Editing Galileo project (section)

===Callisto===
[[File:Callisto, moon of Jupiter, NASA.jpg|thumb|right|Callisto, photographed by ''Galileo'']]
Callisto is the outermost of the Galilean moons, and the most pockmarked, indeed the most of any body in the Solar system. So many craters must have taken billions of years to accumulate, which gave scientists the idea that its surface was as much as four billion years old, and provided a record of meteor activity in the Solar system. ''Galileo'' visited Callisto on orbits C3, C9 and C100 during the prime mission, and then on C20, C21, C22 and C23 during the GEM. When the cameras observed Callisto close up, there was a puzzling absence of small craters. The surface features appeared to have been eroded, indicating that they had been subject to active geological processes.{{sfn|Meltzer|2007|pp=273–277}}<ref name="The Galileo Mission to Jupiter and Its Moons">{{cite magazine |last=Johnson |first=Torrence V. |title=The Galileo Mission to Jupiter and Its Moons |magazine=Scientific American |issn=0036-8733 |volume=282 |issue=2 |date=February 2000 |pages=40–49 |doi=10.1038/scientificamerican0200-40 |jstor=26058599 |pmid=10710785 |bibcode=2000SciAm.282b..40J }}</ref>

''Galileo''{{'s}} flyby of Callisto on C3 marked the first time that the Deep Space Network operated a link between its antennae in Canberra and Goldstone that allowed them to [[aperture synthesis|operate as a gigantic array]], thereby enabling a higher bit rate. With the assistance of the antenna at Parkes, this raised the effective bandwidth to as much as 1,000 bits per second.<ref>{{cite press release |title=Galileo makes close pass by Callisto |date=November 4, 1996 |publisher=NASA/Jet Propulsion Laboratory |url=https://www.jpl.nasa.gov/news/galileo-makes-close-pass-by-callisto/ |access-date=January 19, 2021 |archive-date=November 30, 2021 |archive-url=https://web.archive.org/web/20211130052441/https://www.jpl.nasa.gov/news/galileo-makes-close-pass-by-callisto |url-status=live }}</ref>

Data accumulated on C3 indicated that Callisto had a homogeneous composition, with heavy and light elements intermixed. This was estimated to be composed of 60 percent [[silicate]], iron and iron sulfide rock and 40 percent water ice.{{sfn|Harland|2000|p=172}}<ref>{{cite press release |title=Galileo Returns New Insights into Callisto and Europa |date=May 23, 1997 |publisher=NASA/Jet Propulsion Laboratory |url=https://www.jpl.nasa.gov/news/galileo-returns-new-insights-into-callisto-and-europa/ |access-date=December 6, 2020 |archive-date=January 25, 2021 |archive-url=https://web.archive.org/web/20210125212928/https://www.jpl.nasa.gov/news/galileo-returns-new-insights-into-callisto-and-europa/ |url-status=live }}</ref> This was overturned by further radio Doppler observations on C9 and C10, which indicated that rock had settled towards the core, and therefore that Callisto indeed has a differentiated internal structure, although not as much so as the other Galilean moons.{{sfn|Meltzer|2007|pp=273–277}}<ref>{{cite press release |first=Jane |last=Pratt |title=Galileo Mission Finds Strange Interior of Jovian Moon |publisher=NASA |url=https://solarsystem.nasa.gov/news/141/galileo-mission-finds-strange-interior-of-jovian-moon/ |access-date=December 6, 2020 |archive-date=October 17, 2020 |archive-url=https://web.archive.org/web/20201017184949/https://solarsystem.nasa.gov/news/141/galileo-mission-finds-strange-interior-of-jovian-moon/ |url-status=live }}</ref>

[[File:Callisto diagram.svg|thumb|left|The internal structure of Callisto|alt=Cut away diagram of Ganymede, with a solid iron core successively surrounded by liquid iron and iron sulfide, rocky mantle, tetragonal ice, salt water and hexagonal ice.]]
Observations made with ''Galileo''{{'s}} magnetometer indicated that Callisto had no magnetic field of its own, and therefore lacked an iron core like Ganymede's, but that it did have an induced field from Jupiter's magnetosphere. Because ice is too poor a conductor to generate this effect, it pointed to the possibility that Callisto, like Europa and Ganymede, might have a subsurface ocean of brine.{{sfn|Meltzer|2007|pp=273–277}}<ref>{{cite press release |first=Jane |last=Pratt |title=Jupiter's Moon Callisto May Hide Salty Ocean |publisher=NASA |url=https://solarsystem.nasa.gov/news/145/jupiters-moon-callisto-may-hide-salty-ocean/ |access-date=December 6, 2020 |archive-date=December 6, 2020 |archive-url=https://web.archive.org/web/20201206005510/https://solarsystem.nasa.gov/news/145/jupiters-moon-callisto-may-hide-salty-ocean/ |url-status=live }}</ref> ''Galileo'' made its closest encounter with Callisto on C30, when it made a {{convert|138|km|adj=on|sp=us}} pass over the surface, during which it photographed the [[Asgard (crater)|Asgard]], [[Valhalla (crater)|Valhalla]] and Bran craters.{{sfn|Meltzer|2007|pp=273–277}} This was used for slingshot maneuvers to set up the final encounters with Io on I31 and I32.<ref>{{cite press release |first=Guy |last=Webster |title=Galileo Succeeds in its Closest Flyby of a Jovian Moon |publisher=NASA |url=https://solarsystem.nasa.gov/news/196/galileo-succeeds-in-its-closest-flyby-of-a-jovian-moon/ |access-date=December 6, 2020 |archive-date=December 26, 2020 |archive-url=https://web.archive.org/web/20201226145659/https://solarsystem.nasa.gov/news/196/galileo-succeeds-in-its-closest-flyby-of-a-jovian-moon/ |url-status=live }}</ref>{{Clear}}