What is Vulcanoid asteroid?
'''Vulcanoid asteroids''' are a special group of [[asteroid]]s which may [[orbit]] close to the [[Sun]], closer than the orbit of the [[planet]] [[Mercury (planet)|Mercury]].<ref name=Evans>{{cite journal|title=Possible Long-Lived Asteroid Belts in the Inner Solar System|journal=Nature|volume=399|issue=6731|pages=41–43|year=1999|arxiv=astro-ph/9905067|doi=10.1038/19919|bibcode = 1999Natur.399...41E |s2cid=4418335|last1=Evans|first1=N. Wyn|last2=Tabachnik|first2=Serge}}</ref> No vulcanoid has ever been discovered; it is not known if they ever existed. Because they would orbit so close to the Sun they could only be seen during twilight, or a [[solar eclipse]].<ref name=PlanSoc>{{cite web | title = Vulcanoids | publisher = The Planetary Society | url = http://www.planetary.org/programs/projects/vulcanoids/ | accessdate = 2008-12-25 | archive-date = 2009-01-08 | archive-url = https://web.archive.org/web/20090108102412/http://planetary.org./programs/projects/vulcanoids/ | url-status = dead }}</ref> Their very small size could make them impossible to see. This part of the [[Solar System]] is described as being gravitationally stable, and every other similar stable area has asteroids.<ref name=Britt>{{cite web | last = Britt | first = Robert Roy | title = Vulcanoid search reaches new heights | publisher = Space.com| year=2004| url = http://www.msnbc.msn.com/id/4066544/ | accessdate = 2008-12-25}}</ref> If they do exist, vulcanoids would be made of material that could help explain the formation of the planets.<ref name=Dryden>{{cite news | title = NASA Dryden, Southwest Research Institute Search for Vulcanoids | publisher = NASA | year = 2002 | url = http://www.nasa.gov/centers/dryden/news/NewsReleases/2002/02-20.html | accessdate = 2008-12-25 | archive-date = 2019-05-03 | archive-url = https://web.archive.org/web/20190503104116/https://www.nasa.gov/centers/dryden/news/NewsReleases/2002/02-20.html | url-status = dead }}</ref> If they do not exist, then theories about how the planets were formed might have to change.<ref