Editing 243 Ida (section)

=== Discoveries ===
The data returned from the ''Galileo'' flybys of Gaspra and Ida, and the later ''[[NEAR Shoemaker]]'' asteroid mission, permitted the first study of asteroid [[geology]].<ref name="GeisslerPetitGreenberg1996p57">{{harvnb|Geissler|Petit|Greenberg|1996|p=57}}</ref> Ida's relatively large surface exhibited a diverse range of geological features.<ref name="ChapmanBeltonVeverkaNeukum1994p238">{{harvnb|Chapman|Belton|Veverka|Neukum|1994|p=238}}</ref> The discovery of Ida's moon [[Dactyl (moon)#Dactyl|Dactyl]], the first confirmed satellite of an asteroid, provided additional insights into Ida's composition.<ref name="Chapman1996p709">{{harvnb|Chapman|1996|p=709}}</ref>

Ida is classified as an [[S-type asteroid]] based on ground-based [[Spectroscopy|spectroscopic measurements]].<ref name="ByrnesD'Amario1994">{{harvnb|Byrnes|D'Amario|1994}}</ref> The composition of S-types was uncertain before the ''Galileo'' flybys, but was interpreted to be either of two minerals found in meteorites that had fallen to the Earth: [[ordinary chondrite]] (OC) and [[Stony-iron meteorite|stony-iron]].<ref name="WilsonKeilLove1999p479">{{harvnb|Wilson|Keil|Love|1999|p=479}}</ref> Estimates of Ida's density are constrained to less than 3.2&nbsp;g/cm<sup>3</sup> by the long-term stability of Dactyl's orbit.<ref name="ByrnesD'Amario1994" /> This all but rules out a stony-iron composition; were Ida made of 5&nbsp;g/cm<sup>3</sup> iron- and nickel-rich material, it would have to contain more than 40% empty space.<ref name="Chapman1996p709" />

The Galileo images also led to the discovery that [[space weathering]] was taking place on Ida, a process which causes older regions to become more red in color over time.<ref name="Chapman1996p700">{{harvnb|Chapman|1996|p=700}}</ref><ref name="Chapman1996p710">{{harvnb|Chapman|1996|p=710}}</ref> The same process affects both Ida and its moon, although Dactyl shows a lesser change.<ref name="Chapman1995p496">{{harvnb|Chapman|1995|p=496}}</ref> The weathering of Ida's surface revealed another detail about its composition: the reflection spectra of freshly exposed parts of the surface resembled that of OC meteorites, but the older regions matched the spectra of S-type asteroids.<ref name="Chapman1996p699" />[[File:NWA869Meteorite.jpg|thumb|Polished section of an [[ordinary chondrite]] meteorite]]Both of these discoveries—the space weathering effects and the low density—led to a new understanding about the relationship between S-type asteroids and OC meteorites. S-types are the most numerous kind of asteroid in the inner part of the asteroid belt.<ref name="Chapman1996p699"/> OC meteorites are, likewise, the most common type of meteorite found on the Earth's surface.<ref name="Chapman1996p699"/> The reflection spectra measured by remote observations of S-type asteroids, however, did not match that of OC meteorites. The ''Galileo'' flyby of Ida found that some S-types, particularly the Koronis family, could be the source of these meteorites.<ref name="Chapman1995p496"/>