Editing 5145 Pholus (section)

== Physical characteristics ==
=== Spectral type and color ===
After its discovery, Pholus was quickly found to be very red in color. The color has been speculated to be due to organic compounds on its surface.<ref name="Wilson-1994" /> It is classified as a Z-class object on the [[Tholen classification|Tholen]] taxonomic scheme.<ref name="jpldata" />

The object has been classified by astronomers as [[Trans-Neptunian object#Colours|RR]] and [[Trans-Neptunian object#Colours|RR-U]] type, respectively.<ref name="Perna-2010" /><ref name="Belskaya-2015" /> Polarimetric observations with ESO's [[Very Large Telescope]] in 2007 and 2008, revealed noticeable negative polarization at certain phase angles, distinctly different from that of trans-Neptunian objects. Pholus appears to have a rather homogeneous surface with a small amount of water frost on its darker regions.<ref name="Belskaya-2015" />

The surface composition of Pholus has been estimated from its reflectance spectrum using two spatially segregated components:<ref name="Cruikshank-1998" /> dark [[amorphous carbon]] and an intimate mixture of [[water]] ice, [[methanol]] ice, [[olivine]] grains, and complex organic compounds ([[tholin]]s). The [[carbon black]] component was used to match the low [[albedo]] of the object. Unlike [[2060 Chiron|Chiron]], Pholus has shown no signs of [[comet]]ary activity.

=== Diameter and albedo ===
Diameter calculations range from 99 to 190 kilometers with a corresponding [[Geometric albedo|albedo]] between 0.155 and 0.04.<ref name="johnstonsarchive-TNO-list" /><ref name="Tegler-2005" /><ref name="Duffard-2014" /><ref name="lcdb" /><ref name="Davies-1995" />

According to the [[Herschel Space Observatory]] with its [[Herschel Space Observatory#PACS|PACS]] instrument, Pholus measures 99 kilometers in diameter and its surface has an [[astronomical albedo|albedo]] of 0.155,<ref name="Duffard-2014" /> while a study from 1996 derived a diameter of 185&nbsp;km.<ref name="Davies-1995" /> During 2003–2004, observations with the 1.8-meter [[Vatican Advanced Technology Telescope]] (VATT) on [[Mount Graham Observatory]], Arizona, determined an elongated shape, {{val|310|x|160|x|150|u=km}}, with a mean diameter of 190 kilometers, based on a low albedo of 0.04.<ref name="Tegler-2005" /> Johnston's archive lists a diameter of 107&nbsp;km with an albedo of 0.126,<ref name="johnstonsarchive-TNO-list" /> and ''Collaborative Asteroid Lightcurve Link'' assumes a standard albedo of a [[C-type asteroid|carbonaceous]] body of 0.057 and derives a diameter of 165&nbsp;km based on an [[absolute magnitude]] of 7.64.<ref name="lcdb" />

=== Rotation period ===
In March 2005, a rotational [[lightcurve]] of Pholus was obtained from [[Photometry (astronomy)|photometric]] observations by Tegler using the VATT at Mount Graham. Lightcurve analysis gave a [[rotation period]] of 9.980 hours with a brightness amplitude of 0.60 [[Magnitude (astronomy)|magnitude]] ({{small|[[LCDB quality code|U=3-]]}}).<ref name="Tegler-2005" /> Alternative period determinations were also conducted by Hoffmann, Franham, and Buie with concurring results of 9.977, 9.982, and 9.983 hours, respectively ({{small|[[LCDB quality code|U=3/3/3]]}}).<ref name="Hoffmann-1992" /><ref name="Farnham-2001b" /><ref name="Buie-1992" />