Editing Protoplanet (section)

==Evidence in the Solar System - surviving remnant protoplanets==
In the case of the [[Solar System]], it is thought that the collisions of planetesimals created a few hundred planetary embryos. Such embryos were similar to [[Ceres (dwarf planet)|Ceres]] and [[Pluto]] with masses of about 10<sup>22</sup> to 10<sup>23</sup>&nbsp;kg and were a few thousand kilometers in diameter.{{fact|date=October 2022}}

According to the [[giant impact hypothesis]], the [[Moon]] formed from a colossal impact of a hypothetical protoplanet called [[Theia (planet)|Theia]] with Earth, early in the [[Formation and evolution of the Solar System|Solar System's history]].<ref name="Nace2016">{{cite web
 |last1=Nace |first1=Trevor
 |title = New Evidence For 4.5 Billion Year Old Impact Formed Our Moon
 |work = [[Forbes]]
 |url = https://www.forbes.com/sites/trevornace/2016/01/30/new-evidence-4-5-billion-year-old-impact-formed-moon/
 |date = 2016-01-30
 |access-date = 2016-01-30
}}</ref><ref>{{cite journal |last1=Young |first1=E. D. |last2=Kohl |first2=I. E. |last3=Warren |first3=P. H. |last4=Rubie |first4=D. C. |last5=Jacobson |first5=S. A. |last6=Morbidelli |first6=A. |title=Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact |journal=Science |date=28 January 2016 |volume=351 |issue=6272 |pages=493–496 |doi=10.1126/science.aad0525|pmid=26823426 |arxiv=1603.04536 |bibcode=2016Sci...351..493Y |s2cid=6548599 }}</ref><ref>{{cite web|last1=Wolpert|first1=Stuart|title=Moon was produced by a head-on collision between Earth and a forming planet|date=January 28, 2016|url=http://newsroom.ucla.edu/releases/moon-was-produced-by-a-head-on-collision-between-earth-and-a-forming-planet|website=UCLA newsroom|publisher=UCLA}}</ref>

In the inner Solar System, the three protoplanets to survive more-or-less intact are the [[asteroid]]s [[Ceres (dwarf planet)|Ceres]], [[2 Pallas|Pallas]], and [[4 Vesta|Vesta]]. [[16 Psyche|Psyche]] is likely the survivor of a violent hit-and-run with another object that stripped off the outer, rocky layers of a protoplanet.<ref name=NASA15-196>{{cite web|url=http://www.nasa.gov/press-release/nasa-selects-investigations-for-future-key-planetary-mission|title=NASA Selects Investigations for Future Key Planetary Mission|date=30 September 2015 }}</ref> The asteroid [[9 Metis|Metis]] may also have a similar origin history to that of Psyche.<ref name="Kelley00">{{cite journal|last=Kelley |first=Michael S|author2=Michael J. Gaffey
|title=9 Metis and 113 Amalthea: A Genetic Asteroid Pair|journal=Icarus|volume=144 |issue=1 |pages=27–38 |date=2000|doi=10.1006/icar.1999.6266 |bibcode=2000Icar..144...27K}}</ref> The asteroid [[21 Lutetia|Lutetia]] also has characteristics that resemble a protoplanet.<ref>{{cite web
|title = BIG PIC: 2 Pallas, the Asteroid with Protoplanetary Attitude|work = Discovery Space| publisher = [[Discovery Communications]]| date = 2009-10-08| url = http://dsc.discovery.com/space/big-pic/hubble-pallas-asteroid-protoplanet.html| access-date = 2009-10-08}}</ref><ref>{{cite web| last = Klotz| first = Irene| title = ASTEROID FAILS TO MAKE IT BIG: A newly studied asteroid is actually a planetary building block that stopped growing.| work = [[Discovery News]]| publisher = [[Discovery Communications]]| date = 2011-10-27|url=http://news.discovery.com/space/asteroid-protoplanet-lutetia-rosetta-111027.html| access-date = 2011-10-27}}</ref> [[Kuiper belt|Kuiper-belt]] [[dwarf planet]]s have also been referred to as protoplanets.<ref name=msnbc>{{cite web|date=2009-10-08|title=Protoplanet frozen in time|publisher=[[MSNBC]]|author=Alan Boyle|url=http://cosmiclog.msnbc.msn.com/archive/2009/10/08/2092402.aspx|archive-url=https://web.archive.org/web/20091010023833/http://cosmiclog.msnbc.msn.com/archive/2009/10/08/2092402.aspx|url-status=dead|archive-date=2009-10-10|access-date=2009-09-12}}</ref> Because [[iron meteorite]]s have been found on Earth, it is deemed likely that there once were other metal-cored protoplanets in the [[asteroid belt]] that since have been disrupted and that are the source of these meteorites.{{fact|date=October 2022}}