Editing 243 Ida (section)

== Exploration ==
=== ''Galileo'' flyby ===
Ida was visited in 1993 by the [[Jupiter]]-bound space probe ''[[Galileo (spacecraft)|Galileo]]''. Its encounters of the asteroids [[951 Gaspra|Gaspra]] and Ida were secondary to the Jupiter mission. These were selected as targets in response to a new NASA policy directing mission planners to consider asteroid flybys for all spacecraft crossing the belt.<ref name="D'AmarioBrightWolf1992p26">{{harvnb|D'Amario|Bright|Wolf|1992|p=26}}</ref> No prior missions had attempted such a flyby.<ref name="Chapman1996p699">{{harvnb|Chapman|1996|p=699}}</ref> ''Galileo'' was launched into orbit by the [[Space Shuttle Atlantis|Space Shuttle ''Atlantis'']] mission [[STS-34]] on 18 October 1989.<ref name="D'AmarioBrightWolf1992p24">{{harvnb|D'Amario|Bright|Wolf|1992|p=24}}</ref> Changing ''Galileo's'' trajectory to approach Ida required that it consume {{convert|34|kg|lb|abbr=on}} of [[propellant]].<ref name="D'AmarioBrightWolf1992p72">{{harvnb|D'Amario|Bright|Wolf|1992|p=72}}</ref> Mission planners delayed the decision to attempt a flyby until they were certain that this would leave the spacecraft enough propellant to complete its Jupiter mission.<ref name="D'AmarioBrightWolf1992p36">{{harvnb|D'Amario|Bright|Wolf|1992|p=36}}</ref>

''Galileo's'' trajectory carried it into the asteroid belt twice on its way to Jupiter. During its second crossing, it flew by Ida on 28 August 1993 at a speed of {{convert|12400|m/s|abbr=on}} relative to the asteroid.<ref name="D'AmarioBrightWolf1992p36"/> The onboard imager observed Ida from a distance of {{convert|240350|km|mi|abbr=on|sigfig=5}} to its closest approach of {{convert|2390|km|mi|abbr=on|sigfig=3}}.<ref name="NASA2005"/><ref name="SullivanGreeleyPappalardoAsphaug1996p120">{{harvnb|Sullivan|Greeley|Pappalardo|Asphaug|1996|p=120}}</ref> Ida was the second asteroid, after Gaspra, to be imaged by a spacecraft.<ref name="Cowen1993p215">{{harvnb|Cowen|1993|p=215}} {{quote|Nearly a month after a successful photo session, the Galileo spacecraft last week finished radioing to Earth a high-resolution portrait of the second asteroid ever to be imaged from space. Known as 243 Ida, the asteroid was photographed from an average distance of just 3,400 kilometers some 3.5 minutes before Galileo's closest approach on Aug. 28.}}</ref> About 95% of Ida's surface came into view of the probe during the flyby.<ref name="ThomasBeltonCarcichChapman1996">{{harvnb|Thomas|Belton|Carcich|Chapman|1996}}</ref>

Transmission of many Ida images was delayed due to a permanent failure in the spacecraft's [[directional antenna|high-gain antenna]].<ref name="Chapman1994p358">{{harvnb|Chapman|1994|p=358}}</ref> The first five images were received in September 1993.<ref name="Chapman1996p707">{{harvnb|Chapman|1996|p=707}}</ref> These comprised a high-resolution [[Image stitching|mosaic]] of the asteroid at a resolution of 31–38&nbsp;m/[[pixel]].<ref name="ChapmanBeltonVeverkaNeukum1994p237">{{harvnb|Chapman|Belton|Veverka|Neukum|1994|p=237}}</ref><ref name="GreeleySullivanPappalardoVeverka1994p469">{{harvnb|Greeley|Sullivan|Pappalardo|Veverka|1994|p=469}}</ref> The remaining images were sent in February 1994,<ref name="Holm1994" /> when the spacecraft's proximity to the Earth allowed higher speed transmissions.<ref name="Chapman1996p707"/><ref name="MonetStoneMonetDahn1994p2293">{{harvnb|Monet|Stone|Monet|Dahn|1994|p=2293}}</ref>

{{Multiple image
| direction         = horizontal
| image1            = Animation of Galileo trajectory.gif
| image2            = Galileo trajectory Ida.svg
| total_width       = 600
| image3            = Ida-approach.gif
| alt1              = Animation of Galileo's trajectory
| caption1          = Animation of ''Galileo''{{'s}} trajectory from 19 October 1989 to 30 September 2003 <br /> {{legend2|magenta|''Galileo''}}{{·}}{{legend2|lime|[[Jupiter]]}}{{·}}{{legend2|royalblue|[[Earth]]}}{{·}}{{legend2|PaleGreen| [[Venus]]}}{{·}}{{legend2| Gold |[[951 Gaspra]]}}{{·}}{{legend2| Cyan |243 Ida}}
| alt2              = Trajectory of Galileo
| caption2          = Trajectory of Galileo from launch to Jupiter orbital insertion
| caption3          = Images from the flyby, starting 5.4 hours before closest approach and showing Ida's rotation
| alt3              = Images from the flyby
| align             = center
}}

=== 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"/>