Editing 243 Ida (section)

== Physical characteristics ==
{{Multiple image
| image1            = Asteroid size comparison.jpg
| image2            = 243 Ida rotation.jpg
| total_width       = 400
| align             = left
| direction         = horizontal
| alt1              = Size comparison of Ida
| caption1          = Size comparison of Ida, several other asteroids, the dwarf planet Ceres, and Mars
| alt2              = Images of Ida rotating
| caption2          = Successive images of a rotating Ida
}}
Ida's mass is between 3.65 and 4.99&nbsp;×&nbsp;10<sup>16</sup>&nbsp;kg.<ref name="PetitDurdaGreenbergHurford1997p179t180">{{harvnb|Petit|Durda|Greenberg|Hurford|1997|pp=179–180}}</ref> Its [[gravitational field]] produces an acceleration of about 0.3 to 1.1&nbsp;cm/s<sup>2</sup> over its surface.<ref name="ThomasBeltonCarcichChapman1996"/> This field is so weak that an astronaut standing on its surface could leap from one end of Ida to the other, and an object moving in excess of {{convert|20|m/s|ft/s|sigfig=1|abbr=on}} could [[escape velocity|escape]] the asteroid entirely.<ref name="GeisslerPetitDurdaGreenberg1996p142">{{harvnb|Geissler|Petit|Durda|Greenberg|1996|p=142}}</ref><ref name="LeeVeverkaThomasHelfenstein1996p99">{{harvnb|Lee|Veverka|Thomas|Helfenstein|1996|p=99}}</ref>

Ida is a distinctly elongated asteroid,<ref name="GeisslerPetitGreenberg1996p58">{{harvnb|Geissler|Petit|Greenberg|1996|p=58}}</ref> with an irregular surface.<ref name="Chapman1994p363">{{harvnb|Chapman|1994|p=363}}</ref><ref name="BottkeCellinoPaolicchiBinzel2002p10">{{harvnb|Bottke|Cellino|Paolicchi|Binzel|2002|p=10}}</ref> Ida is 2.35 times as long as it is wide,<ref name="GeisslerPetitGreenberg1996p58"/> and a "waist" separates it into two geologically dissimilar halves.<ref name="Chapman1996p707"/> This constricted shape is consistent with Ida being made of two large, solid components, with loose [[debris]] filling the gap between them. However, no such debris was seen in high-resolution images captured by ''Galileo''.<ref name="BottkeCellinoPaolicchiBinzel2002p10"/> Although there are a few steep slopes tilting up to about 50° on Ida, the slope generally does not exceed 35°.<ref name="ThomasBeltonCarcichChapman1996"/> Ida's irregular shape is responsible for the asteroid's very uneven gravitational field.<ref name="Cowen1995">{{harvnb|Cowen|1995}}</ref> The surface acceleration is lowest at the extremities because of their high rotational speed. It is also low near the "waist" because the mass of the asteroid is concentrated in the two halves, away from this location.<ref name="ThomasBeltonCarcichChapman1996"/>