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PLANET SYSTEM DISCOVERY REVEALS STRIKING SIMILARITIES
By John Gribbin
LONDON, from THE GUARDIAN -- The discovery of three planets orbiting a pulsar known as PSR B1257+12 has revealed a system with properties that almost exactly match those of the Inner Solar System, made up of Mercury, Venus and Earth. The similarities are so striking that it seems there may be a law of nature which ensures that planets always form in certain orbits and always have certain sizes; and it leads credence to the significance of a mathematical relationship that relates the orbits of the planets in our Solar System, which many astronomers have dismissed as mere numerology.
PSR B1257+12 is a rapidly spinning neutron star, containing slightly more matter than our Sun, packed into a sphere only about 10 kilometers across. As the star spins, it flicks a beam of radio noise around, like the beam of a lighthouse, producing regularly spaced pulses of radio noise detectable on Earth. It can only have been produced in a supernova explosion, long ago, which would have disrupted any planetary system the star possessed at the time. So the present planets associated with the pulsar are thought to have formed from the debris of a companion star also disrupted by the pulsar.
The three planets cannot be seen directly, but are revealed by the way in which they change the period of the pulsar's pulses as they orbit around it. There is enough information revealed in the changing pulses to show that the three planets have masses roughly equal to 2.98 times the mass of the Earth, 3.4 times the mass of the Earth and 1.5 per cent of the mass of the Earth. And they are spaced, respectively, at distances from the pulsar equivalent to 47 per cent the distance from the Earth to the Sun, 36 per cent of the Sun-Earth distance, and 19 per cent of the Sun- Earth distance.
Tsevi Mazeh and Itzhak Goldman, of Tel Aviv University, have pointed out (in a paper to be published by the Astronomical Society of the Pacific) that the ratio of these distances, 1:0.77:0.4, is extremely close to the ratio of distances of the Earth, Venus and Mercury, which is 1:0.72:0.39.
And the masses of the three inner planets of the Solar System are one Earth mass, 82 per cent of the mass of the Earth, and 5.5 per cent of the mass of the Earth. In each case, two outer planets with roughly the same mass have an inner companion with a much smaller mass.
All this is doubly intriguing because for more then 200 years astronomers have puzzled over a relationship called Bode's law, which concerns the orbits of the planets in the Solar System. The law says that if you take the sequence 0, 3, 6, 12 ... (with each number after 3 twice the previous number in the sequence), add 4 to each number and divide by 10 you end up with the distances of the planets from the Sun in terms of the distance to the third planet (Earth, in the case of the Solar System). Bode's law works out as far as the orbit of Uranus, but nobody knows why; now, it seems that it also works for the planets of pulsar PSR B1257+12.
The indications are that there is a universal mechanism for the formation of planets around stars. If it works for systems as diverse as a pulsar and our Sun, the chances are that it works for all stars and that "Solar" Systems, very much like our own may be the rule, rather than the exception, among the stars of the Milky Way and the universe. Reprinted from AstroNet.
My comment.
Bode's Law demonstrates a clear mathematical pattern from Mercury to Neptune; why shouldn't this be normal throughout the universe? Also, surely planets are the rule. Why wouldn't they be? Only if they are all asteroid belts? (That's a very good question).