Editing 243 Ida (section)

{{short description|Main-belt asteroid}}
{{About|an asteroid|other uses|Ida (disambiguation)}}
{{pp-move-indef}}
{{Infobox planet
| background = #D6D6D6
| minorplanet = yes
| mpc_name = (243) Ida
| name = Ida
|named_after=[[Ida (nurse of Zeus)]]
| pronounced = {{IPAc-en|ˈ|aɪ|d|ə}}<ref>Noah Webster (1884) ''A Practical Dictionary of the English Language''</ref>
| adjectives = Idean (Idæan) {{IPAc-en|aɪ|ˈ|d|iː|ə|n}}<ref>{{OED|Idæan}}</ref>
| image = File:243 ida crop.jpg
| image_scale =
| caption = ''[[Galileo (spacecraft)|Galileo]]'' image of 243 Ida. [[Pola Regio]] is located on the right "tip" of the asteroid. The dot to the right is its moon [[Dactyl (moon)|Dactyl]].
| discovery_ref = <ref name="Raab2002"/>
| discoverer = [[Johann Palisa]]
| discovery_site = [[Vienna Observatory]]
| discovered = September 29, 1884
| mp_category = Main belt ([[Koronis family]])<ref name="Holm1994"/>
| orbit_ref = <ref name="JPL2008">{{harvnb|JPL|2008}}</ref>
| epoch = 31 July 2016 ([[Julian day|JD]] 2457600.5)
| semimajor = {{convert|2.861|AU|m|abbr=on}}
| perihelion = {{convert|2.743|AU|m|abbr=on}}
| aphelion = {{convert|2.979|AU|m|abbr=on}}
| eccentricity = 0.0411
| period = {{convert|1767.644|d|yr}}
| inclination = 1.132°
| asc_node = 324.016°
| arg_peri = 110.961°
| mean_anomaly = 38.707°
| avg_speed = 0.2036°/d
| satellites = Dactyl
| dimensions = 59.8 × 25.4 × 18.6&nbsp;km<ref name="Belton1996">{{harvnb|Belton et al.|1996}}</ref>
| mean_radius = 15.7&nbsp;km<ref name="BrittYeomansHousenConsolmagno2002p486">{{harvnb|Britt|Yeomans|Housen|Consolmagno|2002|p=486}}</ref>
| mass = 4.2 ± 0.6 ×10<sup>16</sup>&nbsp;kg<ref name="BrittYeomansHousenConsolmagno2002p486"/>
| density = 2.6 ± 0.5&nbsp;g/cm<sup>3</sup><ref name="Belton1995"/>
| surface_grav = 0.3–1.1&nbsp;cm/s<sup>2</sup><ref name="ThomasBeltonCarcichChapman1996"/>
| rotation = {{convert|4.63|h|d}}<ref name="VokrouhlickyNesvornyBottke2003p147"/>
| spectral_type = [[S-type asteroid|S]]<ref name="WilsonKeilLove1999p479"/>
| abs_magnitude = 9.94<ref name="JPL2008"/>
| albedo = 0.2383<ref name="JPL2008"/>
| right_asc_north_pole = 168.76°<ref name="Archinal2018"/>
| declination = −87.12°<ref name="Archinal2018"/>
| single_temperature = {{convert|200|K|C}}<ref name="Holm1994"/>
}}

'''243 Ida''' is an [[asteroid]] in the [[Koronis family]] of the [[asteroid belt]]. It was discovered on 29 September 1884 by Austrian astronomer [[Johann Palisa]] at [[Vienna Observatory]] and named after [[Ida (nurse of Zeus)|a nymph from Greek mythology]]. Later telescopic observations categorized Ida as an [[S-type asteroid]], the most numerous type in the inner [[asteroid belt]]. On 28 August 1993, Ida was visited by the uncrewed ''[[Galileo (spacecraft)|Galileo]]'' spacecraft while en route to [[Jupiter]]. It was the second asteroid visited by a spacecraft and the first found to have a natural satellite.

Ida's orbit lies between the planets [[Mars]] and Jupiter, like all main-belt asteroids. Its orbital period is 4.84 years, and its rotation period is 4.63 hours. Ida has an average diameter of {{convert|31.4|km|mi|abbr=on}}. It is irregularly shaped and elongated, apparently composed of two large objects connected together. Its surface is one of the most heavily cratered in the Solar System, featuring a wide variety of crater sizes and ages.

Ida's moon [[Dactyl (moon)|Dactyl]] was discovered by mission member Ann Harch in images returned from ''Galileo''. It was named after the [[Dactyls (mythology)|Dactyls]], creatures which inhabited Mount Ida in Greek mythology. Dactyl is only {{convert|1.4|km|mi}} in diameter, about 1/20 the size of Ida. Its orbit around Ida could not be determined with much accuracy, but the constraints of possible orbits allowed a rough determination of Ida's density and revealed that it is depleted of metallic minerals. Dactyl and Ida share many characteristics, suggesting a common origin.

The images returned from ''Galileo'' and the subsequent measurement of Ida's mass provided new insights into the geology of S-type asteroids. Before the ''Galileo'' flyby, many different theories had been proposed to explain their mineral composition. Determining their composition permits a correlation between meteorites falling to the Earth and their origin in the asteroid belt. Data returned from the flyby pointed to S-type asteroids as the source for the [[ordinary chondrite]] meteorites, the most common type found on the Earth's surface.