

For hundreds of millions of years the young planets and moons were bombarded by leftover debris. Finally the planetary system became established: in our case, with four small, rocky inner planets, and four giant outer planets, mostly consisting of hydrogen and helium, and their systems of moons; an odd ball rocky planet, Pluto, in the “wrong’ place at the edge of the system; and assorted debris of rock and ice- the asteroids, comets and meteoric bodies.

The Earth’s Magnetism

The earth as a strong bipolar magnetic field, as if there was a large bar magnet in its core. In fact, electrical currents in the churning, liquid outer core produce a self sustaining dynamo. The influence of the magnetic field extends beyond the planet. The field meets charged particles streaming from the Sun in a shock wave about 50,000 Km above the Earth and slows hem from 400 to 250 Km per second. The solar wind, as these particles are known sweeps the Earth’s magnetic field into a six million Km tail. Solar flares on the surface of the Sun result in magnetic storms on Earth to days later. There are belts of solar particles trapped in the magnetic field about 3,000 and 25,000Km above the equator, called the Van Allen belts. Aurorae occur where charged particles trapped by the Earth’s magnetic field stream towards the poles.

The earth’s magnetic axis is 11 degree west of the North Pole and is slowly wandering. Eddy currents in the core and magnetism trapped in rocks produce local anomalies. In the geological past, the magnetic field have reversed many times. Between 118 and 83 million years ago it did not reverse at all. For the last few million years it has reversed about once every 220,000 years, revealed by the magnetic alignment in volcanic rocks. We are overdue for another reversal.