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RE: The planet Vulcan
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Title: An Intra-Mercurial Planet
Authors: Russell, F. A. R.

The discussion as to the existence of a planet within the orbit of Mercury leads me to communicate an observation made many years ago, which I believe nothing but the existence of an unknown planet between us and the sun can explain. On Sunday, January 29, 1860, the sun rose in a fog in London, so that he could be steadily looked at as if through a dark glass. Soon after eight o'clock a perfectly round black object was seen by four persons, including myself, clearly denned upon the lower half, according to my recollection, of the sun's disc. It passed slowly across his face and made its egress at about half-past nine A.M. In apparent size it was equal to the representations I have seen of Mercury in transit.

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Shortly after eight o'clock on the morning of 29 January 1860, F A R Russell and three other people saw an alleged transit of an intra-Mercurial planet from London.[10] An American observer, Richard Covington, many years later claimed to have seen a well-defined black spot progress across the Suns disk around 1860, when he was stationed in Washington Territory.
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Vulcanoids
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Title: A Search for Vulcanoids with the STEREO Heliospheric Imager
Authors: A. J. Steffl, N. J. Cunningham, A. B. Shinn, D. D. Durda, S. A. Stern

Interior to the orbit of Mercury, between 0.07 and 0.21 AU, is a dynamically stable region where a population of asteroids, known as Vulcanoids, may reside. We present the results from our search for Vulcanoids using archival data from the Heliospheric Imager-1 (HI-1) instrument on NASA's two STEREO spacecraft. Four separate observers independently searched through images obtained from 2008-12-10 to 2009-02-28. Roughly, all Vulcanoids with e<=0.15 and i<=15deg will pass through the HI-1 field of view at least twice during this period. No Vulcanoids were detected. Based on the number of synthetic Vulcanoids added to the data that were detected, we derive a 3 sigma upper limit (i.e. a confidence level >0.997) that there are presently no Vulcanoids larger than 5.7 km in diameter, assuming an R-band albedo of p_R=0.05 and a Mercury-like phase function. The present-day Vulcanoid population, if it exists at all, is likely a small remnant of the hypothetical primordial Vulcanoid population due to the combined effects of collisional evolution and subsequent radiative transport of collisional fragments. If we assume an extant Vulcanoid population with a collisional equilibrium differential size distribution with a power law index of -3.5, our limit implies that there are no more than 76 Vulcanoids larger than 1 km.

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RE: The planet Vulcan
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On March 26, 1859, a French medical doctor and amateur astronomer named Lescarbault claimed to have observed a planet closer to the sun than Mercury. He called it Vulcan, after the Roman god of fire.

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On 2 January 1860 Urbain Jean Joseph Le Verrier announced the discovery of Vulcan to a meeting of the Académie des Sciences in Paris. Lescarbault, for his part, was awarded the Légion d'honneur and invited to appear before numerous learned societies.
Not everyone accepted the veracity of Lescarbault's "discovery", however. An eminent French astronomer, Emmanuel Liais, who was working for the Brazilian government in Rio de Janeiro in 1859, claimed to have been studying the surface of the Sun with a telescope twice as powerful as Lescarbault's at the very moment that Lescarbault said he observed his mysterious transit. Liais, therefore, was "in a condition to deny, in the most positive manner, the passage of a planet over the sun at the time indicated".

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Vulcanoids
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Vulcanoid Search Continues as MESSENGER Reaches Orbital Perihelion

Today MESSENGER will pass within 0.308 astronomical units (AU) of the Sun (one AU is Earth's distance from the Sun, approximately 150 million kilometers or 93 million miles), providing MESSENGER scientists with another opportunity to search for vulcanoids. Named after the hypothetical planet Vulcan, whose existence was disproven in 1915, vulcanoids are asteroids that orbit the Sun inside the orbit of the planet Mercury.
No vulcanoids have yet been discovered, and it is not known if any exist. But should they be found, these small, rocky asteroids may yield insights into the formation and early evolution of the solar system. They might contain material left over from the earliest period of planet formation and help determine the conditions under which the terrestrial planets, particularly Mercury, formed. Vulcanoids would also represent an additional population of impactors that contributed to the cratering history of Mercury much more than that of any other body. Impacts by vulcanoids would make the planet's surface appear older, relative to the surfaces of the Moon and other inner planets, than it actually is.

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Posts: 131433
Date:
The planet Vulcan
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On March 26, 1859, a French medical doctor and amateur astronomer named Lescarbault claimed to have observed a planet closer to the sun than Mercury. He called it Vulcan, after the Roman god of fire. He calculated the planet's movements and sent the information onto Urbain Le Verrier, France's most famous astronomer.

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