Editing 243 Ida (section)

=== Orbit ===
[[File:Dactyl potential orbits.svg|thumb|Diagram of potential orbits of Dactyl around Ida|left]]
Dactyl's orbit around Ida is not precisely known. ''Galileo'' was in the [[orbital plane|plane]] of Dactyl's orbit when most of the images were taken, which made determining its exact orbit difficult.<ref name="ByrnesD'Amario1994" /> Dactyl orbits in the [[retrograde and prograde motion|prograde]] direction<ref name="PetitDurdaGreenbergHurford1997p179">{{harvnb|Petit|Durda|Greenberg|Hurford|1997|p=179}}</ref> and is inclined about 8° to Ida's equator.<ref name="PetitDurdaGreenbergHurford1997p177" /> Based on computer simulations, Dactyl's [[apsis|pericenter]] must be more than about {{convert|65|km|mi|abbr=on}} from Ida for it to remain in a stable orbit.<ref name="PetitDurdaGreenbergHurford1997p195">{{harvnb|Petit|Durda|Greenberg|Hurford|1997|p=195}}</ref> The range of orbits generated by the simulations was narrowed down by the necessity of having the orbits pass through points at which ''Galileo'' observed Dactyl to be at 16:52:05 UT on 28 August 1993, about {{convert|90|km|mi|abbr=on}} from Ida at longitude 85°.<ref name="PetitDurdaGreenbergHurford1997p188">{{harvnb|Petit|Durda|Greenberg|Hurford|1997|p=188}}</ref><ref name="PetitDurdaGreenbergHurford1997p193">{{harvnb|Petit|Durda|Greenberg|Hurford|1997|p=193}}</ref> On 26 April 1994, the [[Hubble Space Telescope]] observed Ida for eight hours and was unable to spot Dactyl. It would have been able to observe it if it were more than about {{convert|700|km|mi|abbr=on}} from Ida.<ref name="ByrnesD'Amario1994" />

If in a circular orbit at the distance at which it was seen, Dactyl's orbital period would be about 20 hours.<ref name="ChapmanKlaasenBeltonVeverka1994p455" /> Its orbital speed is roughly {{convert|10|m/s|ft/s|abbr=on}}, "about the speed of a fast run or a slowly thrown baseball".<ref name="ByrnesD'Amario1994" />