Volcano (planet)

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The planet Vulcano in an illustration of the solar system from 1846

Vulkan (or Vulcanus ) is the name of a hypothetical planet within Mercury's orbit that was previously adopted to fully explain Mercury's perihelion rotation . When the perihelion of Mercury could be explained by the general theory of relativity , the volcano hypothesis lost its necessity and at the same time its meaning.

The hypothesis

In the 19th century, observations of the orbit of Mercury revealed that its actual orbit deviated from the shape of a Kepler ellipse . During each orbit orbit, the perihelion of Mercury shifts ( perihelion rotation ). This deviation was determined to be 574 ″ ( arcseconds ) per 100 years and could largely be explained by the interference from the other planets using Newton's law of gravitation . The error could be reduced to 43 "per century . Although this amount is very small, the result is inconsistent with the celestial mechanics of Isaac Newton . Only with Albert Einstein's general theory of relativity can this effect of perihelion rotation be adequately explained.

The existence of a planet within Mercury's orbit was postulated in 1859 by the French mathematician and astronomer Urbain Le Verrier to explain this deviation. In a lecture on January 2, 1860 in Paris, he argued for his assumption with good reason. In 1846 Le Verrier had already calculated the orbit of the then undiscovered planet Neptune by observing the orbital disturbances of Uranus . A short time later, Johann Gottfried Galle discovered the planet just one degree away from the predicted position. Against this historical background, the existence of Vulkan seemed plausible to Le Verrier; and numerous astronomers around the world tried to find it.

The search for volcano

Observing an object within Mercury's orbit is very difficult because the telescope has to be aimed at a point very close to the Sun , where the sky is never black. In addition, an error in the alignment of the telescope can damage the optics and cause severe, irreversible damage to the observer's eyes. The extreme brightness can also cause light reflections in the optics that confuse the observer and allow him to see objects that do not exist.

For over half a century, astronomers tried to track down the hypothetical planet Volcano, especially during solar eclipses . There were numerous false alarms and mix-ups, or optically adjacent stars were mistaken for the planet being sought. This is what happened to the asteroid researcher James Craig Watson .

When Le Verrier died in 1877, he was still convinced that he had found Vulkan. With his death, the search for the planetary fiction declined sharply, as most astronomers now doubt its existence after years of fruitless search. The 123-time asteroid discoverer Johann Palisa tried again on a Tahiti expedition in 1883.

Another earlier explanation for the anomalies of Mercury's orbit postulated a flattening of the sun, but this could not be proven to a sufficient extent.

Since Einstein published his general theory of relativity in 1916 and almost completely explained the perihelion of Mercury with the effect of the sun on the surrounding spatial structure, the Vulcan hypothesis has been superfluous, but some researchers have now postulated a thin asteroid belt of so-called volcanoes in its place . Possible preferred orbital areas of these potential asteroids were calculated at 0.18 and 0.15 AU distances from the sun.

The volcano hypothesis briefly resurrected around 1970 when some researchers believed they had observed faint objects near the sun during the total solar eclipse that year. The American astronomer Henry Courten, professor at Dowling College in Oakdale (USA), believed to have found important clues for such a so-called intramercurial planet. According to his calculations, the volcano with a major orbit half-axis of 14.4 million kilometers should orbit the sun once in about eleven days and have a diameter between 300 and 800 kilometers. Remarkably, this mean distance from the sun of 0.096 astronomical units could be inserted very well into the Titius-Bode series if the factor −1 is used for Vulkan (0.4 + 0.3 × −1 = 0.1 AU). The observed objects may have been faint comets , similar to the later ones that could be observed near the sun and in some cases even fell into it.

Volcanic transit

Volcanic transit is the hypothetical passing of the volcano in front of the solar disk observed from Earth , which would have to happen very often with a planet so close to the sun. In the 18th and 19th centuries in particular, there were repeated reports of such observations.

It could never be clarified what the observers saw then in front of the solar disk. In some cases it is likely to have been a matter of optical errors, but at least one case is known from the 18th century in which two observers at different locations noted the passage of an unknown object in front of the sun.

This could have been an asteroid. However, no asteroid transit in front of the sun has yet been recorded. In any case, sunspots can be ruled out, as they take more than ten days from one side of the sun to the other and were already known in the 18th century.

Volcano in science fiction

The name volcano has also been used by science fiction writers to refer to planets, with some of these fictional planets outside of our solar system:

The planet Vulkan in the universe of the Star Trek films and TV series is located about 16  light years from Earth and orbits the star Keid . Its inhabitants are Vulcans .

In the Sten Chronicles by Allan Cole and Chris Bunch , Vulkan is an artificial planet. Vulkan was originally an industrial space station , which grew more and more with the addition of new manufacturing facilities and thus assumed planet-like dimensions.

The volcano theory inspired some authors (for example Nikolai von Michalewsky ) to revive the Pythagorean idea of ​​a counter- earth , a planet that orbits the sun in the same orbit as the earth , but is constantly facing it in conjunction with the sun.

See also

literature

  • Carus Sterne: The sun's closest neighbor . In: The Gazebo . Issue 39, 1878, pp. 642–644 ( full text [ Wikisource ]).
  • Theodor von Oppolzer: About the intramercurial planet . In: Wilhelm Sklarek (Ed.): The natural scientist . No. 20 . Berlin May 17, 1879, p. 196 .
  • Christian Heinrich Friedrich Peters: About the intramercurial planet Vulcan . In: Wilhelm Sklarek (Ed.): The natural scientist . No. 22 . Berlin May 31, 1879, p. 213 .

Web links

Individual evidence

  1. ↑ Explanation of the perihelion movement of Mercury from the general theory of relativity . In: Session reports of the Royal Prussian Academy of Sciences . tape XLVII , November 18, 1915, pp. 831-839 ( full text ).
  2. ↑ Paul Schlyter: Hypothetical Planets. In: nineplaneten.de. April 10, 2014, accessed January 1, 2011 .