Editing 243 Ida (section)

== Composition ==
Ida was classified as an [[S-type asteroid]] based on the similarity of its reflectance spectra with similar asteroids.<ref name="WilsonKeilLove1999p479" /> S-types may share their composition with stony-iron or [[ordinary chondrite]] (OC) meteorites.<ref name="WilsonKeilLove1999p479" /> The composition of the interior has not been directly analyzed, but is assumed to be similar to OC material based on observed surface color changes and Ida's [[bulk density]] of 2.27–3.10 g/cm<sup>3</sup>.<ref name="Chapman1995p496" /><ref name="WilsonKeilLove1999p480">{{harvnb|Wilson|Keil|Love|1999|p=480}}</ref> OC meteorites contain varying amounts of the silicates [[olivine]] and [[pyroxene]], [[iron]], and [[feldspar]].<ref name="Lewis1996p89">{{harvnb|Lewis|1996|p=89}} {{quote|The chondrites fall naturally into five composition classes, of which three have very similar mineral contents, but different proportions of metal and silicates. All three contain abundant iron in three different forms (ferrous iron oxide in silicates, metallic iron, and ferrous sulfide), usually with all three abundant enough to be classified as potential ores. All three contain feldspar (an aluminosilicate of calcium, sodium, and potassium), pyroxene (silicates with one silicon atom for each atom of magnesium, iron, or calcium), olivine (silicates with two iron or magnesium atoms per silicon atom), metallic iron, and iron sulfide (the mineral [[troilite]]). These three classes, referred to collectively as the ordinary chondrites, contain quite different amounts of metal.}}</ref> Olivine and pyroxene were detected on Ida by ''Galileo''.<ref name="Holm1994" /> The mineral content appears to be homogeneous throughout its extent. ''Galileo'' found minimal variations on the surface, and the asteroid's spin indicates a consistent density.<ref name="ThomasProckter2004p21">{{harvnb|Thomas|Prockter|2004|p=21}}</ref><ref name="SullivanGreeleyPappalardoAsphaug1996p135">{{harvnb|Sullivan|Greeley|Pappalardo|Asphaug|1996|p=135}}</ref> Assuming that its composition is similar to OC meteorites, which range in density from 3.48 to 3.64 g/cm<sup>3</sup>, Ida would have a [[porosity]] of 11–42%.<ref name="WilsonKeilLove1999p480" />

Ida's interior probably contains some amount of impact-fractured rock, called ''[[regolith|megaregolith]]''. The megaregolith layer of Ida extends between hundreds of meters below the surface to a few kilometers. Some rock in Ida's core may have been fractured below the large craters Mammoth, Lascaux, and Undara.<ref name="SullivanGreeleyPappalardoAsphaug1996p135" />