Editing Galileo project (section)

===Atmospheric probe===
[[File:Descent Module.jpeg|thumb|right|Inner descent module of the ''Galileo'' entry probe|alt=Spherical spaccreaft with some portuding instruments]]
The descent probe awoke in response to an alarm at 16:00 UTC and began powering up its instruments. It passed through the [[rings of Jupiter]] and encountered a previously undiscovered [[radiation belt]] ten times as strong as Earth's [[Van Allen radiation belt]] {{convert|31,000|mi|order=flip|sp=us}} above Jupiter's cloud tops.{{sfn|Ragent|Colburn|Avrin|Rages|1996|pp=854–856 }}{{sfn|Meltzer|2007|pp=202–204}} It had been predicted that the probe would pass through three layers of clouds; an upper one consisting of [[ammonia]]-ice particles at a pressure of {{convert|0.5|to|0.6|bar|psi}}; a middle one of [[ammonium hydrosulfide]] ice particles at a pressure of {{convert|1.5|to|2|bar|psi}}; and one of water vapor at {{convert|4|to|5|bar|psi}}.{{sfn|Meltzer|2007|p=212}} The atmosphere through which the probe descended was much denser and hotter than expected. Jupiter was also found to have only half the amount of helium expected and the data did not support the three-layered cloud structure theory: only one significant cloud layer was measured by the probe, at a pressure of around {{convert|1.55|bar|psi}} but with many indications of smaller areas of increased particle densities along the whole length of its trajectory.{{sfn|Ragent|Colburn|Avrin|Rages|1996|pp=854–856 }}

The descent probe entered [[atmosphere of Jupiter|Jupiter's atmosphere]], defined for the purpose as being {{convert|450|km|sp=us}} above the {{convert|1|bar|psi|adj=on}} pressure level,{{sfn|Young|1998|p=22,776}} without any braking at 22:04 UTC on December 7, 1995. At this point it was moving at {{convert|170700|km/h|sp=us}} relative to Jupiter.<ref name="Probe Events">{{cite web |url=http://spaceprojects.arc.nasa.gov/Space_Projects/galileo_probe/htmls/probe_events.html |archive-url=https://web.archive.org/web/20070102143553/http://spaceprojects.arc.nasa.gov/Space_Projects/galileo_probe/htmls/probe_events.html |archive-date=January 2, 2007 |title=Galileo Probe Mission Events |publisher=NASA |url-status=dead |date=June 14, 1996 }}</ref> This was by far the most difficult [[atmospheric entry]] yet attempted by any spacecraft; the probe had to withstand a peak [[deceleration]] of {{convert|228|g0|lk=in|abbr=on}}.{{sfn|Heppenheimer|2009|p=257}}<ref>{{cite news |url=http://www.space.com/searchforlife/070719_seti_probing.html |title=Probing Planets: Can You Get There From Here? |first=Lisa |last=Chu-Thielbar |date=July 19, 2007 |publisher=[[Space.com]] |access-date=2007-07-27 |archive-date=February 12, 2009 |archive-url=https://web.archive.org/web/20090212005251/http://www.space.com/searchforlife/070719_seti_probing.html |url-status=live }}</ref> The rapid flight through the atmosphere produced a plasma with a temperature of about {{convert|14,000|C}}, and the probe's [[carbon phenolic]] heat shield lost more than half of its mass, {{convert|80|kg|sp=us}}, during the descent.{{sfn|Meltzer|2007|p=118}}<ref>{{cite web|url=http://spaceprojects.arc.nasa.gov/Space_Projects/galileo_probe/htmls/Heat_Shield.html |title=''Galileo'' Probe Heat Shield Ablation |first=Julio |last=Magalhães |publisher=NASA Ames Research Center |date=1997-09-17 |access-date=2006-12-12 |url-status=dead |archive-url=https://web.archive.org/web/20060929185050/http://spaceprojects.arc.nasa.gov/Space_Projects/galileo_probe/htmls/Heat_Shield.html |archive-date=2006-09-29 }}</ref><ref>{{cite web |url=http://spaceprojects.arc.nasa.gov/Space_Projects/galileo_probe/htmls/probe_spacecraft.html |title=The ''Galileo'' Probe Spacecraft |first=Julio |last=Magalhães |publisher=NASA Ames Research Center |date=1996-12-06 |access-date=2006-12-12 |url-status=dead |archive-url=https://web.archive.org/web/20070101114453/http://spaceprojects.arc.nasa.gov/Space_Projects/galileo_probe/htmls/probe_spacecraft.html |archive-date=2007-01-01 }}</ref> As the probe passed through Jupiter's cloud tops, it started transmitting data to the orbiter, {{convert|215000|km|sp=us}} above.{{sfn|Harland|2000|p=105}} The data was not immediately relayed to Earth, but a single bit was transmitted from the orbiter as a notification that the signal from the probe was being received and recorded, which would then take days to be transmitted using the LGA.{{sfn|Meltzer|2007|pp=202–204}}

The atmospheric probe deployed its {{convert|2.5|m|ft|abbr=off|adj=on|sp=us}} [[parachute]] fifty-three seconds later than anticipated, resulting in a small loss of upper-atmospheric readings. This was attributed to wiring problems with an accelerometer that determined when to begin the parachute deployment sequence. The probe then dropped its heat shield, which fell into Jupiter's interior.{{sfn|Harland|2000|p=105}}<ref name="gpr">{{cite web |url=http://www2.jpl.nasa.gov/sl9/gll38.html |title=Galileo Probe Science Results |date=January 22, 1996 |first1=Douglas |last1=Isbell |first2=David |last2=Morse |publisher=NASA/Jet Propulsion Laboratory |access-date=March 4, 2016 |archive-url=https://web.archive.org/web/20220424134149/http://www2.jpl.nasa.gov/sl9/gll38.html |archive-date=24 April 2022 }}</ref><ref>{{cite web |title=The Galileo Probe Mission Events Timeline |publisher=NASA |url=http://ccf.arc.nasa.gov/galileo_probe/htmls/probe_mission_events.html |archive-url=https://web.archive.org/web/19990424091538/http://ccf.arc.nasa.gov/galileo_probe/htmls/probe_mission_events.html |archive-date=1999-04-24 |url-status=dead |df=mdy-all}}</ref><ref>{{cite web |title=In Depth |publisher=Galileo – NASA Solar System Exploration |url=https://solarsystem.nasa.gov/missions/galileo/in-depth/ |access-date=6 March 2021 |archive-date=February 19, 2018 |archive-url=https://web.archive.org/web/20180219070520/https://solarsystem.nasa.gov/missions/galileo/in-depth/ |url-status=live }}</ref> The parachute reduced the probe's speed to {{convert|430|km/h|sp=us}}. The signal from the probe was no longer detected by the orbiter after 61.4 minutes, at an elevation of {{convert|112|miles|order=flip|sp=us}} below the cloud tops and a pressure of {{convert|22.7|atm|bar psi atm|order=out}}.<ref>{{cite web |title=In Depth Galileo Probe |url=https://solarsystem.nasa.gov/missions/galileo-probe/in-depth/ |website=NASA Solar System Exploration |access-date=3 July 2023 |archive-date=January 27, 2023 |archive-url=https://web.archive.org/web/20230127141502/https://solarsystem.nasa.gov/missions/galileo-probe/in-depth/ |url-status=live }}</ref> It was believed that the probe continued to fall at [[terminal velocity]], as the temperature increased to {{convert|1700|C}} and the pressure to {{convert|5000|atm|bar psi atm|order=out}}, destroying it.{{sfn|Meltzer|2007|pp=204–205}}

<gallery class="center" mode="packed" heights="240px">
File:Galileo Probe - AC81-0174.jpg|Artist's impression of the probe's entry into [[Atmosphere of Jupiter|Jupiter's atmosphere]] |alt=refer to caption
Image:Galileo atmospheric probe.jpg|Timeline of the probe's atmospheric entry |alt=Probe enters, deploys parachute, transmission ends 61.4 minutes after entry where the pressure is ~<!--(The Probe transmitted data to the Orbiter continuously for 57.6 minutes reaching a depth of 23 bars but the relay link to the Orbiter began at four minutes after entry, so transmission ended 61.4 minutes after entry.) -->
File:Jupiter's clouds.jpg|Jupiter's clouds – expected and actual results of ''Galileo''{{'}}s atmospheric probe mission |alt=The clouds of [[ammonia]] and [[ammonium sulfide]] were much thinner than expected, and clouds of water vapor were not detected.
</gallery>

The probe detected less lightning, less water, but stronger winds than expected. Scientists had expected to find wind speeds of up to {{convert|220|mph|order=flip|sp=us}}, but winds of up to {{convert|330|mph|order=flip|sp=us}} were detected. The implication was that the winds are not produced by heat generated by sunlight (as Jupiter gets less sunlight than Earth) or the condensation of water vapor (the main causes on Earth), but are due to an internal heat source. It was already well known that the atmosphere of Jupiter was mainly composed of hydrogen, but the clouds of [[ammonia]] and [[ammonium sulfide]] were much thinner than expected, and clouds of water vapor were not detected. This was the first observation of ammonia clouds in another planet's atmosphere. The atmosphere creates ammonia-ice particles from material coming up from lower depths.<ref name="endkit">{{cite web |url=https://solarsystem.nasa.gov/system/downloadable_items/1028_galileo-end_presskit.pdf |title=Galileo End of Mission Press Kit |access-date=October 29, 2011 |archive-date=October 23, 2020 |archive-url=https://web.archive.org/web/20201023104131/https://solarsystem.nasa.gov/system/downloadable_items/1028_galileo-end_presskit.pdf |url-status=live }}</ref>

The atmosphere was more turbulent than expected. Wind speeds in the outermost layers were {{convert|290|to|360|km/h|sp=us}}, in agreement with previous measurements from afar, but those wind speeds increased dramatically at pressure levels of {{convert|1|to|4|bar|psi}}, then remaining consistently high at around {{convert|170|m/s|km/h|disp=flip|sp=us}}.{{sfn|Atkinson|Ingersoll|Seiff|1997|pages=649–650}} The abundance of [[nitrogen]], [[carbon]] and [[sulfur]] was three times that of the Sun, raising the possibility that they had been acquired from other bodies in the Solar system,<ref>{{cite web |title=Galileo Probe Mission Science Summary |publisher=NASA |url=http://spaceprojects.arc.nasa.gov/Space_Projects/galileo_probe/htmls/Science_summary.html |archive-url=https://web.archive.org/web/20060221225640/http://spaceprojects.arc.nasa.gov/Space_Projects/galileo_probe/htmls/Science_summary.html |archive-date=2006-02-21 |url-status=dead |df=mdy-all}}</ref><ref name=gpr/> but the low abundance of water cast doubt on theories that Earth's water had been acquired from comets.<ref>{{cite news |title=Jupiter Retains Atmosphere of Mystery; Surprise Galileo Data Could Force New Theories of Planetary Formation|last=Sawyer |first=Kathy |newspaper=[[The Washington Post]] |date=January 23, 1996 |page=A.03 |url=https://www.washingtonpost.com/archive/politics/1996/01/23/jupiter-retains-atmosphere-of-mystery/07c4f386-749d-43d5-8adf-c9fa3fb1cc28/ |access-date=23 May 2024}}</ref>

There was far less lightning activity than expected, only about a tenth of the level of activity on Earth, but this was consistent with the lack of water vapor. More surprising was the high abundance of [[noble gas]]es ([[argon]], [[krypton]] and [[xenon]]), with abundances up to three times that found in the Sun. For Jupiter to trap these gases, it would have had to be much colder than today, around {{convert|-240|C|F|0}}, which suggested that either Jupiter had once been much further from the Sun, or that the interstellar debris that the Solar system had formed from was much colder than had been thought.<ref>{{cite press release |publisher=NASA/Jet Propulsion Laboratory |title=Galileo Probe Results Suggest Jupiter Had an Ancient, Chilly Past |url=https://www.jpl.nasa.gov/news/galileo-probe-results-suggest-jupiter-had-an-ancient-chilly-past/ |date=November 17, 1999 |access-date=January 19, 2021 |archive-date=November 30, 2021 |archive-url=https://web.archive.org/web/20211130054857/https://www.jpl.nasa.gov/news/galileo-probe-results-suggest-jupiter-had-an-ancient-chilly-past |url-status=live }}</ref>