社科类雅思阅读：Bode's law lives

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SOMEWHERE, the spirit of Johann Elert Bode is smiling. Bode was a German astronomer who popularised a mathematical rule, which came to be known as Bode’s law, in a book published in 1772. According to Bode’s law, there is a hidden pattern in the spacing of the orbits of the planets. The orbits of Mercury, Venus, Earth, Mars, Jupiter and Saturn fit neatly into this pattern; Uranus, discovered in 1781, also obeyed the law. But there was a problem: Bode’s law predicted that there ought to be a planet between Mars and Jupiter. It was only in 1801 with the discovery of Ceres, the largest of the asteroids, that this gap was neatly plugged.

In the two centuries since, however, Bode’s law has fallen from grace. Ceres turned out to be just one of many asteroids orbiting between Mars and Jupiter, rather than a proper planet. Neptune, discovered in 1846, had a much smaller orbit than the law predicted; and Pluto, which is now classed as a "dwarf planet", also failed to fit in with Bode’s neat pattern when it was found in 1930. Bode’s law, it seemed, was just a coincidence, an example of the human mind’s tendency to find a meaningful pattern where none exists.

But the discovery of a new planetary system by a group of astronomers at the European Southern Observatory, led by Christophe Lovis of the University of Geneva, has reawakened interest in the old rule. Indeed, their paper announcing the discovery rers to Bode’s law by name (it actually calls it the Titius-Bode law, namechecking the Prussian astronomer whose idea Bode stole). The system consists of at least five, and possibly as many as seven, planets orbiting a sun-like star called HD 10180, located 127 light-years away in the constellation of Hydrus. As the planets orbit the star, they pull it to and fro, causing telltale wobbles in the star’s light that can be detected from Earth. Carul analysis of these wobbles reveals the masses of the planets and the sizes and spacing of their orbits.

And it turns out that the spacing of the orbits of the planets around HD 10180 obey a version of Bode’s law. The planets look very different from those in the Earth’s solar system: five of them are about the size of Neptune, and are closer to their star than Mars is to the sun. The other two planets, for which the evidence is not quite so strong, are a Saturn-like planet orbiting further out, and a planet only slightly heavier than Earth orbiting very close to the star, so that it completes an orbit every 1.18 Earth days. But never mind that. The fit with Bode’s law is striking, and the astronomers show in their paper that a few other known multiplanetary systems around other stars exhibit a similar fit too, though with fewer planets.