Editing 243 Ida (section)

=== Physical characteristics ===
Dactyl is an "egg-shaped"<ref name="Chapman1996p709" /> but "remarkably spherical"<ref name="Schmadel2003p37" /> object measuring {{convert|1.6 by 1.4 by 1.2|km|mi}}.<ref name="Chapman1996p709" /> It is oriented with its longest axis pointing towards Ida.<ref name="Chapman1996p709" /> Like Ida, Dactyl's surface exhibits saturation cratering.<ref name="Chapman1996p709" /> It is marked by more than a dozen craters with a diameter greater than {{convert|80|m|ft|abbr=on}}, indicating that the moon has suffered many collisions during its history.<ref name="NASA2005" /> At least six craters form a linear chain, suggesting that it was caused by locally produced debris, possibly ejected from Ida.<ref name="Chapman1996p709" /> Dactyl's craters may contain central peaks, unlike those found on Ida.<ref name="AsphaugRyanZuber2003p463">{{harvnb|Asphaug|Ryan|Zuber|2003|p=463}}</ref> These features, and Dactyl's [[spheroid]]al shape, imply that the moon is gravitationally controlled despite its small size.<ref name="AsphaugRyanZuber2003p463" /> Like Ida, its average temperature is about {{convert|200|K|C F|abbr=on}}.<ref name="Holm1994" />

Dactyl shares many characteristics with Ida. Their [[albedo]]s and reflection [[Spectrum|spectra]] are very similar.<ref name="ChapmanKlaasenBeltonVeverka1994p455">{{harvnb|Chapman|Klaasen|Belton|Veverka|1994|p=455}}</ref> The small differences indicate that the space weathering process is less active on Dactyl.<ref name="Chapman1995p496" /> Its small size would make the formation of significant amounts of [[regolith]] impossible.<ref name="Chapman1995p496" /><ref name="BeltonCarlson1994" /> This contrasts with Ida, which is covered by a deep layer of regolith.

The two largest imaged craters on Dactyl were named Acmon {{IPAc-en|ˈ|æ|k|m|ə|n}} and Celmis {{IPAc-en|ˈ|s|ɛ|l|m|ᵻ|s}}, after two of the mythological dactyls. Acmon is the largest crater in the above image, and Celmis is near the bottom of the image, mostly obscured in shadow. The craters are 300 and 200 meters in diameter, respectively.<ref name=dactylnamedfeatures>{{cite web|title=Planetary Names: Dactyl|url=http://planetarynames.wr.usgs.gov/Page/DACTYL/target|publisher=IAU|access-date=18 July 2015|archive-url=https://web.archive.org/web/20150701152709/http://planetarynames.wr.usgs.gov/Page/DACTYL/target|archive-date=2015-07-01|url-status=dead}}</ref>