Vulcan

{{hatnote|This article is not about the {{wpl|Vulcan (Star Trek)|planet}} from which [[Star Trek|Mr. Spock]] comes.}}

[[File:Planet-Vulcan 1846 003790.jpg|thumb|right|165px|Hypothetical planet, Vulcan, from an 1846 lithograph.]]{{astronomy}}
'''Vulcan''' is a hypothetical [[planet]] that was thought to orbit the [[Sun]] in an orbit inner to [[Mercury (planet)|Mercury]] before the 20<sup>th</sup> century, named after the [[Classical mythology|Roman god]] {{wpl|Vulcan (mythology)|of the same name}} equivalent to the Greek {{wpl|Hephaestus||.}}

== Theory and observations ==
Claims about objects seen transiting in front of the Sun have existed since the invention of the telescope, back in the 17<sup>th</sup> century<ref>{{cite journal | last = Drobyshevskii | first = E. M. | title = Impact Avalanche Ejection of Silicates from Mercury and the Evolution of the Mercury / Venus System | journal = Soviet Astr | volume = 36 | issue = 4 | pages = 436–443 | date=1992| bibcode = 1992SvA....36..436D}}</ref> and reaching a maximum in the 19<sup>th</sup> century,<ref>{{Cite journal|url=https://babel.hathitrust.org/cgi/pt?id=njp.32101064253428;view=2up;seq=112;skin=mobile|title=The Monthly magazine. v.45 (1818)|journal=Monthly Magazine and Critical Register of Books|year=1796|language=en|access-date=2017-07-04|last1=Blake|first1=William}}</ref><ref name="articles.adsabs.harvard.edu">{{Cite journal |title=The Supposed New Planet Vulcan|journal=Astronomical Register|volume = 7|page=164|last=Elger|first=T.G.E.|date=May 4, 1869|bibcode=1869AReg....7..164E}}</ref><ref name="articles.adsabs.harvard.edu"/> even if most if not all of them are more than likely to have been just reports of the observations of sunspots if they were real at all.

Theories about an innermost planet to Mercury began circulating in that century<ref name=Baum>,{{cite book
| last1=Baum
| first1=Richard P.
| last2=Sheehan
| first2=William
| title=In Search of Planet Vulcan: The Ghost in Newton's Clockwork
| date=August 2003
| publisher=Basic Books
| location=New York
| isbn=0738208892}}</ref> and were followed by observations that hoped to spot the planet when it passed in front of the Sun, given that seeing it after sunset or before dawn would be very difficult or outright impossible with it lost the Sun's glare.<ref name=Baum/> All of them, of course, came up empty or were impossible to replicate, suggesting that if the planet existed at all it would be very small and would orbit close to the Sun, as otherwise it would have been detected before—either transiting in front of the Sun or during a solar eclipse, as such closeness to the Sun means a lot of solar irradiation such that that it would have been quite bright, especially in the case of a large planet.

== Enter Einstein==
Anomalies in Mercury's orbit that models of the latter failed to account for, causing astronomers to think the gravity of planet(s) orbiting closer to the Sun were responsible, were a mystery until 1915, when [[Einstein]]'s [[Theory of Relativity]] showed they were caused by space-time being warped by the Sun, matching almost exactly the observations done in the previous century,<ref>[https://www.oddsalon.com/jan-2-1860-the-discovery-of-planet-vulcan/ Kurt Larson, Jan 2, 1860: The Discovery of Planet Vulcan, oddsalon.com]</ref> with such prediction being confirmed during the solar eclipse of May 29, 1919 catapulting Einstein to fame and Vulcan's existence being no longer needed.<ref name="baron">{{cite book |title=American Eclipse |author=David Baron |year=2017 |publisher=Liveright |isbn=9781631490163}}</ref>

== Today ==	
Earth-based searches have been supplemented by observations from space using telescopes such as {{wpl|Solar_and_Heliospheric_Observatory|SOHO}}, to spacecraft 
that have boldly gone where no spacecraft has gone before
 positioned within Mercury's orbit, such as [[NASA]]'s {{wpl|Parker Solar Probe||}}, that have not only failed to find such a planet, but also revealed that the space within Mercury's orbit is devoid of bodies of significant size, with a {{wpl|Vulcanoid|proposed population of asteroids}} that would be there as an alternative to the existence of such planet having also failed to materialize, besides the occasional [[comet]] or {{wpl|Atira asteroid|asteroid.}}
 
Many other star systems contain planets ({{wpl|TRAPPIST-1|sometimes}} {{wpl|Kepler-11|very}} {{wpl|Kepler-80|comfortably}}) within a radius equivalent to Mercury's orbit. Whether this is simply an observational [[bias]] (as such kind of planetary systems are easier to detect with our current technology), or the lack of them in our [[Solar System]] is actually a ''feature'' 
and not a bug
 is a mystery.

The name "Vulcan" being still today reserved for a planet that turned out not to exist is the reason why he is the only Olympian not to have an object in the solar system named after him.

== References ==
{{reflist|2|80%}}

[[Category:Astronomy]]
[[Category:Planets]]
[[Category:Additional planets]]

Categories: Astronomy, Planets, Additional planets