Physical characteristics← Previous revisionRevision as of 04:17, 1 November 2026 Line 104: Line 104: The diameter of {{mp|2026 ED|138}} has not been measured but is inferred to be between {{cvt|600 and 1500|km|mi|sigfig=1}} based on the object's [[absolute magnitude#Solar System bodies (H)|absolute visual magnitude]] of {{val|3.19|0.04}} per Rubin Observatory estimates. The [[JPL Small-Body Database]] instead estimates the object's absolute magnitude as {{val|2.85|0.23}}. With an absolute magnitude of 3.19, {{mp|2026 ED|138}} would be the tenth brightest known TNO in terms of absolute magnitude, between {{dp|Chiminigagua}} and [[28978 Ixion|Ixion]]. With an absolute magnitude of 2.85, it would be the ninth, between {{dp|Quaoar}} and Chiminigagua. The diameter of {{mp|2026 ED|138}} has not been measured but is inferred to be between {{cvt|600 and 1500|km|mi|sigfig=1}} based on the object's [[absolute magnitude#Solar System bodies (H)|absolute visual magnitude]] of {{val|3.19|0.04}} per Rubin Observatory estimates. The [[JPL Small-Body Database]] instead estimates the object's absolute magnitude as {{val|2.85|0.23}}. With an absolute magnitude of 3.19, {{mp|2026 ED|138}} would be the tenth brightest known TNO in terms of absolute magnitude, between {{dp|Chiminigagua}} and [[28978 Ixion|Ixion]]. With an absolute magnitude of 2.85, it would be the ninth, between {{dp|Quaoar}} and Chiminigagua. The unknown diameter of {{mp|2026 ED|138}} stems from its unknown [[Geometric albedo|albedo]] or reflectivity: if it has a dark surface, it should be at the large end of its estimated size range, whereas if it has a bright surface, it should be at the small end.{{efn|The relationship between a Solar System body's diameter (D), albedo (p), and absolute magnitude (H) is mathematically written as D = \frac{1329 \mathrm{km}}{\sqrt{p}} \times 10^{-0.2H} (see [[Absolute magnitude#Solar System bodies (H)]]). What this equation shows is that the diameter must be small if the albedo is high, and conversely the diameter must be large if the albedo is low.}} Icy bodies in the upper end of this size range are expected to be rounded by their gravity, so {{mp|2026 ED|138}} is a [[dwarf planet candidate]]—potentially among the largest known. Its minimum likely diameter (at H = 3.19 and albedo = 0.25) would be comparable to that of [[Eris (dwarf planet)|Eris]]' moon [[Dysnomia (moon)|Dysnomia]],{{efn|Dysnomia's diameter is measured to be {{val|615|u=km}}, which is close to {{mp|2026 ED|138}}'s minimum diameter of 612 km.}} while its maximum diameter (at H = 2.62 and albedo = 0.04) would approach that of Eris. If its albedo were 0.10, seen in several large TNOs, and H = 3.19, its diameter would be about {{cvt|970|km|mi|sigfig=2}}, comparable to that of [[Ceres (dwarf planet)|Ceres]]. A diameter between 612 and 968 km (H = 3.15–3.23 and albedo = 0.25–0.10) is considered likely.{{rp|9}} The unknown diameter of {{mp|2026 ED|138}} stems from its unknown [[Geometric albedo|albedo]] or reflectivity: if it has a dark surface, it should be at the large end of its estimated size range, whereas if it has a bright surface, it should be at the small end.{{efn|The relationship between a Solar System body's diameter (D), albedo (p), and absolute magnitude (H) is mathematically written as D = \frac{1329 \mathrm{km}}{\sqrt{p}} \times 10^{-0.2H} (see [[Absolute magnitude#Solar System bodies (H)]]). What this equation shows is that the diameter must be small if the albedo is high, and conversely the diameter must be large if the albedo is low.}} Icy bodies in the upper end of this size range are expected to be rounded by their gravity, so {{mp|2026 ED|138}} is a [[dwarf planet candidate]]—potentially among the largest known. Its minimum likely diameter (at H = 3.19 and albedo = 0.25) would be comparable to that of [[Eris (dwarf planet)|Eris]]' moon [[Dysnomia (moon)|Dysnomia]],{{efn|Dysnomia's diameter is measured to be {{val|615|u=km}}, which is close to {{mp|2026 ED|138}}'s minimum diameter of 612 km.}} while its maximum diameter (at H = 2.85 and albedo = 0.04) would approach that of Eris. If its albedo were 0.10, seen in several large TNOs, and H = 3.19, its diameter would be about {{cvt|968|km|mi|sigfig=2}}, comparable to that of [[Ceres (dwarf planet)|Ceres]]. A diameter between 612 and 968 km (H = 3.15–3.23 and albedo = 0.25–0.10) is considered likely.{{rp|9}} Regardless of its size, {{mp|2026 ED|138}} is unlikely to hold an [[atmosphere]] containing either [[methane]], [[carbon monoxide]], or [[nitrogen]] because it would [[atmospheric escape|entirely escape from its surface]] over the age of the Solar System. The theoretical albedo limit for retaining carbon monoxide is