Editing Planets beyond Neptune (section)

===Kuiper cliff and "Planet Ten"===
Additionally, speculation of a possible trans-Neptunian planet has revolved around the so-called "[[Kuiper Belt#Kuiper cliff|Kuiper cliff]]". The Kuiper belt terminates suddenly at a distance of {{convert|48|AU|e9km e9mi|abbr=unit}} from the Sun. Brunini and Melita have speculated that this sudden drop-off may be attributed to the presence of an object with a mass between those of Mars and Earth located beyond 48&nbsp;AU.<ref name="Brunini2002">{{Cite journal |last1=Brunini |first1=A |last2=M.D. Melita |name-list-style=amp |date=November 2002 |title=The Existence of a Planet beyond 50 AU and the Orbital Distribution of the Classical Edgeworth–Kuiper-Belt Objects |url=https://linkinghub.elsevier.com/retrieve/pii/S0019103502969356 |journal=Icarus |volume=160 |issue=1 |pages=32–43 |bibcode=2002Icar..160...32B |doi=10.1006/icar.2002.6935 |hdl-access=free |hdl=11336/37037}}</ref>

The presence of an object with a mass similar to that of Mars in a circular orbit at {{convert|60|AU|e9km e9mi|abbr=unit}} leads to a trans-Neptunian object population incompatible with observations. For instance, it would severely deplete the [[plutino]] population.<ref name=LykawaMukai/> Astronomers have not excluded the possibility of an object with a mass similar to that of Earth located farther than {{convert|100|AU|e9km e9mi|abbr=unit}} with an [[orbital eccentricity|eccentric]] and inclined orbit. Computer simulations by Patryk Lykawka of [[Kobe University]] have suggested that an object with a mass between {{earth mass|0.3~0.7}}, ejected outward by Neptune early in the Solar System's formation and currently in an elongated orbit between {{convert|101|and|200|AU|e9km e9mi|abbr=unit}} from the Sun, could explain the Kuiper cliff and the peculiar [[detached object]]s such as Sedna and {{mpl|2012 VP|113}}.<ref name=LykawaMukai />

Although some astronomers, such as Renu Malhotra and David Jewitt, have cautiously supported these claims, others, such as Alessandro Morbidelli, have dismissed them as "contrived".<ref name="planetx">{{Cite news |last=Schilling |first=Govert |date=2008-01-11 |title=The mystery of Planet&nbsp;X |url=http://allesoversterrenkunde.nl/#!/actueel/artikelen/_detail/gli/the-mystery-of-planet-x/ |access-date=2008-06-25 |work=[[New Scientist]] |pages=30–33 |df=dmy-all}}</ref> Malhotra & Volk (2017)<ref name=ARX-20170619/> argued that an unexpected variance in inclination for KBOs farther than the cliff at {{convert|50|AU|e9km e9mi|abbr=unit}} provided evidence of a possible Mars-sized planet, possibly up to {{earth mass|2.4}}, residing at the edge of the Solar System, which many news sources began referring to as "Planet&nbsp;Ten".<ref name=NSW-20170623>{{cite news |last=Osbourne |first=Hannah |date=23 June 2017 |title=Forget Planet&nbsp;9 - there's evidence of a tenth planet lurking at the edge of the solar system |magazine=[[Newsweek]] |url=http://www.newsweek.com/planet-10-lurking-edge-solar-system-628517 |access-date=23 June 2017 }}</ref><ref name=ARX-20170619>{{cite journal |last1=Volk |first1=Kathryn |last2=Malhotra |first2=Renu |year=2017 |title=The curiously warped mean plane of the Kuiper belt |journal=[[The Astronomical Journal]] |volume=154 |issue=2 |page=62 |bibcode=2017AJ....154...62V |s2cid=5756310 |arxiv=1704.02444 |doi=10.3847/1538-3881/aa79ff |doi-access=free }}</ref><ref>{{cite news |title=Planet 10? Another Earth-size world may lurk in the outer solar system |date=22 June 2017 |website=[[Space.com]]  |url=https://www.space.com/37295-possible-planet-10.html}}</ref><ref>{{cite web |url=https://www.science.org/content/article/forget-about-planet-nine-here-s-evidence-planet-10|title=Forget about Planet Nine. Here's evidence for Planet 10 |website=www.science.org}}</ref> Shortly after it was proposed, Lorenzo Iorio showed that the hypothetical planet's existence cannot be ruled out by [[Cassini (spacecraft)|Cassini]] ranging data.<ref>{{cite journal |last1=Iorio |first1=Lorenzo |year=2017 |title=Is the recently proposed Mars-sized perturber at 65–80&nbsp;{{sc|AU}} ruled out by the Cassini ranging data? |journal=Frontiers in Astronomy and Space Sciences |volume=4 |page=28 |doi=10.3389/fspas.2017.00028 |doi-access=free |arxiv=1407.5894 |bibcode=2017FrASS...4...28I |s2cid=26844167}}</ref>

Starting in 2018, several surveys have discovered multiple objects located beyond the Kuiper Cliff. Some of these new discoveries are close to the [[Heliopause (astronomy)|heliopause]] (120 AU) or well beyond it ({{mpl|2018 VG|18}}, {{mpl|2018 AG|37}}, {{mpl|2020 BE|102}}, {{mpl|2020 MK|53}}). An analysis of the TNO data available prior to September 2023 shows that there is a gap at about 72 AU, far from any mean-motion resonances with Neptune.<ref name="KuiperGap">{{Cite journal |last1=de La Fuente Marcos |first1=C. |last2=de La Fuente Marcos |first2=R. |date=October 2023 |title=Past the outer rim, into the unknown: structures beyond the Kuiper Cliff |journal=Monthly Notices of the Royal Astronomical Society: Letters |language=en |volume=527 |issue=1 |pages=L110–L114 |doi=10.1093/mnrasl/slad132 |doi-access=free |issn=1745-3925|arxiv=2309.03885 |bibcode=2024MNRAS.527L.110D }}</ref> Such a gap may have been induced by a massive perturber located further away.