Editing Vulcanoid (section)

==Physical characteristics==

Any vulcanoids that exist must be relatively small. Previous searches, particularly from the [[STEREO]] spacecraft, rule out asteroids larger than {{convert|6|km|mi}} in diameter.<ref name=Steffl2013/> The minimum size is about {{convert|100|m|ft}};<ref name=Evans/> particles smaller than 0.2&nbsp;[[Micrometre|μm]] are strongly repulsed by radiation pressure, and objects smaller than 70&nbsp;m would be drawn into the Sun by [[Poynting–Robertson effect|Poynting–Robertson drag]].<ref name=Schumacher/> Between these upper and lower limits, a population of asteroids between {{convert|1|km|mi}} and {{convert|6|km|mi}} in diameter is thought to be possible.<ref name=Whitehouse>{{cite news | last = Whitehouse | first = David | title = Vulcan in the Twilight Zone | work = BBC News | url = http://news.bbc.co.uk/2/hi/science/nature/2063200.stm | access-date = 2008-12-25 | date=2002-06-27}}</ref> They would be almost hot enough to glow red hot.<ref name=Noll/>
 
It is thought that the vulcanoids would be very rich in [[Chemical element|elements]] with a high [[melting point]], such as [[iron]] and [[nickel]]. They are unlikely to possess a [[regolith]] because such fragmented material heats and cools more rapidly, and is affected more strongly by the [[Yarkovsky effect]], than solid rock.<ref name=Roach/> Vulcanoids are probably similar to Mercury in colour and albedo,<ref name=VulcFAQ/> and may contain material left over from the earliest stages of the Solar System's formation.<ref name=Dryden>{{cite news | title = NASA Dryden, Southwest Research Institute Search for Vulcanoids | publisher = NASA | date = 2002 | url = http://www.nasa.gov/centers/dryden/news/NewsReleases/2002/02-20.html | access-date = 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>

There is evidence that Mercury was struck by a large object relatively late in its development,<ref name=Roach/> a collision which stripped away much of Mercury's crust and mantle,<ref name=Chapman>{{citation | first = C.R.  | last =  Chapman |author2=Merline, W.J. |author3=Solomon, S.C. |author4=Head, J.W. III |author5=Strom, R.G.   | title = First ''MESSENGER'' Insights Concerning the Early Cratering History of Mercury | publisher = Lunar and Planetary Institute |date=2008| url = http://www.lpi.usra.edu/meetings/bombardment2008/pdf/3014.pdf | access-date= 2008-12-26}}</ref> and explaining the thinness of Mercury's [[mantle (geology)|mantle]] compared to the mantles of the other [[terrestrial planet]]s. If such an impact occurred, much of the resulting debris might still be orbiting the Sun in the vulcanoid zone.<ref name=Alexander>{{cite news| last = Alexander| first = Amir| title = Small, Faint, and Elusive: The Search for Vulcanoids| publisher = The Planetary Society| date = 2004| url = http://www.planetary.org/news/2004/0202_Small_Faint_and_Elusive_The_Search.html| access-date = 2008-12-25| url-status = dead| archive-url = https://web.archive.org/web/20081011231437/http://www.planetary.org/news/2004/0202_Small_Faint_and_Elusive_The_Search.html| archive-date = 2008-10-11}}</ref>