Editing Comet Hyakutake (section)

=== Spacecraft passes through the tail ===
[[File:Animation of Ulysses trajectory.gif|thumb|right|Animation of ''Ulysses''{{'}} trajectory from 6 October 1990 to 29 June 2009<br/>{{legend2|magenta|''Ulysses''}}{{·}}{{legend2|Royalblue|[[Earth]]}}{{·}}{{legend2|Gold|[[Jupiter]]}}{{·}}{{legend2|Cyan|[[C/2006 P1]]}}{{·}}{{legend2|Lime|C/1996 B2}}{{·}}{{legend2|OrangeRed|[[C/1999 T1]]}}]]
The [[Ulysses (spacecraft)|''Ulysses'' spacecraft]] made an unexpected pass through the tail of the comet on 1 May 1996.{{r|physicsworld1}} Evidence of the encounter was not noticed until 1998. Astronomers analysing old data found that ''Ulysses''{{'}} instruments had detected a large drop in the number of [[proton]]s passing, as well as a change in the direction and strength of the local [[magnetic field]]. This implied that the spacecraft had crossed the 'wake' of an object, most likely a comet; the object responsible was not immediately identified.{{r|Jones_2002}}

In 2000, two teams independently analyzed the same event. The [[magnetometer]] team realized that the changes in the direction of the magnetic field mentioned above agreed with the "draping" pattern expected in a comet's ion, or plasma tail. The magnetometer team looked for likely suspects. No known comets were located near the satellite, but looking further afield, they found that Hyakutake, {{convert|500|e6km|AU|abbr=unit}} away, had crossed ''Ulysses''{{'}} orbital plane on 23 April 1996. The [[solar wind]] had a velocity at the time of about {{cvt|750|km/s}}, at which speed it would have taken eight days for the tail to be carried out to where the spacecraft was situated at 3.73&nbsp;AU, approximately 45 degrees out of the [[ecliptic]] plane. The orientation of the ion tail inferred from the magnetic field measurements agreed with the source lying in Comet Hyakutake's orbital plane.{{r|Jones_2000}}

The other team, working on data from the spacecraft's ion composition spectrometer, discovered a sudden large spike in detected levels of [[ion]]ised particles at the same time. The relative abundances of chemical elements detected indicated that the object responsible was definitely a comet.{{r|Gloeckler_2000}}

Based on the ''Ulysses'' encounter, the comet's tail is known to have been at least 570&nbsp;million&nbsp;km (360&nbsp;million&nbsp;miles; 3.8&nbsp;AU) long. This is almost twice as long as the previous longest-known cometary tail, that of the [[Great Comet of 1843]], which was 2&nbsp;AU long.{{r|Jones_2000}} This  record was broken in 2002 by comet [[153P/Ikeya–Zhang]], which had a tail-length of at least {{val|7.46|u=AU}}.{{r|Jones_2006}}