Editing Halley's Comet (section)

===After 1986===
[[File:ESO-Comet Halley at 28 AU-phot-27a-03-fullres.jpg|thumb|right|Halley's Comet observed in 2003 at 28 au from the Sun|alt=Grainy, white-on-black image showing Halley as a barely distinguishable black dot]]

On 12 February 1991, at a distance of {{convert|14.3|au|km|abbr=on}} from the Sun, Halley displayed an outburst that lasted for several months.<ref name="Gronkowski2002"/><ref name="graw"/> The comet released dust with a total mass of about 10<sup>8</sup> kg, which spread into an elongated cloud roughly {{cvt|374,000|km}} by {{cvt|269,000|km}} in size.<ref name="West1991"/> The outburst likely started in December 1990, and then the comet brightened from about magnitude 25 to magnitude 19.<ref name="Prialnik1992"/><ref name="Gronkowski2002"/> Comets rarely show outburst activity at distances beyond 5 au from the Sun.<ref name="Gronkowski2002"/> Different mechanisms have been proposed for the outburst, ranging from interaction with the solar wind to a collision with an undiscovered [[asteroid]].<ref name="Hughes1991"/> The most likely explanation is a combination of two effects, the [[polymerization|polymerisation]] of [[hydrogen cyanide]] and a [[phase transition]] of [[Phases of ice|amorphous water ice]], which raised the temperature of the nucleus enough for some of the more volatile compounds on its surface to sublime.<ref name="Gronkowski2002"/>

Halley was most recently observed in 2003 by three of the [[Very Large Telescope]]s at Paranal, Chile, when Halley's magnitude was 28.2. The telescopes observed Halley, at the faintest and farthest any comet had ever been imaged, in order to verify a method for finding very faint [[trans-Neptunian object]]s.<ref name="ESO2003"/> Astronomers are now able to observe the comet at any point in its orbit.<ref name="ESO2003"/>

On 9 December 2023, Halley's Comet reached the farthest and slowest point in its orbit from the Sun when it was travelling at {{convert|0.91|km/s|mph|abbr=on}} with respect to the Sun.<ref name="Horizons2023"/><ref name=seeker2013>{{Cite web|url=https://www.seeker.com/lets-plan-for-a-rendezvous-with-halleys-comet-1767783657.html|title=Let's Plan For a Rendezvous With Halley's Comet|last=DNews|date=3 September 2013|website=Seeker|access-date=29 October 2019|archive-url=https://web.archive.org/web/20221128171635/https://www.seeker.com/lets-plan-for-a-rendezvous-with-halleys-comet-1767783657.html|archive-date=28 November 2022|url-status=dead}}</ref>